An idea to explore lunar lava tubes

I’ve written before that Designing a practical lunar base is hard.  Having something easy to build while keeping astronauts safe from radiation and micrometeorites is a challenge.  One location for a base that is already safe from micrometeorites – and some radiation – would be in lunar lava tubes.  I was thinking about this one day, and I wondered how could we explore them?  They don’t seem to just open in the side of a cliff allowing us to just walk in.  The only way in seem to be these “skylights” where part of the roof has collapsed.  After some thought, I came up with this four-step plan on exploring a lunar lava tube.

Step 1

This would be a basic, solar powered rover, that would land a kilometer or so from a skylight.  It would then drive to within about twenty meters of the opening.  The last thing we want is to make the skylight bigger, so I want to be as careful as we can around these.  Attached to the rover would be a forty-meter cable with a set of lights and cameras on the end.  This would be fired into the skylight with a compressed gas canister.  The cameras would – hopefully – be able to give a view of the immediate area under the skylight.  There might even be LED “flares” that could be shot out to give a better illumination of the floor.  The main purposes of the mission would be to determine how thick the roof is, how deep it is to the floor, and if the floor is smoothish or just a jumble of rocks.

If the roof seems thick enough, and the cameras aren’t just hitting the wall, the rover could drive forward a meter or so at a time.  By taking more pictures, you could then build up a good 3D map of the area right under the skylight.

Hopefully, from the landing to the mapping could be done in less than two weeks.  That’s because as a solar powered rover, I don’t know if it would survive the lunar night.  I think some solar powered landers and rovers have, but if we don’t have to design for it to survive the night it would be cheaper. 

Step 2

This would use a bigger rover, powered by an RTG.  If the roof was thick enough, and you could pinpoint a landing, you could use just a lander, but a rover would make things easier.  It would again land a kilometer or so away, and drive to within ten or twenty meters of the edge.  It would then unroll a cable designed to reach the bottom of the lava tube, with some meters of slack.  At the end of the cable would be a base station.  This base station would use an airbag system like the Mars Pathfinder.  At the bottom of the skylight, the base station would deflate the airbags and unfold.  The communication and power would go up and down the cable, since you probably wouldn’t be able to communicate with Earth from the bottom.  And like Mars Pathfinder, this base station would have a rover, either wheeled if the bottom is smooth enough, or an insect like one if the floor is just a jumble of rocks.  The rover/walker would go out to explore, but would come back to plug back into the base station to recharge its batteries.  To do this, the base station may need a little robotic arm to reach out and plug the rover in.  

One option for this would be to have the base station with the cable land as a separate mission.  That way you’re not trying to fit it all on a rover that also has to fit on a rocket.  You could land the big RTG rover and have it spend a year or so doing various studies, and then you land the station and have the rover pick it up and take it to the skylight.

Step 3

Human exploration.  The main part of this step is an elevator.  I imagine you’d make some structure that would spread the weight out along the edge of the skylight, because you don’t want to make the skylight bigger.  This structure might even hang over the edge a few meters, depending on the walls and floor.  From the structure you could load astronauts and cargo into the elevator.  Set twenty or so meters back from the edge would be the power system to run the elevator’s winch.  I imagine you’d send two astronauts down while two remained to make sure the winch worked.  In case of an emergency, there would probably be a knotted rope type thing the astronauts could clip onto and climb out with. 

Assuming everything still works with the RTG rover from Step 2, that could be used as a communication system for the astronauts.  Or they could just bring larger, more capable rovers that could recharge off this RTG. 

Step 4

Building a base.  More missions would bring solar panels and battery packs, and maybe a small reactor.  These would be brought near the edge and the power cords lowered down.  The first outpost would be a prefab unit that would be lowered with the elevator and built.  The crew would spend most of their time down in the tube with as much work as possible on the surface down with robots. 

But to really build a colony would require better access to the tube.  This would be done either by finding an appropriate spot to tunnel out to the surface so you could just drive in, or by building a ramp at the skylight.  Both would probably require a lot of time and resources, but one future moon buggy will probably carry more people and cargo than can fit in the elevator.  And any burgeoning lunar base would have several.

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We’re in the beginnings of a new era of lunar exploration.  Will something like this happen?  Only time will tell.