Another Way to Land on the Moon

New post up at Air & Space in which I describe my idea for a robotic mission to the lunar poles that uses multiple hard landing probes to measure water contents.  Comment on the idea here, if so inclined.

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18 Responses to Another Way to Land on the Moon

  1. This is a good idea, as we do need multiple sample points. Have you considered using penetrators instead, that would put instruments into direct contact with the volatiles and possibly could detect layers in the deposits by using a decelerometer. This might also allow a larger science package as the penetrator might weigh less than the crushable package. The main question is the ability of the payload to withstand the shock of the penetration itself. and whether the higher shock rated instruments would cost a lot more. Cubesats might be able to deploy test decelerators and see if they survive or tests on earth on glaciers might work. An orbit of as low as 5 km might also be possible to reduce the impact velocity. It is not clear how the instruments would measure the water content. Does the site need the impact to disturb the target material before it can be measured?

    • Paul Spudis says:


      Penetrators (arrow-like darts that dig into the surface) have been considered for planetary missions for some time. The problem with their use on the Moon is that they must be 3-axis stabilized to assure proper orientation (the vacuum of the lunar surface precludes aerodynamic orientation). This means more mass, more power, more cost and less probes — the simple design I am proposing allows us to make dozens of them.

      There is no particular advantage to getting below the surface for neutron spectroscopy, which measures the integrated neutron flux from the upper meter or so of the Moon. Flight instruments for hard landings have been tested at a variety of impact speeds; the speeds I propose for this mission are well within survivability bounds.

  2. Thanks for the interesting article Dr. Spudis.

    What sort of timetable do you contemplate for such a mission? How early do you think such a mission could be approved by NASA and Congress and how early could it be launched to the lunar poles?


    • Paul Spudis says:


      Right now, the only NASA program under which this mission would fit is the Discovery line. A new call for Discovery proposals won’t occur for another two years (or possibly longer, if two missions are selected in the current round, as has been hinted at recently). After selection, it would take another 3-4 years to build and fly.

      Of course, if someone decided that we need to build a lunar outpost to harvest water, such a mission could be designed, built and flown within 3 years.

      • Joe says:

        Obviously like the second schedule better, but a couple of questions in the meantime:

        (1) Have you reached the point of scoping the total mass of the vehicle?
        (2) If so, how big would the booster have to be?

        • Paul Spudis says:


          I have not, but it would be reasonably modest, on the order of a 1000 kg class spacecraft (about the size of Lunar Reconnaissance Orbiter). Such a spacecraft easily fits on one of the smaller Atlas vehicles.

  3. hopdavid says:

    2.38 km/s? That’s about lunar escape. From an earth to Luna Hohmann, impact would be 2.53 km/s.

  4. billgamesh says:

    Go big or don’t bother and stay home; a good first SLS mission would be to bomb as many as possible of the biggest possible ice deposits with these things. The NewSpace mob is always wailing and gnashing their teeth that it has no mission; this is the mission they would choke on.

    It is a Moon rocket so send it to the Moon.

    • billgamesh says:

      I would add that once the ice deposits are found and confirmed to be sheets with the necessary volatiles, the first generation of a very long production run of robot landers would be next. These semi-expendable landers could harvest the ice as water and also use the trapped volatiles to manufacture propellant for ascending back into lunar orbit to ferry the water-as-radiation shielding. Each of these robots could possibly last long enough to ferry thousands of tons of water into orbit.

      As I have commented in the past, partially filling spent upper SLS stages in lunar orbit turns them into near-sea-level radiation sanctuaries proof against the worst possible solar events and cosmic radiation. A tether system attached to two such workshops would provide Earth gravity. The hundreds of tons of water in each shield would serve as a medium for a closed loop life support system. These true space stations would allow long duration human habitation Beyond Earth Orbit with no ill effects.

      No radiation exposure, no hypo-gravity debilitation, and by mating the station with a nuclear propulsion system it becomes……a spaceship.

    • I agree. Congress needs to get on with the business of funding the development of a reusable single stage Extraterrestrial Landing Vehicle (ETLV) for the SLS. That shouldn’t cost more than $1 to $1.5 billion a year over the next five to seven years. Plus a single stage vehicle should be a lot faster and cheaper to build than a two staged landing vehicle.

      Such a vehicle could be deployed to EML1 by the SLS. At EML1 the ETLV could transport crews or multiple small mobile vehicles from EML1 to the lunar surface and back on a single fueling of LOX/LH2.

      With the RL-10 engine’s ability to throttle to as low as 8% of maximum thrust, an ETLV could also be used to land humans and mobile robots on the tiny moons of Mars.

      With NASA’s future ADEPT deceleration shield, a lunar ETLV could also be used to land crews or mobile vehicles on Mars and transport astronauts or the mobile vehicles back to low Mars orbit.

      With SLS deployed propellant depots at LEO and EML1, an ETLV could also be used as an orbital transfer vehicle, transporting crews between LEO and EML1 and then on to the lunar surface. So such a vehicle, with propellant depots, could also give Commercial Crew passengers access to the lunar surface. You could even derive the propellant depots from the ETLV vehicle architecture.

      If full funding for an ETLV started in 2017 then Extraterrestrial Landing Vehicles could be transporting humans to the lunar surface well before 2025.


      • billgamesh says:

        Propellant depots are not practical- at any lagrange point, LEO, or wherever. There is no need for them and storing in space and transferring large quantities of cryogenic propellants, especially hydrogen, is a fools game.

