The Endless Moon vs. Mars debate

After reading an apparently endless number of “Mars is the next step” op-eds in two weeks, I had to vent.  New post at Air & Space is up on why the Moon should be the next destination for the American civil space program.  Comment here, if so inclined.

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19 Responses to The Endless Moon vs. Mars debate

  1. A permanent human return to the surface of the Moon won’t happen in the near future, IMO, unless NASA is finally allowed to commit some significant funds ($1 to $2 billion annually) towards the development of a single staged crewed lunar lander.

    Single staged reusable (at least 10 times) Lunar landing vehicles that take full advantage of the large diameter of the SLS cargo fairing would be my preference. Xeus type vehicles developed by private commercial entities could also be a possibility. But with spacecraft development times usually taking between 6 to 10 years, NASA needs to get going on this. Such spacecraft, also, have to be designed to be able to eventually take advantage of lunar oxygen and hydrogen resources.


    • Paul Spudis says:

      I think that ULA’s Xeus lander will be flight-ready much sooner than a resurrected Altair might be.

      • DougSpace says:

        Agreed. Masten told me that it would take between 1.5 and 2 years to modify one of the Centaur stages that ULS has on loan to him to be able to be a “Terrestrial Demonstrator” able to conduct the entire DV for the terminal landing sequence. Given that such a lander would be single stage, comparatively low max-Q, and the stage and RL-10 engines are well experienced, then I would tend to believe that it should cost less to develop than what it cost NASA to have SpaveX develop the F9 in a fixed-price contract. That was $390 M total which was about 1/8thr cost had it been developed using a cost-plus approach. Much less than the Altair or an SLS-derived lsmder.

      • Joe says:

        If I might a few points:

        (1) There are more similarities between the Altair and Xeus vehicles than there might seem. Both (for instance) rely on variants of the RL-10 engines.

        (2) The problem with the Altair was its constantly changing top level design requirements, because of warring objectives for the Constellation Lunar Mission (as has been well documented by Dr. Spudis on this website).
        – One faction wanted a lunar base for which the Altair would be a crew transport only (with its first stage adaptable to support a one way cargo lander). That version could have been a smaller/simpler and thus cheaper lander.
        – Another faction wanted a series of sortie missions to various Lunar sites to be selected (fought over) at a later date. After those missions were completed Lunar activities would have again been abandoned in favor of “pushing on” to Mars. The scenario required a larger/more complex and thus more expensive lander that (among other things) had an ascent stage that could serve not only as a transport but a base for weeks at a time in addition to carrying new rovers to each sortie site. Because those discrepancies were never resolved, the Altair ended up with requirements to serve both missions.

        (3) Because of the situation described in (2) the first objective of any successful lander program must be to establish a set of very narrowly defined and stable top level requirements (e.g. what do you want the lander to do).

        (4) With due respect to Masten, it would a mistake to closely conflate his assertions with ULA’s proposals. Never the less with the right requirements a lander capable of supporting the initial phases of Lunar Base development should be possible faster and cheaper than the Altair model would indicate.

        • Paul Spudis says:


          All correct, to the best of my knowledge. Moreover, the last design iteration of the Altair was to be powered by LOX-methane instead of LOX-LH, so as to better fit the requirements of the “Mars Forward” idea.

          I was referring to the XEUS concept described in ULA’s Cislunar 1000 concept.

          • Joe says:


            Thanks. I worked on Constellation Systems in Requirements/Verification Requirements for the EVA System from February 2007 to November 2010 and had the chance to observe (but not directly participate in) the whole debate over the Altair’s capabilities in the Constellation Systems Architecture Requirements Document (CARD).

            You are, of course, correct about introduction of methane into Altair’s propellant system.

            The whole thing was driving the engineers working on the Altair “up a wall”.

            Understood on the Cislunar 1000 XEUS concept. While I think design changes would occur as development proceeded, I agree it is a good starting point for developing a practical/affordable Lunar Lander.

            Thanks for the link to the pitch. Did not have it before, but it is now part of my library.

