Author Topic: Space Elevator for Mars  (Read 13174 times)

Online sanman

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Space Elevator for Mars
« on: 05/26/2015 11:19 AM »
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-possible

and another from Quora:

http://www.quora.com/Would-it-be-easier-building-a-space-elevator-on-Mars-or-the-Moon


What is the theoretical feasibility?
Where would the key technical challenges be?
« Last Edit: 05/26/2015 12:06 PM by sanman »

Online A_M_Swallow

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Re: Space Elevator for Mars
« Reply #1 on: 05/26/2015 03:38 PM »
A Mars space elevator may be within the physical strength of existing modern materials such as M5 and Zylon. Things like resistance to frequent temperature change, ultra violet light and chemicals in Mars's atmosphere need investigating.

M5 fibre https://en.wikipedia.org/wiki/M5_fiber


Zylon https://en.wikipedia.org/wiki/Zylon


Lunar Space Elevator https://en.wikipedia.org/wiki/Lunar_space_elevator

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.

edit: correct link
« Last Edit: 05/27/2015 03:22 PM by A_M_Swallow »

Offline Dudely

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Re: Space Elevator for Mars
« Reply #2 on: 05/27/2015 12:34 PM »
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 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
« Last Edit: 05/27/2015 01:00 PM by Dudely »

Offline Burninate

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Re: Space Elevator for Mars
« Reply #3 on: 05/27/2015 01:24 PM »
on G-LOC in prone positions, presumably before the development of flight G-suits: "Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.[3]"

The Olympus Mons Mass Driver:  300km length, up to 17G acceleration for 59.4 seconds in an evacuated tube, up to 10.1km/s muzzle velocity at 60pa summit pressure, sufficient to achieve a shortened direct transfer back to Earth, and just about what you need to meet up with an Aldrin cycler.

I'm not aware of a serious investigation into whether space elevators are practical to construct;  You don't just need static strength of the tether and static counterweight balance, they also need to deal with orbital and atmospheric perturbations safely without using propellant, and I'm dubious about whether they could be built in such a way that they'd be stable at every single phase of assembly;  We can't exactly build scaffolding for these things.

But mass drivers?  We build more complicated structures all the time, on safe ground tracks.
« Last Edit: 05/27/2015 01:33 PM by Burninate »

Online A_M_Swallow

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Re: Space Elevator for Mars
« Reply #4 on: 05/27/2015 02:56 PM »
on G-LOC in prone positions, presumably before the development of flight G-suits: "Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.[3]"

The Olympus Mons Mass Driver:  300km length, up to 17G acceleration for 59.4 seconds in an evacuated tube, up to 10.1km/s muzzle velocity at 60pa summit pressure, sufficient to achieve a shortened direct transfer back to Earth, and just about what you need to meet up with an Aldrin cycler.

{snip}

The payload will need a fairing. Mars may have a thin atmosphere but at 10.1km/s there will still be significant heating.

Online A_M_Swallow

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Re: Space Elevator for Mars
« Reply #5 on: 05/27/2015 03:15 PM »
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 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?

{snip}

According to Wikipedia Phobos moves at 2.138 km/s, it orbits at ~6000 km above the surface of Mars and its orbital period is 7 hours 39.2 minutes.
https://en.wikipedia.org/wiki/Phobos_%28moon%29

The closest approximation to docking to the end of the ribbon I can think of is an in-flight refuelling. The docking port may need its own RCS to handle small movements. Large movements - just accept it is a gigantic pendulum and plan for instantaneous launchs.

Offline Dudely

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Re: Space Elevator for Mars
« Reply #6 on: 05/27/2015 04:14 PM »
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 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?

{snip}

According to Wikipedia Phobos moves at 2.138 km/s, it orbits at ~6000 km above the surface of Mars and its orbital period is 7 hours 39.2 minutes.
https://en.wikipedia.org/wiki/Phobos_%28moon%29

The closest approximation to docking to the end of the ribbon I can think of is an in-flight refuelling. The docking port may need its own RCS to handle small movements. Large movements - just accept it is a gigantic pendulum and plan for instantaneous launchs.

