1.
Electric sail
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An electric sail is a proposed form of spacecraft propulsion using the dynamic pressure of the solar wind as a source of thrust. It creates a sail by using small wires to form an electric field that deflects solar wind protons. It was invented by Pekka Janhunen in 2006 at the Finnish Meteorological Institute, to test the technology, a new European Union-backed electric sail study project was announced by the FMI in December 2010. The EU funding contribution was 1.7 million euros and its goal was to build laboratory prototypes of the key components, it involved five European countries and ended in November 2013. In the EU evaluation, the project got the highest marks in its category, the technology could enable faster and cheaper access to the Solar System, and in the longer run may enable an economic utilisation of asteroid mining. An attempt was made to test the principles of the electric sail in low Earth orbit by Estonian nanosatellite ESTCube-1. In subsequent ground-based testing, a reason for the failure was found in a slipring contact which was likely physically damaged by launch vibration. With the expected time of May 2016, the Finnish Aalto-1 nanosatellite will test the electric sail. An international research team that includes Janhunen received funding through a 2015 NIAC Phase II solicitation for further development at NASAs Marshall Space Flight Center and their research project is called Heliopause Electrostatic Rapid Transit System. The electric sail consists of a number of thin, long and conducting tethers which are kept in a positive potential by an onboard electron gun. The positively charged tethers deflect solar wind protons, thus extracting momentum from them, simultaneously they attract electrons from the solar wind plasma, producing an electron current. The electron gun compensates for the electric current. One way to deploy the tethers is to rotate the spacecraft, by fine-tuning the potentials of individual tethers and thus the solar wind force individually, the spacecrafts attitude can be controlled. E-sail missions can be launched at almost any time only minor variations in travel time. By contrast, conventional slingshot missions must wait for the planets to reach a particular alignment, the electric sail probably cannot be used inside planetary magnetospheres because the solar wind does not penetrate them, allowing only slower plasma flows and magnetic fields. While modest variation of the thrust direction can be achieved by inclining the sail and it has been estimated that maximum operational inclination would be 60°, resulting in a thrusting angle of 30° from the outward radial direction. The electric solar wind sail has little in common with the solar sail. The E-sail gets its momentum from the solar wind ions, whilst a photonic sail is propelled by photons, in the E-sail, the part of the sail is played by straightened conducting tethers which are placed radially around the host ship
2.
Magnetic sail
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A magnetic sail could also thrust directly against planetary and solar magnetospheres. The magnetic sail was proposed by Dana Andrews and Robert Zubrin working in collaboration in 1988 and he asked Zubrin to help him compute the drag that the magnetic scoop would create against the interplanetary medium. Zubrin agreed, but found that the created by the scoop would be much greater than the thrust created by the ion drive. He therefore proposed that the ion drive component of the system be dropped, Andrews agreed, and the magsail was born. The two then proceeded to elaborate their analysis of the magsail for interplanetary, interstellar, and planetary orbital propulsion in a series of papers published from 1988 through the 1990s and it can thus reduce the delta-V propulsion required for an interstellar mission by a factor of two. This capability is the most unusual feature of the magsail, in typical magnetic sail designs, the magnetic field is generated by a loop of superconducting wire. One advantage of magnetic or solar sails over reaction thrusters is that no mass is depleted or carried in the craft. For a sail in the wind one AU away from the Sun. Zubrins proposed magnetic sail design would create a bubble of space of 100 km in diameter where solar-wind ions are substantially deflected using a hoop 50 km in radius. The minimum mass of such a coil is constrained by material strength limitations at roughly 40 tonnes and it would generate 70 N of thrust, if operated within the solar system, high temperature superconducting wire would be required to make the magsail practical. If operated in interstellar space conventional superconductors would be adequate, the operation of magnetic sails using plasma wind is analogous to the operation of solar sails using the radiation pressure of photons emitted by the Sun. Although solar wind particles have rest mass and photons do not, therefore, a magnetic sail must deflect a proportionally larger area of the solar wind than a comparable solar sail to generate the same amount of thrust. However, it need not be as massive as a solar sail because the wind is deflected by a magnetic field instead of a large physical sail. Conventional materials for solar sails weigh around 7 g/m2, giving a thrust of 0.01 mPa at 1 AU and this gives a mass/thrust ratio of at least 700 kg/N, similar to a magnetic sail, neglecting other structural components. The solar and magnetic sails have a thrust that falls off as the square of the distance from the Sun, in this approach, called mini-magnetospheric plasma propulsion, currents that run through the plasma will augment and partially replace the currents in the coil. This is expected to be especially useful far from the Sun, the original NASA design proposes a spacecraft containing a can-shaped electromagnet into which a plasma is injected. The plasma pressure stretches the magnetic field and inflates a bubble of plasma around the spacecraft, the plasma then generates a kind of miniaturized magnetosphere around the spacecraft, analogous to the magnetosphere that surrounds the Earth. The protons and electrons which make up the wind are deflected by this magnetosphere
3.
LightSail 2
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The spacecraft core measures 10 by 10 by 30 centimeters, and its kite-shaped solar sail deploys into a total area of 32 square meters. On May 20,2015, a nearly identical spacecraft, LightSail 1, was launched. In 2005, The Planetary Society attempted to send a larger solar sail named Cosmos 1 into space, but the spacecrafts Russian Volna launch vehicle failed to reach orbit. In 2009, the Society began working on a CubeSat-based solar sail based on NASAs NanoSail-D project, the original estimated cost of the LightSail project was US$1.8 million, which was raised from membership dues and private sources. The prototype spacecraft LightSail 1 was built in San Luis Obispo by Stellar Exploration Inc, as a solar sail, LightSail 2s propulsion is dependent on solar radiation alone. Solar photons exert radiation pressure on the sail, producing a small degree of acceleration, thus, the solar sail will be propelled by pressure from sunlight itself, and not by the charged particles of the solar wind. The Planetary Society expects LightSail 2s orbit to increase by as much as a kilometer per day, LightSail 2s modular design is based on a modular three-unit CubeSat, a small satellite format created for university-level space projects. One CubeSat-sized module carries the cameras, sensors and control systems, the spacecraft contains four triangular sails, which combine to form a rectangular-shaped surface. The sails are made of Mylar, a polyester film. LightSail 2s goal is to test whether solar sails are a form of spacecraft propulsion for CubeSats. The spacecraft team will measure whether there is any increase in LightSail 2s altitude after the spacecraft is deployed from a spacecraft, Prox-1. Prox-1 and LightSail 2 are secondary payloads aboard the first operational SpaceX Falcon Heavy launch, two days after the launch, however, the spacecraft suffered a software malfunction which made it unable to deploy the solar sail or to communicate. On 31 May 2015, The Planetary Society reported having regained contact with LightSail 1, after the solar panels were deployed on 3 June 2015, communications with the spacecraft were lost once more on 4 June. In this case, a fault with the system was suspected. Contact was then reestablished on 6 June, and the deployment was initiated on 7 June. At a conference on 10 June 2015, after photos of deployment were downloaded, the spacecraft reentered the atmosphere on 14 June 2015, ending the test flight
4.
Laser (dinghy)
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The International Laser Class sailboat, also called Laser Standard and the Laser One is a popular one-design class of small sailing dinghy. According to the Laser Class Rules the boat may be sailed by one or two people, though it is rarely sailed by two. The design, by Bruce Kirby, emphasizes simplicity and performance, the dinghy is manufactured by independent companies in different parts of the world, including LaserPerformance Europe, Performance Sailcraft Australia and Performance Sailcraft Japan. The Laser is one of the most popular single-handed dinghies in the world, as of 2012, there are more than 200,000 boats worldwide. A commonly cited reason for its popularity is that it is robust and simple to rig, the Laser also provides very competitive racing due to the very tight class association controls which eliminate differences in hull, sails and equipment. The term Laser is often used to refer to the Laser Standard, however, there are two other sail plan rigs available for the Laser Standard hull and a series of other Laser-branded boats which are of completely different hull designs. Examples include the Laser 2 and Laser Pico, the Laser Standard, Laser Radial and Laser 4.7 are three types of Laser administered by the International Laser Class Association. The lasers hull is made out of GRP, Glass Reinforced Plastics, the deck has a foam layer underneath for strength. The boats history began with a call between Canadians Bruce Kirby and Ian Bruce. While discussing the possibility of a car-topped dinghy for a line of camping equipment, the plans stayed with Kirby until 1970 when One Design and Offshore Yachtsman magazine held a regatta for boats under $1000, called Americas Teacup. After a few modifications, the Laser easily won its class. The prototype was named the Weekender, the sail held the letters TGIF. In December 1970 Dave Balfour, a McGill engineering student, suggested the name Laser, the Laser sailboat was officially unveiled at the New York Boat Show in 1971. The first world championship was held in 1974 in Bermuda, entrants came from 24 countries, and first place was won by Peter Commette from the United States. The Laser became a mens Olympic-class boat at the 1996 Summer Olympics in Atlanta, a version with a smaller sail, the Laser Radial, was first sailed as a womens Olympic-class boat at the 2008 Summer Olympics. Arguably the greatest champion of the Laser Class is Robert Scheidt from Brazil, he won the championship eight times. The Laser is manufactured by different companies in different regions and they include LaserPerformance in Europe and the Americas, Performance Sailcraft Australia in Oceania and Performance Sailcraft. As a one-design class of sailboat, all Lasers are built to the same specifications, the hull is 4.19 metres long, with a waterline length of 3.81 m
5.
IKAROS
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IKAROS is a Japan Aerospace Exploration Agency experimental spacecraft. The spacecraft was launched on 21 May 2010, aboard an H-IIA rocket, together with the Akatsuki probe, IKAROS is the first spacecraft to successfully demonstrate solar sail technology in interplanetary space. On 8 December 2010, IKAROS passed by Venus at about 80,800 km distance, completing the mission successfully. The IKAROS probe is the worlds first spacecraft to use solar sailing as the main propulsion, the probes ALADDIN instrument measured the variation in dust density while its Gamma-Ray Burst Polarimeter measured the polarization of gamma-ray bursts during its six-month cruise. IKAROS is to be followed by a 50 m sail, intended to journey to Jupiter, the square sail, deployed via a spinning motion using 0. 5-kilogram tip masses, is 20 m on the diagonal and is made of a 7. 5-micrometre thick sheet of polyimide. The polyimide sheet had a mass of about 10 grams per metre, resulting in a total sail mass of 2 kilograms, excluding tip masses, attached panels. A thin-film solar array is embedded in the sail, powerFilm, Inc. provided the thin-film solar array. Eighty blocks of LCD panels are embedded in the sail, whose reflectance can be adjusted for attitude control, the sail also contains eight dust counters on the opposite face as part of the science payload. IKAROS was successfully launched together with Akatsuki aboard an H-IIA rocket from the Tanegashima Space Center on 21 May 2010, IKAROS spun at 20–25 revolutions per minute and finished unfurling its sail on 10 June 2010. The craft contains two tiny ejectable cameras, DCAM1 and DCAM2, DCAM2 was used to photograph the sail after deployment on 14 July 2010. Acceleration and attitude control were successfully tested during the remaining six-month voyage to Venus, on 9 July 2010, JAXA confirmed that IKAROS is being accelerated by its solar sail, and on 23 July announced successful attitude control. IKAROS continues to spin at approximately 2 rpm, requiring the LCD panels to be cycled at that rate for attitude control. According to JAXA, IKAROS finished all planned experiments in Dec 2010, as of 2012, the IKAROS continued to spin, but its attitude control had degraded. This resulted in unexpected sail motions and as a result, downlink through the antenna was only intermittently available. The project team was dissolved on 28 March 2013, although a trial receipt of data was planned for a later date. The project was reactivated on 20 June 2013 in the expectation that the satellite would wake up from a state as more power from the solar panels became available. The team was able to receive telemetry from the IKAROS between 20 June and 12 September 2013, after contact was again lost. The loss of contact was around the time of the spacecraft again entering a low-power hibernation mode as power from the solar panels decreased
6.