        A human-rated reusable lander is an entirely different proposition than a semi-expendable robot lander so we do not really agree Marcel. Any conveyance that is going to descend into and out of the lunar gravity well with humans will be much more difficult to maintain than any type of terrestrial aircraft. Performing maintenance and fueling will require a pressurized underground hangar and unless we find some lava tubes to move into that may take awhile. I consider Mars and LEO to be dead ends.

        The fuel depot miracle has never been anything more than an argument to justify smaller, nearly useless inferior lift hobby rockets and an excuse to cancel any Super Heavy Lift Vehicle. It is a transparent marketing ploy and has never been considered seriously in 40 years of LEO operations. There is a reason for that- it is a hopelessly complicated mess. The only place there will ever be any large fuel farms is under the surface of the Moon.

        The ULA plan to use a piston engine to manage cryogenic boil-off is very clever but it will not solve any of the major technical obstacles concerning propellant depots. It can manage LOX and methane well enough on the way to the Moon and for limited duration missions in lunar orbit but it will not work to re-liquify hydrogen.

        • One of the primary purposes of sending humans back to the Moon is to start utilizing lunar resources in order to live off the land and to export some of those lunar resources (water, oxygen, hydrogen, regolith, and even iron) in order to lower the cost of space travel within cis-lunar space and interplanetary space.

          The ISS already produces oxygen through the electrolysis of water, simply throwing away the hydrogen produced. Propellant depots on the Moon and in orbit will simply liquefy the H2 using cryocooler technology already invented by NASA. Cryocoolers can also eliminate the boil-off of ullage gasses.

          Heavy lift vehicles will enable NASA to deploy water/propellant depots and large reusable LOX/LH2 interplanetary vehicles capable of transporting hundreds of tonnes of cargo and crew to Mars orbit.

          A reusable crew lander that is also capable of being utilized as an– unmanned– transport to deploy multiple small mobile robots, each perhaps weighing 100 kilograms or less, would be quite useful, IMO. Such a vehicle could be used to retrieve as much as a tonne of regolith samples from the lunar poles and other interesting regions on the Moon and return those samples to EML1 for human return to Earth via the Orion or other vehicles capable of traveling between LEO and the Lagrange points.

          Performing maintenance duties on the ISS or, in the future, on the surfaces of the Moon and Mars will be just part of the essential pioneering experience.


          • billgamesh says:

            It is discouraging to argue with another space enthusiast about fantastical technical details- it is counterproductive.

            I completely blame the NewSpace movement for this.

            It is now set in the public awareness that “space must be cheap” and billionaire hobbyists are much smarter than NASA engineers. In reality the basic requirements were all worked out in the 60’s and the laws of physics and materials science have not and are not going to change.

            This “corrupted paradigm” and endless marketing of dollar sign hyperbole has found it’s way into all discussions about space. No one dares to stand up for the idea that some things do cost money and you get what you pay for.

            Sadly, it now causes the majority of people with a fair amount of common sense and some technical knowledge to err on the side of the fairy tale instead of the slide rule.

  5. billgamesh says:

    I would add that I realize Dr. Spudis has proposed refueling vehicles in cislunar space as a necessary operation in some of his material and I do not doubt this, in some form, perhaps transporting tanks and using certain types of propellents. What I doubt is this whole mythology that has arisen that it will be as easy as going to the gas station. A blatant deception NewSpace shills have relied on for years.

  6. Vladislaw says:

    Dr. Spudis, GREAT Idea! As a proof of concept could just one or two probes be launched on any of the new smaller launch vehicles coming online? Like Rocket Labs etc… I believe the google entrant from Israel is going to use one of the smaller rockets to get their entrance hardware to the moon.

    • Paul Spudis says:

      Yes, you could do a smaller pallet of two or three crash landers (or even one) and have it kick off a descending soft lander from an appropriate altitude and velocity. If the instrument successfully deploys and sends data, a dedicated spacecraft for the full-up mission could be flown.

  7. Grand Lunar says:

    Never thought of a landing on the Moon this way. Interesting!

    Also gives insight into the history of the Ranger probes that I wasn’t aware of.

  8. billgamesh says:

    In regards to these “reusable landers” being proposed- having worked on airplanes most of my life it is my considered opinion that such vehicles are nowhere near as “simple” as proponents claim.

    Inserting into orbit, descending, ascending, and departing the Moon was originally accomplished with pressure-fed hypergolic engines. No turbopumps, no regenerative cooling, with only the descent engine on the lander even having a variable thrust mode. The 20,000 pound thrust of the service module (actually twice as powerful as necessary), the 10,000 pound thrust descent engine, and the 3500 pound thrust ascent engine required no ignition systems or cryogenic management and used high pressure helium bottles to pressurize the fuel tanks. Not much could go wrong and these engines were not even test fired before actual use.

    However simple does not mean cheap. The absolute reliability required meant a phenomenal amount of work went into these systems. The ascent engine in particular had no failure mode- no back-up. It had to work. Armstrong actually suggested a manual lever to actuate the ascent engine to get rid of the electrical system. Making these engines “reusable” would have made them more expensive and far more complicated- and increased the possibility of failure. Using cryogenic propellants and regenerative cooling for a longer service life would again make them much more complicated. This kind of craft would require a pressurived and radiation shielded (underground) hangar, mechanics, spare parts, and support equipment to keep flying- there is no way around it.

    The rocket equation is merciless and imposes severe limitations not only on performance but on “reusability.” Future developments in beam propulsion, which would use a monopropellant in a much different fashion than conventional rocket engines, might reduce complexity and increase reliability- but require a Moon base of course.

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