| MadSci Network: Physics |
Astronaut suits consist of several layers of materials that together give an airtight enclosure capable of resisting most micrometeor impacts, scraps and punctures while keeping the astronaut at a comfortable temperature.
The NASA Web sites have information on the spacesuits construction, operating systems and accessories. Wardrobe for Space has some background historical infomation. Information on the shuttle spacesuits can be found under the Space Suit General Description. Spacelink can provide more information and has a search engine.
Spacesuits started out as modified a U.S. Navy high altitude jet aircraft pressure suit. The Mercury suits consisted of an inner layer of Neoprene-coated nylon fabric and a restraint outer layer of aluminized nylon. Joint mobility at the elbow and knees was provided by simple fabric break lines sewn into the suit. The suit was worn in the unpressurized or "soft" condition and would have inflated only in the event of an emergency. Limited mobility made the suit unsuitable for wearing and working with it pressurized.
To improve mobility, the Gemini spacesuit had a combination of a pressure bladder and a link-net restraint layer that made the whole suit flexible when pressurized. Other changes were also made in the construction of the spacesuit. The gas-tight, man-shaped pressure bladder was made of Neoprene-coated nylon and covered by loadbearing link-net woven from Dacron and Teflon cords. The net layer, being slightly smaller than the pressure bladder, reduced the stiffness of the suit when pressurized and served as a sort of structural shell, much like a tire contained the pressure load of the innertube in the era before tubeless tires. Improved arm and shoulder mobility resulted from the multilayer design of the Gemini suit.
The biggest challenge to the Apollo spacesuits was a need to protect the astronauts for extended periods on the Moon's surface while allowing them mobility for exploration. Micrometeorites, jagged rocks, ultraviolet radiation and extremes of temperature were only some of the problems needed to be overcome. The astronauts also needed to be able to handle delicate equipment and later in the program sit in the lunar rover.
Apollo spacesuit mobility was improved over earlier suits by use of bellows-like molded rubber joints at the shoulders, elbows, hips and knees. Modifications to the suit waist for Apollo 15 through 17 missions added flexibility at the wast to make it easier for crewmen to sit on the lunar rover vehicle.
From the skin out, the Apollo A7LB spacesuit began with an astronaut-worn liquid-cooling garment, similar to a pair of longjohns with anetwork of spaghettilike tubing sewn onto the fabric. Cool water, circulating through the tubing, transferred metabolic heat from the Moon explorer's body to the backpack and thence to space.
Next came a comfort and donning improvement layer of lightweight nylon, followed by a gas-tight pressure bladder of Neoprene-coated nylon or bellows-like molded joints components, a nylon restraint layer to prevent the bladder from ballooning, a lightweight thermal superinsulation of alternating layers of thin Kapton and glass-fiber cloth, several layers of Mylar and spacer material, and finally, protective outer layers of Tefloncoated glass-fiber Beta cloth.
Apollo space helmets were formed from high strength polycarbonate and were attached to the spacesuit by a pressure-sealing neckring. Unlike Mercury and Gemini helmets, which were closely fitted and moved with the crewman's head, the Apollo helmet was fixed and the head was free to move within. While walking on the Moon, Apollo crewmen wore an outer visor ssembly over the polycarbonate helmet to shield against eye damaging lutraviolet radiation, and to maintain head and face thermal comfort.
Completing the Moon explorer's ensemble were lunar gloves and boots, both designed for the rigors of exploring, and the gloves for adjusting sensitive instruments. The lunar surface gloves consisted of integral structural restraint and pressure bladders, molded from casts of the crewmen's hands, and covered by multilayered superinsulation for thermal and abrasion protection. Thumb and fingertips were molded of silicone rubber to permit a degree of sensitivity and "feel." Pressure-sealing disconnects, similar to the helmet-to-suit connection, attached the gloves to the spacesuit arms.
The lunar boot was actually an overshoe that the Apollo lunar explorer slipped on over the integral pressure boot of the spacesuit. The outer layer of the lunar boot was made from metal-woven fabric, except for the ribbed silicone rubber sole; the tongue area was made from Teflon-coated glass-fiber cloth. The boot inner layers were made from Teflon-coated glass-fiber cloth followed by 25 alternating layers of Kapton film and glass-fiber cloth to form an efficient, lightweight thermal insulation.
The Apollo-Soyuz and Skylab missions did not need all the abilities of the Apollo spacesuits. Instead, they used simplified versions of the Apollo spacesuits while doing EVA work such as changing film cannisters on teh telescope. The spacesuit changes from Apollo to Skylab included a less expensive to manufacture and lightweight thermal micrometeoroid overgarment, elimination of the lunar boots, and a simplified and less expensive extravehicular visor assembly over the helmet. The liquidcooling garment was retained from Apollo, but umbilicals and astronaut life support assembly (ALSA) replaced backpacks for life support during spacewalks.
