The gravitational force, or more g-force, is a measurement of the type of acceleration that causes a perception of weight. Despite the name, it is incorrect to consider g-force a fundamental force, as "g-force" is a type of acceleration that can be measured with an accelerometer. Since g-force accelerations indirectly produce weight, any g-force can be described as a "weight per unit mass"; when the g-force acceleration is produced by the surface of one object being pushed by the surface of another object, the reaction force to this push produces an equal and opposite weight for every unit of an object's mass. The types of forces involved are transmitted through objects by interior mechanical stresses; the g-force acceleration is the cause of an object's acceleration in relation to free fall. The g-force acceleration experienced by an object is due to the vector sum of all non-gravitational and non-electromagnetic forces acting on an object's freedom to move. In practice, as noted, these are surface-contact forces between objects.
Such forces cause stresses and strains on objects, since they must be transmitted from an object surface. Because of these strains, large g-forces may be destructive. Gravitation acting alone does not produce a g-force though g-forces are expressed in multiples of the acceleration of a standard gravity. Thus, the standard gravitational acceleration at the Earth's surface produces g-force only indirectly, as a result of resistance to it by mechanical forces; these mechanical forces produce the g-force acceleration on a mass. For example, the 1 g force on an object sitting on the Earth's surface is caused by mechanical force exerted in the upward direction by the ground, keeping the object from going into free fall; the upward contact force from the ground ensures that an object at rest on the Earth's surface is accelerating relative to the free-fall condition.. Stress inside the object is ensured from the fact that the ground contact forces are transmitted only from the point of contact with the ground.
Objects allowed to free-fall in an inertial trajectory under the influence of gravitation only, feel no g-force acceleration, a condition known as zero-g. This is demonstrated by the "zero-g" conditions inside an elevator falling toward the Earth's center, or conditions inside a spacecraft in Earth orbit; these are examples of coordinate acceleration without a sensation of weight. The experience of no g-force, however it is produced, is synonymous with weightlessness. In the absence of gravitational fields, or in directions at right angles to them and coordinate accelerations are the same, any coordinate acceleration must be produced by a corresponding g-force acceleration. An example here is a rocket in free space, in which simple changes in velocity are produced by the engines and produce g-forces on the rocket and passengers.. The unit of measure of acceleration in the International System of Units is m/s2. However, to distinguish acceleration relative to free fall from simple acceleration, the unit g is used.
One g is the acceleration due to gravity at the Earth's surface and is the standard gravity, defined as 9.80665 metres per second squared, or equivalently 9.80665 newtons of force per kilogram of mass. Note that the unit definition does not vary with location—the g-force when standing on the moon is about 0.181 g. The unit g is not one of the SI units. "g" should not be confused with "G", the standard symbol for the gravitational constant. This notation is used in aviation in aerobatic or combat military aviation, to describe the increased forces that must be overcome by pilots in order to remain conscious and not G-LOC. Measurement of g-force is achieved using an accelerometer. In certain cases, g-forces may be measured using suitably calibrated scales. Specific force is another name, used for g-force; the term g-force is technically incorrect. While acceleration is a vector quantity, g-force accelerations are expressed as a scalar, with positive g-forces pointing downward, negative g-forces pointing upward.
