A multistage rocket, or step rocket, is a launch vehicle that uses two or more rocket stages, each of which contains its own engines and propellant. A tandem or serial stage is mounted on top of another stage; the result is two or more rockets stacked on top of or attached next to each other. Two-stage rockets are quite common, but rockets with as many as five separate stages have been launched. By jettisoning stages when they run out of propellant, the mass of the remaining rocket is decreased; each successive stage can be optimized for its specific operating conditions, such as decreased atmospheric pressure at higher altitudes. This staging allows the thrust of the remaining stages to more accelerate the rocket to its final speed and height. In serial or tandem staging schemes, the first stage is at the bottom and is the largest, the second stage and subsequent upper stages are above it decreasing in size. In parallel staging schemes solid or liquid rocket boosters are used to assist with launch.
These are sometimes referred to as "stage 0". In the typical case, the first-stage and booster engines fire to propel the entire rocket upwards; when the boosters run out of fuel, they fall away. The first stage burns to completion and falls off; this leaves a smaller rocket, with the second stage on the bottom, which fires. Known in rocketry circles as staging, this process is repeated until the desired final velocity is achieved. In some cases with serial staging, the upper stage ignites before the separation—the interstage ring is designed with this in mind, the thrust is used to help positively separate the two vehicles. A multistage rocket is required to reach orbital speed. Single-stage-to-orbit designs have not yet been demonstrated; the reason multi-stage rockets are required is the limitation the laws of physics place on the maximum velocity achievable by a rocket of given fueled-to-dry mass ratio. This relation is given by the classical rocket equation: Δ v = v e ln where: Δ v is delta-v of the vehicle.
The delta v required to reach low Earth orbit requires a wet to dry mass ratio larger than can realistically be achieved in a single rocket stage. The multistage rocket overcomes this limit by splitting the delta-v into fractions; as each lower stage drops off and the succeeding stage fires, the rest of the rocket is still traveling near the burnout speed. Each lower stage's dry mass includes the propellant in the upper stages, each succeeding upper stage has reduced its dry mass by discarding the useless dry mass of the spent lower stages. A further advantage is that each stage can use a different type of rocket engine, each tuned for its particular operating conditions, thus the lower-stage engines are designed for use at atmospheric pressure, while the upper stages can use engines suited to near vacuum conditions. Lower stages tend to require more structure than upper as they need to bear their own weight plus that of the stages above them. Optimizing the structure of each stage decreases the weight of the total vehicle and provides further advantage.
The advantage of staging comes at the cost of the lower stages lifting engines which are not yet being used, as well as making the entire rocket more complex and harder to build than a single stage. In addition, each staging event is a possible point of launch failure, due to separation failure, ignition failure, or stage collision; the savings are so great that every rocket used to deliver a payload into orbit has had staging of some sort. One of the most common measures of rocket efficiency is its specific impulse, defined as the thrust per flow rate of propellant consumption: I s p = T d m d t g 0 When rearranging the equation such that thrust is calculated as a result of the other factors, we have: T = I s p g 0 d m d t These equations show that a higher specific impulse means a more efficient rocket engine, capable of burning for longer periods of time. In terms of staging, the initial rocket stages have a lower specific impulse rating, trading efficiency for superior thrust in order to push the rocket into higher altitudes.
Stages of the rocket have a higher specific impulse rating because the vehicle is further outside the atmosphere and the exh
Atmospheric diving suit
An atmospheric diving suit is a small one-person articulated anthropomorphic submersible which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere. The ADS can be used for deep dives of up to 2,300 feet for many hours, eliminates the majority of physiological dangers associated with deep diving. Divers do not need to be skilled swimmers. Atmospheric diving suits in current use include the Newtsuit and the WASP, all of which are self-contained hard suits that incorporate propulsion units; the hardsuit is constructed from cast aluminum. The WASP is of glass-reinforced plastic body tube construction. In 1715, British inventor John Lethbridge constructed a "diving suit". A wooden barrel about 6 feet in length with two holes for the diver's arms sealed with leather cuffs, a 4-inch viewport of thick glass, it was used to dive as deep as 60 feet, was used to salvage substantial quantities of silver from the wreck of the East Indiaman Vansittart, which sank in 1719 off the Cape Verde islands.