Spacecraft propulsion
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Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. Each method has drawbacks and advantages, and spacecraft propulsion is an area of research. However, most spacecraft today are propelled by forcing a gas from the back/rear of the vehicle at high speed through a supersonic de Laval nozzle. This sort of engine is called a rocket engine, all current spacecraft use chemical rockets for launch, though some have used air-breathing engines on their first stage. Most satellites have simple reliable chemical thrusters or resistojet rockets for orbital station-keeping, soviet bloc satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north-south stationkeeping and orbit raising. Interplanetary vehicles mostly use chemical rockets as well, although a few have used ion thrusters, artificial satellites must be launched into orbit and once there they must be placed in their nominal orbit. Once in the orbit, they often need some form of attitude control so that they are correctly pointed with respect to Earth, the Sun. They are also subject to drag from the atmosphere, so that to stay in orbit for a long period of time some form of propulsion is occasionally necessary to make small corrections. Many satellites need to be moved from one orbit to another time to time. A satellites useful life is usually over once it has exhausted its ability to adjust its orbit, spacecraft designed to travel further also need propulsion methods. They need to be launched out of the Earths atmosphere just as satellites do, once there, they need to leave orbit and move around. For interplanetary travel, a spacecraft must use its engines to leave Earth orbit, once it has done so, it must somehow make its way to its destination. Current interplanetary spacecraft do this with a series of short-term trajectory adjustments, in between these adjustments, the spacecraft simply falls freely along its trajectory. The most fuel-efficient means to move from one orbit to another is with a Hohmann transfer orbit. The spacecraft falls freely along this elliptical orbit until it reaches its destination, special methods such as aerobraking or aerocapture are sometimes used for this final orbital adjustment. The concept has been tested by the Japanese IKAROS solar sail spacecraft. Spacecraft for interstellar travel also need propulsion methods, no such spacecraft has yet been built, but many designs have been discussed. Because interstellar distances are great, a tremendous velocity is needed to get a spacecraft to its destination in a reasonable amount of time
7.
Radiation pressure
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Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. Radiation pressure implies an interaction between radiation and bodies of various types, including clouds of particles or gases. The interactions can be absorption, reflection, or some of both, bodies also emit radiation and thereby experience a resulting pressure. For example, had the effects of the radiation pressure on the spacecraft of the Viking program been ignored. This article addresses the macroscopic aspects of radiation pressure, detailed quantum mechanical aspects of interactions are addressed in specialized articles on the subject. The details of how photons of various wavelengths interact with atoms can be explored through links in the See also section, johannes Kepler put forward the concept of radiation pressure back in 1619 to explain the observation that a tail of a comet always points away from the Sun. The pressure is very feeble, but can be detected by allowing the radiation to fall upon a delicately poised vane of reflective metal in a Nichols radiometer, radiation pressure can be analyzed as interactions by either electromagnetic waves or particles. The waves and photons both have the property of momentum, which allows their interchangeability under classical conditions, according to Maxwells theory of electromagnetism, an electromagnetic wave carries momentum, which can be transferred to a reflecting or absorbing surface hit by the wave. The component of the normal to the surface creates the pressure on the surface. The component tangent to the surface does not contribute to the pressure, electromagnetic radiation is quantized in particles called photons, the particle aspect of its wave–particle duality. Photons are best explained by quantum mechanics, although photons are zero-rest mass particles, they have the properties of energy and momentum, and thus exhibit the property of mass as they travel at light speed. The momentum of a photon is given by, p = h λ where p is momentum, h is Plancks constant, λ is wavelength and this expression shows the wave–particle duality. E = p c is the relationship where E is the energy. Then p = E c The generation of radiation pressure results from the property of photons, specifically. The surface exerts a force on the photons in changing their momentum by Newtons Second Law, a reactive force is applied to the body by Newtons Third Law. The orientation of a reflector determines the component of normal to its surface. Each factor contributes a cosine function, reducing the pressure on the surface, bodies radiate thermal energy according to their temperature. The emissions are electromagnetic radiation, and therefore have the properties of energy, the energy leaving a body tends to reduce its temperature
8.
Laser propulsion
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Laser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass. This form of propulsion differs from a chemical rocket where both energy and reaction mass come from the solid or liquid propellants carried on board the vehicle. The basic concepts underlying a photon-propelled sail propulsion system were developed by Eugene Sanger, Propulsion concepts using laser-energized rockets were developed by Arthur Kantrowitz and Wolfgang Moekel in the 1970s. An exposition of Kantrowitzs laser propulsion ideas were published in 1988, laser propulsion systems may transfer momentum to a spacecraft in two different ways. The first way uses photon radiation pressure to drive momentum transfer and is the principle behind solar sails, the second method uses the laser to help expel mass from the spacecraft as in a conventional rocket. This is the more frequently proposed method, but is limited in final spacecraft velocities by the rocket equation. Laser-pushed sails are examples of beam-powered propulsion, a laser-pushed lightsail is a thin reflective sail similar to a solar sail, in which the sail is being pushed by a laser, rather than the sun. Further analysis of the concept was done by Landis, Mallove and Matloff, Andrews and this gets more important when going from interplanetary travel to interstellar travel, and when going from a fly-by mission, to a landing mission, to a return mission. The laser may alternatively be a phased array of small devices. The laser-pushed sail is proposed as a method of propelling a small interstellar probe by the Breakthrough Starshot project, PLT is predicted to be able to provide the thrust to power ratio approaching that of conventional thrusters, such as laser ablation thrusters and electrical thrusters. There are several forms of propulsion in which the laser is used as an energy source to provide momentum to propellant that is carried on board the rocket. The use of a laser as the energy source means that the energy provided to the propellant is not limited by the energy of the propellant. The laser thermal rocket is a rocket in which the propellant is heated by energy provided by an external laser beam. The beam heats a heat exchanger, which in turn heats an inert liquid propellant. This is similar in principle to nuclear thermal and solar thermal propulsion, using a large flat heat exchanger allows the laser beam to shine directly on the heat exchanger without focusing optics on the vehicle. The HX thruster has the advantage of working well with any laser wavelength and both CW and pulsed lasers, and of having an efficiency approaching 100%. The HX thruster is limited by the heat exchanger material and by radiative losses to relatively low gas temperatures, the HX laser thruster concept was developed by Jordin Kare in 1991, a similar microwave thermal propulsion concept was developed independently by Kevin L. Parkin at Caltech in 2001. A variation on this concept was proposed by Prof, john Sinko and Dr. Clifford Schlecht as a redundant safety concept for assets on orbit
9.
Interplanetary spaceflight
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Interplanetary spaceflight or interplanetary travel is travel between planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System, the most distant spacecraft, Voyager 1, has left the Solar System, while Pioneer 10, Pioneer 11, Voyager 2 and New Horizons are on course to leave it. In general, planetary orbiters and landers return much more detailed, the NEAR Shoemaker mission in 2000 orbited the large near-Earth asteroid 433 Eros, and was even successfully landed there, though it had not been designed with this maneuver in mind. The Japanese ion-drive spacecraft Hayabusa in 2005 also orbited the small near-Earth asteroid 25143 Itokawa, landing on it briefly, another powerful ion-drive mission, Dawn, has orbited the large asteroid Vesta and later moved on to the dwarf planet Ceres, arriving in March 2015. The Huygens probe successfully landed on Saturns moon, Titan, no manned missions have been sent to any planet of the Solar System. NASAs Apollo program, however, landed twelve people on the Moon, however, on February 1,2010, President Barack Obama proposed cancelling the program in Fiscal Year 2011. Many astronomers, geologists and biologists believe that exploration of the Solar System provides knowledge that could not be gained by observations from Earths surface or from orbit around Earth. Those who pay for such missions are more likely to be interested in benefits for themselves or for the race as a whole. So far the only benefits of this type have been spin-off technologies which were developed for space missions, other practical motivations for interplanetary travel are more speculative, because our current technologies are not yet advanced enough to support test projects. But science fiction writers have a good track record in predicting future technologies — for example geosynchronous communications satellites. Some point out that such techniques may be the way to provide rising standards of living without being stopped by pollution or by depletion of Earths resources. Finally, colonizing parts of the Solar System would prevent the whole human species from being exterminated by any one of a number of possible events. One of these events is an asteroid impact like the one which may have resulted in the Cretaceous–Paleogene extinction event. Although various Spaceguard projects monitor the Solar System for objects that might come dangerously close to Earth, current asteroid deflection strategies are crude, to make the task more difficult, carbonaceous chondrites are rather sooty and therefore very hard to detect. Although carbonaceous chondrites are thought to be rare, some are very large, some scientists, including members of the Space Studies Institute, argue that the vast majority of mankind eventually will live in space and will benefit from doing this. One of the challenges in interplanetary travel is producing the very large velocity changes necessary to travel from one body to another in the Solar System. Due to the Suns gravitational pull, a spacecraft moving farther from the Sun will slow down, then, if additionally the spacecraft wishes to enter into orbit around the destination planet, it must match the planets orbital speed around the Sun, usually requiring another large velocity change. Simply doing this by brute force – accelerating in the shortest route to the destination, thus, several techniques have been devised to reduce the fuel requirements of interplanetary travel.8 km/s
10.
Flight dynamics (fixed-wing aircraft)
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Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the center of mass, known as pitch, roll and yaw. Aerospace engineers develop control systems for a vehicles orientation about its center of mass, for example, a pitching moment is a vertical force applied at a distance forward or aft from the aerodynamic center of the aircraft, causing the aircraft to pitch up or down. Roll, pitch and yaw refer to rotations about the respective axes starting from a steady flight equilibrium state. The equilibrium roll angle is known as wings level or zero bank angle, the equilibrium pitch angle in submarine and airship parlance is known as trim, but in aircraft, trim usually refers to the equilibrium angle of attack, rather than orientation. However, common usage ignores this distinction between equilibrium and dynamic cases, the most common aeronautical convention defines the roll as acting about the longitudinal axis, positive with the starboard wing down. The yaw is about the body axis, positive with the nose to starboard. Pitch is about a perpendicular to the longitudinal plane of symmetry. A fixed-wing aircraft increases or decreases the lift generated by the wings when it pitches nose up or down by increasing or decreasing the angle of attack. The roll angle is known as bank angle on a fixed-wing aircraft. Three right-handed, Cartesian coordinate systems see frequent use in flight dynamics, the other two reference frames are body-fixed, with origins moving along with the aircraft, typically at the center of gravity. The Earth frame is a convenient frame to express aircraft translational and rotational kinematics, the Earth frame is also useful in that, under certain assumptions, it can be approximated as inertial. Additionally, one acting on the aircraft, weight, is fixed in the +zE direction. The body frame is often of interest because the origin and the axes remain fixed relative to the aircraft and this means that the relative orientation of the Earth and body frames describes the aircraft attitude. Also, the direction of the force of thrust is generally fixed in the frame, though some aircraft can vary this direction. The wind frame is a convenient frame to express the aerodynamic forces, in particular, the net aerodynamic force can be divided into components along the wind frame axes, with the drag force in the −xw direction and the lift force in the −zw direction. In addition to defining the reference frames, the orientation of the reference frames can be determined. Many Euler angle conventions exist, but all of the rotation sequences presented below use the z-y-x convention and this convention corresponds to a type of Tait-Bryan angles, which are commonly referred to as Euler angles
11.
