Maintenance of Lunar RLVs

Just wanted to post a few random, half-baked thoughts before I forget them about lunar RLVs. Back in the day, I had this thought-excercise going called the Prometheus Downport Project, which I recently dug up via the Wayback Machine on archive.org. The stuff is hopelessly obsolete by this point, but interesting nonetheless. Anyhow, back in 2003, in some of my copious free-time then, I got into some email conversations with a few friends about this, including Randall Clague (of XCOR fame). Randall got me thinking in some new directions (he was the one who mentioned the importance of the buddy system for lunar landings for instance), and raised some interesting questions. When I started gravitating toward the idea of a reusable lunar lander (one that goes from L1/LUNO to the surface and then back to L1/LUNO), Randall asked me how I intended on doing maintenance and repairs on the system. You could tell who had been working for a company that was actually flying rocket vehicles at that point.

Anyhow I was thinking about it again on the way home from work today. One thing that I have become a huge fan of for VTVL vehicles of any sort is the idea of system-level propulsion redundancy, with engine modules that are modular, and easily removeable (ie they are “Line Replaceable Units”), so that you can repair them offline. If one of them breaks down on the Moon, the repair method would be to swap out the damaged module and repair it somewhere out of the vacuum. If you’re not in a place where you can easily do that (ie if you’re at a remote exploration site, or on a first landing), you have enough extra engine capacity to make it “back to civilization” where you can swap out the engine for a spare while it’s being replaced.

Which leads me to my one of my thoughts for maintenance/repairs of lunar RLVs. I have another one I will writeup at some point in the future, but here’s one for now:

Sundancer On the Moon
Something like Bigelow’s proposed “Sundancer” module would be the perfect starting place for any lunar outpost or spaceport. Back when I took a tour of Bigelow Aerospace during the Return to the Moon conference in 2005, I asked one of the engineers there if Bigelow intended to offer any smaller commercial modules than Nautilus, and mentioned that a smaller, lighter version of Nautilus might be useful. I doubt my suggest is why they did Sundancer, the idea makes too much sense for them to have not come up with it themselves, but I’m glad they did. 20klb is just about light enough that you could reasonably land such a beast on the moon. The 40-50klb Nautilus station would’ve been a little too heavy to land easily. As it is though, Sundancer is a wonderful size–170 m^3. Compared to the size of the proposed CEV and LSAM put together, the Sundancer module would be tons more roomy. There’d be enough room in a single such module for small sleeping quarters for 4-6, a bathroom, life support equipment, a kitchen/galley, a small lab, and most importantly a roomy workshop. If the airlock is big enough (or if the equipment is collapsible enough like the original moon buggies), you could bring a whole rover inside for repair and maintenance in a shirtsleeve environment. Bringing engines in and working on them indoors would be possible too. At that point you don’t need exotic tools or anything–it’s no more difficult than maintaining or repairing an engine on earth.

Your source of spare engines and parts might very well be the lander that brings the Sundancer module down. Early on you’re not going to have a lot of spare propellants on the moon, and most propellants for a reusable lunar lander will be transferred from incoming tankers on orbit, so you might not be able to immediately reuse “one-way” cargo landers that are used to land extra-heavy cargoes like Sundancer modules. Even if you only cannabalize that first cargo lander, you’ll have enough spare parts to keep a small fleet of 2-3 reusable landers maintained and in working order for quite some time.

One other related thought. When I was talking to the Bigelow engineer about how they intend on orbiting Nautilus (since it was spec’d out at 40-60klb fully loaded in LEO), he mentioned that if push came to shove, it could be shipped up “empty” and fitted out in orbit on subsequent flights. While I’m not sure exactly what that would mean in our situation, it might well make it so you could land a Sundancer module empty (on a smaller cargo lander), and land the rest of the stuff to fit out the Sundancer on a second shipment. That would probably drop the mass of the module to a low enough number that you could land it using two flights of the same lander design as would be used for a 2-person landing mission.

Oh, and in a low-G field (as opposed to microgravity), the life support equipment for the Nautilus can be made much more robust and reliable (and inexpensive too). No need to deal with phase separators, no issues with lack of natural convection causing concentrations of moisture or CO2, no need for a fancy zero-G toilet…

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and the founder and CEO of Altius Space Machines, a space robotics startup that he sold to Voyager Space in 2019. Jonathan is currently the Product Strategy Lead for the space station startup Gravitics. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
Jonathan Goff

About Jonathan Goff

Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and the founder and CEO of Altius Space Machines, a space robotics startup that he sold to Voyager Space in 2019. Jonathan is currently the Product Strategy Lead for the space station startup Gravitics. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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18 Responses to Maintenance of Lunar RLVs

  1. Anonymous says:

    Jon

    As one of the people working with NASA on lunar surface architecture, this is already being considered. The approach that we are taking is to shift as soon as possible over to as much ISRU hardware as possible. This includes habitation and other lunar surface facilities.

