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...
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...
posted by Jon Goff at 11:05 PM
12 Comments:
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
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
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
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
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
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
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
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"
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.
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
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
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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