Space suit

Space suit is a complex system of garments, equipment and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space. This applies to extra-vehicular activity (EVA) outside spacecraft orbiting Earth, and has applied to walking, and riding the Lunar Rover, on the Moon.

Some of these requirements also apply to pressure suits worn for other specialized tasks, such as high-altitude reconnaissance flight. Above Armstrong's Line (around 19,000 m/62,000 ft), the atmosphere is so thin that pressurized suits are needed. Hazmat suits that superficially resemble space suits are sometimes used when dealing with biological hazards.

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 Union SK-1 series.

Spacesuit requirements

A 3D anaglyph of a space suit. 3D red cyan glasses are recommended to view this image correctly.

A space suit must perform several functions to allow its occupant to work safely and comfortably. It must provide:

A stable internal pressure. This can be less than earth's atmosphere, as there is usually no need for the spacesuit to carry nitrogen (which comprises about 78% of earth's atmosphere and is not used by the body). 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 typically opposed by the pressure of the suit; mobility is achieved by careful joint design. See the Theories of spacesuit design section.

Breathable oxygen. Circulation of cooled and purified oxygen is controlled by the Primary Life Support System.

Temperature regulation. 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 space suit. Since the temperature on the outside of the suit varies greatly between sunlight and shadow, the suit is heavily insulated, and the temperature inside the suit is regulated by a Liquid Cooling Garment in contact with the astronaut's skin, as well as air temperature maintained by the Primary Life Support System.

Shielding against ultraviolet radiation

Limited shielding against particle radiation

Protection against small micrometeoroids, provided by a Thermal Micrometeoroid Garment, which is the outermost layer of the suit

A communication system

Means to recharge and discharge gases and liquids

Means to maneuver, dock, release, and/or tether onto spacecraft

Means of collecting and containing solid and liquid waste (such as a Maximum Absorbency Garment)

As part of astronautical hygiene control (i.e., protecting astronauts from extremes of temperature, radiation, etc.), a spacesuit is essential for extravehicular activity. Within its 18,000 or so parts, it contains everything an astronaut needs to stay alive, including oxygen, water, temperature control, and carbon dioxide removal. Because of the hazards from micro-meteoroids traveling at 27,000 kilometers per hour, it is important that the outer layer of the suit be puncture-resistant. The Apollo/Skylab A7L suit included eleven layers in all: an inner liner, a liquid cooling and ventilation garment, a pressure bladder, a restraint layer, another liner, and a thermal micrometeoroid garment consisting of five aluminized insulation layers and an external layer of white Ortho-Fabric. This spacesuit is capable of protecting the astronaut from temperatures ranging from -156 °C to +121 °C.

It is expected that manned exploration of the Moon and Mars will occur within the next two decades. During exploration, there will be the potential for lunar/Martian dust to be retained on the spacesuit. When the spacesuit 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 spacesuits, 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".

Operating pressure

Generally, to supply enough oxygen for respiration, a spacesuit using pure oxygen must have a pressure of about 32.4 kPa (240 Torr; 4.7 psi), equal to the 20.7 kPa (160 Torr; 3.0 psi) partial pressure of oxygen in the Earth's atmosphere at sea level, plus 5.3 kPa (40 Torr; 0.77 psi) CO2 and 6.3 kPa (47 Torr; 0.91 psi) water vapor pressure, both of which must be subtracted from the alveolar pressure to get alveolar oxygen partial pressure in 100% oxygen atmospheres, by the alveolar gas equation.[1] The latter two figures add to 11.6 kPa (87 Torr, 1.7 psi), which is why many modern spacesuits do not use 20.7 kPa (160 Torr; 3.0 psi), but 32.4 kPa (240 Torr; 4.7 psi) (this is a slight overcorrection, as alveolar partial pressures at sea level are slightly less than the former). In spacesuits that use 20.7 kPa, the astronaut gets only 20.7 kPa − 11.7 kPa = 9.0 kPa (68 Torr; 1.3 psi) of oxygen, which is about the alveolar oxygen partial pressure attained at an altitude of 1,860 m (6,100 ft) above sea level. This is about 78% of normal sea level pressure, about the same as pressure in a commercial passenger jet aircraft, and is the realistic lower limit for safe ordinary space suit pressurization which allows reasonable capacity for work.