  2. Vladislaw says:

    Although I have advocated for neither Mars or Luna but have instead argued for commercial fuel depots and NASA focus on space based reusable “gas n’ go” vehicles and just do road trips until we have fuel handing in a hard vacuum and zero G nailed down. I am pleased to say I have moved into your court Dr. Spudis. It appears a decision is coming on down on one or the other regardless so I am chosing Luna.

    Here is my reasoning. I believe once we commit to landing it will bog the Nation down to one place like the ISS in LEO. So which location will be easier and cheaper to support. That falls to Luna.

    Regardless of what and where the private sector wants to take us (Blue Origin, ULA SpaceX) It call only be tested in Cis Lunar space. So if Congress is going to fund a landing I hope they start with the Luna.

    • John E Bowen says:

      Hey Vladislaw,

      About: “commercial fuel depots and NASA focus on space based reusable “gas n’ go” vehicles” I agree. Getting depots to work well and on a routine basis is the key for cislunar operations and beyond. Therefore, depots, including the fuel handling you mentioned and the vehicles designed to be easily refueled and reused, are together more important than any one single “exploration” mission.

      So, putting on my magic hat, if I were on some selection/approval committee, and heard objections like “I can’t do refueling, it’s too hard. Just give me my giant rocket” I would pass over that mission in favor of one that embraced the benefits of a real infrastructure. Yes, some of the steps are hard, but they are exactly what we need to be doing.

  3. I think you’re probably right!

    But I think if Boeing Aerospace could commit to an Altair-like– single stage– landing vehicle that could accommodate a crew module or cargo, using its already developed and tested ultralight weight 2.4 meter in diameter hydrogen tanks, they might be able to develop and deploy the LOX and LH2 vehicle relatively quickly.

    As a cargo vehicle, such a 7.2 meter in diameter lunar lander might be able to deploy habitat modules with diameters exceeding 8.4 meters. That would allow the deployment of relatively cheap habitat modules derived from repurposed EUS hydrogen tanks, giving astronauts spacious multilevel habitats with the room of a small home.

    If NASA wants to develop multiple crewed landing vehicles using a Commercial Crew-like method, they still better get started soon because Boeing/ULA and Space X seem to be taking forever to get their Commercial Crew vehicles deployed and operational for LEO:-)


  4. John E Bowen says:

    Nice article. First, I like the split approach of a short note and a link to your article in Air Space Mag with wide circulation, plus the community comments here; keep it up.

    Next, you’re right, it does seem a veritable storm of Mars First, Mars Only! articles. Some are well thought out, but many are superficial pieces run as “filler” material on news sites that appear, to me at least, to be technical in nature but only superficially interested in the space industry.

    OK, so be it. It’s an ongoing battle, updating, refining and restating ideas hoping to reach a few. What’s the saying, support for space activities is a mile wide – and an inch deep. The up side is that a few who really care could make a difference.

    I have actually seen a fair bit of activity in the area of return to the Moon, for cislunar development and the gateway so much more. Coming from many sources, the mechanism and timing of how we do this is obviously all over the map.

    Regarding: “choices were made in the technical approach that favored the big, the massive, and the disposable.”

    I’d favor a COTS-like approach. Announce the plan, invite private partners. Pay fixed price for pre-agreed milestones. Give a lot of weight to real world milestones such as successful docking with depot, successful landing and deployment of rovers, other equipment. Encourage competition further in that the solutions, the intellectual property, remains with the companies. Reserve the right to drop one of the competitors and replace it with another, as happened during COTS.

    The result is not one but two or more solutions, lander vehicles, for less cost and less time than if done the old way. This could be done as one program, or a cargo lander first, followed by a very similar program for a personnel lander. Again, this is roughly the same as commercial cargo followed by commercial crew to the ISS.

    I fully agree that success in this, getting two or more landers for redundant capability, is not accomplished by simply shouting “COTS!” However, I still contend it is the right approach for landers. For launchers, any combination of smaller competitive vehicles vs. the big, the massive, the disposable, Ares V, excuse me, SLS.