The first armored suit with real joints, designed as leather pieces with rings in the shape of a spring, was designed by Englishman W. H. Taylor in 1838; the diver's hands and feet were covered with leather. Taylor devised a ballast tank attached to the suit that could be filled with water to attain negative buoyancy. While it was patented, the suit was never produced, it is considered that its bulk would have rendered it nearly immobile underwater. Lodner D. Phillips designed the first enclosed ADS in 1856, his design comprised a barrel-shaped upper torso with domed ends and included ball and socket joints in the articulated arms and legs. The arms had joints at shoulder and elbow, the legs at knee and hip; the suit included a ballast tank, a viewing port, entrance through a manhole cover on top, a hand-cranked propeller, rudimentary manipulators at the ends of the arms. Air was to be supplied from the surface via hose. There is no indication, Phillips' suit was constructed; the first properly anthropomorphic design of ADS, built by the Carmagnolle brothers of Marseilles, France in 1882, featured rolling convolute joints consisting of partial sections of concentric spheres formed to create a close fit and kept watertight with a waterproof cloth.
The suit had 22 of these joints: four in each leg, six per arm, two in the body of the suit. The helmet possessed 25 individual 2-inch glass viewing ports spaced at the average distance of the human eyes. Weighing 830 pounds, the Carmagnole ADS never worked properly and its joints never were waterproof, it is now on display at the French National Navy Museum in Paris. Another design was patented in 1894 by inventors John Buchanan and Alexander Gordon from Melbourne, Australia; the construction was based on a frame of spiral wires covered with waterproof material. The design was improved by Alexander Gordon by attaching the suit to the helmet and other parts and incorporating jointed radius rods in the limbs; this resulted in a flexible suit. The suit was manufactured by British firm Siebe Gorman and trialed in Scotland in 1898. American designer MacDuffy constructed the first suit to use ball bearings to provide joint movement in 1914. A year Harry L. Bowdoin of Bayonne, New Jersey, made an improved ADS with oil-filled rotary joints.
The joints use a small duct to the interior of the joint to allow equalization of pressure. The suit was designed to have four joints in each arm and leg, one joint in each thumb, for a total of eighteen. Four viewing ports and a chest-mounted lamp were intended to assist underwater vision. There is no evidence that Bowdoin's suit was built, or that it would have worked if it had been. Atmospheric diving suits built by German firm Neufeldt and Kuhnke were used during the salvage of gold and silver bullion from the wreck of the British ship SS Egypt, an 8,000 ton P&O liner that sank in May 1922; the suit was relegated to duties as an observation chamber at the wreck's depth, was used to direct mechanical grabs which opened up the bullion storage. In 1917, Benjamin F. Leavitt of Traverse City, dived on the SS Pewabic which sank to a depth of 182 feet in Lake Huron in 1865, salvaging 350 tons of copper ore. In 1923, he went on to salvage the wreck of the British schooner Cape Horn which lay in 220 feet of water off Pichidangui, salvaging $600,000 worth of copper.
Leavitt's suit was of his own construction. The most innovative aspect of Leavitt's suit was the fact that it was self-contained and needed no umbilical, the breathing mixture being supplied from a tank mounted on the back of the suit; the breathing apparatus incorporated a scrubber and an oxygen regulator and could last for up to a full hour. In 1924 the Reichsmarine tested the second generation of the Neufeldt and Kuhnke suit to 530 feet, but limb movement was difficult and the joints were judged not to be fail-safe, in that if they were to fail, there was a possibility that the suit's integrity would be violated. However, these suits were used by the Germans as armored divers during World War II and were taken by the Western Allies aft
In modern language, a missile known as a guided missile, is a guided self-propelled system, as opposed to an unguided self-propelled munition, referred to as a rocket. Missiles have four system components: targeting or missile guidance, flight system and warhead. Missiles come in types adapted for different purposes: surface-to-surface and air-to-surface missiles, surface-to-air missiles, air-to-air missiles, anti-satellite weapons. All known existing missiles are designed to be propelled during powered flight by chemical reactions inside a rocket engine, jet engine, or other type of engine. Non-self-propelled airborne explosive devices are referred to as shells and have a shorter range than missiles. In ordinary British-English usage predating guided weapons, a missile is such as objects thrown at players by rowdy spectators at a sporting event; the first missiles to be used operationally were a series of missiles developed by Nazi Germany in World War II. Most famous of these are the V-1 flying bomb and V-2 rocket, both of which used a simple mechanical autopilot to keep the missile flying along a pre-chosen route.
