Space suit

2008/9 Schools Wikipedia Selection. Related subjects: Space transport

A 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 (~63,000 ft/~19,000 m), pressurized suits are needed in the sparse atmosphere. Hazmat suits that superficially resemble space suits are sometimes used when dealing with biological hazards.

Spacesuit requirements

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. Lower pressure allows for greater mobility, but introduces the requirement of pre-breathing 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 only be lost 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)

Operating pressure

Generally, to supply enough oxygen for respiration, a spacesuit using pure oxygen must have a pressure of about 4.7 psi (32.4  kPa), equal to the 3 psi (20.7 kPa) partial pressure of oxygen in the Earth's atmosphere at sea level, plus 40  torr (5.3 kPa) CO₂ and 47 torr (6.3 kPa) 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. The latter two figures add to 87 torr (11.6 kPa, 1.7 psi), which is why many modern spacesuits do not use 3 psi, but 4.7 psi (this is a slight overcorrection, as alveolar partial pressures at sea level are not a full 3 psi, but a bit less). In spacesuits that use 3 psi, the astronaut gets only 3 - 1.7 = 1.3 psi (9 kPa) of oxygen, which is about the alveolar oxygen partial pressure attained at an altitude of 6100  ft (1860  m) 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 work capacity.

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 your suit. It also makes delicate movements very difficult. The work required to bend a joint is dictated by the formula

where V_i and V_f are respectively the initial and final volume of the joint, P is the pressure in the suit, and W is the resultant work. Because pressure is dictated by life support requirements, the only means of 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.

There are three theoretical approaches to suit design:

Hard-shell suits

Hard-shell suits are usually made of metal or composite materials. While they resemble suits of armor, they are also designed to maintain a constant volume. However they tend to be difficult to move, as they rely on bearings instead of bellows over the joints, and often end up in odd positions that must be manipulated to regain mobility.

Mixed suits

Mixed suits have hard-shell parts and fabric parts. NASA's Extravehicular Mobility Unit uses a fibreglass Hard Upper Torso (HUT) and fabric limbs. ILC Dover's I-Suit replaces the hard upper torso with a fabric soft upper torso to save weight, restricting the use of hard components to the joint bearings, helmet, waist seal, and rear entry hatch. Virtually all workable spacesuit designs incorporate hard components, particularly at interfaces such as is the waist seal, bearings, and in the case of rear-entry suits, the back hatch, where all-soft alternatives are not viable.

Skintight suits

Skintight suits, also known as mechanical counterpressure suits or space activity suits, are a proposed design which would use a heavy elastic body stocking to compress the body. The head is in a pressurized helmet, but the rest of the body is pressurized only by the elastic effect of the suit. This eliminates the constant volume problem, reduces the possibility of a space suit depressurization and gives a very lightweight suit. However, these suits are very difficult to put on and face problems with providing a constant pressure everywhere. Most proposals use the body's natural sweat to keep cool.

Contributing technologies

Related preceding technologies include the gas mask used in WWII, the oxygen mask used by pilots of high flying bombers in WWII, the high altitude or vacuum suit required by pilots of the Lockheed U-2 and SR-71 Blackbird, the diving suit, rebreather, scuba diving gear, and many others.

The development of the spheroidal dome helmet was key in balancing the need for field of view, pressure compensation, and low weight. One inconvenience with some spacesuits is the head being fixed facing forwards and being unable to turn to look sideways. Astronauts call this effect "alligator head".

Spacesuit models of historical significance

High altitude suits

• Evgeniy Chertanovskiy created his full-pressure suit or high-altitude "skafandr" (скафандр) in 1931. (скафандр also means " diving apparatus").
• Wiley Post experimented with a number of hard-shell designs for record-breaking flights.
• Russell Colley created the spacesuits worn by the Project Mercury astronauts, including fitting Alan B. Shepard Jr. for his historic ride as America's first man in space on May 5, 1961.