An orbital period of 7 hours 39.2 minutes combined with Mar's rotational period of 24 hours 39 minutes means a cord hanging from this down to 100km above the surface would be moving, relative to the rotating surface of Mars, at something just shy of 2,000 km/h, which is about 0.5 km/s. This represents 10% of escape velocity from Mars.

Once you go up the thread to Phobos, you will be roughly 9,500 km above mars and travelling at about 2.0 km/s.


So, using a cord dangling from phobos as a space elevator saves us about 15% of the total energy needed to leave Mars. Meh.

Offline nadreck

Re: Space Elevator for Mars
« Reply #7 on: 05/27/2015 06:09 PM »


So, using a cord dangling from phobos as a space elevator saves us about 15% of the total energy needed to leave Mars. Meh.

But dangle a cord of the other side of Phobos to well past geo synch altitude and you can be dangling off that cord and launch back to Earth or to other system destinations (yes timing is everything, but a surprising number of launch windows would exist)
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Dudely

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Re: Space Elevator for Mars
« Reply #8 on: 05/27/2015 06:55 PM »


So, using a cord dangling from phobos as a space elevator saves us about 15% of the total energy needed to leave Mars. Meh.

But dangle a cord of the other side of Phobos to well past geo synch altitude and you can be dangling off that cord and launch back to Earth or to other system destinations (yes timing is everything, but a surprising number of launch windows would exist)

You'd need a counter-weight on the end of that cord. Since the cable is only going down to Phobos, it will be about 9,000 km shorter, so the counterweight could be much smaller than an elevator that reaches all the way to Mars.

I think at this point it would be easier to just make a "normal" space elevator.


However, you've touched on something cool, and I now think the idea of building a space elevator on Phobos is amazing, for a slightly different reason.

Standing on Mars you can get up to phobos pretty easily, even without a space elevator- you only need about 1.5 km/s. However, launching out of the gravity well of Mars completely takes more than triple the energy. The key to making this work is the fact that Phobos is significantly BELOW geostationary orbit. As I mentioned above having a cord that has a counterweight above geo, but without the mass of cord reaching all the way to the surface, makes the total amount of mass needed to produce sufficient centrifugal force much less. This means the cord can be made of much weaker materials.

The magic here come from the fact that Phobos is essentially acting like a tower that reaches 70% of the way to geo already. Not only that but it's a tower that's made out of a high % of volatiles, including carbon and water. Sound slike a wonderful place to put a manufacturing plant, don't you think? And look at that, it's conveniently located next to a space elevator!

Hmm, space elevators are looking like a much better idea than I thought. . .
« Last Edit: 05/27/2015 06:58 PM by Dudely »

Online KelvinZero

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Re: Space Elevator for Mars
« Reply #9 on: 05/27/2015 11:26 PM »
An orbital period of 7 hours 39.2 minutes combined with Mar's rotational period of 24 hours 39 minutes means a cord hanging from this down to 100km above the surface would be moving, relative to the rotating surface of Mars, at something just shy of 2,000 km/h, which is about 0.5 km/s. This represents 10% of escape velocity from Mars.

Once you go up the thread to Phobos, you will be roughly 9,500 km above mars and travelling at about 2.0 km/s.

So, using a cord dangling from phobos as a space elevator saves us about 15% of the total energy needed to leave Mars. Meh.
That looks very attractive to me. The delta-v from mars to low mars orbit is apparently 4.1km/s. (im not sure if Mar's rotational speed has been considered in that). Due to the exponential relation of propellent to delta-v I think a shuttle that only needs to handle 0.5km/s compared to 4km/s would be a huge difference. That part has to be chemical.

Once you are at phobos you can go with SEP, or just extend the tether up further, or maybe you just wanted to visit phobos for a weekend anyway.

Online Robotbeat

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Re: Space Elevator for Mars
« Reply #10 on: 05/27/2015 11:50 PM »
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 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?

{snip}

According to Wikipedia Phobos moves at 2.138 km/s, it orbits at ~6000 km above the surface of Mars and its orbital period is 7 hours 39.2 minutes.
https://en.wikipedia.org/wiki/Phobos_%28moon%29

The closest approximation to docking to the end of the ribbon I can think of is an in-flight refuelling. The docking port may need its own RCS to handle small movements. Large movements - just accept it is a gigantic pendulum and plan for instantaneous launchs.