Thus, a g-force is a vector of acceleration. It is an acceleration that must be produced by a mechanical force, cannot be produced by simple gravitation. Objects acted upon only by gravitation experience no g-force, are weightless. G-forces, when multiplied by a mass upon which they act, are associated with a certain type of mechanical force in the correct sense of the term force, this force produces compressive stress and tensile stress; such forces result in the operational sensation of weight, but the equation carries a sign change due to the definition of positive weight in the direction downward, so the direction of weight-force is opposite to the direction of g-force acceleration: Weight = mass × −g-forceThe reason for the minus sign is that the actual force on an object produced by a g-force is in the opposite direction to the sign of the g-force, since in physics, weight is not the force that produces the acceleration, but rather the equal-and-opposite reaction force to it. If the direction upward is taken as positive positive g-force produces a force/w
A transdermal patch is a medicated adhesive patch, placed on the skin to deliver a specific dose of medication through the skin and into the bloodstream. This promotes healing to an injured area of the body. An advantage of a transdermal drug delivery route over other types of medication delivery such as oral, intravenous, etc. is that the patch provides a controlled release of the medication into the patient through either a porous membrane covering a reservoir of medication or through body heat melting thin layers of medication embedded in the adhesive. The main disadvantage to transdermal delivery systems stems from the fact that the skin is a effective barrier. A wide variety of pharmaceuticals are now available in transdermal patch form; the first commercially available prescription patch was approved by the U. S. Food and Drug Administration in December 1979; these patches administered scopolamine for motion sickness. The highest selling transdermal patch in the United States of America is the nicotine patch, which releases nicotine in controlled doses to help with cessation of tobacco smoking.
The first commercially available vapour patch to reduce smoking was approved in Europe in 2007. Two opioid medications used to provide round-the-clock relief for severe pain are prescribed in patch form, fentanyl CII and buprenorphine CIII. Hormonal patches estrogen patches are sometimes prescribed to treat menopausal symptoms and to transgender women as a type of hormone replacement therapy. Contraceptive patch and testosterone CIII patches for both women. Nitroglycerin patches are sometimes prescribed for the treatment of angina in lieu of sublingual pills. Transdermal scopolamine is used as a treatment for motion sickness; the anti-hypertensive drug clonidine is available in transdermal patch form Emsam, a transdermal form of the MAOI selegiline, became the first transdermal delivery agent for an antidepressant approved for use in the U. S. in March 2006. Daytrana, the first methylphenidate transdermal delivery system for the treatment of Attention Deficit Hyperactivity Disorder, was approved by the FDA in April 2006.
Vitamin B12 may be administered through a transdermal patch. Cyanocobalamin, a stable form of vitamin B12, is compatible with transdermal patching. 5-Hydroxytryptophan can be administered through a transdermal patch, launched in the United Kingdom in early 2014. Rivastigmine, an Alzheimer's treatment medication, was released in patch form in 2007, under the brand name Exelon In 2005, the FDA announced that they were investigating reports of death and other serious adverse events related to narcotic overdose in patients using Duragesic, the fentanyl transdermal patch for pain control; the Duragesic product label was subsequently updated to add safety information in June 2005. In 2007, Shire and Noven Pharmaceuticals, manufacturers of the Daytrana ADHD patch, announced a voluntary recall of several lots of the patch due to problems with separating the patch from its protective release liner. Since no further problems with either the patch or its protective packaging have been reported. In 2008, two manufacturers of the Fentanyl patch, ALZA Pharmaceuticals and Sandoz, subsequently issued a recall of their versions of the patch due to a manufacturing defect that allowed the gel containing the medication to leak out of its pouch too which could result in overdose and death.
As of March 2009, Sandoz—now manufactured by ALZA—no longer uses gel in its transdermal fentanyl patch. In 2009, the FDA announced a public health advisory warning of the risk of burns during MRI scans from transdermal drug patches with metallic backings. Patients should be advised to remove any medicated patch prior to an MRI scan and replace it with a new patch after the scan is complete. In 2009, an article in Europace journal detailed stories of skin burns that occurred with transdermal patches that contain metal caused by shock therapy from external as well as internal cardioverter defibrillators; the main components to a transdermal patch are: Liner - Protects the patch during storage. The liner is removed prior to use. Drug - Drug solution in direct contact with release liner Adhesive - Serves to adhere the components of the patch together along with adhering the patch to the skin Membrane - Controls the release of the drug from the reservoir and multi-layer patches Backing - Protects the patch from the outer environment Permeation Enhancer - These are permeation promoters for drugs, which increase delivery of drug.
