What Is a Spacesuit? A Spacecraft Shaped Like a Person

Each layer of a suit exists because of a specific way that vacuum kills:

• •Pressure, since at vacuum the water in tissue would vaporise, a condition called ebullism, and the lungs cannot transfer oxygen without a pressure gradient. The suit holds roughly a third of an atmosphere of pure oxygen, which is enough to breathe and low enough to keep the suit flexible
• •Oxygen supply and carbon dioxide removal, the latter handled by a lithium hydroxide canister or a regenerable bed, because carbon dioxide accumulating in a sealed volume incapacitates long before oxygen runs out
• •Temperature, managed not by insulation alone but by a garment threaded with about a hundred metres of tubing circulating chilled water, because a working body generates more heat than a vacuum lets it shed
• •Micrometeoroid and debris protection, through multiple layers of tough fabric
• •Radiation, partially, since a suit cannot stop the worst of it and the mission is planned around avoiding exposure instead
• •Mobility, which is the hardest engineering problem, because a pressurised bag resists bending in exactly the way a balloon does

Inflate a sealed garment and it becomes rigid, and every joint a person bends compresses the volume on one side, which the pressure resists. Early suits were exhausting to work in for this reason, and hand fatigue remains the limiting factor on spacewalk duration, since closing a pressurised glove against internal pressure for hours is genuinely tiring and fingernail injuries are a documented occupational problem. The solutions are geometric: joints are built with convoluted bellows, cable restraints and rotating bearings so that bending moves material from one side to the other at constant volume rather than compressing it. The suits worn on the Apollo lunar surface achieved this well enough for astronauts to walk, kneel, use tools and, in the later missions, drive, and they were made by a company better known for manufacturing brassieres, whose seamstresses sewed the twenty-one layers by hand to tolerances of a fraction of a millimetre without pinning through the pressure layer.

Suits divide by purpose and the difference is substantial. Intravehicular suits, worn during launch and re-entry, are pressure garments for emergency use only, comparatively light and not designed for work outside; the orange suits worn on the shuttle and the current commercial launch suits are of this type. Extravehicular units are self-contained spacecraft with a life support backpack, and the American design used on the space station dates in its essentials to 1981 and has been maintained and refurbished far beyond its intended life, with a well-documented water leak into a helmet in 2013 that nearly drowned an astronaut. The Russian Orlan suit takes a different approach with a rear entry hatch that allows a single person to put it on in a few minutes, against the hours and the assistance the American design requires. Lunar surface suits need a separate capability set, including walking, kneeling, dust tolerance and far greater mobility at the hip and waist, and new designs are being developed for that purpose.

Lunar dust turned out to be one of the more serious obstacles to sustained surface operations, and it was underestimated. The material is not weathered like terrestrial dust but fractured by micrometeorite impact, so the grains are sharp and jagged, and constant bombardment leaves them electrostatically charged so that they cling to everything. Apollo crews reported that dust abraded the outer layers of their suits noticeably over three days of surface activity, jammed zips and seals, coated visors, and could not be brushed off. It was carried into the lunar module on the suits, floated in the cabin in weightlessness, and was inhaled, with several astronauts reporting irritation and one describing hay fever symptoms. Any programme intending to stay for months rather than days must solve this, which is why proposed designs include suits that dock to the outside of a vehicle so that the dusty exterior never enters the habitat.

A different approach has existed on paper since the 1960s. A mechanical counterpressure suit would squeeze the body directly with elastic material rather than surrounding it with pressurised gas, supplying pressure to the skin while leaving only the helmet gas-filled. The advantages would be considerable: far greater mobility, much lower bulk, no risk of catastrophic decompression from a puncture since a tear affects only the area around it, and easier storage. The obstacles are that applying even pressure to a complex and moving shape is extremely difficult, particularly at the hands, armpits and groin, that getting into a garment tight enough to work is a serious problem, and that heat removal without a gas layer needs a different solution. Work at MIT and elsewhere has produced prototypes using shape-memory alloys that tighten when heated, and nothing has flown. The suits people wear today remain gas-pressurised balloons with extremely clever joints.

A spacesuit is a crewed spacecraft, holding about a third of an atmosphere of pure oxygen, scrubbing carbon dioxide, circulating chilled water through a hundred metres of tubing to shed body heat, and stopping micrometeorites. Mobility is the hardest problem, because a pressurised garment resists bending, and it is solved with bellows joints and rotating bearings, with hand fatigue still limiting spacewalk length. Lunar dust, sharp and electrostatically charged, abraded Apollo suits within three days, and the mechanical counterpressure alternative has never flown.