Less well known were a series of anti-shipping and anti-aircraft missiles based on a simple radio control system directed by the operator. However, these early systems in World War II were only built in small numbers. Guided missiles have a number of different system components: Guidance system Targeting system Flight system Engine Warhead The most common method of guidance is to use some form of radiation, such as infrared, lasers or radio waves, to guide the missile onto its target; this radiation may emanate from the target, it may be provided by the missile itself, or it may be provided by a friendly third party. The first two are known as fire-and-forget as they need no further support or control from the launch vehicle/platform in order to function. Another method is to use a TV guidance, with a visible light or infrared picture produced in order to see the target; the picture may be used either by a human operator who steering the missile onto its target or by a computer doing much the same job.
One of the more bizarre guidance methods instead used a pigeon to steer a missile to its target. Some missiles have a home-on-jam capability to guide itself to a radar-emitting source. Many missiles use a combination of two or more of the methods to improve accuracy and the chances of a successful engagement. Another method is to target the missile by knowing the location of the target and using a guidance system such as INS, TERCOM or satellite guidance; this guidance system guides the missile by knowing the missile's current position and the position of the target, calculating a course between them. This job can be performed somewhat crudely by a human operator who can see the target and the missile and guide it using either cable- or radio-based remote control, or by an automatic system that can track the target and the missile. Furthermore, some missiles use initial targeting, sending them to a target area, where they will switch to primary targeting, using either radar or IR targeting to acquire the target.
Whether a guided missile uses a targeting system, a guidance system or both, it needs a flight system. The flight system uses the data from the targeting or guidance system to maneuver the missile in flight, allowing it to counter inaccuracies in the missile or to follow a moving target. There are two main systems: aerodynamic maneuvering. Missiles are powered by an engine either a type of rocket engine or jet engine. Rockets are of the solid propellant type for ease of maintenance and fast deployment, although some larger ballistic missiles use liquid-propellant rockets. Jet engines are used in cruise missiles, most of the turbojet type, due to its relative simplicity and low frontal area. Turbofans and ramjets are the only other common forms of jet engine propulsion, although any type of engine could theoretically be used. Long-range missiles may have multiple engine stages in those launched from the surface; these stages may all be of similar types or may include a mix of engine types − for example, surface-launched cruise missiles have a rocket booster for launching and a jet engine for sustained flight.
Some missiles may have additional propulsion from another source at launch. Missiles have one or more explosive warheads, although other weapon types may be used; the warheads of a missile provide its primary destructive power. Warheads are most of the high explosive type employing shaped charges to exploit the accuracy of a guided weapon to destroy hardened targets. Other warhead types include submunitions, nuclear weapons, biological or radiological weapons or kinetic energy penetrators. Warheadless missiles are used for testing and training purposes. Missiles are categorized by their launch platform and intended target. In broadest terms, these will either be surface or air, t
Diving equipment is equipment used by underwater divers to make diving activities possible, safer and/or more comfortable. This may be equipment intended for this purpose, or equipment intended for other purposes, found to be suitable for diving use; the fundamental item of diving equipment used by divers is underwater breathing apparatus, such as scuba equipment, surface supplied diving equipment, but there are other important pieces of equipment that make diving safer, more convenient or more efficient. Diving equipment used by recreational scuba divers is personal equipment carried by the diver, but professional divers when operating in the surface supplied or saturation mode, use a large amount of support equipment not carried by the diver. Equipment, used for underwater work or other activities, not directly related to the activity of diving, or which has not been designed or modified for underwater use by divers is excluded. Surface supplied diving - used in professional diving; this category includes: Surface oriented surface supplied diving, where the diver starts and finishes the dive at normal atmospheric pressure.
