How do spacesuits keep astronauts safe?

When it’s time to venture outside, astronauts on the international space station first don one of two types of spacesuit: NASA’s extravehicular mobility unit, introduced in 1984, and the Russian Orlan suit, which has been updated since its debut in the 1960s. Through decades of refinement, they are modern feats of engineering.

Not only must they provide oxygen, scrub carbon dioxide from the air and provide hydration (and a toilet), spacesuits must also protect astronauts against bits of debris hurtling around the Earth and the intensely cold conditions of space.

To see how they protect their precious contents from the perils of a spacewalk, let’s go through the various bits and pieces of the extravehicular mobility unit.

Helmet

An inner clear plastic bubble contains pressurised oxygen that the astronaut breathes. If they get thirsty, they can bite down on a small tube and suck liquid kept in a 0.95-litre bag attached to the inside of the torso segment.

An outer helmet surrounds the bubble, featuring a gold-coated visor to provide protection from sunlight, lights and a moveable camera to let astronauts and ground crew see events in real time. The helmet is made from polycarbonate, the same material found in bulletproof glass, to provide protection from tiny fragments of rock known as micrometeorites and other debris that would smash normal glass.

To keep contact with other astronauts and mission control on Earth, a headpiece colloquially referred to as the “snoopy cap” containing a microphone and headset is also worn inside the helmet.

Upper torso

A single piece of fibreglass, the hard upper torso forms the core of the suit. It’s the mounting point for life support and control modules.

The display and control module are up front, which the astronaut uses to adjust an array of settings including temperature, volume and oxygen. The helmet blocks the astronaut from looking down, so labels on the module are written backwards and can be read with a wrist-mounted mirror.

Arms

The arm assembly screws on the torso and is available in a range of sizes to suit different arm lengths. The arms – and the rest of the suit – comprise 14 layers.

The first three layers closest to the skin are the liquid cooling and ventilation garment, made from nylon and spandex. A urethane-coated nylon bladder maintains pressure, while a restraint pressure garment made from polyethylene terephthalate (more commonly known as PET) keeps the suit’s shape. Next is a layer of ripstop nylon which is covered by seven layers of aluminium-coated polyester (Mylar) designed to insulate and stop micrometeorites and small debris punching through the suit. The outer skin is an insulating layer made from a waterproof, bulletproof and fire-resistant mix of Gore-Tex, Kevlar and Nomex.

Attached to the arms are gloves. A bearing in each wrist means the hand can be rotated. As the hands tend to feel the cold most in space, the gloves have heated fingertips.

A wrist-mounted checklist lets the spacewalker see what needs to be completed during the spacewalk.

Lower torso

A connection ring joins the upper and lower torso together via a bearing that lets the parts rotate and the astronaut to twist. Unique red or ‘candy cane’ stripe patterns identify the astronaut.

A screw system is again used for legs and boots. Boots used by astronauts on the space station have almost no grip unlike those used by the Apollo missions. These featured a grippy sole to cling to the lunar surface.

Two D-rings complete the torso, attaching tethers that prevent the astronaut from drifting away.

Primary life support subsystem

Attached to the rear of the suit, a bit like a backpack, is the primary life support subsystem. Lithium hydroxide canisters pull carbon dioxide from the air as the astronaut breathes, similar to rebreathers used by scuba divers.

Oxygen tanks refresh the circulating pure oxygen air. The suit can run seven hours with a half hour of emergency reserve.

A battery powers a fan that moves the oxygen around. The liquid cooling and ventilation garment, worn under the spacesuit, has pipes running down the astronaut’s arms and legs. Cooling water supplied by the primary life support subsystem keeps heat in check, and sweat is absorbed to prevent condensation.

A warning system alerts the astronaut if the suit malfunctions.

If the astronaut becomes detached from the station or spacecraft, the suit has a type of space-lifejacket. Known as the simplified aid for extravehicular activity rescue, it features nitrogen-powered thrusters and a control stick to let the astronaut propel and steer to safety.

Some spacewalks can last up to seven hours and this creates the issue of what to do when someone needs the toilet.

In space, it’s highly impractical to just come inside and get out of the suit so astronauts instead wear an adult nappy that has increased absorbance called the maximum absorbance garment.

Related reading: How to build a spacesuit