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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
Several things are needed for the space suit to function properly in space. It must provide:
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.[1] 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
- Failed to parse (Missing texvc executable; please see math/README to configure.): W=\int_{V_i}^{V_f} \,P\,dV
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. 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 round the spaceman'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 fiberglass 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
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Voskhod-2 airlock and spacesuit.jpg
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Soviet moon suit side.jpg
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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.[2]
- 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.
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MOL spacesuit.jpg
Manned Orbiting Laboratory MH-7 space suit
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Apollo/Skylab A7L EVA and moon suit
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KSC-95EC-0908.jpg
Advance Crew Escape System Pressure Suit
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GPN-2000-001069.jpg
Extravehicular Mobility Unit
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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 7 space suit. New space suits for the extra vehicular activity (舱外航天服) will be used, notably made with intelligent materials (“聪明材”).[3] The suit is designed for a spacewalk mission of up to seven hours.[4]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.[5]
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/57kPa), 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 health risks such as the bends which can occur with rapid depressurization from an atmosphere containing Nitrogen.
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 fiberglass 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.[6] 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.[7]
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[citation needed] 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.[8] 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 a space suit system to meet the needs of Project Constellation.[9] NASA foresees a single suit capable of supporting: survivability during launch, entry and abort; zero-gravity EVA; lunar surface EVA; and Mars surface EVA.
Spacesuits in fiction
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For as long as there has been fiction set in space, authors have tried to describe 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.
See also
References
- ^ http://www.globalrph.com/martin_4_most2.htm
- ^ "Siegfried Hansen, space suit father; inventor was 90", New York Times, 2002-07-24. Retrieved on 2008-02-09.
- ^ http://scitech.people.com.cn/GB/4650572.html
- ^ China's astronaut outfitters design material for spacewalk suits. Xinhua (June 1, 2007). Retrieved on June 1, 2007.
- ^ Chinese astronauts begin training for spacewalk. People Daily Online (July 18, 2007). Retrieved on August 1, 2007.
- ^ http://ssl.umd.edu/projects/MARSsuit/index.shtml
- ^ Jacobs, Shane; Akin, Dave, Braden, Jeffrey (July 2006). "System Overview and Operations of the MX-2 Neutral Buoyancy Space Suit Analogue". International Conference On Environmental Systems. Retrieved on 2007-06-12.
- ^ http://www.signonsandiego.com/uniontrib/20060507/news_1n7suit.html
- ^ http://prod.nais.nasa.gov/cgi-bin/eps/synopsis.cgi?acqid=121486
External links
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