Newton (unit)
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The newton is the International System of Units derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, see below for the conversion factors. One newton is the force needed to one kilogram of mass at the rate of one metre per second squared in direction of the applied force. In 1948, the 9th CGPM resolution 7 adopted the name newton for this force, the MKS system then became the blueprint for todays SI system of units. The newton thus became the unit of force in le Système International dUnités. This SI unit is named after Isaac Newton, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. Newtons second law of motion states that F = ma, where F is the applied, m is the mass of the object receiving the force. The newton is therefore, where the symbols are used for the units, N for newton, kg for kilogram, m for metre. In dimensional analysis, F = M L T2 where F is force, M is mass, L is length, at average gravity on earth, a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force, which we measure as the apples weight, for example, the tractive effort of a Class Y steam train and the thrust of an F100 fighter jet engine are both around 130 kN. One kilonewton,1 kN, is 102.0 kgf,1 kN =102 kg ×9.81 m/s2 So for example, a platform rated at 321 kilonewtons will safely support a 32,100 kilograms load. Specifications in kilonewtons are common in safety specifications for, the values of fasteners, Earth anchors. Working loads in tension and in shear, thrust of rocket engines and launch vehicles clamping forces of the various moulds in injection moulding machines used to manufacture plastic parts
12.
Electrically powered spacecraft propulsion
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An electrically powered spacecraft propulsion system uses electrical energy to change the velocity of a spacecraft. Most of these kinds of spacecraft propulsion systems work by electrically expelling propellant at high speed, Electric thrusters typically use much less propellant than chemical rockets because they have a higher exhaust speed than chemical rockets. Due to limited electric power the thrust is much weaker compared to chemical rockets, Electric propulsion can achieve high speeds over long periods and thus can work better than chemical rockets for some deep space missions. Electric propulsion is now a mature and widely used technology on spacecraft, Russian satellites have used electric propulsion for decades and it is predicted that by 2020, half of all new satellites will carry full electric propulsion. As of 2013, over 200 spacecraft operated throughout the system use electric propulsion for station keeping, orbit raising. Also, an electro-rocket with a power source has a theoretical possibility for interstellar flight. However, electric propulsion is not a suitable for launches from the Earths surface. The idea of electric propulsion for spacecraft dates back to 1911, earlier, Robert Goddard had noted such a possibility in his personal notebook. The first designed and tested electric propulsion in the world was in 1929-1931 in Leningrad, already in 1950 at the initiative of S. P. Korolev, I. V. Kurchatov and L. A. Artsimovich it adopted a program of research, electrically powered propulsion with a nuclear reactor was considered by Dr. The demonstration of electric propulsion was an ion engine carried on board the SERT-1 spacecraft, launched on 20 July 1964 and it operated for 31 minutes. A follow-up mission launched on 3 February 1970, SERT-2, carried two ion thrusters, one operated for more than five months and the other for almost three months and this type of rocket-like reaction engine uses electric energy to obtain thrust from propellant carried with the vehicle. Unlike rocket engines, these kinds of engines do not necessarily have rocket nozzles, the thermal energy imparted to the propellant gas is then converted into kinetic energy by a nozzle of either solid material or magnetic fields. Low molecular weight gases are preferred propellants for this kind of system, performance of electrothermal systems in terms of specific impulse is somewhat modest, but exceeds that of cold gas thrusters, monopropellant rockets, and even most bipropellant rockets. In the USSR, electrothermal engines were used since 1971, the Soviet Meteor-3, Meteor-Priroda, Resurs-O satellite series, electrothermal systems by Aerojet are currently used on Lockheed Martin A2100 satellites using hydrazine as a propellant. See Laser propulsion, Photonic Laser Thruster, Photon rocket, Electric potential is generated across a conductive tether by its motion through the Earths magnetic field. The choice of the conductor to be used in an electrodynamic tether is determined by a variety of factors. Primary factors usually include high electrical conductivity, and low density, secondary factors, depending on the application, include cost, strength, and melting point
13.
Johannes Kepler
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Johannes Kepler was a German mathematician, astronomer, and astrologer. A key figure in the 17th-century scientific revolution, he is best known for his laws of motion, based on his works Astronomia nova, Harmonices Mundi. These works also provided one of the foundations for Isaac Newtons theory of universal gravitation, Kepler was a mathematics teacher at a seminary school in Graz, where he became an associate of Prince Hans Ulrich von Eggenberg. Later he became an assistant to the astronomer Tycho Brahe in Prague and he was also a mathematics teacher in Linz, and an adviser to General Wallenstein. Kepler lived in an era when there was no distinction between astronomy and astrology, but there was a strong division between astronomy and physics. Kepler was born on December 27, the feast day of St John the Evangelist,1571 and his grandfather, Sebald Kepler, had been Lord Mayor of the city. By the time Johannes was born, he had two brothers and one sister and the Kepler family fortune was in decline and his father, Heinrich Kepler, earned a precarious living as a mercenary, and he left the family when Johannes was five years old. He was believed to have died in the Eighty Years War in the Netherlands and his mother Katharina Guldenmann, an innkeepers daughter, was a healer and herbalist. Born prematurely, Johannes claimed to have weak and sickly as a child. Nevertheless, he often impressed travelers at his grandfathers inn with his phenomenal mathematical faculty and he was introduced to astronomy at an early age, and developed a love for it that would span his entire life. At age six, he observed the Great Comet of 1577, in 1580, at age nine, he observed another astronomical event, a lunar eclipse, recording that he remembered being called outdoors to see it and that the moon appeared quite red. However, childhood smallpox left him with vision and crippled hands. In 1589, after moving through grammar school, Latin school, there, he studied philosophy under Vitus Müller and theology under Jacob Heerbrand, who also taught Michael Maestlin while he was a student, until he became Chancellor at Tübingen in 1590. He proved himself to be a mathematician and earned a reputation as a skilful astrologer. Under the instruction of Michael Maestlin, Tübingens professor of mathematics from 1583 to 1631 and he became a Copernican at that time. In a student disputation, he defended heliocentrism from both a theoretical and theological perspective, maintaining that the Sun was the source of motive power in the universe. Despite his desire to become a minister, near the end of his studies, Kepler was recommended for a position as teacher of mathematics and he accepted the position in April 1594, at the age of 23. Keplers first major work, Mysterium Cosmographicum, was the first published defense of the Copernican system
14.
Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model
15.
James Clerk Maxwell
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James Clerk Maxwell FRS FRSE was a Scottish scientist in the field of mathematical physics. Maxwells equations for electromagnetism have been called the great unification in physics after the first one realised by Isaac Newton. With the publication of A Dynamical Theory of the Electromagnetic Field in 1865, Maxwell proposed that light is an undulation in the same medium that is the cause of electric and magnetic phenomena. The unification of light and electrical phenomena led to the prediction of the existence of radio waves, Maxwell helped develop the Maxwell–Boltzmann distribution, a statistical means of describing aspects of the kinetic theory of gases. He is also known for presenting the first durable colour photograph in 1861 and his discoveries helped usher in the era of modern physics, laying the foundation for such fields as special relativity and quantum mechanics. Many physicists regard Maxwell as the 19th-century scientist having the greatest influence on 20th-century physics and his contributions to the science are considered by many to be of the same magnitude as those of Isaac Newton and Albert Einstein. In the millennium poll—a survey of the 100 most prominent physicists—Maxwell was voted the third greatest physicist of all time, behind only Newton and Einstein. On the centenary of Maxwells birthday, Einstein described Maxwells work as the most profound and the most fruitful that physics has experienced since the time of Newton. James Clerk Maxwell was born on 13 June 1831 at 14 India Street, Edinburgh, to John Clerk Maxwell of Middlebie, an advocate and his father was a man of comfortable means of the Clerk family of Penicuik, holders of the baronetcy of Clerk of Penicuik. His fathers brother was the 6th Baronet, James was the first cousin of the artist Jemima Blackburn and cousin of the civil engineer William Dyce Cay. They were close friends and Cay acted as his best man when Maxwell married, Maxwells parents met and married when they were well into their thirties, his mother was nearly 40 when he was born. They had had one child, a daughter named Elizabeth. When Maxwell was young his family moved to Glenlair House, which his parents had built on the 1,500 acres Middlebie estate, all indications suggest that Maxwell had maintained an unquenchable curiosity from an early age. By the age of three, everything moved, shone, or made a noise drew the question, whats the go o that. And show me how it doos is never out of his mouth and he also investigates the hidden course of streams and bell-wires, the way the water gets from the pond through the wall. Recognising the potential of the boy, Maxwells mother Frances took responsibility for Jamess early education. At eight he could recite long passages of Milton and the whole of the 119th psalm, indeed, his knowledge of scripture was already very detailed, he could give chapter and verse for almost any quotation from the psalms. His mother was ill with abdominal cancer and, after an unsuccessful operation
16.
Momentum
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In classical mechanics, linear momentum, translational momentum, or simply momentum is the product of the mass and velocity of an object, quantified in kilogram-meters per second. It is dimensionally equivalent to impulse, the product of force and time, Newtons second law of motion states that the change in linear momentum of a body is equal to the net impulse acting on it. If the truck were lighter, or moving slowly, then it would have less momentum. Linear momentum is also a quantity, meaning that if a closed system is not affected by external forces. In classical mechanics, conservation of momentum is implied by Newtons laws. It also holds in special relativity and, with definitions, a linear momentum conservation law holds in electrodynamics, quantum mechanics, quantum field theory. It is ultimately an expression of one of the symmetries of space and time. Linear momentum depends on frame of reference, observers in different frames would find different values of linear momentum of a system. But each would observe that the value of linear momentum does not change with time, momentum has a direction as well as magnitude. Quantities that have both a magnitude and a direction are known as vector quantities, because momentum has a direction, it can be used to predict the resulting direction of objects after they collide, as well as their speeds. Below, the properties of momentum are described in one dimension. The vector equations are almost identical to the scalar equations, the momentum of a particle is traditionally represented by the letter p. It is the product of two quantities, the mass and velocity, p = m v, the units of momentum are the product of the units of mass and velocity. In SI units, if the mass is in kilograms and the velocity in meters per second then the momentum is in kilogram meters/second, in cgs units, if the mass is in grams and the velocity in centimeters per second, then the momentum is in gram centimeters/second. Being a vector, momentum has magnitude and direction, for example, a 1 kg model airplane, traveling due north at 1 m/s in straight and level flight, has a momentum of 1 kg m/s due north measured from the ground. The momentum of a system of particles is the sum of their momenta, if two particles have masses m1 and m2, and velocities v1 and v2, the total momentum is p = p 1 + p 2 = m 1 v 1 + m 2 v 2. If all the particles are moving, the center of mass will generally be moving as well, if the center of mass is moving at velocity vcm, the momentum is, p = m v cm. This is known as Eulers first law, if a force F is applied to a particle for a time interval Δt, the momentum of the particle changes by an amount Δ p = F Δ t
17.