When space suits below a specific operating pressure are used from craft that are pressurized to normal atmospheric pressure (such as the space shuttle), this requires astronauts to "pre-breathe" (meaning pre-breathe pure oxygen for a period) before donning their suits and depressurizing in the air lock. This procedure purges the body of dissolved nitrogen, so as to avoid decompression sickness ("the bends") due to overrapid depressurization from a nitrogen-containing atmosphere.

Exposure to space without a spacesuit

The human body can briefly survive the hard vacuum of space unprotected, despite contrary depictions in some popular science fiction. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. No snap freeze effect occurs because all heat must be lost through thermal radiation or the evaporation of liquids, and the blood does not boil because it remains pressurized within the body. The greatest danger is in attempting to hold one's breath before exposure, as the subsequent explosive decompression can damage the lungs. These effects have been confirmed through various accidents (including in very high altitude conditions, outer space and training vacuum chambers). Human skin does not need to be protected from vacuum and is gas-tight by itself. Instead it only needs to be mechanically compressed to retain its normal shape. This can be accomplished with a tight-fitting elastic body suit and a helmet for containing breathing gases, known as a Space activity suit.

Theories of spacesuit design

A space suit should allow its user natural unencumbered movement. Nearly all designs try to maintain a constant volume no matter what movements the wearer makes. This is because mechanical work is needed to change the volume of a constant pressure system. If flexing a joint reduces the volume of the spacesuit, then the astronaut must do extra work every time he bends that joint, and he has to maintain a force to keep the joint bent. Even if this force is very small, it can be seriously fatiguing to constantly fight against one's suit. It also makes delicate movements very difficult. The work required to bend a joint is dictated by the formula

where Vi and Vf are respectively the initial and final volume of the joint, P is the pressure in the suit, and W is the resultant work. It is generally true that all suits are more mobile at lower pressures. However, because a minimum internal pressure is dictated by life support requirements, the only means of further reducing work is to minimize the change in volume.

All space suit designs try to minimize or eliminate this problem. The most common solution is to form the suit out of multiple layers. The bladder layer is a rubbery, airtight layer much like a balloon. The restraint layer goes outside the bladder, and provides a specific shape for the suit. Since the bladder layer is larger than the restraint layer, the restraint takes all of the stresses caused by the pressure inside the suit. Since the bladder is not under pressure, it will not "pop" like a balloon, even if punctured. The restraint layer is shaped in such a way that bending a joint causes pockets of fabric, called "gores", to open up on the outside of the joint, while folds called "convolutes" fold up on the inside of the joint. The gores make up for the volume lost on the inside of the joint, and keep the suit at a nearly constant volume. However, once the gores are opened all the way, the joint cannot be bent any further without a considerable amount of work.

In some Russian space suits, strips of cloth were wrapped tightly around the cosmonaut's arms and legs outside the spacesuit to stop the spacesuit from ballooning when in space.

The outermost layer of a space suit, the Thermal Micrometeoroid Garment, provides thermal insulation, protection from micrometeoroids, and shielding from harmful solar radiation.

Space walk Milestones

The first untethered spacewalk was made by American Bruce McCandless II on February 7, 1984, during Challenger mission STS-41-B, utilizing the Manned Maneuvering Unit. He was subsequently joined by Robert L. Stewart during the 5 hour 55 minute spacewalk. See photo at right. Such a self-contained spacewalk was first attempted by Eugene Cernan in 1966 on Gemini 9A, but Cernan could not reach the maneuvering unit without tiring.