Saturation diving, where the diver remains under pressure in an underwater habitat or saturation spread between underwater excursions. Standard diving dress - used in professional diving. Of historical interest now. Airline or Hookah diving. "Compressor diving" - a rudimentary form of surface supplied diving used in the Philippines by artisanal fishermen. Recreational forms like snuba. Scuba diving - The use of self-contained underwater breathing apparatus; this category includes: Open-circuit scuba consisting of diving cylinder and diving regulator Rebreather, closed-circuit or semi-closed-circuit scuba Free diving or breathhold diving, where the diver completes the dive on a single breath of air taken at the surface before the dive. Snorkel allows breathing at the surface with the face submerged, is used as an adjunct to free diving and scuba. Atmospheric diving suits and other submersibles which isolate the diver from the ambient environment; these are not considered here. Liquid breathing systems are rare and at an early experimental stage.
It is hoped that some day practical systems will allow deep diving. This is not considered here; this is the diving equipment worn by or carried by the diver for personal protection or comfort, or to facilitate the diving aspect of the activity, may include a selection from: Scuba equipment: Primary cylinder, carried back-mounted or side mounted and open circuit regulator, or rebreather sets. Alternative air source such as bailout bottle or pony bottle, decompression cylinders and their associated regulators. Secondary demand valve. Surface supplied equipment: Helmet or full face mask, diver's umbilical, bailout block, bailout cylinder and regulator. Thermal and abrasion protection. In cold water, a diving suit such as a dry suit, a wet suit, or a Hot water suit is necessary. Boiler suit overalls are worn over the thermal protection suit by commercial divers as abrasion protection In warm water, many types of tough, everyday clothing provide protection, as well as purpose made garments such as dive skins and shorty wetsuits.
In some cases, simple regular swimsuits are used. Diving gloves, including wetsuit gloves and dry gloves and three-finger mitts Diving hoods Diving boots - With dry suits, the boots are integrated. Safety helmet for scuba diving. Diving chain mail may be used as protection against bites by large marine animals Diver's cages may be used as protection against large predators A backplate is a structure onto which the back-mounted diving cylinders are mounted linking the buoyancy compensator with the weight of the diving cylinders and provided with a harness of straps which secures the scuba set to the diver's back. A backplate is used with a back inflation type buoyancy compensator, but can be used without any buoyancy compensator. Buoyancy compensator known as Buoyancy Control Device, BCD or BC - is a back mounted or sleeveless jacket style device which includes an inflatable bladder used to adjust the buoyancy of the diver under water, provide positive buoyancy at the surface; the buoyancy compensator is an integral part of the harness system used to secure the scuba set to the diver.
The earlier collar style buoyancy compensator is used any more. Diver Propulsion Vehicle - to increase the range of the diver underwater Diving weighting system - to counteract the buoyancy of the diving suit and diver to allow descent. Professional divers may use additional weighting to ensure stability when working on the bottom Fins for efficient propulsion Depth gauge lets the diver monitor depth maximum depth and, when used with a watch and Decompression tables allows the diver to monitor decompression requirements; some digital depth gauges indicate ascent rate, an important factor in avoiding decompression sickness Pneumofathometer is the surface supplied diving depth gauge which displays the depth of the diver at the surface control panel. Dive computer helps the diver to avoid decompression sickness by indicating the decompression stops needed for the dive profile. Most dive computers indicate depth and ascent rate; some indicate oxygen toxicity exposure and water temperature, may provide other functions.
Dive timer is an instrument that records depth and elapsed time during the dive. It is possibl
Project Gemini was NASA's second human spaceflight program. Conducted between projects Mercury and Apollo, Gemini started in 1961 and concluded in 1966; the Gemini spacecraft carried a two-astronaut crew. Ten Gemini crews flew low Earth orbit missions during 1965 and 1966, putting the United States in the lead during the Cold War Space Race against the Soviet Union. Gemini's objective was the development of space travel techniques to support the Apollo mission to land astronauts on the Moon, it performed missions long enough for a trip to the Moon and back, perfected working outside the spacecraft with extra-vehicular activity, pioneered the orbital maneuvers necessary to achieve space rendezvous and docking. With these new techniques proven by Gemini, Apollo could pursue its prime mission without doing these fundamental exploratory operations. All Gemini flights were launched from Launch Complex 19 at Cape Kennedy Air Force Station in Florida, their launch vehicle was the Gemini -- a modified Intercontinental Ballistic Missile.