Matrix Filler - Provides bulk to the matrix, some act as matrix stiffening agents. Other components include: Stabilizer, Preservatives etc. There are five main types of transdermal patches; the adhesive layer of this system contains the drug. In this type of patch the adhesive layer not only serves to adhere the various layers together, along with the entire system to the skin, but is responsible for the releasing of the drug; the adhesive layer is surrounded by a backing. The multi-layer drug-in-adhesive patch is similar to the single-layer system.
A space suit is a garment worn to keep a human alive in the harsh environment of outer space and temperature extremes. Space suits are worn inside spacecraft as a safety precaution in case of loss of cabin pressure, are necessary for extravehicular activity, work done outside spacecraft. Space suits have been worn for such work in Earth orbit, on the surface of the Moon, en route back to Earth from the Moon. Modern space suits augment the basic pressure garment with a complex system of equipment and environmental systems designed to keep the wearer comfortable, to minimize the effort required to bend the limbs, resisting a soft pressure garment's natural tendency to stiffen against the vacuum. A self-contained oxygen supply and environmental control system is employed to allow complete freedom of movement, independent of the spacecraft. Three types of space suits exist for different purposes: IVA, EVA, IEVA. IVA suits are meant to be worn inside a pressurized spacecraft, are therefore lighter and more comfortable.
IEVA suits are meant for use such as the Gemini G4C suit. They include more protection from the harsh conditions of space, such as protection from micrometeorites and extreme temperature change. EVA suits, such as the EMU, are used outside spacecraft, for either planetary exploration or spacewalks, they must protect the wearer against all conditions of space, as well as provide mobility and functionality. Some of these requirements apply to pressure suits worn for other specialized tasks, such as high-altitude reconnaissance flight. At altitudes above the Armstrong limit, around 19,000 m, water boils at body temperature and pressurized suits are needed; the first full-pressure suits for use at extreme altitudes were designed by individual inventors as early as the 1930s. The first space suit worn by a human in space was the Soviet SK-1 suit worn by Yuri Gagarin in 1961. A space suit must perform several functions to allow its occupant to work safely and comfortably, inside or outside a spacecraft.
It must provide: A stable internal pressure. This can be less than earth's atmosphere, as there is no need for the space suit to carry nitrogen. Lower pressure allows for greater mobility, but requires the suit occupant to breathe pure oxygen for a time before going into this lower pressure, to avoid decompression sickness. Mobility. Movement is opposed by the pressure of the suit. See the Theories of space suit design section. Supply of breathable oxygen and elimination of carbon dioxide. Unlike on Earth, where heat can be transferred by convection to the atmosphere, in space, heat can be lost only by thermal radiation or by conduction to objects in physical contact with the exterior of the suit. Since the temperature on the outside of the suit varies between sunlight and shadow, the suit is insulated, air temperature is maintained at a comfortable level. A communication system, with external electrical connection to the spacecraft or PLSS Means of collecting and containing solid and liquid bodily waste Advanced suits better regulate the astronaut's temperature with a Liquid Cooling and Ventilation Garment in contact with the astronaut's skin, from which the heat is dumped into space through an external radiator in the PLSS.
Additional requirements for EVA include: Shielding against ultraviolet radiation Limited shielding against particle radiation Means to maneuver, release, and/or tether onto a spacecraft Protection against small micrometeoroids, some traveling at up to 27,000 kilometers per hour, provided by a puncture-resistant Thermal Micrometeoroid Garment, the outermost layer of the suit. Experience has shown the greatest chance of exposure occurs near the gravitational field of a moon or planet, so these were first employed on the Apollo lunar EVA suits; as part of astronautical hygiene control, a space suit is essential for extravehicular activity. The Apollo/Skylab A7L suit included eleven layers in all: an inner liner, a LCVG, a pressure bladder, a restraint layer, another liner, a Thermal Micrometeoroid Garment consisting of five aluminized insulation layers and an external layer of white Ortho-Fabric; this space suit is capable of protecting the astronaut from temperatures ranging from −156 °C to 121 °C.
