How Long Can a Spacesuit Keep You Alive on Mars?

Oct 24

3 min read

Step outside on Mars without a suit and you have about fifteen seconds before you pass out. With a good suit, you have hours. This post explains where that difference comes from, what runs out first, and why the suits of Vostok, the Russian settlement in ICARUS, are the weak point of every walk outside.

A worn spacesuit glove with a dust-clogged wrist ring and a helmet with a repaired crack on a workshop bench in a Mars settlement

Fifteen seconds without a suit

The air on Mars is mostly carbon dioxide, and its pressure at the surface is less than one percent of Earth's. At that pressure, water boils below body temperature. Saliva and tears would start to bubble, and the lungs could not take in oxygen. ESA's Stefaan de Mey told Space.com that a person exposed to vacuum loses consciousness within 10 to 15 seconds. The thin Martian air changes almost nothing. Without help, brain death follows within minutes. On Mars, a suit is a small spacecraft shaped like a person.

What a suit actually does

A suit keeps a bubble of pressure around the body. NASA's spacewalk suit, the EMU, holds about 30 kilopascals of pure oxygen, roughly a third of sea-level pressure. It removes the carbon dioxide you breathe out, cools you with water running through tubes in an undergarment, and carries a radio and a battery. Mars adds its own demands. The average temperature is around minus 60 degrees Celsius, so a Mars suit has to keep you warm at night and get rid of your body heat during hard work.

Why the limit is counted in hours

The EMU supports an astronaut for about 8 hours, plus a 30-minute emergency reserve. The limit comes from the things a suit uses up: oxygen, the filter that absorbs carbon dioxide, cooling water and battery power. The person inside wears out too. Moving in a pressurized suit is hard work, and the hands tire quickly against stiff gloves. A walk outside on Mars would be planned the same way: out and back long before the reserve is touched.

What wears a suit down on Mars

Over weeks and months, two other dangers count more. The first is radiation. The Curiosity rover measured about 0.64 millisieverts per day at the surface, as Space.com reported. That is about what a person on Earth receives from natural background radiation in three months, and a suit does little against it. The second is dust. Martian dust is finer than flour and electrically charged, so it clings to fabric and works its way into joints, bearings and seals. Every walk outside leaves a little more of it in the suit.

The suits of Vostok

In ICARUS, Vostok has received nothing from Moscow for years, and its suits show it: scratched panels, hastily replaced joints, fading insignia. In the first chapter, Major Ivanov grabs his temporary suit, a slightly heavier model designed to be worn outside for hours if necessary, with a repaired crack running across the visor. Every patch on such a suit raises the same question: how many more hours will it hold? The chapter, When the Sky Turned Red, begins as a great storm approaches. Why the wind itself is not the danger, the dome post explains. You can also step into the Mítosz exhibition, where Luna, one of the Twin Robots, guides you across Mars.