Gemini was the first program to use the newly built Mission Control Center at the Houston Manned Spacecraft Center for flight control. The astronaut corps that supported Project Gemini included the "Mercury Seven", "The New Nine", the 1963 astronaut class. During the program, three astronauts died in air crashes during training, including both members of the prime crew for Gemini 9; this mission was flown by the backup crew, the only time a backup crew has replaced a prime crew on a mission in NASA's history to date. Gemini was robust enough that the United States Air Force planned to use it for the Manned Orbital Laboratory program, canceled. Gemini's chief designer, Jim Chamberlin made detailed plans for cislunar and lunar landing missions in late 1961, he believed that Gemini spacecraft could fly in lunar operations before Project Apollo, cost less. NASA's administration did not approve those plans. In 1969, McDonnell-Douglas proposed a "Big Gemini" that could have been used to shuttle up to 12 astronauts to the planned space stations in the Apollo Applications Project.
The only AAP project funded was Skylab – which used existing spacecraft and hardware – thereby eliminating the need for Big Gemini. The constellation for which the project was named is pronounced, the last syllable rhyming with eye. However, staff of the Manned Spacecraft Center, including the astronauts, tended to pronounce the name, rhyming with knee. NASA's public affairs office issued a statement in 1965 declaring "Jeh-mih-nee" to be the "official" pronunciation. Gus Grissom, acting as Houston capsule communicator when Ed White performed his spacewalk on Gemini 4, is heard on flight recordings pronouncing the spacecraft's call sign "Jeh-mih-nee 4", the NASA pronunciation is used in the movie First Man; the Apollo program was conceived in early 1960 as a three-man spacecraft to follow Project Mercury. Jim Chamberlin, the head of engineering at the Space Task Group, was assigned in February 1961 to start working on a bridge program between Mercury and Apollo, he presented two initial versions of a two-man spacecraft designated Mercury Mark II, at a NASA retreat at Wallops Island in March 1961.
Scale models were shown in July 1961 at the McDonnell Aircraft Corporation's offices in St. Louis. After Apollo was chartered to land men on the Moon by President John F. Kennedy on May 25, 1961, it became evident to NASA officials that a follow-on to the Mercury program was required to develop certain spaceflight capabilities in support of Apollo. NASA approved the two-man program rechristened Project Gemini, in reference to the third constellation of the Zodiac with its twin stars Castor and Pollux, on December 7, 1961. McDonnell Aircraft was contracted to build it on December 22, 1961; the program was publicly announced on January 3, 1962, with these major objectives: To demonstrate endurance of humans and equipment in spaceflight for extended periods, at least eight days required for a Moon landing, to a maximum of two weeks To effect rendezvous and docking with another vehicle, to maneuver the combined spacecraft using the propulsion system of the target vehicle To demonstrate Extra-Vehicular Activity, or space-"walks" outside the protection of the spacecraft, to evaluate the astronauts' ability to perform tasks there To perfect techniques of atmospheric reentry and touchdown at a pre-selected location on land Canadian engineer Jim Chamberlin designed the Gemini capsule, which carried a crew of two.
He was the chief aerodynamicist on Avro Canada's Avro Arrow fighter interceptor program. Chamberlin joined NASA along with 25 senior Avro engineers after cancellation of the Arrow program, became head of the U. S. Space Task Group's engineering division in charge of Gemini; the prime contractor was McDonnell Aircraft Corporation, the prime contractor for the Project Mercury capsule. Astronaut Gus Grissom was involved in the development and design of the Gemini spacecraft. What other Mercury astronauts dubbed "Gusmobile" was so designed around Grissom's 5'6" body that, when NASA discovered in 1963 that 14 of 16 astronauts would not fit in the spacecraft, the interior had to be redesigned. Grissom wrote in his posthumous 1968 book Gemini! that the realization of Project Mercury's end and the unlikelihood of his having another flight in that program prompted him to focus all of his efforts on the upcoming Gemini program. The Gemini program was managed by the Manned Spacecraft Center, located in Houston, under direction of the Office of Manned Space Flight, NASA Headquarters, Washington, D.