Maxwell's equations
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Maxwells equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits. They underpin all electric, optical and radio such as power generation, electric motors, wireless communication, cameras, televisions. Maxwells equations describe how electric and magnetic fields are generated by charges, currents, one important consequence of the equations is the demonstration of how fluctuating electric and magnetic fields can propagate at the speed of light. This electromagnetic radiation manifests itself in ways from radio waves to light. The equations have two major variants, the microscopic Maxwell equations have universal applicability but are unwieldy for common calculations. They relate the electric and magnetic fields to total charge and total current, including the complicated charges, the macroscopic Maxwell equations define two new auxiliary fields that describe the large-scale behaviour of matter without having to consider atomic scale details. However, their use requires experimentally determining parameters for a description of the electromagnetic response of materials. The term Maxwells equations is used for equivalent alternative formulations. The space-time formulations, are used in high energy and gravitational physics because they make the compatibility of the equations with special and general relativity manifest. In many situations, though, deviations from Maxwells equations are immeasurably small, exceptions include nonclassical light, photon-photon scattering, quantum optics, and many other phenomena related to photons or virtual photons. In the electric and magnetic field there are four equations. The two inhomogeneous equations describe how the fields vary in space due to sources, Gausss law describes how electric fields emanate from electric charges. Gausss law for magnetism describes magnetic fields as closed field lines not due to magnetic monopoles, the two homogeneous equations describe how the fields circulate around their respective sources. A separate law of nature, the Lorentz force law, describes how the electric and magnetic field act on charged particles, a version of this law was included in the original equations by Maxwell but, by convention, is no longer. The precise formulation of Maxwells equations depends on the definition of the quantities involved. Conventions differ with the systems, because various definitions and dimensions are changed by absorbing dimensionful factors like the speed of light c. This makes constants come out differently, the vector calculus formulation below has become standard. For formulations using tensor calculus or differential forms, see alternative formulations, for relativistically invariant formulations, see relativistic formulations
18.
Sunlight
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Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through Earths atmosphere, and is obvious as daylight when the Sun is above the horizon, when the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, the World Meteorological Organization uses the term sunshine duration to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an Average over the earth of 164 Watts per square meter over a 24 hour day. The ultraviolet radiation in sunlight has both positive and negative effects, as it is both a principal source of vitamin D3 and a mutagen. Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the center of the Sun and changing every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface. Researchers may record sunlight using a sunshine recorder, pyranometer, or pyrheliometer, to calculate the amount of sunlight reaching the ground, both Earths elliptical orbit and the attenuation by Earths atmosphere have to be taken into account. In this formula dn–3 is used, because in modern times Earths perihelion, the closest approach to the Sun and, therefore, the value of 0.033412 is determined knowing that the ratio between the perihelion squared and the aphelion squared should be approximately 0.935338. The solar illuminance constant, is equal to 128×103 lx, the atmospheric extinction brings the number of lux down to around 100000. The total amount of energy received at ground level from the Sun at the zenith depends on the distance to the Sun and it is about 3. 3% higher than average in January and 3. 3% lower in July. In terms of energy, sunlight at Earths surface is around 52 to 55 percent infrared,42 to 43 percent visible, and 3 to 5 percent ultraviolet. At the top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet, direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. This is higher than the efficacy of most artificial lighting, which means using sunlight for illumination heats up a less than using most forms of artificial lighting. Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98000 lux on a surface at sea level. The illumination of a surface will be considerably less than this if the Sun is not very high in the sky. Averaged over a day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole, dividing the irradiance of 1050 W/m2 by the size of the suns disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. Multiplying this by π gives a limit to the irradiance which can be focused on a surface using mirrors,48.5 MW/m2
19.
Jules Verne
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Jules Gabriel Verne was a French novelist, poet, and playwright. Verne is generally considered a literary author in France and most of Europe. Verne has been the second most-translated author in the world since 1979 and he has sometimes been called the Father of Science Fiction, a title that has also been given to H. G. Wells and Hugo Gernsback. His parents were Pierre Verne, an originally from Provins, and Sophie Allote de la Fuÿe. In 1829, the Verne family moved some hundred meters away to No.2 Quai Jean-Bart, three sisters, Anna, Mathilde, and Marie, would follow. In 1834, at the age of six, Verne was sent to boarding school at 5 Place du Bouffay in Nantes, the teacher, Mme Sambin, was the widow of a naval captain who had disappeared some 30 years before. Mme Sambin often told the students that her husband was a shipwrecked castaway, the theme of the Robinsonade would stay with Verne throughout his life and appear in many of his novels, including The Mysterious Island, Second Fatherland, and The School for Robinsons. In 1836, Verne went on to École Saint‑Stanislas, a Catholic school suiting the pious religious tastes of his father, Verne quickly distinguished himself in mémoire, geography, Greek, Latin, and singing. In the same year,1836, Pierre Verne bought a house at 29 Rue des Réformés in the village of Chantenay on the Loire River. In his brief memoir Souvenirs d’enfance et de jeunesse, Verne recalled a deep fascination with the river and with the many merchant vessels navigating it. He also took vacations at Brains, in the house of his uncle Prudent Allotte, a retired shipowner, who had gone around the world and served as mayor of Brains from 1828 to 1837. Verne took joy in playing interminable rounds of the Game of the Goose with his uncle, and both the game and his uncles name would be memorialized in two late novels. It is now known that the legend is a tale invented by Vernes first biographer, his niece Marguerite Allotte de la Füye. In 1840, the Vernes moved again to an apartment at No.6 Rue Jean-Jacques-Rousseau. In the same year Verne entered another school, the Petit Séminaire de Saint-Donatien. His unfinished novel Un prêtre en 1839, written in his teens, from 1844 to 1846, Verne and his brother were enrolled in the Lycée Royal in Nantes. After finishing classes in rhetoric and philosophy, he took the baccalauréat at Rennes, however, his father took it for granted that Verne, being the firstborn son of the family, would not attempt to make money in literature but would instead inherit the family law practice. In 1847, Vernes father sent him to Paris, primarily to begin his studies in law school, and secondarily to distance him temporarily from Nantes
20.
Pyotr Lebedev
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Pyotr Nikolaevich Lebedev was a Russian physicist. His name was transliterated as Peter Lebedew and Peter Lebedev. He made his doctoral degree in Strasbourg under the supervision of August Kundt in 1887–1891, in 1891 he started working in Moscow State University in the group of Alexander Stoletov. There he made his famous studies of electromagnetic waves. He was the first to measure the pressure of light on a body in 1899. The discovery was announced at the World Physics Congress in Paris in 1900, in 1901 he became a professor of Moscow State University, however he quit the University in 1911, protesting against the politics of the Ministry of Education. In the same year he received an invitation to become a professor in Stockholm, the Lebedev Physical Institute in Moscow and the lunar crater Lebedev are named after him
21.
Nichols radiometer
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A Nichols radiometer was the apparatus used by Ernest Fox Nichols and Gordon Ferrie Hull in 1901 for the measurement of radiation pressure. It consisted of a pair of small silvered glass mirrors suspended in the manner of a balance by a fine quartz fibre within an enclosure in which the air pressure could be regulated. The torsion head to which the fiber was attached could be turned from the outside by means of a magnet, a beam of light was directed first on one mirror and then on the other, and the opposite deflections observed with mirror and scale. By turning the system around so as to receive the light on the unsilvered side. This influence was found to be of almost negligible value at an air pressure of about 16 mmHg. The radiant energy of the incident beam was deduced from its effect upon a small blackened silver disk. With this apparatus the experimenters were able to obtain an agreement between observed and computed radiation pressures within about 0. 6%, the original apparatus is at the Smithsonian Institution. This apparatus is sometimes confused with the Crookes radiometer of 1873, experimental examination of light pressure, Annalen der Physik,6,433. E. F. Nichols and G. F. Hull, A Preliminary communication on the pressure of heat and light radiation, Phys
22.
Svante Arrhenius
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Svante August Arrhenius was a Nobel-Prize winning Swedish scientist, originally a physicist, but often referred to as a chemist, and one of the founders of the science of physical chemistry. He received the Nobel Prize for Chemistry in 1903, becoming the first Swedish Nobel laureate, Arrhenius was born on 19 February 1859 at Vik, near Uppsala, Sweden, the son of Svante Gustav and Carolina Thunberg Arrhenius. His father had been a surveyor for Uppsala University, moving up to a supervisory position. At the age of three, Arrhenius taught himself to read without the encouragement of his parents, and by watching his fathers addition of numbers in his account books, in later life, Arrhenius enjoyed using masses of data to discover mathematical relationships and laws. At age eight, he entered the cathedral school, starting in the fifth grade, distinguishing himself in physics and mathematics. His work focused on the conductivities of electrolytes, in 1884, based on this work, he submitted a 150-page dissertation on electrolytic conductivity to Uppsala for the doctorate. It did not impress the professors, among whom was Cleve, and he received a fourth-class degree, later, extensions of this very work would earn him the 1903 Nobel Prize in Chemistry. Arrhenius put forth 56 theses in his 1884 dissertation, most of which would still be accepted today unchanged or with minor modifications, Arrhenius explanation was that in forming a solution, the salt disassociates into charged particles. Faradays belief had been that ions were produced in the process of electrolysis, Arrhenius proposed that, even in the absence of an electric current and he thus proposed that chemical reactions in solution were reactions between ions. They were far more impressed, and Ostwald even came to Uppsala to persuade Arrhenius to join his research team, Arrhenius declined, however, as he preferred to stay in Sweden for a while and had received an appointment at Uppsala. In an extension of his ionic theory Arrhenius proposed definitions for acids and bases and he believed that acids were substances that produce hydrogen ions in solution and that bases were substances that produce hydroxide ions in solution. The Arrhenius equation gives the basis of the relationship between the activation energy and the rate at which a reaction proceeds. In 1891 he became a lecturer at the Stockholm University College, being promoted to professor of physics in 1895, and rector in 1896. He was married twice, first to his former pupil Sofia Rudbeck, with whom he had one son Olof Arrhenius, about 1900, Arrhenius became involved in setting up the Nobel Institutes and the Nobel Prizes. He was elected a member of the Royal Swedish Academy of Sciences in 1901, for the rest of his life, he would be a member of the Nobel Committee on Physics and a de facto member of the Nobel Committee on Chemistry. He used his positions to arrange prizes for his friends and to attempt to deny them to his enemies, in 1901 Arrhenius was elected to the Swedish Academy of Sciences, against strong opposition. In 1903 he became the first Swede to be awarded the Nobel Prize in chemistry, in 1905, upon the founding of the Nobel Institute for Physical Research at Stockholm, he was appointed rector of the institute, the position where he remained until retirement in 1927. He was elected a Foreign Member of the Royal Society in 1910, in 1911 he won the first Willard Gibbs Award
23.
