Lunar tethers actually look like they will be feasible sooner than Earth tethers! The lack of atmosphere, micrometeorites, and lower gravity (g) makes them scale better.
Whether tethers are useful on the moon depends on the mission you want to do. Like you point out, low delta-V missions probably don’t need a tether when rockets work just fine. But if you want to take lunar material to low earth orbit or send it to Mars, a lunar tether is a great option.
The near-term application I’m most excited about is liquid oxygen. Getting oxygen from the moon to LEO requires less delta V than going from the Earth to LEO! Regolith is ~45% oxygen by mass and a fully-fueled Starship is 80% LOX by mass. So refueling ships in LEO with lunar O2 could be viable.
Even better, the falling lunar oxygen can spin up a tether in LEO which can use that momentum to boost a Starship to other parts of the solar system.
Very interesting. Love the idea of torturing mathematicians by making them calculate these crazy-precise orbits, but I guess machines can do most of that(a shame).
How often could a tether actually be used for resource launches though? Assuming only one tether is in operation, would its orbital cycles be quick enough to transport materials consistently for a large lunar mining operation?
Also, I’m not super informed on lunar space debris, but I imagine that would pile up quickly as lunar space operations began. I think most debris here on Earth would be outside the domain of tethers, but I can’t find many numbers on the hypothetical orbits of lunar debris. I assume, though, that it would be very different due to the lack of atmosphere to burn up debris and the differing gravity. I figure you could make a tether capable of withstanding this, but how would orbits be calculated and rockets properly tethered with interference? Assuming that this is an actual problem.
Bit of a tangent, but I think space debris is one of my favorite hypothetical future problems, because it has a very similar and equally interesting set of fields which it intertwines with as climate change, while also not being a real problem I have to worry about killing me(like climate change)
The launch cadence is an interesting topic that I haven’t had a chance to tackle. The rotational frequency limits how often you can boost stuff.
Since time is money you would want a shorter and faster tether, but a shorter time of rotation means that your time window to dock with the tether is smaller, so there’s an optimization problem there as well.
It’s a little easier when you’ve got catapults on the moon’s surface. You can have two running side by side and transfer energy between them electrically. So load up catapult #1, spin it up, launch the payload, and then transfer the remaining energy to catapult #2. You can get much higher launch cadence that way.
Oops yes, that should read “Getting oxygen from the moon to LEO requires less delta V than going from the Earth to LEO!”. I edited the original comment.
Lunar tethers actually look like they will be feasible sooner than Earth tethers! The lack of atmosphere, micrometeorites, and lower gravity (g) makes them scale better.
In fact, you can even put a small tether system on the lunar surface to catapult payloads to orbit: https://splittinginfinity.substack.com/p/should-we-get-material-from-the-moon
Whether tethers are useful on the moon depends on the mission you want to do. Like you point out, low delta-V missions probably don’t need a tether when rockets work just fine. But if you want to take lunar material to low earth orbit or send it to Mars, a lunar tether is a great option.
The near-term application I’m most excited about is liquid oxygen. Getting oxygen from the moon to LEO requires less delta V than going from the Earth to LEO! Regolith is ~45% oxygen by mass and a fully-fueled Starship is 80% LOX by mass. So refueling ships in LEO with lunar O2 could be viable.
Even better, the falling lunar oxygen can spin up a tether in LEO which can use that momentum to boost a Starship to other parts of the solar system.
Very interesting. Love the idea of torturing mathematicians by making them calculate these crazy-precise orbits, but I guess machines can do most of that(a shame). How often could a tether actually be used for resource launches though? Assuming only one tether is in operation, would its orbital cycles be quick enough to transport materials consistently for a large lunar mining operation? Also, I’m not super informed on lunar space debris, but I imagine that would pile up quickly as lunar space operations began. I think most debris here on Earth would be outside the domain of tethers, but I can’t find many numbers on the hypothetical orbits of lunar debris. I assume, though, that it would be very different due to the lack of atmosphere to burn up debris and the differing gravity. I figure you could make a tether capable of withstanding this, but how would orbits be calculated and rockets properly tethered with interference? Assuming that this is an actual problem.
Bit of a tangent, but I think space debris is one of my favorite hypothetical future problems, because it has a very similar and equally interesting set of fields which it intertwines with as climate change, while also not being a real problem I have to worry about killing me(like climate change)
The launch cadence is an interesting topic that I haven’t had a chance to tackle. The rotational frequency limits how often you can boost stuff.
Since time is money you would want a shorter and faster tether, but a shorter time of rotation means that your time window to dock with the tether is smaller, so there’s an optimization problem there as well.
It’s a little easier when you’ve got catapults on the moon’s surface. You can have two running side by side and transfer energy between them electrically. So load up catapult #1, spin it up, launch the payload, and then transfer the remaining energy to catapult #2. You can get much higher launch cadence that way.
I think there might be a typo?
Oops yes, that should read “Getting oxygen from the moon to LEO requires less delta V than going from the Earth to LEO!”. I edited the original comment.