C. Dr. George E. Mueller, Associate Administrator of NASA for Manned Space Flight, served as acting director of the Gemini progra
A launch pad is an above-ground facility from which a rocket-powered missile or space vehicle is vertically launched. A spaceport is a facility which includes, provides required support for, one or more launch pads. A launch pad includes a launch mount or launch platform—to support the vehicle and its service structure with umbilicals to provide propellants, cryogenic fluids, electrical power and telemetry prior to launch—plus storage facilities for propellants and gases, access roads and all the requisite infrastructure to support rocket vehicle launches; some launch pads include service structures to provide one or more access platforms to inspect and maintain the vehicle and to allow access to the crew cabin for vehicles carrying humans. The pad may contain a flame deflection structure to prevent the intense heat of the rocket exhaust from damaging the vehicle or pad structures, a sound suppression system spraying large quantities of water may be employed; the pad may be protected by lightning arresters.
A launch pad is distinct from a missile launch facility, which launches a missile vertically but is located underground in order to help harden it against enemy attack, or conceal it from surveillance. Cryogenic propellants need to be continuously topped off during the launch sequence, as the vehicle awaits liftoff; this becomes important as complex sequences may be interrupted by planned or unplanned holds to fix problems. Most rockets need stable support for a few seconds after ignition while the engines build up to stable, full thrust. Therefore, the vehicle is held on the pad by hold-down arms or explosive bolts, which are triggered when the vehicle is stable and ready to fly, at which point all umbilical connections with the pad are released. There are several different types of launch site, determined by the means by which the space vehicle gets to the pad; the first large rocket, the V-2, travelled horizontally with its tail forward to the launch site on a transporter erector launcher which raised it to the vertical position.
This method was subsequently used for all large Soviet rockets, including the Soyuz, N1 and Energia, is used by SpaceX for its Falcon rockets. In a similar manner, at the Soviet launch site near Volgograd, a silo used to launch test rockets would have its top opened and a second stage and payload would be driven in horizontally and tilted on top of a first stage in the silo, the nose cone and some of the second stage remaining visible above ground. Hence no surface pad is used; this method was only used for the Cosmos series of small satellite launching vehicles. A method of assembling a large space vehicle vertically in a Vehicle Assembly Building on a Mobile Launcher Platform, which contained the umbilical structure, was developed for the Apollo/Saturn V manned Moon landing vehicle; the MLP is carried by a Crawler-transporter, which drives to one of two pads at Launch Complex 39 at the Kennedy Space Center. This facility was used for the smaller Apollo/Saturn IB, the Space Shuttle. A similar system is used to launch Ariane 5 rockets at ELA-3 at Guiana Space Centre, a French spaceport near Kourou in French Guiana.
The Titan III and Titan IV launch vehicles were transported with a mobile launcher platform on two parallel standard gauge railroad tracks from the integration building to launch areas at Cape Canaveral Air Force Station Space Launch Complex 40 and 41. This system is still in use for the Atlas V. At Vandenberg Air Force Base, in California, the Titan series of rockets were set up vertically in a gantry in a windowless building at SLC-4, the outside walls of which were rolled away just at launch; this was done for purposes of military secrecy. Similar systems are used at SLC-6 and LC37 at Cape Canaveral Air Force Station for the Delta IV rocket, ELA-1 & 2 at CSG for the Ariane 1-4, Kagoshima for the M-V. In the 1920s, Hermann Oberth described a method in which the vehicle is assembled vertically on a floating barge, which he used in the movie Frau im Mond; this was considered for use at Kennedy Space Center Launch Complex 39 for the Saturn V, but was rejected due to the instability of the top-heavy unfuelled rocket and gantry.
However, the Sea Launch service uses the converted self-propelled oil drilling platform Ocean Odyssey to transport Zenit 3SL rockets horizontally to the Equator, to erect and launch them into geostationary transfer orbits. Dnepr rockets are transported vertically and inserted into a silo, as they are converted cold-launch R-36 Voevoda ICBMs. Ground segment Launch vehicle List of rocket launch sites Missile launch facility Non-rocket spacelaunch Pad abort test Rocket launch Service structure Spaceport Stratolaunch Systems Transporter erector launcher
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