A space suit is a pressurized garment that keeps an astronaut alive outside a spacecraft by providing oxygen, removing carbon dioxide, regulating temperature, and shielding against radiation and micrometeorites. It functions as a personal spacecraft, containing every system a human body needs to survive in the vacuum of space. The version currently used on the International Space Station weighs about 319 pounds on Earth and maintains an internal pressure roughly equal to the inflation pressure of a basketball.
Why You Can’t Survive in Space Without One
Space presents a combination of lethal conditions all at once. There is no breathable air, no atmospheric pressure to keep your blood from boiling, and temperatures that swing from around 250°F in direct sunlight to minus 250°F in shadow. Micrometeorites, tiny particles of space debris, travel fast enough to puncture skin and metal. Unfiltered solar radiation, including ultraviolet and infrared light, would cause severe burns in minutes.
A space suit addresses every one of these threats simultaneously. It creates a sealed, pressurized environment around the body, supplies oxygen, scrubs out exhaled carbon dioxide, manages heat, and absorbs impacts. Losing any one of those functions during a spacewalk would be life-threatening within minutes.
Pressure and Oxygen
The suit used on the ISS, called the Extravehicular Mobility Unit (EMU), operates at an internal pressure of 4.3 psi. That’s far lower than the 14.7 psi we experience at sea level, but it’s enough to keep the body functioning normally. Running the suit at a lower pressure makes the joints easier to bend. At higher pressures, the suit would balloon outward and become so stiff that simple hand movements would exhaust the astronaut.
Before a spacewalk, astronauts go through a pre-breathing protocol, inhaling pure oxygen to flush nitrogen out of their bloodstream. This prevents decompression sickness, the same condition scuba divers call “the bends,” when transitioning from the station’s higher-pressure cabin atmosphere to the suit’s lower pressure.
The Life Support Backpack
The large backpack on the suit is a portable life support system. It holds tanks of oxygen for breathing, removes exhaled carbon dioxide, circulates cooling water, manages humidity, and powers the suit’s electronics. On the ISS version, this backpack plus the suit and a small jetpack rescue device bring the total weight to roughly 319 pounds on Earth. In microgravity, astronauts don’t feel the weight, but they still feel the mass, meaning it takes real effort to start and stop moving.
The backpack’s primary structural components are built from titanium, chosen for its strength-to-weight ratio and resistance to corrosion. Everything inside it is designed with redundancy in mind: backup oxygen supplies, secondary fans, and spare regulators so that a single failure doesn’t end the spacewalk.
Temperature Control
Underneath the outer suit, astronauts wear a full-body undergarment laced with thin plastic tubing. Cold water circulates through this tubing to pull heat away from the skin. Gas also vents through the garment to help evaporate sweat. Without this system, body heat generated during physical work would build up inside the sealed suit with no way to escape, and core body temperature would rise dangerously within an hour.
The astronaut can adjust the water flow rate using a dial on the suit’s chest panel, turning up the cooling during heavy exertion like turning bolts or carrying equipment, and dialing it back during rest periods.
Layers of Protection
A space suit is not a single shell. It’s built from roughly 14 layers of material, each with a specific job. The innermost layer is the cooling garment. Above that sits a pressure bladder that holds in the suit’s atmosphere, followed by a restraint layer that prevents the bladder from expanding like a balloon. The outer layers include insulation, puncture-resistant fabrics to stop micrometeorites, and a reflective coating to manage solar heat.
The helmet includes an outer visor assembly with two specialized layers. One has a gold optical coating that filters harsh sunlight, ultraviolet rays, and infrared radiation. The other provides thermal control. Together, they also guard against micrometeorite impacts. The gold layer is thin enough to see through but reflective enough to block the wavelengths of light that would damage the astronaut’s eyes.
Communication Inside the Helmet
Astronauts can’t reach their ears while wearing a pressurized helmet, so all communication runs through a fabric cap worn underneath, informally called the “Snoopy cap.” It holds two earphones, two microphones, and duplicate cables connecting everything. The redundancy matters: if one microphone or earphone fails, the backup keeps the astronaut in contact with the crew and mission control. A cable from the cap connects to the suit’s communication wiring, which relays audio either through the suit’s own systems or through hardwired connections inside the spacecraft.
Mobility and Fit
One of the hardest engineering challenges in suit design is letting astronauts move. Pressurized joints resist bending, so suits use specially designed bearings and pleated fabric at the shoulders, elbows, wrists, hips, and knees. Even with these features, working in a pressurized suit is physically exhausting. Astronauts regularly compare a six-hour spacewalk to a full day of manual labor.
Sizing has historically been a limitation. Earlier suits were built in a narrow range of body sizes, which restricted who could perform spacewalks. The next generation of suits, being developed for NASA’s Artemis moon missions, addresses this directly with increased sizing options and adjustability to fit a wider range of crew members. These newer suits also offer improved joint flexibility, making it possible to bend down to collect rock samples and perform tasks on the lunar surface that older suits simply couldn’t accommodate.
How the Newest Suits Are Different
The suits being built for the Artemis program represent the first major redesign in over 40 years. The current ISS suits entered service in the 1980s and have been maintained, repaired, and upgraded, but their fundamental design is decades old. The new Axiom Extravehicular Mobility Unit is purpose-built for moonwalks, with better lower-body mobility since astronauts will be walking on a surface rather than floating. It also incorporates updated life support systems and stronger protection against lunar dust, which is abrasive, electrostatically charged, and far more damaging to equipment than anything encountered on the ISS.
These suits will need to handle conditions the ISS suits never faced: longer periods of sun exposure on the lunar surface, temperature swings specific to the Moon’s south pole, and the physical demands of hiking over uneven terrain in partial gravity. The shift from orbital spacewalks to surface exploration is driving nearly every design change.