During exploration of the moon or Mars, there will be the potential for lunar/Martian dust to be retained on the space suit. When the space suit is removed on return to the spacecraft, there will be the potential for the dust to contaminate surfaces and increase the risks of inhalation and skin exposure. Astronautical hygienists are testing materials with reduced dust retention times and the potential to control the dust exposure risks during planetary exploration. Novel ingress/egress approaches, such as suitports, are being explored as well. In NASA space suits, communications are provided via a cap worn over the head, which includes earphones and a microphone. Due to the coloration of the version used for Apollo and Skylab, which resembled the coloration of the comic strip character Snoopy, these caps became known as "Snoopy caps." To supply enough oxygen for respiration, a space suit using pure oxygen must have a pressure of about 32.4 kPa, equal to the 20.7 kPa partial pres
Extravehicular activity is any activity done by an astronaut or cosmonaut outside a spacecraft beyond the Earth's appreciable atmosphere. The term most applies to a spacewalk made outside a craft orbiting Earth, but has applied to lunar surface exploration performed by six pairs of American astronauts in the Apollo program from 1969 to 1972. On each of the last three of these missions, astronauts performed deep-space EVAs on the return to Earth, to retrieve film canisters from the outside of the spacecraft. Astronauts used EVA in 1973 to repair launch damage to Skylab, the United States' first space station. A "Stand-up" EVA is when an astronaut does not leave a spacecraft, but is reliant on the spacesuit for environmental support, its name derives from the astronaut "standing up" in the open hatch to record or assist a spacewalking astronaut. EVAs may be untethered. Untethered spacewalks were only performed on three missions in 1984 using the Manned Maneuvering Unit, on a flight test in 1994 of the Simplified Aid For EVA Rescue, a safety device worn on tethered U.
S. EVAs; the Soviet Union/Russia, the United States, China have conducted EVAs. NASA planners invented the term extravehicular activity in the early 1960s for the Apollo program to land men on the Moon, because the astronauts would leave the spacecraft to collect lunar material samples and deploy scientific experiments. To support this, other Apollo objectives, the Gemini program was spun off to develop the capability for astronauts to work outside a two-man Earth orbiting spacecraft. However, the Soviet Union was fiercely competitive in holding the early lead it had gained in manned spaceflight, so the Soviet Communist Party, led by Nikita Khrushchev, ordered the conversion of its single-pilot Vostok capsule into a two- or three-person craft named Voskhod, in order to compete with Gemini and Apollo; the Soviets were able to launch two Voskhod capsules before U. S. was able to launch its first manned Gemini. The Voskhod's avionics required cooling by cabin air to prevent overheating, therefore an airlock was required for the spacewalking cosmonaut to exit and re-enter the cabin while it remained pressurized.
By contrast, the Gemini avionics did not require air cooling, allowing the spacewalking astronaut to exit and re-enter the depressurized cabin through an open hatch. Because of this, the American and Soviet space programs developed different definitions for the duration of an EVA; the Soviet definition begins when the outer airlock hatch is open and the cosmonaut is in vacuum. An American EVA began; the USA has changed its EVA definition since. The first EVA was performed on March 18, 1965, by Soviet cosmonaut Alexei Leonov, who spent 12 minutes outside the Voskhod 2 spacecraft. Carrying a white metal backpack containing 45 minutes worth of breathing and pressurization oxygen, Leonov had no means to control his motion other than pulling on his 15.35 m tether. After the flight, he claimed this was easy, but his space suit ballooned from its internal pressure against the vacuum of space, stiffening so much that he could not activate the shutter on his chest-mounted camera. At the end of his space walk, the suit stiffening caused a more serious problem: Leonov had to re-enter the capsule through the inflatable cloth airlock, 1.2 m in diameter and 2.5 m long.