    As far as repair is concerned our baseline architecture level requirement is to dictate that the systems be modular, and more than just modular, have common systems that can easily be taken from one vehicle and used on another type of vehicle.

    Dennis Wingo

  2. Bill White says:

    Lunar RLVs are the only route for making routine lunar access affordable. If littering the Atlantic with expendable hardware is dumb, littering the lunar surface with expendable hardware is double dumb.

    That said, without lunar LOX production, lunar RLVs probably are not really feasible.

  3. Anonymous says:

    Bill

    With Lunar LOX and H2 (hopefully from the ice) there is nothing keeping the LSAM from being reusable. It would be easy to remove the ascent stage propulsion system and fuel and use the LSAM in round trip mode. We have already done some work on this.

    Dennis

  4. Pete says:

    Although I have not been otherwise busy the last few months, I wrote some thoughts on this a while back – how and why to do hangers, wherever, for such maintenance work:

    http://kiteflyingengineer.blogspot.com/2006/09/hanger-workshops-in-leo.html

    There is also some other related stuff there. Anyways, the next step beyond Sundancer is perhaps to start tweaking the design to make it more suitable to such tasks, a bigger air lock comes to mind. The very abrasive lunar dust still poses a serious problem to air lock design and use.

  5. Pete says:

    Whoops, delete the “not”.

  6. tankmodeler says:

    Lunar Dust

    Yeah, I’ve been kinda wondering about this over the last little while. All of the Apollo moonwalkers talk about how nasty that stuff is and they were only exposed for 3 days, max. Froma simple mechanical engineer’s standpoint, how are we going to keep the dust problem at bay?

    There are a number of decontamination procedures used here on earth for nasty chemicals or particles, but they all require volumes of material to wash/blow/wipe away the contaminant. How will we clean a rover or spacesuits when the requirements is for 60-100 egresses per 6 month tour and with facilities that should last more than one tour?

    Can static electricity do the job? Recycled fluids? A nice no-touch rover wash down the street?

    Interesting problem that is given little discussion in the general press/blogosphere.

    Paul

  7. Jon Goff says:

    Dennis,
    What exactly do you mean by:
    The approach that we are taking is to shift as soon as possible over to as much ISRU hardware as possible. This includes habitation and other lunar surface facilities.

    Are you talking about ISRU propellant stuff, or actually trying to construct the lunar habitats and such from local materials?

    Both are good and useful, but will probably take lots of experimentation with boots on the ground. The sooner we can make that the reality, the better.

    As for using a modular architecture, that is definitely the way too go. It does drive up the mass a little bit, but it makes maintenance and operations easier.

    ~Jon

  8. Jon Goff says:

    Bill,
    Lunar RLVs are feasible even before LOX is available, they are just not as big of a performance win. You won’t get quite as much payload down to the surface per given sized lander (since it’s a single-stage instead of two stages), but on the other hand, you don’t have to ship the lander along each time, so it might be close to a wash mass-wise.

    Costwise, reusing the lander is a huge win. Depending on the design details, it might even be possible to test the lander out (partially fueled and without any cargo) on the earth’s surface. Having the peace of mind of knowing that your hardware has worked before is a lot nicer than crossing your fingers and hoping the QA guys know what they’re doing.

    ~Jon

  9. Jon Goff says:

    Dennis,
    The idea of using the LSAM descent stage as a reusable LSAM (once you have lunar LOX and LH2) is an interesting idea. It isn’t the height of perfection, but I have to admit the idea has some merit.

    ~Jon

  10. Jon Goff says:

    Paul,
    The dust issue is both huge, while also probably solveable. The old Apollo suits were almost worn out to the point of failure after only three EVAs. There have been lots of ideas discussed over the years on how to improve on that, but by far the best way to test them out will be with boots on the ground.

    Solving the problem for airlocks and pressurized modules while still and issue worries me less than solving it for spacesuits. But the reality is that unless a huge leap is made in spacesuit reliability, even a full ESAS spec LSAM crew is likely only going to be able to get 3-5 sorties done before they start running into issues, instead of the 7 or so sorties as advertised.

    ~Jon

  11. murphydyne says:

    I’m kind of with Paul in wondering about de-dusting issues. I’ve been thinking along the lines of electrostatic or electromagnetic solutions. At least the guy that microwaved his Lunar soil sample provided us with a few clues in that regard.

    I’ve also been wondering about how the Lunakhods functioned during their sojourns on the Moon. Would it be as easy as designing a lid to flip over the telescopes at Lunar dawn and crepuscule?

    Or could we just generate a weak electromagnetic field around the instruments to deflect charged particles?

    I’ve also wondered about electromagnetic ceramic bearings. Could the micro-g wizards come up with a ceramic piece that can generate a toroidal field through the center of which passes the shaft of the axle? The axle might be milled in such a way that dust accumulation on the shaft is directed outward. By avoiding actual contact between the axle and its bearing some of the dust issues might be strongly mitigated.