Panspermia
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Some organisms may travel dormant for an extended amount of time before colliding randomly with other planets or intermingling with protoplanetary disks. If met with ideal conditions on a new planets surfaces, the organisms become active, panspermia is not meant to address how life began, just the method that may cause its distribution in the Universe. From the early 1970s it was becoming evident that interstellar dust consisted of a component of organic molecules. Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust, the dust plays a critical role of shielding the molecules from the ionizing effect of ultraviolet radiation emitted by stars. The chemistry leading to life may have begun shortly after the Big Bang,13.8 billion years ago, though life is confirmed only on the Earth, some think that extraterrestrial life is not only plausible, but probable or inevitable. The first known mention of the term was in the writings of the 5th century BC Greek philosopher Anaxagoras, fred Hoyle and Chandra Wickramasinghe were influential proponents of panspermia. In 1974 they proposed the hypothesis that some dust in space was largely organic. Several simulations in laboratories and in low Earth orbit suggest that ejection, entry, in 2015, remains of biotic material were found in 4.1 billion-year-old rocks in Western Australia, when the young Earth was about 400 million years old. According to one of the researchers, If life arose relatively quickly on Earth … then it could be common in the universe, panspermia can be said to be either interstellar or interplanetary, its transport mechanisms may include comets, radiation pressure and lithopanspermia. Interplanetary transfer of nonliving material is well documented, as evidenced by meteorites of Martian origin found on Earth, Space probes may also be a viable transport mechanism for interplanetary cross-pollination in the Solar System or even beyond. Deliberate directed panspermia from space to seed Earth or sent from Earth to seed other planetary systems have also been proposed, arrhenius argued that particles at a critical size below 1.5 μm would be propagated at high speed by radiation pressure of the Sun. However, because its effectiveness decreases with increasing size of the particle, the main criticism of radiopanspermia hypothesis came from Shklovskii and Sagan, who pointed out the proofs of the lethal action of space radiations in the cosmos. Then, data gathered by the orbital experiments ERA, BIOPAN, EXOSTACK and EXPOSE, determined that isolated spores, including those of B. Though minimal protection is required to shelter a spore against UV radiation, exposure to solar UV and cosmic ionizing radiation of unprotected DNA, break it up into its bases. The feasibility of other means of transport for the more massive shielded spores into the outer Solar System – for example, lithopanspermia, the transfer of organisms in rocks from one planet to another either through interplanetary or interstellar space, remains speculative. Although there is no evidence that lithopanspermia has occurred in the Solar System, to determine the effect of acceleration during ejection on microorganisms, rifle and ultracentrifuge methods were successfully used under simulated outer space conditions. Survival in transit — The survival of microorganisms has been studied using both simulated facilities and in low Earth orbit. A large number of microorganisms have been selected for exposure experiments and it is possible to separate these microorganisms into two groups, the human-borne, and the extremophiles
24.
Konstantin Tsiolkovsky
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Konstantin Eduardovich Tsiolkovsky was a Russian and Soviet rocket scientist and pioneer of the astronautic theory. Along with the French Robert Esnault-Pelterie, the German Hermann Oberth and his works later inspired leading Soviet rocket engineers such as Sergei Korolev and Valentin Glushko and contributed to the success of the Soviet space program. Tsiolkovsky spent most of his life in a log house on the outskirts of Kaluga, a recluse by nature, he appeared strange and bizarre to his fellow townsfolk. He was born in Izhevskoye, in the Russian Empire, to a middle-class family and his father, Edward Tsiolkovsky, was a Polish-born Russian Orthodox, his mother, Maria Ivanovna Yumasheva belonged to Russian nobility of Volga Tatar origin. His father was successively a forester, teacher, and minor government official, at the age of 10, Konstantin caught scarlet fever and became hard of hearing. When he was 13, his mother died and he was not admitted to elementary schools because of his hearing problem, so he was self-taught. As a reclusive home-schooled child, he passed much of his time by reading books, as a teenager, he began to contemplate the possibility of space travel. After falling behind in his studies, Tsiolkovsky spent three years attending a Moscow library where Russian cosmism proponent Nikolai Fyodorov worked and he later came to believe that colonizing space would lead to the perfection of the human race, with immortality and a carefree existence. Additionally, inspired by the fiction of Jules Verne, Tsiolkovsky theorized many aspects of space travel and he is considered the father of spaceflight and the first person to conceive the space elevator, becoming inspired in 1895 by the newly constructed Eiffel Tower in Paris. Afterwards, Tsiolkovsky passed the exam and went to work at a school in Borovsk near Moscow. He also met and married his wife Varvara Sokolovaya during this time, despite being stuck in Kaluga, a small town far from major learning centers, Tsiolkovsky managed to make scientific discoveries on his own. The first two decades of the 20th century were marred by personal tragedy, Tsiolkovskys son Ignaty committed suicide in 1902, and in 1908 many of his accumulated papers were lost in a flood. In 1911, his daughter Lyubov was arrested for engaging in revolutionary activities and this section has recently been partly machine translated from the Russian article. Please supply an improved translation if possible, Tsiolkovsky stated that he developed the theory of rocketry only as a supplement to philosophical research on the subject. He wrote more than 400 works including approximately 90 published pieces on space travel, Tsiolkovskys first scientific study dates back to 1880–1881. Undaunted, he pressed ahead with his work, The Mechanics of the Animal Organism. It received favorable feedback, and Tsiolkovsky was made a member of the Society, in 1892, he was transferred to a new teaching post in Kaluga where he continued to experiment. Tsiolkovsky developed the first aerodynamics laboratory in Russia in his apartment, in 1897, he built the first Russian wind tunnel with an open test section and developed a method of experimentation using it
25.
Friedrich Zander
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Friedrich Zander, was a Baltic German pioneer of rocketry and spaceflight in the Russian Empire and the Soviet Union. He designed the first liquid-fueled rocket to be launched in the Soviet Union, GIRD-X, Zander was born in Riga, Russian Empire, into a Baltic German family. His father Artur was a doctor, but Friedrich Zander was fascinated by other natural sciences, Zander was enrolled in the Riga urban technical high school in 1898, for a seven-year program in which he was a top student. During this time, he acquainted with the work of Konstantin Tsiolkovsky. While studying engineering at the Riga Polytechnic Institute, he carried out trajectory calculations for a flight to Mars, Mars held a special fascination to Zander, and Forward to Mars. He graduated with his degree in 1914, moved to Moscow in 1915. He worked at the Provodnik rubber plant, then in 1919 worked at Aircraft Factory No.4, in 1923, he was married to A. F. Milyukova, and they had a daughter named Astra and a son named Mercury. Mercury died of fever in 1929. In 1908, he made notes about the problems of interplanetary travel in which he addressed issues such as life support, in 1921, he presented his material to the Association of Inventors, where he met and discussed space travel with V. I. Lenin, who was attending the conference, in 1924, he published it in the journal of Technology and Life. 1924 was an active year for Zander. Zander took advantage of this by promoting Tsiolkovskys work, and developing it further, together with Vladimir Vetchinkin and members of a rocketry club at the airforce academy, he founded the Society for Studies of Interplanetary Travel. In an early publication, they would be the first to suggest using the Earths atmosphere as a way of braking a re-entering spacecraft. During questioning after the lecture, he summarised the importance of reaching this planet in particular, because it has an atmosphere, Mars is also known as the red star and this is the emblem of our grand Soviet army. Around this time, Zander became the first to suggest the solar sail as a means of spacecraft propulsion, in 1929-1930, while at the IAM, Zander worked on his first engine, OR-1, which ran on compressed air and gasoline and was based on a modified blowtorch. He also taught courses at the Moscow Aviation Institute during this time, in 1931, Zander was a founding member of GIRD in Moscow. As head of brigade #1, Zander worked on the OR-2 rocket engine and he also worked on the engine and rocket GIRD-10, which flew successfully on 25 November 1933. Zander had designed the rocket, but did not live to see it fly, the crater Tsander on the Moon is named after him
26.
J. B. S. Haldane
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His article on abiogenesis in 1929 introduced the Primordial Soup Theory, and it became the foundation to build physical models for the chemical origin of life. Haldane established human gene maps for haemophilia and colour blindness on the X chromosome and he correctly proposed that sickle-cell disease confers some immunity to malaria. In 1957 he articulated Haldanes dilemma, a limit on the speed of evolution which subsequently proved incorrect. He willed his body for medical studies, as he wanted to remain even in death. Arthur C. Clarke credited him as perhaps the most brilliant science populariser of his generation, nobel laureate Peter Medawar called Haldane the cleverest man I ever knew. Haldane was born in Oxford to John Scott Haldane, a physiologist, scientist, a philosopher and a Liberal, and Louisa Kathleen Trotter and his younger sister, Naomi Mitchison, became a writer, and his uncle was Viscount Haldane and his aunt the author Elizabeth Haldane. Descended from an aristocratic and secular family of the Clan Haldane and he grew up at 11 Crick Road, North Oxford. He learnt to read at the age of three, and at four, after injuring his forehead he asked the doctor, Is this oxyhaemoglobin or carboxyhaemoglobin. From age eight he worked with his father in their home laboratory where he experienced his first self-experimentation and he and his father became their own human guinea pigs, such as in their investigation on the effects of poison gases. In 1899 his family moved to Cherwell, a late Victorian house at the outskirts of Oxford having its private laboratory and his formal education began in 1897 at Oxford Preparatory School, where he gained a First Scholarship in 1904 to Eton. In 1905 he joined Eton, where he experienced severe abuse from senior students for allegedly being arrogant, the indifference of authority left him with a lasting hatred for the English education system. However, the ordeal did not stop him from becoming Captain of the school and he studied mathematics and classics at New College at the University of Oxford and obtained first-class honours in mathematical moderations in 1912 and a first-class honours in 1914. With his father he published his first scientific paper, age 20 and he became engrossed in genetics and presented a paper on gene linkage in vertebrates in the summer of 1912. His first technical paper, a 30-page long article on function, was published. He was promoted to lieutenant on 18 February 1915 and to temporary captain on 18 October. He served in France and Iraq, where he was wounded and he relinquished his commission on 1 April 1920, retaining his rank of captain. For his ferocity and aggressiveness in battles, his commander called him the bravest and dirtiest officer in my Army, between 1919 and 1922 he was a Fellow of New College, Oxford, where he researched physiology and genetics. He then moved to the University of Cambridge, where he accepted a readership in Biochemistry, from 1927 until 1937 he was also Head of Genetical Research at the John Innes Horticultural Institution
27.