He improperly got stuck sideways. He could not get back in without reducing the pressure in his suit, risking "the bends"; this added another 12 minutes to his time in vacuum, he was overheated by 1.8 °C from the exertion. It would be four years before the Soviets tried another EVA, they misrepresented to the press how difficult Leonov found it to work in weightlessness and concealed the problems encountered until after the end of the Cold War. The first American spacewalk was performed on June 3, 1965, by Ed White from the second manned Gemini flight, Gemini 4, for 21 minutes. White was tethered to the spacecraft, his oxygen was supplied through a 25-foot umbilical, which carried communications and biomedical instrumentation, he was the first to control his motion in space with a Hand-Held Maneuvering Unit, which worked well but only carried enough propellant for 20 seconds. White found his tether useful for limiting his distance from the spacecraft but difficult to use for moving around, contrary to Leonov's claim.
However, a defect in the capsule's hatch latching mechanism caused difficulties opening and closing the hatch, which delayed the start of the EVA and put White and his crewmate at risk of not getting back to Earth alive. No EVAs were planned on the next three Gemini flights; the next EVA was planned to be made by David Scott on Gemini 8, but that mission had to be aborted due to a critical spacecraft malfunction before the EVA could be conducted. Astronauts on the next three Gemini flights, performed several EVAs, but none was able to work for long periods outside the spacecraft without tiring and overheating. Cernan attempted but failed to test an Air Force Astronaut Maneuvering Unit which included a self-contained oxygen system. On November 13, 1966, Edwin "Buzz" Aldrin became the first to work in space without tiring, on the Gemini 12 last flight. Aldrin worked outside the spacecraft for 2 hours and 6 minutes, in additio
Space adaptation syndrome
Space adaptation syndrome or space sickness is a condition experienced by as many as half of all space travelers during their adaptation to weightlessness once in orbit. It is the opposite of terrestrial motion sickness since it occurs when the environment and the person appear visually to be in motion relative to one another though there is no corresponding sensation of bodily movement originating from the vestibular system; when the vestibular system and the visual system report incongruous states of motion, the result is nausea and other symptoms of disorientation known as motion sickness. According to contemporary sensory conflict theory, such conditions happen when the vestibular system and the visual system do not present a synchronized and unified representation of one's body and surroundings; this theory is known as neural mismatch, implying a mismatch occurring between ongoing sensory experience and long-term memory rather than between components of the vestibular and visual systems, emphasizing "the limbic system in integration of sensory information and long-term memory, in the expression of the symptoms of motion sickness, the impact of anti-motion-sickness drugs and stress hormones on limbic system function.
The limbic system may be the neural mismatch center of the brain." At present a "fully adequate theory of motion sickness is not presently available" but at present the sensory conflict theory, referring to "a discontinuity between either visual and somatosensory input, or semicircular canal and otolith input", may be the best available. Space adaptation syndrome or space sickness is a kind of motion sickness that can occur when one's surroundings visually appear to be in motion, but without a corresponding sense of bodily motion; this incongruous condition can occur during space travel when changes in g-forces compromise one's spatial orientation. According to Science Daily, "Gravity plays a major role in our spatial orientation. Changes in gravitational forces, such as the transition to weightlessness during a space voyage, influence our spatial orientation and require adaptation by many of the physiological processes in which our balance system plays a part; as long as this adaptation is incomplete, this can be coupled to nausea, visual illusions, disorientation."