An orbital period of 7 hours 39.2 minutes combined with Mar's rotational period of 24 hours 39 minutes means a cord hanging from this down to 100km above the surface would be moving, relative to the rotating surface of Mars, at something just shy of 2,000 km/h, which is about 0.5 km/s. This represents 10% of escape velocity from Mars.

Once you go up the thread to Phobos, you will be roughly 9,500 km above mars and travelling at about 2.0 km/s.


So, using a cord dangling from phobos as a space elevator saves us about 15% of the total energy needed to leave Mars. Meh.
More than just 15%.You can always keep climbing beyond Phobos.
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Offline Burninate

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Re: Space Elevator for Mars
« Reply #11 on: 05/28/2015 06:37 AM »
on G-LOC in prone positions, presumably before the development of flight G-suits: "Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.[3]"

The Olympus Mons Mass Driver:  300km length, up to 17G acceleration for 59.4 seconds in an evacuated tube, up to 10.1km/s muzzle velocity at 60pa summit pressure, sufficient to achieve a shortened direct transfer back to Earth, and just about what you need to meet up with an Aldrin cycler.

{snip}

The payload will need a fairing. Mars may have a thin atmosphere but at 10.1km/s there will still be significant heating.

Sure, but it can be a long tube behind an ablative tip.  If John Hunter can launch from behind 100,000pa with QuickLaunch and his equations suggest 6km/s is workable, then ~4.5km/s (LMO) is certainly workable from behind 50pa, and 10km/s is likely workable.

Offline Dudely

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Re: Space Elevator for Mars
« Reply #12 on: 05/28/2015 12:54 PM »
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 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?

{snip}

According to Wikipedia Phobos moves at 2.138 km/s, it orbits at ~6000 km above the surface of Mars and its orbital period is 7 hours 39.2 minutes.
https://en.wikipedia.org/wiki/Phobos_%28moon%29

The closest approximation to docking to the end of the ribbon I can think of is an in-flight refuelling. The docking port may need its own RCS to handle small movements. Large movements - just accept it is a gigantic pendulum and plan for instantaneous launchs.

An orbital period of 7 hours 39.2 minutes combined with Mar's rotational period of 24 hours 39 minutes means a cord hanging from this down to 100km above the surface would be moving, relative to the rotating surface of Mars, at something just shy of 2,000 km/h, which is about 0.5 km/s. This represents 10% of escape velocity from Mars.

Once you go up the thread to Phobos, you will be roughly 9,500 km above mars and travelling at about 2.0 km/s.


So, using a cord dangling from phobos as a space elevator saves us about 15% of the total energy needed to leave Mars. Meh.
More than just 15%.You can always keep climbing beyond Phobos.

Yeah I realized that eventually. Now that I've actually done the math I think climbing from Phobos to GEO is the most attractive part of it. Combined with the water and carbon on Phobos itself this one structure could allow us access to absolutely massive quantities of dv. We just need a way to mine volatiles on Phobos. The elevator to GEO could be used to deliver the propellent pretty much anywhere in the inner solar system. Such as a depot at Earth-Luna L2. Or simply use it to refuel the craft that went from the surface of Mars up to Phobos, allowing it the dv necessary for travel from martian GEO to LEO. It's practically begging to be done.
« Last Edit: 05/28/2015 12:56 PM by Dudely »

Online A_M_Swallow

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Re: Space Elevator for Mars
« Reply #13 on: 05/28/2015 02:10 PM »
Both Mars and Phobos can be mined permitting big delta-v (and cost) savings against bring propellant from Earth.

The initial counterweight on the Phobos-GEO tether can be the satellite and empty reel used to deploy the tether. More mass can be carried up the tether to the counterweight, permitting an increase in payload.

If the tether goes through a Lagrange point that is a good place to dock to the tether since the mass of the spacecraft is 'carried' by gravity. The tether just has to support the mass of the climber and payload.