John Desmond Bernal
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John Desmond Bernal FRS was a scientist and was a pioneer in X-ray crystallography in molecular biology. He also published extensively on the history of science, in addition, Bernal was a political supporter of Communism and wrote popular books on subjects connecting science and society. His family was Irish, of mixed Italian and Spanish/Portuguese Sephardic Jewish origin on his fathers side and his American mother, née Elizabeth Miller, whose mother was from Antrim, was a graduate of Stanford University and a journalist and had converted to Catholicism. Bernal was educated in England first, for one term, at Stonyhurst College which he hated, because of this he was moved to Bedford School at the age of thirteen. In 1919, he went to Emmanuel College, Cambridge with a scholarship, at Cambridge, Bernal read both mathematics and science for a B. A. degree in 1922, which he followed by another year of natural sciences. Whilst at Cambridge, he became known as Sage, a nickname given to him about 1920 by a young woman working in C. K. Ogdens Bookshop at the corner of Bridge Street. After graduation, Bernal began research under Sir William Bragg at the Davy Faraday Laboratory at the Royal Institution in London, in 1924 he determined the structure of graphite and also did work on the crystal structure of bronze. In 1927, he was appointed as the first lecturer in Structural Crystallography at Cambridge, while at Cambridge, he analysed vitamin B1, pepsin, vitamin D2, the sterols, and the tobacco mosaic virus. He also worked on the structure of water, showing the boomerang shape of its molecule. It was in Bernals research group where, following a working with Tiny Powell at Oxford. Max Perutz arrived as a student from Vienna in 1936 and started the work on haemoglobin that would occupy him most of his career, the same year he was elected as a Fellow of the Royal Society. After the second world war he established Birkbecks Biomolecular Research Laboratory in two Georgian houses in Torrington Square with 15 researchers, aaron Klug worked on ribonuclease whilst Andrew Booth developed some of the earliest computers to help with the computation. Rosalind Franklin joined from Kings College and did pioneering work on viruses until her death in 1957. His Guthrie lecture of 1947 concentrated on proteins as the basis of life, but it was Perutz, still at Cambridge, in the early thirties Bernal had been arguing for peace, but the Spanish civil war changed that. Their subsequent analysis of the effects of bombs on Birmingham and Hull showed that city bombing produced little disruption and production was affected by direct hits on factories. From 1942 he and Zuckerman served as advisers to Lord Louis Mountbatten. Bernal was able to argue on both sides of Project Habbakuk, Pykes proposal to build huge aircraft landing platforms in the North Atlantic made of ice and he rescued Max Perutz from internment, getting him to perform experiments in a meat store freezer below Smithfield Meat Market. After the disaster of the Dieppe raid, Bernal was determined that these mistakes not be repeated in Operation Overlord and he demonstrated the advantages of an artificial harbour to the participants of the Quebec Conference in 1943, as the only British scientist present
28.
Jet Propulsion Laboratory
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The Jet Propulsion Laboratory is a federally funded research and development center and NASA field center in La Cañada Flintridge, California and Pasadena, California, United States. The JPL is managed by the nearby California Institute of Technology for NASA, the laboratorys primary function is the construction and operation of planetary robotic spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASAs Deep Space Network and they are also responsible for managing the JPL Small-Body Database, and provides physical data and lists of publications for all known small Solar System bodies. The JPLs Space Flight Operations Facility and Twenty-Five-Foot Space Simulator are designated National Historic Landmarks, JPL traces its beginnings to 1936 in the Guggenheim Aeronautical Laboratory at the California Institute of Technology when the first set of rocket experiments were carried out in the Arroyo Seco. Malinas thesis advisor was engineer/aerodynamicist Theodore von Kármán, who arranged for U. S. Army financial support for this GALCIT Rocket Project in 1939. In 1941, Malina, Parsons, Forman, Martin Summerfield, in 1943, von Kármán, Malina, Parsons, and Forman established the Aerojet Corporation to manufacture JATO motors. The project took on the name Jet Propulsion Laboratory in November 1943, during JPLs Army years, the laboratory developed two deployed weapon systems, the MGM-5 Corporal and MGM-29 Sergeant intermediate range ballistic missiles. These missiles were the first US ballistic missiles developed at JPL and it also developed a number of other weapons system prototypes, such as the Loki anti-aircraft missile system, and the forerunner of the Aerobee sounding rocket. At various times, it carried out testing at the White Sands Proving Ground, Edwards Air Force Base. A lunar lander was developed in 1938-39 which influenced design of the Apollo Lunar Module in the 1960s. The team lost that proposal to Project Vanguard, and instead embarked on a project to demonstrate ablative re-entry technology using a Jupiter-C rocket. They carried out three successful flights in 1956 and 1957. Using a spare Juno I, the two organizations then launched the United States first satellite, Explorer 1, on February 1,1958, JPL was transferred to NASA in December 1958, becoming the agencys primary planetary spacecraft center. JPL engineers designed and operated Ranger and Surveyor missions to the Moon that prepared the way for Apollo, JPL also led the way in interplanetary exploration with the Mariner missions to Venus, Mars, and Mercury. In 1998, JPL opened the Near-Earth Object Program Office for NASA, as of 2013, it has found 95% of asteroids that are a kilometer or more in diameter that cross Earths orbit. JPL was early to employ women mathematicians, in the 1940s and 1950s, using mechanical calculators, women in an all-female computations group performed trajectory calculations. In 1961, JPL hired Dana Ulery as their first woman engineer to work alongside male engineers as part of the Ranger and Mariner mission tracking teams, when founded, JPLs site was a rocky flood-plain just outside the city limits of Pasadena. Almost all of the 177 acres of the U. S, the city of La Cañada Flintridge, California was incorporated in 1976, well after JPL attained international recognition with a Pasadena address
29.
Halley's Comet
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Halleys Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years. Halley is the only known short-period comet that is visible to the naked eye from Earth. Halley last appeared in the parts of the Solar System in 1986. Halleys returns to the inner Solar System have been observed and recorded by astronomers since at least 240 BC, clear records of the comets appearances were made by Chinese, Babylonian, and medieval European chroniclers, but were not recognized as reappearances of the same object at the time. The comets periodicity was first determined in 1705 by English astronomer Edmond Halley, Comet Halley is commonly pronounced /ˈhæli/, rhyming with valley, or /ˈheɪli/, rhyming with daily. Spellings of Edmond Halleys name during his lifetime included Hailey, Haley, Hayley, Halley, Hawley, Halley was the first comet to be recognized as periodic. Until the Renaissance, the consensus on the nature of comets. This idea was disproved in 1577 by Tycho Brahe, who used parallax measurements to show that comets must lie beyond the Moon, many were still unconvinced that comets orbited the Sun, and assumed instead that they must follow straight paths through the Solar System. In 1687, Sir Isaac Newton published his Philosophiæ Naturalis Principia Mathematica, in which he outlined his laws of gravity and his work on comets was decidedly incomplete. Halley thus concluded that all three comets were, in fact, the same object returning every 76 years, a period that has since been amended to every 75–76 years. After a rough estimate of the perturbations the comet would sustain from the attraction of the planets. Halley died in 1742 before he could observe this himself, Halleys prediction of the comets return proved to be correct, although it was not seen until 25 December 1758, by Johann Georg Palitzsch, a German farmer and amateur astronomer. It did not pass through its perihelion until 13 March 1759 and this effect was computed prior to its return by a team of three French mathematicians, Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute. The confirmation of the return was the first time anything other than planets had been shown to orbit the Sun. It was also one of the earliest successful tests of Newtonian physics, the comet was first named in Halleys honour by French astronomer Nicolas Louis de Lacaille in 1759. Some scholars have proposed that first-century Mesopotamian astronomers already had recognized Halleys Comet as periodic and this theory notes a passage in the Bavli Talmud that refers to a star which appears once in seventy years that makes the captains of the ships err. It was necessary to use ancient Chinese comet observations to constrain their calculations, Halleys orbital period over the last 3 centuries has been between 75–76 years, although it has varied between 74–79 years since 240 BC. Its orbit around the Sun is highly elliptical, with an eccentricity of 0.967
30.
Sailboat
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A sailboat or sailing boat is a boat propelled partly or entirely by sails smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region, although sailboat terminology has varied across history, many terms have specific meanings in the context of modern yachting. A great number of sailboat-types may be distinguished by size, hull configuration, keel type, purpose, number and configuration of masts, and sail plan. Once a common racing configuration, today it gives versatility to cruising boats, a catboat has a single mast mounted far forward and does not carry a jib. Most modern designs have only one sail, the mainsail, however, a dinghy is a type of small open sailboat commonly used for recreation, sail training, and tending a larger vessel. They are popular in youth sailing programs for their short LOA, simple operation and they have three sails, the mainsail, jib, and spinnaker. Ketches are similar to a sloop, but there is a shorter mast astern of the mainmast. The second mast is called the mizzen mast and the sail is called the mizzen sail, a ketch can also be Cutter-rigged with two head sails. A schooner has a mainmast taller than its foremast, distinguishing it from a ketch or a yawl, a schooner can have more than two masts, with the foremast always lower than the foremost main. Traditional topsail schooners have topmasts allowing triangular topsails sails to be flown above their gaff sails, the most common modern sailboat is the sloop, which features one mast and two sails, typically a Bermuda rigged main, and a headsail. This simple configuration is very efficient for sailing into the wind, a smaller headsail is easier for a short-handed crew to manage. A yawl is similar to a ketch, with a mizzen mast carried astern the rudderpost more for balancing the helm than propulsion. Traditional sailboats are monohulls, but multi-hull catamarans and trimarans are gaining popularity, monohull boats generally rely on ballast for stability and usually are displacement hulls. This stabilizing ballast can, in boats designed for racing, be as much as 50% of the weight of the boat and it creates two problems, one, it gives the monohull tremendous inertia, making it less maneuverable and reducing its acceleration. Secondly, unless it has built with buoyant foam or air tanks, if a monohull fills with water. Multihulls rely on the geometry and the stance of the multiple hulls for their stability. Indeed, multihulls are designed to be as light-weight as possible and this absence of ballast also results in some very real performance gains in terms of acceleration, top speed, and maneuverability. The lack of ballast makes it easier to get a multihull on plane, reducing its wetted surface area and thus its drag. The absence of drag improves wind precision
31.
Sailing ship
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A modern sailing ship or sailship is any large wind-powered vessel. Traditionally a sailing ship is a vessel that carries three or more masts with square sails on each. Large sailing vessels that are not ship-rigged may be more referred to by their sail rig, such as schooner, barque, brig. There are many different types of sailing ships, but they all have certain basic things in common, every sailing ship has a hull, rigging and at least one mast to hold up the sails that use the wind to power the ship. The crew who sail a ship are called sailors or hands and they take turns to take the watch, the active managers of the ship and her performance for a period. Watches are traditionally four hours long, some sailing ships use traditional ships bells to tell the time and regulate the watch system, with the bell being rung once for every half hour into the watch and rung eight times at watch end. A severe storm could lead to shipwreck, and the loss of all hands, Sailing ships are limited in their maximum size compared to ships with heat engines, so economies of scale are also limited. The heaviest sailing ships never exceeded 14,000 tons displacement, there are many types of sailing ships, mostly distinguished by their rigging, hull, keel, or number and configuration of masts. There are also types of smaller sailboats not listed here. The steam power was used to drive the winches, hoists, a similar ship Kruzenshtern, a very large sailing vessel without mechanical assists, had a crew of 257 men, compared to the Preussen, which required only 48 men. In 2006, automated control had been taken to the point where sails could be operated by one using a central control unit. The DynaRig technology was first developed in the 1960s in Germany by W. Prolls as an alternative for commercial ships to prepare for a possible future energy crisis. The technology is a version of the same type of sail used by the Preussen. The main difference is that the yards do not swing around a fixed mast but are attached to a rotating mast. DynaRig along with extensive computerization was used in the proof-of-concept Maltese Falcon to enable it to be sailed with no crew aloft, as of 2013, with increasing restrictions on use of bunker fuel, attempts were underway to develop hybrid sailing ships using automated sail and alternative fuels. Tall ship Rigging Sail-plan List of large sailing vessels Cruising Shipbuilding, the History of a Ship from Her Cradle to Her Grave, With a Short Account of Modern Steamships and Torpedoes. The sailing-ship, six years of history. Media related to Sailing ships at Wikimedia Commons
32.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
33.