Sleep deprivation can increase susceptibility to space sickness, making symptoms worse and longer-lasting. According to the sensory conflict hypothesis, space sickness is the opposite of the kinds of motion-related disorientation that occur in the presence of gravity, known as terrestrial motion sickness, such as becoming carsick, seasick, or airsick. In such cases, in contrast to space sickness, one's surroundings seem visually immobile while one's body feels itself to be in motion. Contemporary motion sickness medications can counter all kinds of motion disorientation including space sickness by temporarily suppressing the vestibular system, but are used for space travel because it is considered better to allow space travelers to adapt over the first one to seven days rather than to suffer the drowsiness and other side effects of medication taken over a longer period. However, transdermal dimenhydrinate anti-nausea patches are used whenever space suits are worn because vomiting into a space suit could be fatal by obscuring vision or blocking airflow.
Space suits are worn during launch and landing by NASA crew members and always for extra-vehicular activities. EVAs are not scheduled for the first days of a mission to allow the crew to adapt, transdermal dimenhydrinate patches are used as an additional backup measure. Just as space sickness has the opposite cause compared to terrestrial motion sickness, the two conditions have opposite non-medicinal remedies; the idea of sensory conflict implies that the most direct remedy for motion sickness in general is to resolve the conflict by re-synchronizing what one sees and what one feels. For most kinds of terrestrial motion sickness, that can be achieved by viewing one's surroundings from a window or going up on deck to observe the seas. For space sickness, relief is available via the opposite move of restricting one's vision to a small area such as a book or a small screen, disregarding the overall surroundings until the adaptation process is complete, or to close one's eyes until the nauseated feeling is reduced in intensity during the adjustment period.
Some research indicates that blindness. Space sickness that occurs during space flight can continue for days after landing, until the vestibular system has again adapted to gravity. In August 1961, Soviet Cosmonaut Gherman Titov became the first human to experience space sickness on Vostok II. Apart from that record, space motion sickness was unknown during the earliest spaceflights because these missions were undertaken in spacecraft providing cramped conditions and permitting little room for head movements; as with sea sickness and car sickness, space motion sickness symptoms can vary from mild nausea and disorientation to vomiting and intense discomfort. The most extreme reaction yet recorded was that felt by Senator Jake Garn in 1985. After his flight, NAS
Human spaceflight is space travel with a crew or passengers aboard the spacecraft. Spacecraft carrying people may be operated directly, by human crew, or it may be either remotely operated from ground stations on Earth or be autonomous, able to carry out a specific mission with no human involvement; the first human spaceflight was launched by the Soviet Union on 12 April 1961 as a part of the Vostok program, with cosmonaut Yuri Gagarin aboard. Humans have been continuously present in space for 18 years and 161 days on the International Space Station. All early human spaceflight was crewed, where at least some of the passengers acted to carry out tasks of piloting or operating the spacecraft. After 2015, several human-capable spacecraft are being explicitly designed with the ability to operate autonomously. Russia and China have human spaceflight capability with Shenzhou program. In the United States, SpaceShipTwo reached the edge of space in 2018. All expeditions to the International Space Station use Soyuz vehicles, which remain attached to the station to allow quick return if needed.
The United States is developing commercial crew transportation to facilitate domestic access to ISS and low Earth orbit, as well as the Orion vehicle for beyond-low Earth orbit applications. While spaceflight has been a government-directed activity, commercial spaceflight has been taking on a greater role; the first private human spaceflight took place on 21 June 2004, when SpaceShipOne conducted a suborbital flight, a number of non-governmental companies have been working to develop a space tourism industry. NASA has played a role to stimulate private spaceflight through programs such as Commercial Orbital Transportation Services and Commercial Crew Development. With its 2011 budget proposals released in 2010, the Obama administration moved towards a model where commercial companies would supply NASA with transportation services of both people and cargo transport to low Earth orbit; the vehicles used for these services could serve both NASA and potential commercial customers. Commercial resupply of ISS began two years after the retirement of the Shuttle, commercial crew launches could begin by 2019.
