Martian Space Suits Will Need To Be 40% Lighter

Long before a human ever sets foot on the Red Planet, we already know how hard the environment is. Once one finally does, the only things protecting them from that harsh environment will be the infrastructure we’ve built up there, and the spacesuit that keeps that in a protective bubble. Unfortunately, modern space suits aren’t built with Martian gravity, which is 3/8ths of Earth’s, in mind. To prove that point, a team of NASA and industry engineers made a presentation at the 55th International Conference on Environmental Systems (ICES) that showed that the newest generation of spacesuits are simply too heavy to use on Mars.

That current generation of suit is known as the Exploration Extravehicular Mobility Unit (xEMU). It’s being designed for the Artemis lunar missions coming sometime in the next few years. And it’s a marvel of modern engineering - it can withstand massive pressure differentials, allows extensive lower-body mobility, and is modular, making many pieces easy to replace.

But all that functionality comes at a cost - mass. The xEMU comes in at a heavy 170 kg (376 lbs), almost twice the weight of the average astronaut expected to use it. That might be fine for the Moon, where the gravity is 1/6th that of Earth, and the suit consequently feels more like 28kg (61 lbs). But on Mars, it would still burden an astronaut with an additional 64 kg (141 lbs).

Fraser discusses how spacesuits have become a critical bottleneck for the Artemis missions.

It wouldn’t be a technical report at a conference without some additional math, though, so let’s dive into some assumptions the authors made to calculate how much a reasonably designed Martian spacesuit should be. First, they took a conservative approach and set a baseline astronaut weight of 50 kg (108 lbs), representing the 5th percentile of female human astronauts, though admittedly none to date have ever had that low of weight.

With that weight in mind, the authors note that astronauts are expected to maintain a VO2 max (a measure of their aerobic capacity) of 36 ml/min/kg - which is above the average for middle aged sedentary women. Unfortunately, the authors also note astronauts will also lose 15-25% of their aerobic capacity in the months of travel to Mars, meaning their VO2 max will be lower by the time they actually arrive on the Red Planet.

According to the National Institution of Occupational Safety and Health, the maximum capacity for lifting loads limits at around 23 kg (51 lbs). But there is one advantage - spacesuits are designed to act kind of like a balloon, with its internal pressure taking some of the weight off the astronaut’s shoulders. The authors calculate this to be around 22 kg (48 lbs). Which brings the total absolute maximum that a Mars Exploration Extravehicular Mobility Unit (MxEMU) to 104 kg (229 lbs) - a 40% reduction in mass from the current xEMU.

Fraser discusses the new NASA space suits.

One of the big driving forces of this consideration is the “walkback” scenario. If an unpressurized rover breaks down miles from the habitat, the astronauts will have to walk back on foot. The energy they would expend carrying a heavy EVA suit limits how much oxygen they can use, and therefore has tradeoff consequences for the weight of the suit itself. Even with the weight reduction, to ensure the astronauts return safely, the authors suggest only a 30-minute walkback radius. At a typical walking speed of 3.5 km/h (2.2 mph), this would limit the astronauts to a 1.8 km (1.1 mile) radius for their rover excursions.

So how would spacesuit designers drop 40% of the weight of a suit they already spent years optimizing? The authors offer some potential solutions. Historically, spacesuits allocate about 60% of their weight to the life preserving backpack - the Portable Life Support System (PLSS) - and the other 40% of their weight to the suit itself - in this case, the Pressure Garment System (PGS). Applying this ratio for the stripped down MxEMU leaves 62 kg (137 lbs) for the PLSS and 42 kg (92 lbs) for the pressure garment.

The authors suggest ditching the heavy modularity of the xEMU altogether, and returning to the highly integrated architecture of the Apollo era. Back then, components doubled as part of the physical structure of the suit in order to save weight. Apollo’s design had an unfortunate downside, though - it was only “single fault” tolerant - meaning it could only withstand if one thing went wrong - whereas the modern xEMU suits are double fault tolerant, making them undoubtedly the safer choice for astronauts.

But those are the types of tradeoffs engineers have to make when designing for the unforgiving environment of space. All of the first astronauts that end up going to the Red Planet will understand the risks. But hopefully, the engineers back on Earth will be able to literally take some of the weight off their shoulders before they are saddled with the hopes of the species on a new world.

Learn More:

R. Ogilvie et al - Mars Spacesuit Mass Requirements

UT - Weaving the Future of Space Suits

UT - NASA Continues Testing its New Lunar Spacesuits

UT - Next Generation Spacesuit Gets Tested in Weightlessness