Apollo-type spacesuits were used again in July 1975 when American astronauts and Soviet cosmonauts rendezvoused and docked in Earth orbit in the joint Apollo-Soyuz Test Project (ASTP) flight. Because no spacewalks were planned, U.S. crewmen were equipped with modified A7LB intravehicular Apollo spacesuits fitted with a simple cover layer replacing the thermal micrometeoroid layer.
There are two distinct types of suits worn by the astronauts ona shuttle mission. The first are the pressure suits worn during launch and landing. Strictly speaking these are not spacesuits but more similar to the pressure suits worn by pilots of high flying aircraft such as the SR-71 Blackbird. They provide protection and emergency survival capability should the shuttle encounter problems and the crew need to evacuate the shuttle
The shuttle spacesuit represents a major step forrward in spacesuit design. Previous spacesuits were custom-fitted garments and in some suit models, more than 70 different measurements had to be taken of the astronaut in order to manufacture the suit to the proper fit. As a result, a space suit could be worn by only one astronaut on only one mission. Space suits were stiff, and simple motions such as grasping objects sapped the strength of an astronaut. Even donning the suit was an exhausting process lasting, at times, more than an hour and requiring the help of an assistant. For the Space Shuttle astronauts, a new suit has been developed that offers many improvements in comfort, convenience, and mobility over the previous models. The suit, which is worn only outside the Shuttle, is modular and features many interchangeable parts. Torso, pants, arms, and gloves comes in several different sizes and can be assembled for each mission in the proper combinations to suit individual astronauts.
The Shuttle suit, known as an EMU for Extravehicular Mobility Unit, consists of three main parts: liner, pressure vessel, and primary life support system. These components are supplemented by a drink bag, communications set, helmet, and visor assembly.
The suit liner is technically called the liquid cooling and vent garment. It is quite similar in appearance to long underwear with one important difference. The stretchy, form-fitting nylon Spandex fabric is laced with small Tygon plastic tubes. The outside layers of the Shuttle suit are exceptionally well insulated making body heat dissipation a critical concern. Water cooled in the life support system circulates around the body it encloses through the plastic tubes for temperature control. Openings in the fabric weave also permit ventilation of the body.
The liquid cooling and vent garment is the first major suit component donned by the astronaut. It is followed by the pressure vessel, a multilayered garment. Actually, only one of the layers contains the pressure. The remainder are comprised of alternating layers of aluminized mylar plastic and unwoven Dacron that insulate the suit from the Sun-to-shade temperature extremes of 148 degrees to minus 129 degrees in outer space. On top of those layers is a single outside layer of though Ortho fabric, a combination of Teflon, Kevlar, and Nomex with a neoprene liner, that serves as an abrasion and tear resistant cover as well as the primary micrometeoroid shield.
The principal function of the pressure vessel is the containment of oxygen under pressure to make a livable atmosphere for the astronaut. One layer of Kevlar, lined with a polyurethane plastic bladder and Dacron shell, contains the oxygen at a pressure of 281.24 grams per square centimeter (4 psi). With a normal atmospheric mixture of gasses, this pressure would be hardly livable. However, pure oxygen of the suit atmosphere makes the pressure acceptable.
One of the major challenges in designing space suits has been to make the pressure vessel flexible. With inside pressure, the vessel inflates balloon-like and becomes stiff. On previous models, joint areas such as the shoulders were made of molded neoprene rubber and reinforced with cables. These joints required constant muscle exertion to hold them in a flexed position. The pressure vessel fabric however, permits tucks to be stitched in the shoulder, elbow, wrist, knee, and ankle area. The tucks allow the joints to retain a flexed shape without constant muscle exertion.
Heat transfer in space is almost exclusively by radiation. Within the spae suit, heat is transferred by convestion and conduction. The role of the space suit is to minimize the convection and conduction and, to a lesser extent, radiation to space. It also must be capable of keeping an astronaut cool in low Earth orbit and similar environments where the temperature can easily rise to over 100 F.
From the descriptions of the spacesuits, you will notice that all of them have multiple layers. For those living in colder climates, it is well know that the best way to keep warm when going outside is to wear many layers of clothing. This traps the air and forms a very insulative layer of dead air. The multiple layers in the spacesuits also work in a similar method to some extent. The spacesuits also use low thermal conductivity materials that limit the transfer of heat directly through the suit. Finally, the aluminized layers act like the solar blankets sould in many camping and department stores (they came from the space program). They reflective layer actually reflects the heat back towards the astronaut's body and minimizes heat loss.
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