Human spaceflight capability was first developed during the Cold War between the United States and the Soviet Union, which developed the first intercontinental ballistic missile rockets to deliver nuclear weapons. These rockets were large enough to be adapted to carry the first artificial satellites into low Earth orbit. After the first satellites were launched in 1957 and 1958, the US worked on Project Mercury to launch men singly into orbit, while the USSR secretly pursued the Vostok program to accomplish the same thing; the USSR launched the first human in space, Yuri Gagarin, into a single orbit in Vostok 1 on a Vostok 3KA rocket, on 12 April 1961. The US launched its first astronaut, Alan Shepard, on a suborbital flight aboard Freedom 7 on a Mercury-Redstone rocket, on 5 May 1961. Unlike Gagarin, Shepard manually controlled his spacecraft's attitude, landed inside it; the first American in orbit was John Glenn aboard Friendship 7, launched 20 February 1962 on a Mercury-Atlas rocket. The USSR launched five more cosmonauts in Vostok capsules, including the first woman in space, Valentina Tereshkova aboard Vostok 6 on 16 June 1963.
The US launched a total of two astronauts in suborbital flight and four into orbit through 1963. US President John F. Kennedy raised the stakes of the Space Race by setting the goal of landing a man on the Moon and returning him safely by the end of the 1960s; the US started the three-man Apollo program in 1961 to accomplish this, launched by the Saturn family of launch vehicles, the interim two-man Project Gemini in 1962, which flew 10 missions launched by Titan II rockets in 1965 and 1966. Gemini's objective was to support Apollo by developing American orbital spaceflight experience and techniques to be used in the Moon mission. Meanwhile, the USSR remained silent about their intentions to send humans to the Moon, proceeded to stretch the limits of their single-pilot Vostok capsule into a two- or three-person Voskhod capsule to compete with Gemini, they were able to launch two orbital flights in 1964 and 1965 and achieved the first spacewalk, made by Alexei Leonov on Voskhod 2 on 8 March 1965.
But Voskhod did not have Gemini's capability to maneuver in orbit, the program was terminated. The US Gemini flights did not accomplish the first spacewalk, but overcame the early Soviet lead by performing several spacewalks and solving the problem of astronaut fatigue caused by overcoming the lack of gravity, demonstrating up to two weeks endurance in a human spaceflight, the first space rendezvous and dockings of spacecraft; the US succeeded in developing the Saturn V rocket necessary to send the Apollo spacecraft to the Moon, sent Frank Borman, James Lovell, William Anders into 10 orbits around the Moon in Apollo 8 in December 1968. In July 1969, Apollo 11 accomplished Kennedy's goal by landing Neil Armstrong and Buzz Aldrin on the Moon 21 July and returning them safely on 24 July along with Command Module pilot Michael Collins. A total of six Apollo missions landed 12 men to walk on the Moon through 1972, half of which drove electric powered vehicles on the surface; the crew of Apollo 13, Jack Swigert, Fred Haise, survived a catastrophic in-flight spacecraft failure and returned to Earth safely without landing on the Moon.
Meanwhile, the USSR secretly pursued human lunar landing programs. They developed the three-person Soyuz spacecraft for use in the lunar programs, but faile
A reduced-gravity aircraft is a type of fixed-wing aircraft that provides brief near-weightless environments for training astronauts, conducting research and making gravity-free movie shots. Versions of such airplanes were operated by the NASA Reduced Gravity Research Program; the unofficial nickname "vomit comet" became popular among those. Parabolic flight as a way of simulating weightlessness was first proposed by the German aerospace engineer Fritz Haber and the German physicist Heinz Haber in 1950. Both had been brought to the US after World War II as part of Operation Paperclip. Parabolic flights are used to examine the effects of weightlessness on a living organism. While humans are by far the most common passengers, non-human animals have been involved in experiments, including a notable experiment on how weightlessness affected a domestic cat's righting reflex and a pigeon's attempts to navigate in a weightless state; the aircraft gives its occupants the sensation of weightlessness by following a parabolic flight path relative to the center of the Earth.
