Not only are the lengths of Phobos/Deimos tethers less in total than an equivalent Mars-surface elevator, the strength requirements are a fraction as much. That means the taper (and thus mass) of any given tether-material is vastly less -- less than 1 percent for the full 9000km Phobos tether. Which means you can build a whole Phobos/Deimos tether network for a fraction of the mass, energy and effort as a Mars-surface elevator.Better still, you can build out incrementally. Since Phobos L1/L2 is less than 4km, the minimum self-supporting tether from Phobos's surface is going to be dozen km or so. (As well as reducing the initial tether mass by several more orders of magnitude.) That's pretty close to tethers we've already deployed in experiments. In other words, the technology is already available, we just need to refine the design to make it safer and more reliable.Once you have that anchor to Phobos, you no longer need a lander to move resources from Phobos into Mars orbit. You can slowly increase the length and usefulness of the Phobos tethers as your experience with the technology grows. Whereas a Mars-surface elevator requires the whole thing to be built before it's useful, so you have to already know how to build, maintain and control an ~40,000km tether before you can even start.40,000km vs 12km. Hell of a learning curve difference.
The end of any tether has partial gravity (that is, after all, how tethers work.) So you can hang a simple platform and land income craft on that. You'll need to watch out for the cables/frame holding the platform, but the approach will still be much easier than any conventional docking.To return to Mars, you just roll off the edge of the platform and fall.
Better still, you can build out incrementally.
{snip}Trip from Deimos tether to Phobos tether (or vice versa) takes about 8 hours so this transfer vehicle could be tiny.{snip}
What if a carbonaceous asteroid (or comet? or kuiper object? saturn ring bits?) could be found and orbited around Mars, and a tether then gradually constructed from this body, and then slowly dangled down until it reached the surface?Where would the key technical challenges be?
Quote from: Hop_David on 05/30/2015 09:27 pm{snip}Trip from Deimos tether to Phobos tether (or vice versa) takes about 8 hours so this transfer vehicle could be tiny.{snip}If the vehicle is tiny it can be the same machine as the tether climber.
Why not put a tether between Phobos and Deimos ...
Why not put a tether between Phobos and Deimos
Why not put a tether between Phobos and Deimos and use it to decrease the second's orbit toward geostationary and at the same increasing that of the first one?Then you can think about a tether, anchored or not, between Phobos and Mars.Sorry for my English but I'm Italian, thanks
Could it one day be possible/practical to build a space elevator for Mars? What if a carbonaceous asteroid (or comet? or kuiper object? saturn ring bits?) could be found and orbited around Mars, and a tether then gradually constructed from this body, and then slowly dangled down until it reached the surface?here's a small thread from StackExchange:http://physics.stackexchange.com/questions/33547/space-elevator-on-mars-with-todays-technology-possibleand another from Quora:http://www.quora.com/Would-it-be-easier-building-a-space-elevator-on-Mars-or-the-MoonWhat is the theoretical feasibility?Where would the key technical challenges be?