    The depots could also be private. I’d also support a human tended station, a “gateway,” in L1 or medium lunar orbit. NASA would be a good choice to design and contract the building of this, with close oversight since they’d be so heavily invested in it once humans are aboard. Also, it’s going to need shielding, quite a bit of it, so perhaps government can lead the way. Later, shielding can be transported from the lunar surface, at lower cost, so hopefully we’ll have a nice ecosystem of public and private stations and habitats.

    To recap, I also think “the Moon should be the next destination for the American civil space program.” And although it may seem messy, that space program will benefit greatly by shopping competitively among companies in the American space industry.

  5. Great Article! Your re-iteration of the critical importance of a cis-lunar space transport and logistics system to support lunar and other initiatives is commendable. Your use of the terms “Apollo mode” and “lunar template” have essentially the same meaning as my term “Apollo Mission Model”, which apply to “flags and footprints” type missions anywhere. We are getting more and more agreement, even from Apollo astronauts, that these methods are no longer appropriate or practical.

    We are now at a point where I hope we have heard the last of the impractical “Mars Hype” from the previous administration, and can move forward with action that will put us first into cis-lunar space, next on the Lunar surface, and then on Mars. Unfortunately, we still lack the detailed information about the lunar polar deposits to see if they are indeed mineable for water and other resources. This means that crucial decisions on exploration architectures will have to wait until that information finally comes in, a few years from now. Detailed plans exist for sending rovers to explore those deposits and now await implementation.

    The question that seems to be immediately on the table for NASA is that of the cis-lunar and lunar spacecraft design. Will they be modified, or clean slate designs? Good designs and concepts exist for both approaches. Will they be reusable so the whole space program can become sustainable, and able to support more than one exploration program at once. With the impending advent of very large, reusable boosters after 2020, we will have more freedom to design larger and wider vehicles and infrastructure modules. This will allow us to move into an era of high mass space operations, more suited to commercial ventures. I hope that NASA keeps the private companies in the forefront of vehicle design, development, construction and operation.

    John Strickland

    • Vladislaw says:

      John wrote: “The question that seems to be immediately on the table for NASA is that of the cis-lunar and lunar spacecraft design. Will they be modified, or clean slate designs? ”

      Did you ever see if the GATE I & II proposals by Bigelow Aerospace were ever made public? He had a couple tug designs that looked promising.

  6. Part of the design logic that should go into this is the operating costs. Is a clean slate vehicle cheaper to operate over a decade or more than a “jury-rigged” system (although this term may be an unfair label). Only professional engineers and businessmen working as a team can really answer such questions. Any reusable lander should be able to carry crew, or propellant or cargo either way (up or down), based on what is on top of it (crew cabin, tank, or empty flat bed).

    Some of the existing designs, such as the Masten-ULA Xeus lander concept, based on an RL-10 engine and Centaur stage, would be fine for cargo and propellant but harder to use in a safe manner for crews. The crew cabin would need to leave the lander partly horizontally during an abort, which is much harder to handle during an emergency situation. Building a new, purpose-designed lunar lander might take longer and cost more, but such a lander might be safer for crew members and cheaper to operate, since the crew cabin would leave the lander vertically with a single plane of separation. Safety issues like this become much more important when there are routine (frequent) flight operations underway. Parachutes do NOT work in space.


  7. Vladislaw says:

    Dr. Spudis, You once talked about landing sensors on Luna for ice/water confirmation I believe it was and recently looked at lander. I do not recall what you said the payload package would weigh but I believe it was pretty small. I was curious, using there calculator, How much would it cost to drop one of those on the surface? To me looked like it would not be that expensive.

  8. Grand Lunar says:

    Loved the article.

    I believe a factor in the debate is the lack of information on why we should go back to the Moon and the reason behind it.

    The mass media simply doesn’t report it, so the public is left with a false impression.

    And unfortunately, blogs and articles by popular scientists continue to regurgitate the very things you mention in your article.

    We need an aggressive tactic to get the word out that we have a better choice.

    • Paul Spudis says:

      It’s not just the mass media — NASA and its many supporters often invoke the trite and meaningless “been there, done that” in regard to lunar return. They are incapable of imagining going to the Moon to do anything other than collect rocks and plant the flag because that is what they intend to do on Mars.

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