While following this path, the aircraft and its payload are in free fall at certain points of its flight path. The aircraft is used in this way to demonstrate to astronauts. During this time the aircraft does not exert any ground reaction force on its contents, causing the sensation of weightlessness; the aircraft climbs with a pitch angle of 45 degrees using engine thrust and elevator controls. The sensation of weightlessness is achieved by reducing thrust and lowering the nose to maintain a neutral, or "zero lift", configuration such that the aircraft follows a ballistic trajectory, with engine thrust compensating for drag. Weightlessness begins while ascending and lasts all the way "up-and-over the hump", until the craft reaches a downward pitch angle of around 30 degrees. At this point, the craft is pointing downward at high speed and must begin to pull back into the nose-up attitude to repeat the maneuver; the forces are roughly twice that of gravity on the way down, at the bottom, up again.
This lasts all the way until the aircraft is again halfway up its upward trajectory, the pilot again reduces the thrust and lowers the nose. This aircraft is used to train astronauts in zero-g maneuvers, giving them about 25 seconds of weightlessness out of 65 seconds of flight in each parabola. During such training, the airplane flies about 40–60 parabolic maneuvers. In about two thirds of the passengers, these flights produce nausea due to airsickness, giving the plane its nickname "vomit comet"; the Canadian Space Agency and the National Research Council have a Falcon 20 used for microgravity research. The small plane is not used for people to float and experience weightlessness; the first zero G plane to enter service in Latin America is a T-39 Sabreliner nicknamed CONDOR, operated for the Ecuadorian Civilian Space Agency and the Ecuadorian Air Force since May 2008. On June 19, 2008, this plane carried a seven-year-old boy, setting the Guinness world record for the youngest person to fly in microgravity.
Since 1984, ESA and the CNES have flown reduced-gravity missions in a variety of aircraft, including NASA's KC-135, a Caravelle, an Ilyushin IL-76 MDK and an Airbus A300 known as the Zero-G. In 2014 the A300 was phased out in favor of a more modern Airbus A310 named Zero-G, it is based at Bordeaux-Mérignac airport in France, operated by Novespace, has been flown from Paris Le Bourget airport and Dübendorf Air Base in Switzerland. Since 1997 CNES subsidiary Novespace has handled the management of these flights; this A310 Zero-G aircraft is used to realize commercial flights for public passengers in partnership between operator Novespace and the Avico company, under Air Zero G brand. The aircraft has been used for cinema purposes, with Tom Cruise and Annabelle Wallis filming for The Mummy in 2017. In Russia, commercial flights are offered on the Ilyushin Il-76 jet. S. companies book flights on these jets. OK Go, an American alternative rock band, made a music video for their song "Upside Down & Inside Out" while moving about in microgravity.
The music video was shot on an Il-76 MDK jet as part of an advertising campaign for Russian S7 Airlines. NASA flew zero gravity flights on various aircraft for many years. In 1959 Project Mercury astronauts trained in a C-131 Samaritan aircraft dubbed the "vomit comet". Twin KC-135 Stratotankers were used until December 2004, but retired. One, a KC-135A registered N930NA, flew more than 58,000 parabolas after NASA acquired it in 1973, before being retired in 1995, it is now on display near the Johnson Space Center. The other was used by Universal Pictures and Imagine Entertainment for filming scenes involving weightlessness in the movie Apollo 13. In 2005 NASA replaced the aircraft with a McDonnell Douglas C-9B Skytrain II owned by KLM Royal Dutch Airlines and the United States Navy. NASA canceled the Reduced Gravity Research Program and ceased operations in July 2014; as of 2015 NASA had a microgravity services contract with Zero Gravity Corporation and used its aircraft, G-FORCE ONE, a modified Boeing 727-200.
In late 2004, the Zero Gravity Corporation became the first company in the United States to offer zero-g flights to the general public, using Boeing 727 jets. Each flight consists of around 15 parabolas, including simulations of the gravity levels of the Moon and Mars