4 ms·

How about we harpoon Mars and pull down one end of a space elevator?

pilom 10y ago
The biggest problem with a space elevator on Mars is that the orbit of one of its moons is closer than the minimum height of a space elevator to be stable. Eventually the elevator cable will get hit.
- dTal 10y ago
  Hang the cable from the moon and let the end trail?
dTal 10y ago
Interesting proposal. You still need a lot of delta vee to get a harpoon+cable from orbit to the surface. You can't just fire it straight down, you have to cancel most of your orbital velocity (which would have to be way out at geostationary). Dunno what the strength requirements of the cable would be either, but I imagine the answer is "not small". Doing the same trick to Earth probably wouldn't be that much harder than Mars. So maybe, once you've solved the hard problems, you wouldn't have to worry so much about mass-to-orbit anyway.
- jcoffland 10y ago
  You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable. Many of the ideas for visiting other planets could and should be tested on earth first. I think we need to get comfortable with visiting the moon and performing large scale industrial projects in space before we have any chance of visiting remote planetary bodies and returning.
  - dTal 10y ago
    >You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable. That's what I said. The trouble is there's no "just" about it. A cable long and strong enough is going to be extremely heavy, never mind the "harpoon". In a traditional "harpoon" the cable is a small fraction of the total mass - you can't really afford that kind of design (shoot heavy thing, drag negligible thing behind) so it's not clear how the orbital dynamics would work. You'd be looking more along the lines of little tug rockets spaced along the length of the cable. >Many of the ideas for visiting other planets could and should be tested on earth first. Quite. This Mars stuff is completely pie in the sky. Let's see a self-sustaining habitat in a desert on Earth, never mind even the moon. As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth.
    - jcoffland 10y ago
      The harpoon could be a big heavy thing. Perhaps we crash an astroid into Mars that is trailing a cable. That doesn't really jive with the planetary protection principals but it might be the kind of thing we need to consider to get the job done. > As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth. True. Although sustainable on Earth usually also means economical. I would like to see a sustained habitat on the moon.

pilom 10y ago

The biggest problem with a space elevator on Mars is that the orbit of one of its moons is closer than the minimum height of a space elevator to be stable. Eventually the elevator cable will get hit.

dTal 10y ago
Hang the cable from the moon and let the end trail?

dTal 10y ago

Interesting proposal. You still need a lot of delta vee to get a harpoon+cable from orbit to the surface. You can't just fire it straight down, you have to cancel most of your orbital velocity (which would have to be way out at geostationary). Dunno what the strength requirements of the cable would be either, but I imagine the answer is "not small". Doing the same trick to Earth probably wouldn't be that much harder than Mars. So maybe, once you've solved the hard problems, you wouldn't have to worry so much about mass-to-orbit anyway.

jcoffland 10y ago
You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable. Many of the ideas for visiting other planets could and should be tested on earth first. I think we need to get comfortable with visiting the moon and performing large scale industrial projects in space before we have any chance of visiting remote planetary bodies and returning.
- dTal 10y ago
  >You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable. That's what I said. The trouble is there's no "just" about it. A cable long and strong enough is going to be extremely heavy, never mind the "harpoon". In a traditional "harpoon" the cable is a small fraction of the total mass - you can't really afford that kind of design (shoot heavy thing, drag negligible thing behind) so it's not clear how the orbital dynamics would work. You'd be looking more along the lines of little tug rockets spaced along the length of the cable. >Many of the ideas for visiting other planets could and should be tested on earth first. Quite. This Mars stuff is completely pie in the sky. Let's see a self-sustaining habitat in a desert on Earth, never mind even the moon. As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth.
  - jcoffland 10y ago
    The harpoon could be a big heavy thing. Perhaps we crash an astroid into Mars that is trailing a cable. That doesn't really jive with the planetary protection principals but it might be the kind of thing we need to consider to get the job done. > As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth. True. Although sustainable on Earth usually also means economical. I would like to see a sustained habitat on the moon.