Quote from: A_M_Swallow on 05/26/2015 03:38 pmRather than putting the elevator on Mars it may be better to attach it to the moon Phobos. Aim the ribbon at Mars and use a rocket powered aircraft for the last 100km.Phobos is tidally locked, so at least you don't have to worry about your ribbon facing Mars. But it presents other problems. Phobos is actually LOWER than geostationary orbit, so the ribbon would move around as phobos moves around in orbit. Might not be a problem going down, it's actually even better- just wait until you're at the spot you want at- but if you wanted to get up to it you'd need a launcher that can get you up to speed relative to Mar's rotation. What would that be, a few hundred km/h? How would you dock with the end of the ribbon and keep it stable if it cannot be anchored to the ground? It moves around the planet with Phobos, and you need to reach it with a craft that's also moving very quickly; does this make a dangling ribbon too difficult?*slightly off topic*I've always been partial to orbital rings. Think about it- you could keep a ring of material in orbit if you made it magnetic and put it inside a tube. Then just have maglev engines all over it to accelerate the magnetic particles at a tangent to the surface. Their force against the outside of the ring would keep it in orbit. You could also precess the ring to reach other locations on the surface. The ring would only need to be a few hundred km up. You could easily have multiple rings at different orbital planes and withdraw the rope when they need to pass over one another. Much simpler and more economic than a single very very long elevator. The rope for a orbital ring would not need to be any stronger than kevlar. I think we should seriously consider this on Mars, as there is an easy source of material in the form of Phobos. We would use the carbon and silicon to produce the tube structure, the volatiles to get the energy to move the required 25 million tonnes of this material into lower orbit around Mars, and any metals we find as the magnetic material inside the tube. The only real issues are a) building a massive mining, manufacturing, and transportation operation 75 million miles away, and b) inventing and building huge maglev engines that can operate in space with extreme reliability.Credit for this idea goes to Paul Birch. Though he assumed it would be built around Earth.http://www.orionsarm.com/fm_store/OrbitalRings-III.pdf
Rather than putting the elevator on Mars it may be better to attach it to the moon Phobos. Aim the ribbon at Mars and use a rocket powered aircraft for the last 100km.
Phobos' orbit is the problem here. See my post above about easier mass to obtain for the counterweight.
Quote from: sghill on 06/30/2017 11:14 pmPhobos' orbit is the problem here. See my post above about easier mass to obtain for the counterweight.Low excentricity, low inclination, yet a bit high up. Maybe it would be better to just take the material from phobos and bring it down to a 200km orbit and construct the ring over there. That would also mean, that Phobos doesn't need to be consumed in total.think about the initial ring as a wire rope, just like the ones used in modern elevators, cranes, ski-lifts etc, and then when the initial one is done, go for a few more, up to the thickness of for example the rope used in the golden gate bridge.And then, set up non-orbiting platforms on that ring which levitate magnetically on that ring (at some point, get the plattforms all the way around). With that done, you then can extend kevlar-ropes down to the surface, leading to an orbital ring that is suspended to the surface of Mars. Climb up and down those ropes to transport goods from and to the martian surface.It will be tedious to set up such a structure, but it is easier to do that than to do an elevator with phobos crossing the elevator track.
Solid rings are not stable. [...] There would be a constant expense to keep the ring from crashing into Mars.
Quote from: Hop_David on 07/01/2017 02:50 pmSolid rings are not stable. [...] There would be a constant expense to keep the ring from crashing into Mars.As noted in Isaac Arthur's video, the advantage of orbital rings is that the ring's shell is stationary WRT to the surface, but vastly lower than geostationary (or areostationary) orbit (in theory even inside the atmosphere). That drastically lowers the strength requirements of the ground cables. And since you can use the ring for fast point-to-point ground transport, you end up with a lot of ground cables, stabilising the ring.
My question on the Orbital Ring is, what about the gyroscopic torque?You've got an inner ring spinning at greater than orbital velocity. great, it's holding up a geostationary ring tethered to the ground.Except the geosynchronus ring is rotating once per day, and unless it's precisely equatorial, that's going to cause some pretty severe torque on the ring as you basically force a constant inclination change on the inner ring through the geostationary one.
Quote from: Hotblack Desiato on 07/01/2017 07:12 amQuote from: sghill on 06/30/2017 11:14 pmPhobos' orbit is the problem here. See my post above about easier mass to obtain for the counterweight.like the ones used in modern elevators, cranes, ski-lifts etc, and then when the initial one is done, go for a few more, up to the thickness of for example the rope used in the golden gate bridge....In any case, I don't think the folks suggesting some of these scenarios grasp what 1.1 e16 kilograms is. A civilization capable of moving this mass around is in the distant future.
Quote from: sghill on 06/30/2017 11:14 pmPhobos' orbit is the problem here. See my post above about easier mass to obtain for the counterweight.like the ones used in modern elevators, cranes, ski-lifts etc, and then when the initial one is done, go for a few more, up to the thickness of for example the rope used in the golden gate bridge....