Russian suit models

• SK-1, the space suit of Yuri Gagarin, the first man in space
• Berkut (Беркут = "golden eagle"), the space suit of Alexei Leonov, the cosmonaut who first made a spacewalk
• Krechet (Кречет = " gyrfalcon") suit, designed for the cancelled Soviet manned moon landing
• Yastreb (Ястреб = "hawk") space suit for extra-vehicular activity, based on the Krechet
• Orlan (Орлан = " sea-eagle" or "bald eagle") suits for extra-vehicular activity
• Sokol (Сокол = "falcon") suits worn by Soyuz crew members during lift-off and re-entry
• Strizh (Стриж = "swift (bird)") spacesuit developed for pilots of the Buran space shuttle

American suit models

• In the early 1950s Siegfried Hansen and colleagues at Litton Industries designed and built a working hard-shell suit, which was used inside vacuum chambers and was the predecessor of hard space suits used in NASA missions.
• Navy Mark V high-altitude/vacuum suit used for Project Mercury
• Gemini spacewalk suits, used for Project Gemini
• Manned Orbiting Laboratory MH-7 space suits
• Apollo/Skylab A7L EVA and moon suits. The A7L Apollo & Skylab spacesuit is the primary pressure suit worn by NASA astronauts for Project Apollo, the three manned Skylab flights, and the Apollo-Soyuz Test Project between 1968 and the termination of the Apollo program in 1975.
• Advance Crew Escape System Pressure Suit used on the Space Shuttle. The Advanced Crew Escape Suit or ACES suit, is a full pressure suit currently worn by all Space Shuttle crews for the ascent and entry portions of flight. The suit is a direct descendant of the U.S. Air Force high-altitude pressure suits worn by SR-71 Blackbird and U-2 spy plane pilots, X-15 and Gemini pilot- astronauts, and the Launch-Entry Suits worn by NASA astronauts starting on the STS-26 flight, the first flight after the Challenger Disaster
• Extravehicular Mobility Unit used on both the Space Shuttle and International Space Station. The EMU is an independent anthropomorphic system that provides environmental protection, mobility, life support, and communications for a Shuttle or ISS crew member to perform extra-vehicular activity (EVA) in earth orbit.

Chinese suit models

• Shenzhou 5 space suit. The suit worn by Yang Liwei on Shenzhou 5, the first manned Chinese space flight, closely resembles a Sokol-KV2 suit, but it is believed to be a Chinese-made version rather than an actual Russian suit.

• Shenzhou 6 space suit. Pictures show that the suits worn by Fei Junlong and Nie Haisheng on Shenzhou 6 differ in detail from the earlier suit, they are also reported to be lighter.

• Shenzhou 7 space suit. New space suits for the extravehicular activity (舱外航天服) will be used, notably made with intelligent materials (“聪明材”). . The suit is designed for a spacewalk mission of up to seven hours.The astronauts had been training in the out-of-capsule space suits since July 2007, and movements are seriously restricted in the suits, with a mass of more than 110 kilograms each. Recent reports imply that China bought some Orlan space suits from Russia as an alternative option in the misson.

Emerging technologies

Several companies and universities are developing technologies and prototypes which represent improvements over current spacesuits.

Mark III

The Mark III is a NASA prototype, constructed by ILC Dover, which incorporates a hard lower torso section and a mix of soft and hard components. The Mark III is markedly more mobile than previous suits, despite its high operating pressure (8.3 psi/57 kPa), which makes it a "zero-prebreathe" suit, meaning that astronauts would be able to transition directly from a one atmosphere, mixed-gas space station environment, such as that on the International Space Station, to the suit, without risking decompression sickness, which can occur with rapid depressurization from an atmosphere containing Nitrogen or another inert gas.