    Or perhaps design the bearings to be magnetic and put a coil around it such that the action of the bearings’ movement creates a field which repels the dust.

    And while it may be from science fiction, I do like Homer Hickam’s use of overalls with old tire treads sewn into the booties for his heroes to use on the Moon (over their spacesuits) in “Back to the Moon”

  12. Bill White says:

    Take a look at this link & nasaspaceflight has a story on this as well:

    http://www.juneaucounty.com/economic.asp

    Milk tanks for rocket fuel:

    >> Formed 10 years ago by former aerospace industry engineers, KT aims to tap private commercial manufacturers such as Walker to help it build the rocket at a much lower cost than the traditional aerospace industry.

    >> Typically, the aerospace industry has high fixed costs that come with building factories and hiring employees ‘whose sole purpose is to build a few rockets per year,’ Sisk said. ‘We eliminate all that portion of the business. Essentially, we’re enabling quality vendors’ to handle all the manufacturing.

    >> Walker was selected after KT’s studies found that the best material for its fuel tanks, which will be filled with liquid methane and liquid oxygen, is stainless steel.

    Jon, I know you advocate cryogenic fuel transfer. Yet suppose this Wisconsin dairy tank maker can fabricate inexpensive and durable stainless steel tanks that can be used for LOX and cyro methane.

    When the lunar RLV lands at the Moonbase, swap out the empty tanks and swap in full ones. After the RLV leaves, inspect refurbish and re-fill those tanks for future use.

    If a tank goes bad, use it for scrap. If a tank is integral to the lunar RLV, tank testing and repair would be a big pain in the neck.

    = = =

    A quick and dirty RLV:

    (1) Bigelow module
    (2) RL-10s modified for methane
    (3) Wisconsin milk tanks

    (2) & (3) are fully modular and swappable at the Moonbase — how much does a dry RL-10 weigh, anyway? Keep plenty of spares.

    XCOR, Armadillo and of course Masten can leave the RL-10 in the dust, right? That just makes it easier.

  13. Anonymous says:

    For maintenance of craft in microgravity, one idea I had was to build a sort of ‘garage tent’. Just a big sheet of tough fabric, sprung into a tube with some battens. Attach it on one side to a module that has windows, so that people inside the module can look out into the ‘garage’ and watch work being done there.

    Cap the ends with some battened discs, much like the circular sprung solar screens that you put in your car’s windshield to keep the heat out. They don’t have to be really secure, let alone airtight. The purpose of this enclosed space is:

    – keep items (and people) from floating away if they are ‘dropped’.

    – provide a sunshield and some degree of micrometeoroid protection.

    – provide a place to attach lights and other tools for working on spacecraft.

    it doesn’t have to be expensive; in fact a cheap one could probably be built for figures measured in thousands of dollars. It may very well make the whole job of servicing spacecraft much safer and easier tho. (no more need to be tied down in two places at all times when on EVA).

    –Carl.

  14. Bill White says:

    Jon –

    If you have not read this thread, you should (IMHO):

    http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=1337&start=1

    It covers EML-1 & EML-2 and low luanr orbit. One assertion is that a lack of lunar gravity maps currently renders it impossible to precisely calculate low lunar orbits with any degree of confidence.

    Long term, using both L points for rendevouz and using lunar fuel seems to be the critical step in routine affordable access to the lunar surface.

  15. Pete says:

    One possible solution to the lunar dust problem is to use walking rovers with very long legs. This keeps sensitive equipment above the lunar dust and does little to kick it up in the first place. This still enables general “earth” moving equipment.

    Air locks might also be vertical so that dust naturally falls out of the air lock and the seals can be covered and protected from any falling dust. Vibration might further act to prevent such dust settling on the down facing seal surfaces. Beyond this redundant seals that can be easily cleaned and replaced seem sensible.

  16. jv says:

    There could be another problem with lunar dust to handle – dust ‘storms’ which occur every lunar morning – http://science.nasa.gov/headlines/y2005/07dec_moonstorms.htm

  17. Anonymous says:

    Jon

    On ISRU I mean to go to metals production as soon as possible after oxygen or in parallel with oxygen. Ed McCullough from Boeing has some very interesting, though fairly complex chemical methods to get metals from the regolith. Vapor phase pyrolosys will work as well.

    We get metals, we make plates and beams. With plates and beams you get lebensraum on the Moon. That is, living space, places to live, work, grow food, play.

    Just add nitrogen

  18. Jon Goff says:

    Dennis,
    I agree that being able to produce some materials in-situ as soon as possible is important. I wonder how well you could separate out pure Ni-Fe using magnetic benefaction combined with something like a chain-mill (repeating the steps multiple times)…

    ~Jon

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