The first three-person EVA was performed on May 13, 1992, as the third EVA of STS-49, the maiden flight of Endeavour. Pierre Thuot, Richard Hieb, and Thomas Akers conducted the EVA to hand-capture and repair a non-functional Intelsat VI-F3 satellite. See photo at right.

Stephen Robinson riding the robotic arm during STS-114, doing a first in-flight repair of the Space Shuttle.(Landmass in the backdrop is the Bari region of Somalia).

The first EVA to perform an in-flight repair of the Space Shuttle was by American Steve Robinson on August 3, 2005, during "Return to Flight" mission STS-114. Robinson was sent to remove two protruding gap fillers from Discovery's heat shield, after engineers determined there was a small chance they could affect the shuttle upon re-entry. Robinson successfully removed the loose material while Discovery was docked to the International Space Station. See photo at right.

The longest EVA as of 2007, was 8 hours and 56 minutes, performed by Susan J. Helms and James S. Voss on March 11, 2001.

Personal cumulative duration records

Russian Anatoly Solovyev holds both the record for most EVAs and for the greatest cumulative duration spent in EVA (16 EVAs; 82 hr and 22 min).

Michael Lopez-Alegria holds the American record (10 EVAs; 67 hr and 40 min).

Christer Fuglesang holds the European (non-Russian) record (5 EVAs; 31 hr and 55 min).

National, ethnic and gender firsts

The first woman to perform an EVA was Soviet Svetlana Savitskaya on July 25, 1984 while aboard the Salyut 7 space station. Her EVA lasted 3 hours and 35 minutes.

The first American woman to perform an EVA was Kathryn D. Sullivan on October 11, 1984 during Space Shuttle Challenger mission STS-41-G.

The first EVA by a non-Soviet, non-American was made on December 9, 1988 by Jean-Loup Chrétien of France during a three-week stay on the Mir space station.

The first EVA by a Briton was on February 9, 1995 by Michael Foale (who carries dual British-American citizenship).

The first EVA by a black African-American was on February 9, 1995 by Bernard A. Harris, Jr..

The first EVA by an Australian-born person was on March 13, 2001 by Andy Thomas (although he is a naturalized US citizen).

The first EVA by a Canadian was made on April 22, 2001 by Chris Hadfield. During his spacewalk, Hadfield installed the Canadarm2 onto the International Space Station.

The first EVA by a Chinese astronaut was made on September 27, 2008 by Zhai Zhigang during Shenzhou 7 mission. The spacewalk, using a Feitian space suit, made China the third country to independently carry out an EVA.

The first EVA by a Japanese astronaut was made on November 25, 1997 by Doi Takao during STS-87. During his spacewalk, Doi conducted experiments from the International Space Station.

Space walk

Extra-vehicular activity (EVA) is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth (a spacewalk), but also applies to an EVA made on the surface of the Moon (a moonwalk). In the later lunar landing missions (Apollo 15, 16, and 17) the command module pilot (CMP) did an EVA to retrieve film canisters on the return trip; he was assisted by the lunar module pilot (LMP) who remained at the open command module hatch. These trans-Earth EVAs were the only spacewalks ever conducted in deep space.

A "Stand-up" EVA (SEVA) is where the astronaut does not fully exit a spacecraft, but is completely reliant on the spacesuit for environmental support. Its name derives from the astronaut "standing up" in the open hatch, usually to film or assist a spacewalking astronaut.

EVAs may be either tethered (the astronaut is connected to the spacecraft; oxygen and electrical power can be supplied through an umbilical cable; no propulsion is needed to return to the spacecraft), or untethered. Untethered spacewalks were only performed on three missions in 1984 using the Manned Maneuvering Unit (MMU), and on a flight test in 1994 of the Simplified Aid for EVA Rescue (SAFER). A SAFER is a safety device worn on tethered U.S. EVAs, since the capability of returning to the spacecraft is essential.

Russia, the United States and China have demonstrated the capability to conduct an EVA.

Development history

NASA planners invented the term extra-vehicular 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, and 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 hasty 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 the first manned Gemini was launched.

