I upvoted this post, but I do have a few comments.
For what it’s worth, I like glass fibers. They’re pretty easy to make, the material can be be sourced in space, they can handle large temperature ranges, and they’re resistant to atomic oxygen environments and UV
The matrix holding the fibers together is generally going to be more prone to degradation. Glass fibers have good compressive strength, but carbon fiber would be better here.
Maintaining orbit is one of the key issues. You probably need ion thusters and solar panels. I don’t think electrodynamic tethers actually work, because of friction vs conductivity.
At these scales and speeds, you can’t just think of “solid things” as being rigid. Speed of sound in solid materials becomes a major issue. When something attaches to the tether, there’s a wave of increased tension and stretching that propagates through the tether and sets up a vibration. This is a fatal problem for some tether variants.
The projectile needs to reliably connect to the tether. Docking in space is usually slow and doesn’t involve large forces, and it’s still not easy, but here it needs to be done quickly and establish a strong connection. Here, you could just have a hook grab a perpendicular rope, but if you don’t have any contingency plans, well, “dock or die” isn’t very appealing. Especially if it happens multiple times.
Yes, micrometeoroids are an issue. Even if there aren’t many, the tether might need to be robust to small impacts. A low orbit reduces that risk (but doesn’t eliminate it) but a tether would also have relatively high drag; the surface area per mass is higher than eg the ISS.
The main thing people want to do with rockets has been put satellites in orbit. I don’t see a reason to expect that to change anytime soon.
People have thought of all this decades ago. Maybe check out “LEOBiblio” or something.
Here, you could just have a hook grab a perpendicular rope, but if you don’t have any contingency plans, well, “dock or die” isn’t very appealing. Especially if it happens multiple times.
If the thing you want to accelerate with the tether is cheap but heavy to LEO (e.g. “big dumb tank of fuel”), it might be a reasonable risk to take. Then missions which have more valuable payload like humans can take the safer approach of strapping them to a somewhat larger pile of explosions, and things which need a lot of delta V can get up to LEO with very little fuel left, dock with one of the big dumb tanks of fuel, and then refuel at that point.
Source: I have played a bunch of Kerbal Space Program, and if it works in KSP it will definitely work in real life with no complications.
I think both fiberglass and carbon fiber use organic epoxy that’s prone to UV (and atomic oxygen) degradation? One solution is to avoid epoxy entirely using parallel strands or something like a Hoytether. The other option is to remove old epoxy and reapply over time, if its economical vs just letting the tether degrade.
I worry that low-thrust options like ion engines and sails could be too expensive vs catching falling mass, but I could be convinced either way!
Yeah, some form of vibration damping will be important, I glossed over this. Bending modes are particularly a problem for glass. Though I would guess that vibrations wouldn’t make the force along the tether any higher?
Catching the projectile is a key engineering challenge here! One that I probably can’t solve from my armchair. As for missing the catch, I guess I don’t see this as a huge issue? If the rocket can re-land, missing the catch means that the only loss is fuel. Though colliding with the tether would be a big problem.
Yeah I think low orbits are too challenging for tethers, so they’re definitely going to be at risk of micrometeorite impacts. I see this as a key role of the “safety factor”. Tether should be robust to ~10-50% of fibers being damaged, and there should be a way to replace/repair them as well.
Right, though tethers can’t help satellites get to LEO, they can help them get to higher orbits which seems useful. But the real value-add comes when you want to get to the Moon and beyond.
Good to know! I would love to see more experiments on glass fibers pulled in space, small-scale catches, and data on what kinds of defects form on these materials in orbit.
I upvoted this post, but I do have a few comments.
The matrix holding the fibers together is generally going to be more prone to degradation. Glass fibers have good compressive strength, but carbon fiber would be better here.
Maintaining orbit is one of the key issues. You probably need ion thusters and solar panels. I don’t think electrodynamic tethers actually work, because of friction vs conductivity.
At these scales and speeds, you can’t just think of “solid things” as being rigid. Speed of sound in solid materials becomes a major issue. When something attaches to the tether, there’s a wave of increased tension and stretching that propagates through the tether and sets up a vibration. This is a fatal problem for some tether variants.
The projectile needs to reliably connect to the tether. Docking in space is usually slow and doesn’t involve large forces, and it’s still not easy, but here it needs to be done quickly and establish a strong connection. Here, you could just have a hook grab a perpendicular rope, but if you don’t have any contingency plans, well, “dock or die” isn’t very appealing. Especially if it happens multiple times.
Yes, micrometeoroids are an issue. Even if there aren’t many, the tether might need to be robust to small impacts. A low orbit reduces that risk (but doesn’t eliminate it) but a tether would also have relatively high drag; the surface area per mass is higher than eg the ISS.
The main thing people want to do with rockets has been put satellites in orbit. I don’t see a reason to expect that to change anytime soon.
People have thought of all this decades ago. Maybe check out “LEOBiblio” or something.
If the thing you want to accelerate with the tether is cheap but heavy to LEO (e.g. “big dumb tank of fuel”), it might be a reasonable risk to take. Then missions which have more valuable payload like humans can take the safer approach of strapping them to a somewhat larger pile of explosions, and things which need a lot of delta V can get up to LEO with very little fuel left, dock with one of the big dumb tanks of fuel, and then refuel at that point.
Source: I have played a bunch of Kerbal Space Program, and if it works in KSP it will definitely work in real life with no complications.
Thanks for the comments! Going point-by-point:
I think both fiberglass and carbon fiber use organic epoxy that’s prone to UV (and atomic oxygen) degradation? One solution is to avoid epoxy entirely using parallel strands or something like a Hoytether. The other option is to remove old epoxy and reapply over time, if its economical vs just letting the tether degrade.
I worry that low-thrust options like ion engines and sails could be too expensive vs catching falling mass, but I could be convinced either way!
Yeah, some form of vibration damping will be important, I glossed over this. Bending modes are particularly a problem for glass. Though I would guess that vibrations wouldn’t make the force along the tether any higher?
Catching the projectile is a key engineering challenge here! One that I probably can’t solve from my armchair. As for missing the catch, I guess I don’t see this as a huge issue? If the rocket can re-land, missing the catch means that the only loss is fuel. Though colliding with the tether would be a big problem.
Yeah I think low orbits are too challenging for tethers, so they’re definitely going to be at risk of micrometeorite impacts. I see this as a key role of the “safety factor”. Tether should be robust to ~10-50% of fibers being damaged, and there should be a way to replace/repair them as well.
Right, though tethers can’t help satellites get to LEO, they can help them get to higher orbits which seems useful. But the real value-add comes when you want to get to the Moon and beyond.
Good to know! I would love to see more experiments on glass fibers pulled in space, small-scale catches, and data on what kinds of defects form on these materials in orbit.