Photon
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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and is moving at the speed of light. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a photon may be refracted by a lens and exhibit wave interference with itself. The quanta in a light wave cannot be spatially localized, some defined physical parameters of a photon are listed. The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical model of light. The benefit of the model was that it accounted for the frequency dependence of lights energy. The photon model accounted for observations, including the properties of black-body radiation. In that model, light was described by Maxwells equations, in 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles. After Arthur H. Compton won the Nobel Prize in 1927 for his studies, most scientists accepted that light quanta have an independent existence. In the Standard Model of particle physics, photons and other particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass and it has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, in 1900, the German physicist Max Planck was studying black-body radiation and suggested that the energy carried by electromagnetic waves could only be released in packets of energy. In his 1901 article in Annalen der Physik he called these packets energy elements, the word quanta was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1905, Albert Einstein suggested that waves could only exist as discrete wave-packets. He called such a wave-packet the light quantum, the name photon derives from the Greek word for light, φῶς. Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, the name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolferss and Lewiss theories were contradicted by many experiments and never accepted, in physics, a photon is usually denoted by the symbol γ
34.
Speed of light
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The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299792458 metres per second, it is exact because the unit of length, the metre, is defined from this constant, according to special relativity, c is the maximum speed at which all matter and hence information in the universe can travel. It is the speed at which all particles and changes of the associated fields travel in vacuum. Such particles and waves travel at c regardless of the motion of the source or the reference frame of the observer. In the theory of relativity, c interrelates space and time, the speed at which light propagates through transparent materials, such as glass or air, is less than c, similarly, the speed of radio waves in wire cables is slower than c. The ratio between c and the speed v at which light travels in a material is called the index n of the material. In communicating with distant space probes, it can take minutes to hours for a message to get from Earth to the spacecraft, the light seen from stars left them many years ago, allowing the study of the history of the universe by looking at distant objects. The finite speed of light limits the theoretical maximum speed of computers. The speed of light can be used time of flight measurements to measure large distances to high precision. Ole Rømer first demonstrated in 1676 that light travels at a speed by studying the apparent motion of Jupiters moon Io. In 1865, James Clerk Maxwell proposed that light was an electromagnetic wave, in 1905, Albert Einstein postulated that the speed of light c with respect to any inertial frame is a constant and is independent of the motion of the light source. He explored the consequences of that postulate by deriving the theory of relativity and in doing so showed that the parameter c had relevance outside of the context of light and electromagnetism. After centuries of increasingly precise measurements, in 1975 the speed of light was known to be 299792458 m/s with a measurement uncertainty of 4 parts per billion. In 1983, the metre was redefined in the International System of Units as the distance travelled by light in vacuum in 1/299792458 of a second, as a result, the numerical value of c in metres per second is now fixed exactly by the definition of the metre. The speed of light in vacuum is usually denoted by a lowercase c, historically, the symbol V was used as an alternative symbol for the speed of light, introduced by James Clerk Maxwell in 1865. In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch had used c for a different constant later shown to equal √2 times the speed of light in vacuum, in 1894, Paul Drude redefined c with its modern meaning. Einstein used V in his original German-language papers on special relativity in 1905, but in 1907 he switched to c, sometimes c is used for the speed of waves in any material medium, and c0 for the speed of light in vacuum. This article uses c exclusively for the speed of light in vacuum, since 1983, the metre has been defined in the International System of Units as the distance light travels in vacuum in 1⁄299792458 of a second
35.
Solar constant
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The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite as being 1.361 kilowatts per square meter at solar minimum, the solar constant is not a physical constant in the modern CODATA scientific sense, it varies in value, and has been called a misconception. It has been shown to vary historically in the past 400 years over a range of less than 0.2 percent, solar output is nearly, but not quite, constant. Variations in total solar irradiance were small and difficult to detect accurately with technology available before the satellite era, total solar output is now measured as varying by approximately 0. 1%, see solar variation for details. In 1838, Claude Pouillet made the first estimate of the solar constant, using a very simple pyrheliometer he developed, he obtained a value of 1.228 kW/m², close to the current estimate. In 1875, Jules Violle resumed the work of Pouillet and offered a somewhat larger estimate of 1.7 kW/m² based, in part, in 1884, Samuel Pierpont Langley attempted to estimate the solar constant from Mount Whitney in California. By taking readings at different times of day, he tried to correct for effects due to atmospheric absorption, however, the final value he proposed,2.903 kW/m², was much too large. Between 1902 and 1957, measurements by Charles Greeley Abbot and others at various high-altitude sites found values between 1.322 and 1.465 kW/m², Abbot showed that one of Langleys corrections was erroneously applied. Abbots results varied between 1.89 and 2.22 calories, a variation that appeared to be due to the Sun, in 1954 the solar constant was evaluated as 2.00 cal/min/sq cm ± 2%. Current results are about 2.5 percent lower, thus, for the whole Earth, the power is 1. 730×1017 W, plus or minus 3. 5%. The solar constant does not remain constant over long periods of time and this is because the solar constant is evaluated at a fixed distance of 1 Astronomical Unit while the solar irradiance will be affected by the eccentricity of the Earths orbit. Its distance to the Sun varies annually between 147. 1·106 km at aphelion and 152. 1·106 km at perihelion, the Earth receives a total amount of radiation determined by its cross section, but as it rotates this energy is distributed across the entire surface area. The amount reaching the Earths surface is reduced by atmospheric attenutation. At any given moment, the amount of radiation received at a location on the Earths surface depends on the state of the atmosphere, the locations latitude. The solar constant includes all wavelengths of electromagnetic radiation, not just the visible light. It is positively correlated with the apparent magnitude of the Sun which is −26.8, the solar constant and the magnitude of the Sun are two methods of describing the apparent brightness of the Sun, though the magnitude is based on the Suns visual output only. The angular diameter of the Earth as seen from the Sun is approximately 1/11,700 radians, thus the Sun emits about 2.2 billion times the amount of radiation that is caught by Earth, in other words about 3. 86×1026 watts. Space-based observations of solar irradiance started in 1978 and these measurements show that the solar constant is not constant
36.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
37.
Pascal (unit)
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The pascal is the SI derived unit of pressure used to quantify internal pressure, stress, Youngs modulus and ultimate tensile strength. It is defined as one newton per square meter and it is named after the French polymath Blaise Pascal. Common multiple units of the pascal are the hectopascal which is equal to one millibar, the unit of measurement called standard atmosphere is defined as 101,325 Pa and approximates to the average pressure at sea-level at the latitude 45° N. Meteorological reports typically state atmospheric pressure in hectopascals, the unit is named after Blaise Pascal, noted for his contributions to hydrodynamics and hydrostatics, and experiments with a barometer. The name pascal was adopted for the SI unit newton per square metre by the 14th General Conference on Weights, one pascal is the pressure exerted by a force of magnitude one newton perpendicularly upon an area of one square metre. The unit of measurement called atmosphere or standard atmosphere is 101325 Pa and this value is often used as a reference pressure and specified as such in some national and international standards, such as ISO2787, ISO2533 and ISO5024. In contrast, IUPAC recommends the use of 100 kPa as a standard pressure when reporting the properties of substances, geophysicists use the gigapascal in measuring or calculating tectonic stresses and pressures within the Earth. Medical elastography measures tissue stiffness non-invasively with ultrasound or magnetic resonance imaging, in materials science and engineering, the pascal measures the stiffness, tensile strength and compressive strength of materials. In engineering use, because the pascal represents a small quantity. The pascal is also equivalent to the SI unit of energy density and this applies not only to the thermodynamics of pressurised gases, but also to the energy density of electric, magnetic, and gravitational fields. In measurements of sound pressure, or loudness of sound, one pascal is equal to 94 decibels SPL, the quietest sound a human can hear, known as the threshold of hearing, is 0 dB SPL, or 20 µPa. The airtightness of buildings is measured at 50 Pa, the units of atmospheric pressure commonly used in meteorology were formerly the bar, which was close to the average air pressure on Earth, and the millibar. Since the introduction of SI units, meteorologists generally measure pressures in hectopascals unit, exceptions include Canada and Portugal, which use kilopascals. In many other fields of science, the SI is preferred, many countries also use the millibar or hectopascal to give aviation altimeter settings. In practically all fields, the kilopascal is used instead. Centimetre of water Metric prefix Orders of magnitude Pascals law
38.
Specular reflection
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Specular reflection, also known as regular reflection is the mirror-like reflection of waves, such as light, from a surface. In this process, each incident ray is reflected, with the reflected ray having the same angle to the normal as the incident ray. The result is that an image reflected by the surface is reproduced in mirror-like fashion, the law of reflection states that for each incident ray the angle of incidence equals the angle of reflection, and the incident, normal, and reflected directions are coplanar. This behavior was first described by Hero of Alexandria, when light hits a surface, there are three possible outcomes. Light may be absorbed by the material, light may be transmitted through the surface, or light may be reflected back. Materials often show some mix of these behaviors, with the proportion of light that goes to each depending on the properties of the material, the wavelength of the light, and the angle of incidence. For most interfaces between materials, the fraction of the light that is reflected increases with increasing angle of incidence θ i, reflected light can be divided into two sub-types, specular reflection and diffuse reflection. Specular reflection reflects all light at the angle, whereas diffuse reflection reflects in a broad range of directions. An example of the distinction between specular and diffuse reflection would be glossy and matte paints, matte paints have almost exclusively diffuse reflection, while glossy paints have both specular and diffuse reflection. A surface built from a powder, such as plaster, can be a nearly perfect diffuser. The reflecting material of mirrors is usually aluminum or silver, the law of reflection describes the angle of reflected light, the angle of incident light is the same as the angle of the reflected light. If a mirror becomes very small compared to the wavelength, the law of reflection no longer holds, the law of reflection can also be equivalently expressed using linear algebra. The direction of a ray is determined by the vector of incidence. Different authors may define the incident and reflection directions with different signs, reflectivity is the ratio of the power of the reflected wave to that of the incident wave. It is a function of the wavelength of radiation, and is related to the index of the material as expressed by Fresnels equations. The polarization of the light depends on the symmetry of the arrangement of the incident probing light with respect to the absorbing transitions dipole moments in the material. Measurement of specular reflection is performed with normal or varying incidence reflection spectrophotometers using a scanning variable-wavelength light source, lower quality measurements using a glossmeter quantify the glossy appearance of a surface in gloss units. Specular reflection from a dielectric such as water can affect polarization, the image in a flat mirror has these features, It is the same distance behind the mirror as the object is in front
39.
