The Space Reviewin association with SpaceNews

Mars base illustration
Mars may stack up as a more compelling destination for humans than the Moon. (credit: NASA)

Choosing our destination

NASA’s new vision for space exploration is focused on sending crews back to the Moon and then on to Mars. There is general agreement that moving beyond Earth orbit again is a worthwhile goal for our space program, but finding agreement about which destination should come first has proven to be more difficult. Some believe a Moon mission should have priority and others think a Mars mission shouldn’t wait.

There has been a lot of debate about the relative advantages and disadvantages of the two options. Going back to the Moon is attractive partly because we know that it is possible. We also know that getting to Mars is extremely difficult. Although the Spirit and Opportunity rovers recently landed safely on the surface of Mars, the Beagle 2 lander did not. In fact, a majority of the robotic probes that have been sent to Mars have failed, so there is validity to the idea that we need to build up our expertise with Moon missions before we attempt to send humans to Mars.

On the other hand, the Apollo program was born when President Kennedy said that we should go to the Moon not because it would be easy, but because it would be hard. Today we should not base the vision of our space program on a return to the Moon just because it would be less difficult than launching a successful manned mission to Mars. Instead, we should look at what could be accomplished when we arrive at either location and then make our decision based on which would provide a better return on the investment required to get us there. Considering this, let’s look at a few of the benefits we could hope to get in return for our efforts.

The search for life

Finding life beyond the Earth is one of the main reasons for sending robotic probes and humans into space. From what we currently know about our solar system there are only a few places that might potentially harbor life or contain evidence of past life: Mars is one location along with Europa and Titan, moons of Jupiter and Saturn respectively. Unless there really is a monolith buried there somewhere, the Moon is not one of the locations where we expect to find any direct evidence of life.

Unless there really is a monolith buried there somewhere, the Moon is not one of the locations where we expect to find any direct evidence of life.

The Moon may be an ideal place, though, to look for extraterrestrial intelligence beyond our solar system. Placing a radio telescope on the far side of the moon would shield observations from all of the interfering radio noise coming from Earth. Any plans that don’t involve establishing a base that is devoted, at least in part, to SETI research means that a return to the Moon would not advance our search for life beyond Earth.

A mission to Mars would be a different matter entirely. There have already been hints of possible life including the Mars rock that may contain evidence of microfossils produced by living organisms and also one of the Viking probes’ biological tests that may have returned a positive result. There are also clear signs that frozen water exists at or very near the surface of the planet and there are even geographical features that suggest that liquid water may be present as well.

Stepping stones

A major benefit that is often cited as a reason for returning to the Moon first is that it would serve as an ideal stepping stone for future Mars missions. This is not untrue, but it is a little misleading. Technology and techniques that are developed for a return to the Moon could be reused for a Mars mission (in fact there were preliminary plans to make a trip to Mars using Apollo era equipment) but the Moon would not make a good stopping point for future missions to other places.

To get to the Moon the Apollo missions went straight from Earth to their destination without stopping at a space station along the way. Any mission to Mars would also likely go directly from Earth to Mars without stopping along the way. If for some reason a mission wanted to stop off at the Moon, it would take more energy to get into and then out of the Moon’s gravity well than it would to go directly to Mars. If a literal stepping stone was needed for a Mars mission, the best option would be a space station in low Earth orbit or at one of the Earth-Moon libration points—places that wouldn’t require large amounts of extra energy to reach and depart from.

As for the argument of using a Moon mission to build craft and test procedures for a future Mars mission, this argument can work both ways. The equipment and expertise that would be created by going to Mars first could also be applied to future missions back to the Moon. This stepping stone argument is valid since we will gain valuable knowledge by venturing beyond Earth orbit again, but the argument does not favor one destination over the other.

Living off the land

If we choose to go and do more than just plant “flags and footprints” on the surface of another world, we will want to build bases that will allow for permanent or extended stays at the location. Just like one of the goals of the International Space Station is to establish a continuous human presence in Earth orbit, part of any mission to the Moon or to Mars should be to establish a sustained human presence there.

One of the main difficulties with establishing bases is keeping them supplied with food, water, air, and other necessities. Unlike the space station, which relies on getting all of its supplies from Earth, crews on other planets or moons will be able to take advantage of local resources. For instance, it might be possible to set up a greenhouse at a base that would allow the crew to grow some of its own food. Taking full advantage of what’s available will be crucial because sending a steady amount of supplies to either the Moon or to Mars will quickly become prohibitively expensive.

Just like one of the goals of the International Space Station is to establish a continuous human presence in Earth orbit, part of any mission to the Moon or to Mars should be to establish a sustained human presence there.

What resources are available on the Moon and on Mars that would be available to a local crew? The Moon has no atmosphere, may or may not have water at the poles, and contains rocks that could be broken down to provide oxygen and other resources. Mars has an atmosphere, known water, and local resources that would allow us to produce not just air and water for consumption but fuel for use on the planet and for return missions back home. This is a very simple look at the issue of local resources, but it appears that Mars would offer more to a crew than the Moon would.

Radiation exposure

Another advantage that is often cited as a reason for going back to the Moon first is that a Mars mission would be more hazardous to the crew because of the level of radiation exposure. The crew of a Mars mission would be exposed to more radiation because the overall duration of the mission would be longer than a Moon mission, particularly for the transit phase: up to six months to and from Mars, compared to two or three days to and from the Moon.

Radiation is also a concern for a Moon mission, though, just as it is a concern for crews on the International Space Station. Dealing with this threat is a matter that needs to be addressed for any space mission. Fortunately there are techniques and technologies available that help minimize the amount of radiation exposure. There is also the opportunity to develop advanced ways to further minimize this threat.

A mission to Mars has more to offer. Deciding to go there now rather than later might be the wiser investment in our future.

In transit, the existing supplies carried on board plus the fuel needed for the mission can be kept between the crew and the Sun to act as a shield. A small safe room with extra shielding can also be installed that can be used in the event of a solar flare. It is also possible to consider taking an artificially produced magnetic field with the craft to act as a shield. This technology might also be able to be expanded into a magnetic sail that could be used as propulsion as well as shielding. On the surface, the crew can also be shielded by putting the habitation underground or just by putting sand bags on top of the crew module.

Making the decision

Deciding to return to the Moon first is much more desirable than choosing to keep our space program in Earth orbit indefinitely. Future missions to the Moon would allow us to set up a base, look for water at the poles, set up a radio telescope to search for extraterrestrial intelligence, and learn more about the early history of the Earth and the solar system.

A mission to Mars, though, has more to offer. Getting there safely would certainly be a bigger challenge, but is the extra risk worth the possible reward? Choosing to undertake a mission to Mars would give us many of the same advantages as a Moon mission plus would offer us the additional return of new scientific knowledge of potentially enormous value. Deciding to go there now rather than later might be the wiser investment in our future.