I-Suit

The I-Suit is a spacesuit prototype also constructed by ILC Dover, which incorporates several design improvements over the EMU, including a weight-saving soft upper torso. Both the Mark III and the I-Suit have taken part in NASA's annual Desert Research and Technology Studies (D-RATS) field trials, during which suit occupants interact with one another, and with rovers and other equipment.

Bio-Suit

Bio-Suit is a space activity suit under development at the Massachusetts Institute of Technology, which as of 2006 consists of several lower leg prototypes. Bio-suit is custom fit to each wearer, using laser body scanning.

MX-2

The MX-2 is a space suit analogue constructed at the University of Maryland's Space Systems Laboratory. The MX-2 is used for manned neutral buoyancy testing at the Space Systems Lab's Neutral Buoyancy Research Facility. By approximating the work envelope of a real EVA suit, without meeting the requirements of a flight-rated suit, the MX-2 provides an inexpensive platform for EVA research, compared to using EMU suits at facilities like NASA's Neutral Buoyancy Laboratory.

The MX-2 has an operating pressure of 2.5–4 psi. It is a rear-entry suit, featuring a fibreglass hard upper torso. Air, LCG cooling water, and power are open loop systems, provided through an umbilical. The suit includes a mac mini to capture sensor data, such as suit pressure, inlet and outlet air temperatures, and heart rate. Resizable suit elements and adjustable ballast allow the suit to accommodate subjects ranging in height from 68 in. to 75 in., and with a weight range of 120 lb (54 kg).

North Dakota suit

Beginning in May 2006, five North Dakota schools collaborated on a new spacesuit prototype, funded by a $100,000 grant from NASA, to demonstrate technologies which could be incorporated into a planetary suit. The suit was tested in the Theodore Roosevelt National Park badlands of western North Dakota. The suit weighs 47 pounds without a life support backpack, and costs only a fraction of the standard $22,000,000 cost for a flight-rated NASA spacesuit. The suit was developed in just over a year by students from the University of North Dakota, North Dakota State, Dickinson State, the state College of Science and Turtle Mountain Community College. The mobility of the North Dakota suit can be attributed to its low operating pressure; while the North Dakota suit was field tested at a pressure of 1 psi differential, NASA's EMU suit operates at a pressure of 4.7 psi, a pressure designed to supply approximately sea-level oxygen partial pressure for respiration (see discussion above).

NASA Constellation Space Suit system

On August 2, 2006, NASA indicated plans to issue a Request for Proposal (RFP) for the design, development, certification, production, and sustaining engineering of the Constellation Space Suit to meet the needs of Project Constellation. NASA foresees a single suit capable of supporting: survivability during launch, entry and abort; zero-gravity EVA; lunar surface EVA; and Mars surface EVA.

On June 11, 2008, NASA awarded a $745 million contract to Oceaneering International to create the new spacesuit.

Suitports

A suitport is a theoretical alternative to an airlock, designed for use in hazardous environments and in human spaceflight, especially planetary surface exploration. In a suitport system, a rear-entry space suit is attached and sealed against the outside of a spacecraft, such that an astronaut can enter and seal up the suit, then go on EVA, without the need for an airlock or depressurizing the spacecraft cabin. Suitports require less mass and volume than airlocks, provide dust mitigation, and prevent cross-contamination of the inside and outside environments. Patents for suitport designs were filed in 1996 by Philip Culbertson Jr. of NASA's Ames Research Centre and in 2003 by Joerg Boettcher, Stephen Ransom, and Frank Steinsiek.

Spacesuits in fiction

For as long as there has been fiction set in space, authors have tried to describe or depict the space suits worn by their characters. These fictional suits vary in appearance and technology, and range from the highly authentic to the utterly improbable.

A very early fictional account of space suits can be seen in the book Edison's Conquest of Mars (1898). Later comic book series such as Buck Rogers (1930s) and Dan Dare (1950s) also featured their own takes on space suit design. Science fiction authors such as Robert A. Heinlein contributed to the development of fictional space suit concepts.