How Space Suits Work

Space is a near-perfect vacuum. Without a spacesuit, an unprotected human would lose consciousness within about 15 seconds as dissolved gases in the blood begin to boil (a process called ebullism) at the extremely low pressure. Death would follow within 1–2 minutes from asphyxiation and tissue damage.

A spacesuit maintains an internal pressure of approximately 4.3 psi (29.6 kPa) of pure oxygen — about 30% of sea-level atmospheric pressure. This is enough to prevent ebullism and provide breathable oxygen, while keeping the suit flexible enough for an astronaut to move and work. Higher pressure would make the suit stiffer and harder to operate in.

Because the suit uses pure oxygen at reduced pressure (rather than the normal nitrogen-oxygen mix at sea level), astronauts must "pre-breathe" pure oxygen for several hours before an EVA to purge dissolved nitrogen from their blood — otherwise they risk decompression sickness, similar to "the bends" in diving.

The NASA EMU has 14 distinct material layers, each serving a specific purpose. From innermost to outermost:

Layer 1 — Liquid Cooling and Ventilation Garment (LCVG): A spandex undergarment threaded with thin plastic tubes carrying temperature-controlled water. This is the astronaut's primary cooling system, removing metabolic heat via conduction. It also distributes oxygen flow around the body.

Layers 2–3 — Pressure Bladder + Restraint: A urethane-coated nylon bladder holds the suit's internal pressure. Surrounding it, a Dacron polyester restraint layer prevents the bladder from ballooning outward — without it, the suit would inflate into an immobile ball at 4.3 psi.

Layers 4–10 — Thermal Micrometeoroid Garment (TMG) Inner Layers: Multiple alternating layers of aluminised Mylar and Dacron spacer fabric provide thermal insulation. In direct sunlight, external surfaces can reach +121°C (+250°F); in shadow, −157°C (−250°F). These layers create a vacuum-insulated barrier similar to a thermos.

Layers 11–13 — MMOD Protection: Layers of Kevlar, Nomex and Teflon-coated fibres protect against micrometeoroid and orbital debris (MMOD) impacts. A particle the size of a grain of sand can travel at 7+ km/s in orbit — fast enough to puncture metal. These layers are designed to slow and fragment incoming particles before they reach the pressure bladder.

Layer 14 — Outer Shell: The outermost layer is white Ortho-fabric (Teflon/Nomex/Kevlar blend) that provides abrasion resistance, fire protection and thermal reflection. The white colour reflects solar radiation — essential for temperature management.

The Primary Life Support System (PLSS) is the backpack unit that sustains the astronaut's life during an EVA. It provides:

Oxygen Supply: High-pressure oxygen tanks release a steady flow of breathing gas into the helmet. The suit maintains a partial pressure of oxygen sufficient for respiration at 4.3 psi total.

CO₂ Removal: A lithium hydroxide (LiOH) canister absorbs exhaled carbon dioxide through a chemical reaction. Without this system, CO₂ buildup would cause hypercapnia (CO₂ poisoning) within minutes.

Thermal Regulation: The LCVG water loop runs through a sublimator — a device that routes the heated water to a porous plate exposed to the vacuum of space. The water sublimates (turns directly from liquid to vapour), carrying heat away. This is the suit's "radiator."

Power: Lithium-ion batteries power suit electronics, the water pump, fans, communications and the HUD/displays. Battery capacity limits EVA duration alongside consumable oxygen and water.

Communications: UHF radios in the PLSS connect the astronaut to the spacecraft and Mission Control. Suit telemetry (pressure, temperature, O₂ levels, battery state) is transmitted continuously.

The PLSS weighs approximately 54 kg (119 lb) — nearly half the EMU's total mass. An emergency Secondary Oxygen Pack (SOP) provides approximately 30 minutes of backup breathing oxygen if the PLSS fails.