Emissivity
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The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation and it may include both visible radiation and infrared radiation, which is not visible to human eyes, the thermal radiation from very hot objects is easily visible to the eye. Quantitatively, emissivity is the ratio of the radiation from a surface to the radiation from an ideal black surface at the same temperature as given by the Stefan–Boltzmann law. The ratio varies from 0 to 1, emissivities are important in several contexts, insulated windows. – Warm surfaces are usually cooled directly by air, but they also cool themselves by emitting thermal radiation and this second cooling mechanism is important for simple glass windows, which have emissivities close to the maximum possible value of 1.0. Low-E windows with transparent low emissivity coatings emit less radiation than ordinary windows. In winter, these coatings can halve the rate at which a window loses heat compared to a glass window. – Similarly, solar heat collectors lose heat by emitting thermal radiation, advanced solar collectors incorporate selective surfaces that have very low emissivities. These collectors waste very little of the energy through emission of thermal radiation. – The planets are solar thermal collectors on a large scale, the temperature of a planets surface is determined by the balance between the heat absorbed by the planet from sunlight, heat emitted from its core, and thermal radiation emitted back into space. Emissivity of a planet is determined by the nature of its surface, – Pyrometers and infrared cameras are instruments used to measure the temperature of an object by using its thermal radiation, no actual contact with the object is needed. The calibration of these involves the emissivity of the surface thats being measured. Emissivities ε can be measured using simple devices such as Leslies cube in conjunction with a radiation detector such as a thermopile or a bolometer. The apparatus compares the thermal radiation from a surface to be tested with the radiation from a nearly ideal. The detectors are essentially black absorbers with very sensitive thermometers that record the temperature rise when exposed to thermal radiation. For measuring room temperature emissivities, the detectors must absorb thermal radiation completely at infrared wavelengths near 10×10−6 meters, visible light has a wavelength range of about 0.4 to 0. 7×10−6 meters from violet to deep red. Emissivity measurements for many surfaces are compiled in many handbooks and texts, some of these are listed in the following table. Notes, These emissivities are the total hemispherical emissivities from the surfaces, the values of the emissivities apply to materials that are optically thick
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Solar wind
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The solar wind is a stream of charged particles released from the upper atmosphere of the Sun. This plasma consists of electrons, protons and alpha particles with thermal energies between 1.5 and 10 keV. Embedded within the plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and its particles can escape the Suns gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. At a distance of more than a few radii from the sun. The flow of the wind is no longer supersonic at the termination shock. The Voyager 2 spacecraft crossed the shock more than five times between 30 August and 10 December 2007, Voyager 2 crossed the shock about a billion kilometers closer to the Sun than the 13.5 billion kilometer distance where Voyager 1 came upon the termination shock. The spacecraft moved outward through the shock into the heliosheath. Other related phenomena include the aurora, the tails of comets that always point away from the Sun. The existence of flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare, george FitzGerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days. In 1910 British astrophysicist Arthur Eddington essentially suggested the existence of the wind, without naming it. The idea never caught on even though Eddington had also made a similar suggestion at a Royal Institution address the previous year. In the latter case, he postulated that the material consisted of electrons while in his study of Comet Morehouse he supposed them to be ions. The first person to suggest that the material consisted of both ions and electrons was Kristian Birkeland. His geomagnetic surveys showed that activity was nearly uninterrupted. In 1916, Birkeland proposed that, From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, in other words, the solar wind consists of both negative electrons and positive ions. Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun
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Attitude control
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Attitude control is controlling the orientation of an object with respect to an inertial frame of reference or another entity. The integrated field that studies the combination of sensors, actuators and algorithms is called Guidance, Navigation, a spacecrafts attitude must typically be stabilized and controlled for a variety of reasons. Propulsion system thrusters are fired only occasionally to make desired changes in spin rate, if desired, the spinning may be stopped through the use of thrusters or by yo-yo de-spin. The Pioneer 10 and Pioneer 11 probes in the solar system are examples of spin-stabilized spacecraft. Three-axis stabilization is a method of spacecraft attitude control in which the spacecraft is held fixed in the desired orientation without any rotation. One method is to use thrusters to continually nudge the spacecraft back. Thrusters may also be referred to as control systems, or reaction control systems. The space probes Voyager 1 and Voyager 2 employ this method, another method for achieving three-axis stabilization is to use electrically powered reaction wheels, also called momentum wheels, which are mounted on three orthogonal axes aboard the spacecraft. They provide a means to trade angular momentum back and forth between spacecraft and wheels, to rotate the vehicle on a given axis, the reaction wheel on that axis is accelerated in the opposite direction. To rotate the back, the wheel is slowed. This is done during maneuvers called momentum desaturation or momentum unload maneuvers, most spacecraft use a system of thrusters to apply the torque for desaturation maneuvers. A different approach was used by the Hubble Space Telescope, which had sensitive optics that could be contaminated by thruster exhaust, there are advantages and disadvantages to both spin stabilization and three-axis stabilization. Many spacecraft have components that require articulation, Voyager and Galileo, for example, were designed with scan platforms for pointing optical instruments at their targets largely independently of spacecraft orientation. Many spacecraft, such as Mars orbiters, have solar panels that must track the Sun so they can provide power to the spacecraft. Cassinis main engine nozzles are steerable, knowing where to point a solar panel, or scan platform, or a nozzle — that is, how to articulate it—requires knowledge of the spacecrafts attitude. Because AACS keeps track of the attitude, the Suns location. It logically falls to one subsystem, then, to manage both attitude and articulation, the name AACS may even be carried over to a spacecraft even if it has no appendages to articulate. Many sensors generate outputs that reflect the rate of change in attitude and these require a known initial attitude, or external information to use them to determine attitude
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Center of mass
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The distribution of mass is balanced around the center of mass and the average of the weighted position coordinates of the distributed mass defines its coordinates. Calculations in mechanics are simplified when formulated with respect to the center of mass. It is a point where entire mass of an object may be assumed to be concentrated to visualise its motion. In other words, the center of mass is the equivalent of a given object for application of Newtons laws of motion. In the case of a rigid body, the center of mass is fixed in relation to the body. The center of mass may be located outside the body, as is sometimes the case for hollow or open-shaped objects. In the case of a distribution of separate bodies, such as the planets of the Solar System, in orbital mechanics, the equations of motion of planets are formulated as point masses located at the centers of mass. The center of mass frame is a frame in which the center of mass of a system is at rest with respect to the origin of the coordinate system. The concept of center of mass in the form of the center of gravity was first introduced by the ancient Greek physicist, mathematician, and engineer Archimedes of Syracuse. He worked with simplified assumptions about gravity that amount to a uniform field, in work on floating bodies he demonstrated that the orientation of a floating object is the one that makes its center of mass as low as possible. He developed mathematical techniques for finding the centers of mass of objects of uniform density of various well-defined shapes, Newtons second law is reformulated with respect to the center of mass in Eulers first law. The center of mass is the point at the center of a distribution of mass in space that has the property that the weighted position vectors relative to this point sum to zero. In analogy to statistics, the center of mass is the location of a distribution of mass in space. Solving this equation for R yields the formula R =1 M ∑ i =1 n m i r i, solve this equation for the coordinates R to obtain R =1 M ∭ Q ρ r d V, where M is the total mass in the volume. If a continuous mass distribution has density, which means ρ is constant. The center of mass is not generally the point at which a plane separates the distribution of mass into two equal halves, in analogy with statistics, the median is not the same as the mean. The coordinates R of the center of mass of a system, P1 and P2, with masses m1. The percentages of mass at each point can be viewed as projective coordinates of the point R on this line, another way of interpreting the process here is the mechanical balancing of moments about an arbitrary point
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Solar System
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The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, the heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium, it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic
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Aerobraking
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Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit by flying the vehicle through the atmosphere at the low point of the orbit. The resulting drag slows the spacecraft, Aerobraking is used when a spacecraft requires a low orbit after arriving at a body with an atmosphere, and it requires less fuel than does the direct use of a rocket engine. When an interplanetary vehicle arrives at its destination, it must change its velocity to remain in the vicinity of that body. When a low, near-circular orbit around a body with substantial gravity is needed, if done by direct propulsion, the rocket equation dictates that a large fraction of the spacecraft mass must be fuel. This in turn means the spacecraft is limited to a small science payload and/or the use of a very large. Provided the target body has an atmosphere, aerobraking can be used to reduce fuel requirements, the use of a relatively small burn allows the spacecraft to be captured into a very elongated elliptic orbit. Aerobraking is then used to circularize the orbit, if the atmosphere is thick enough, a single pass through it can be sufficient to slow a spacecraft as needed. However, aerobraking is typically done with many passes through a higher altitude. When aerobraking is done in this way, there is sufficient time after each pass to measure the change in velocity, achieving the final orbit using this method takes a long time, and may require several hundred passes through the atmosphere of the planet or moon. After the last aerobraking pass, the spacecraft must be given more kinetic energy via rocket engines in order to raise the periapsis above the atmosphere. The kinetic energy dissipated by aerobraking is converted to heat, meaning that a spacecraft using the technique needs to be capable of dissipating this heat. The force density, of roughly 0.2 N per square meter, or basically the aerodynamic resistance you experience when walking slowly. Aerocapture is a related but more extreme method in which no initial orbit-injection burn is performed, instead, the spacecraft plunges deeply into the atmosphere without an initial insertion burn, and emerges from this single pass in the atmosphere with an apoapsis near that of the desired orbit. Several small correction burns are used to raise the periapsis. This method was originally planned for the Mars Odyssey orbiter, another related technique is that of aerogravity assist, in which the spacecraft flies through the upper atmosphere and utilises aerodynamic lift instead of drag at the point of closest approach. Since no spacecraft can yet aerobrake safely on its own, this requires constant attention from both human controllers and the Deep Space Network and this is particularly true near the end of the process, when the drag passes are relatively close together. NASA has used aerobraking four times to modify a spacecraft’s orbit to one with lower energy, reduced apoapsis altitude, on 19 March 1991, aerobraking was demonstrated by the Hiten spacecraft. This was the first aerobraking maneuver by a space probe
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Gravitational lens
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A gravitational lens is a distribution of matter between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einsteins general theory of relativity, fritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses. It was not until 1979 that this effect was confirmed by observation of the so-called Twin QSO SBS 0957+561. Unlike an optical lens, a lens produces a maximum deflection of light that passes closest to its center. Consequently, a lens has no single focal point, but a focal line. The term lens in the context of light deflection was first used by O. J. Lodge, who remarked that it is not permissible to say that the gravitational field acts like a lens. If the source, the lensing object, and the observer lie in a straight line. If there is any misalignment, the observer will see an arc segment instead and this phenomenon was first mentioned in 1924 by the St. Petersburg physicist Orest Chwolson, and quantified by Albert Einstein in 1936. It is usually referred to in the literature as an Einstein ring, more commonly, where the lensing mass is complex and does not cause a spherical distortion of space–time, the source will resemble partial arcs scattered around the lens. There are three classes of gravitational lensing,1, strong lensing, where there are easily visible distortions such as the formation of Einstein rings, arcs, and multiple images. The lensing shows up statistically as a stretching of the background objects perpendicular to the direction to the center of the lens. By measuring the shapes and orientations of large numbers of distant galaxies and this, in turn, can be used to reconstruct the mass distribution in the area, in particular, the background distribution of dark matter can be reconstructed. Since galaxies are elliptical and the weak gravitational lensing signal is small. They may also provide an important future constraint on dark energy, Microlensing, where no distortion in shape can be seen but the amount of light received from a background object changes in time. The lensing object may be stars in the Milky Way in one case, with the background source being stars in a remote galaxy, or, in another case. The effect is small, such that even a galaxy with a more than 100 billion times that of the Sun will produce multiple images separated by only a few arcseconds. Galaxy clusters can produce separations of several arcminutes, in both cases the galaxies and sources are quite distant, many hundreds of megaparsecs away from our Galaxy