The Soviets' avionics technology was not as advanced as that of the United States, so the Voskhod cabin could not have been left depressurized by an open hatch; otherwise the air-cooled electronics would have overheated. Therefore a spacewalking cosmonaut would have to enter and exit the spacecraft through an airlock. By contrast, the Gemini capsule's avionics were designed so the cabin could be exposed to the vacuum of space when one of two large hatches was opened, so no airlock was required, and both the spacewalking astronaut and his companion command pilot were in vacuum during the EVA. Due to the different designs of the spacecraft, the American and Soviet space programs define the duration of an EVA differently. The Soviet (now Russian) definition is the time when the outer airlock hatch is open and the cosmonaut is in a vacuum. An American EVA begins when the spacewalking astronaut has at least his head outside of the spacecraft.

As they had with the first satellite and first man in space, the Soviets again stunned the world on March 18, 1965 with the first EVA (commonly referred to as a "space walk") performed by Alexey Leonov from the Voskhod 2 spacecraft, for 12 minutes outside the spacecraft. Leonov had no means to control his motion other than pulling on his 50.7-foot (15.5 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, 3.96 feet (1.21 m) in diameter and 8.25 feet (2.51 m) long. After his spacewalk, he improperly entered the airlock head-first and 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, and he was overheated by 1.8 °C (3.24 °F) from the exertion. It would be almost 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 Edward H. White, II from the second manned Gemini flight, Gemini 4, for 21 minutes, on a 25-foot (7.6 m) tether. White 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 EVA's 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 (Eugene Cernan, Michael Collins and Richard Gordon), performed several EVA's, but none was able to successfully work for long periods outside the spacecraft without tiring and overheating.

Finally, on November 13, 1966, Edwin "Buzz" Aldrin became the first to successfully work in space without tiring, on the Gemini 12 last flight. Aldrin worked outside the spacecraft for 2 hours and 6 minutes, in addition to two stand-up EVA's in the spacecraft hatch for an additional 3 hours and 24 minutes. Aldrin's interest in scuba diving inspired the use of underwater EVA training to simulate weightlessness, which has been used ever since to allow astronauts to practice techniques of avoiding wasted muscle energy.

On January 16, 1969, the Soviet Union achieved the first EVA crew transfer from one spacecraft to another when Aleksei Yeliseyev and Yevgeny Khrunov transferred from Soyuz 5 to Soyuz 4, which were docked together. This was the second Soviet EVA, and it would be almost another nine years before the Soviets performed their third.

The first EVA on the lunar surface was performed by Americans Neil Armstrong and Buzz Aldrin on July 21, 1969 (UTC), after the Apollo 11 Moon landing. This first Moon walk lasted 2 hours, 36 minutes. A total of 15 Moon walks were performed by members of six Apollo crews, including Charles "Pete" Conrad, Alan Bean, Alan Shepard, Edgar Mitchell, David Scott, James Irwin, John Young, Charles Duke, Eugene "Gene" Cernan and Dr. Harrison "Jack" Schmitt. Cernan was the last Apollo astronaut to step off the surface of the Moon.

The first EVA in deep space was made on August 5, 1971, by American Al Worden, to retrieve a film and data recording canister from the Apollo 15 Service Module on the return trip from the Moon. Worden was assisted by James Irwin, doing a standup EVA in the Command Module hatch. This was repeated by Ken Mattingly and Charles Duke on Apollo 16, and by Ronald Evans and Harrison Schmitt on Apollo 17.

The first EVA repairs of a spacecraft were made by Charles "Pete" Conrad, Joseph Kerwin and Paul J. Weitz on May 26, June 7 and June 19, 1973, on the Skylab 2 mission. They rescued the functionality of the launch-damaged Skylab space station by freeing a stuck solar panel, deploying a solar heating shield, and freeing a stuck circuit breaker relay. The Skylab 2 crew made three EVA's, and a total of ten EVA's were made by the three Skylab crews.