by Chris Carberry and Rick Zucker
As a new administration prepares to take office, speculation abounds regarding what direction US space policy will take after the transition, as well as who will assume leadership roles at NASA and in other influential positions. Within this context, rumors are swirling regarding whether our nation will turn away from Mars and instead focus exclusively on the Moon.
One of the central arguments being advocated for “major” lunar activities is the unfortunately misguided notion that the construction of fuel depots on the lunar surface is a necessary precursor to eventual human missions to Mars. The reality, however, is that it’s not clear if there are necessary resources on the Moon that can be used for missions to Mars. In other words, it is questionable whether the enormous expenditure of time and resources that would be required to build up the required infrastructure on the Moon to utilize those resources would actually have any clear benefit to human Mars exploration. Thus, that diversion to the Moon would likely delay human missions Mars by decades or even by generations, and could very well delay other valuable lunar activities as well. In contrast, by aiming for Mars, we might very well get the Moon as a side benefit for the same cost.
Even if we assume, for the sake of argument, that such a process is feasible and could move forward, the costs of the experimental phase and then actually building a functioning production facility and operations are unknown. It would be safe to assume, however, that it would not be an inexpensive proposition. There is also the issue of storing hydrogen and oxygen, probably in liquid form; storing such supercool liquids for extended periods is known as a major technical challenge yet to be addressed.Reports from recent NASA missions have indicated that there is probably some quantity of water ice in the lunar polar regions, in craters that are permanently in shadow from the Sun.
Unfortunately, it is unknown how much ice is there, or what form it is in, or how difficult it will be to extract it. Because of the conditions inherent in those particular regions, prospecting there would not be a task that we would assign to astronauts to perform—and robots may have a hard time operating due to the extreme cold and other hazards. We would certainly have to send many robotic explorers, of a technical complexity not yet attained. Significant experimentation would be required with various techniques that would almost certainly take years, and that would just serve to establish whether or not these regions are a realistic option for fuel generation in the first place.
Then, we would need to get this fuel off the lunar surface to make it accessible to Mars-bound (or other) missions, which would require yet another complex architecture on the surface of the Moon. Launching this hypothetical fuel into space from the Moon would be adding yet another gravity well to overcome. In total, this process would certainly be far more complex and expensive than sending humans to Mars using current mission architecture concepts. Indeed, current NASA Mars mission architectures rely to a great extent on solar electric propulsion, which does not use hydrogen or oxygen as a propellant.
It is also difficult to see a business case or a sufficient return on investment for such fuel depots on the Moon in the near term, aside from the issue of going on to Mars. At least in the foreseeable future, any customer of such depots would be limited to government entities, and even that is far from certain. This would essentially be a case of the “cart being put before the horse.” It would be risky in the extreme to spend all this money up front on infrastructure, essentially betting the house, with such a questionable likelihood of an actual payoff. We can see humans on Mars within the next couple of decades, but we won’t if we wait for a scenario to develop that will, even under the best of circumstances, delay sending humans to Mars.
The fact that the near-term value of lunar fuel depots is questionable does not mean that lunar missions in general should not be encouraged. Limited near-term lunar missions, based on international and US exploration objectives, can have value, but should be done with the goal of moving on to Mars on a clear and aggressive schedule. If private/commercial entities and/or other interests want to build a lunar base and fuel depots, then that should happen independently and on self-sufficient terms. That scenario would be a great accomplishment in its own right and would also likely be based on need. It should not, however, attempt to justify itself, and the required massive technology development project that it would entail, in the guise of enabling human Mars missions.