EVA Backpacks and the Ascent Stage

In the Artemis Project Reference Mission, we have our crew riding in the Ascent Stage as they ferry the core of our lunar exploration base to the surface of the moon. Then, at the end of their stay on the moon, they again board the Ascent Stage for the ride back to lunar orbit. While the crew members are using the Ascent Stage, they will use the resources of the vehicle for life support, rather than using their backpacks.

Life support from the Ascent Stage vehicle

Ascent Stage Liftoff Copyright © 1997 Vik Olliver

The extravehicular activity (EVA) backpack (also called the PLSS, portable life support system) provides power, communications, and oxygen to the space suit. We shouldn't have a problem providing these resources from the Ascent Stage. It has to generate its own power and provide radio communication already. We provide the oxygen by including high-pressure oxygen tanks and hookups for the crew.

We'll need an oxygen tank for life support in the Ascent Stage in any case, because of the scenario where we have a suit puncture during ascent. The crew can't walk back to the habitat, and we have to provide for the scenario where the crew takes a couple of hours to get to the safety of the lunar transfer vehicle (LTV).

The current Shuttle backpack, and the Apollo backpack before it, provides only 30 minutes of oxygen from its secondary oxygen pack (SOP). In actual operations, the SOP can only keep the suit pressure at a safe level for 21 minutes, exhausting through a hole in the suit 1/8 inch in diameter.

So, any time we have the crew in the Ascent Stage, we want them on umbilicals connected to the Ascent Stage instead of using backpacks. This means we'll need to provide storage for the backpacks in the LTV for descent; or we hook it up so that the Ascent Stage can be used in parallel with the backpack.

For descent to the lunar surface, we might have the crew on both backpacks and vehicle supply. The current Shuttle suit is already plumbed so that the crew can switch between their backpacks and an umbilical to the Shuttle airlock, so there's no redesign required for that feature. Whether the backpacks probably will be on the crew members' backs depends on how we design the seats. We might have the crew standing up for descent (so the pilot can see the ground), and lying down for ascent.

Leave the backpacks on the moon

Astronauts working at the space station or using the LTV for paying work in Earth orbit might be able to put those backpacks to good use. However, for the first several Artemis Project moon flights, we can reasonably expect that, pound for pound, lunar material will be worth a lot more to us than the backpacks.

So, for ascent, we want to leave the backpacks on the surface. At 200 lbs each for 3 crew members, that's 600 lbs of junk we don't need for the trip home.

We also can expect that the backpacks will eventually be worth a lot more on the moon than at the space station. Once we've paid to bring a piece of complex machinery to the moon, we will be reluctant to remove it from the moon unless we really need the equipment somewhere else.

So instead of bringing them home, we can leave the used backpacks in storage on the moon until someone salvages them. Eventually we'll come up with a way to verify the integrity of all those used backpacks. If we put them in a thermally conditioned environment, we can store them on the moon for years without measurable deterioration.

More to come in EVA systems development

We'll want to keep in touch with NASA's work on the International Space Station. Until now, we have had the luxury of maintaining space suits and backpacks in laboratories on Earth. The space station changes the situation; NASA will have to learn how to maintain space suits and backpacks in space.

We can't know what lessons NASA will learn about cleaning, testing, and refurbishing EVA equipment in Earth orbit, but certainly everything they learn will be directly applicable to maintaining the same machines on the moon.