Offline Hanelyp

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Re: Space Elevator for Mars
« Reply #14 on: 05/28/2015 06:07 PM »
A ground anchored space elevator on Mars would require moving Phobos, which I recall was brought up in another thread on this site.  But a double space elevator anchored on Phobos combined with single stage to tether is still useful.  That 15% deltaV savings coming up translates to more than that for mass ratio.

An incoming spacecraft docks to "Phobos Far" station at a Lagrange point.  Passengers and cargo travel down a tether to Phobos, take a railroad to the Phobos Low tether, drop to Mars.  Going the other way a single stage spacecraft delivers the pod which catches the Phobos Low tether.  A fair amount of infrastructure to install, but saves a lot of propellant going to and from Mars.

Quick related question, where is Demos relative to the Mars-Phobos outer Lagrange point?  If that's a problem might we still salvage advantage from a similar tether set on Demos?

Offline Dudely

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Re: Space Elevator for Mars
« Reply #15 on: 05/29/2015 12:23 PM »
A ground anchored space elevator on Mars would require moving Phobos, which I recall was brought up in another thread on this site.  But a double space elevator anchored on Phobos combined with single stage to tether is still useful.  That 15% deltaV savings coming up translates to more than that for mass ratio.

An incoming spacecraft docks to "Phobos Far" station at a Lagrange point.  Passengers and cargo travel down a tether to Phobos, take a railroad to the Phobos Low tether, drop to Mars.  Going the other way a single stage spacecraft delivers the pod which catches the Phobos Low tether.  A fair amount of infrastructure to install, but saves a lot of propellant going to and from Mars.

Quick related question, where is Demos relative to the Mars-Phobos outer Lagrange point?  If that's a problem might we still salvage advantage from a similar tether set on Demos?

Deimos is about 25% farther away from the martian surface than geostationary orbit. I would think this precludes it from being of any use, at least tether-wise.
« Last Edit: 05/29/2015 12:23 PM by Dudely »

Online A_M_Swallow

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Re: Space Elevator for Mars
« Reply #16 on: 05/29/2015 10:02 PM »
{snip}But a double space elevator anchored on Phobos combined with single stage to tether is still useful.  That 15% deltaV savings coming up translates to more than that for mass ratio.

An incoming spacecraft docks to "Phobos Far" station at a Lagrange point.  Passengers and cargo travel down a tether to Phobos, take a railroad to the Phobos Low tether, drop to Mars.  Going the other way a single stage spacecraft delivers the pod which catches the Phobos Low tether.  A fair amount of infrastructure to install, but saves a lot of propellant going to and from Mars.
{snip}

The pod probably needs a common connector it can use to connect to the Mars transfer vehicle, the elevator climbers, railroad truck and lander. May be even the rover used to transport it on Mars.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #17 on: 05/30/2015 04:26 PM »
A ground anchored space elevator on Mars would require moving Phobos, which I recall was brought up in another thread on this site.  But a double space elevator anchored on Phobos combined with single stage to tether is still useful.  That 15% deltaV savings coming up translates to more than that for mass ratio.

An incoming spacecraft docks to "Phobos Far" station at a Lagrange point.  Passengers and cargo travel down a tether to Phobos, take a railroad to the Phobos Low tether, drop to Mars.  Going the other way a single stage spacecraft delivers the pod which catches the Phobos Low tether.  A fair amount of infrastructure to install, but saves a lot of propellant going to and from Mars.

Quick related question, where is Demos relative to the Mars-Phobos outer Lagrange point?  If that's a problem might we still salvage advantage from a similar tether set on Demos?

Mars Phobos L1 and L2 are only about 4 kilometers from Phobos' surface.

Here's a pic of a Phobos tether:



Pic is from my blog post Beanstalks, elevators and Clarke Towers

Release points for achieving Mars escape, Trans Earth Insertion and Trans Ceres Insertion are all well below Deimos' orbit.

The tether foot is traveling about .6 km/s with regard to Mars surface.
« Last Edit: 05/30/2015 04:30 PM by Hop_David »

Offline Paul451

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Re: Space Elevator for Mars
« Reply #18 on: 05/30/2015 06:03 PM »
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.
« Last Edit: 05/30/2015 06:14 PM by Paul451 »

Offline Paul451

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Re: Space Elevator for Mars
« Reply #19 on: 05/30/2015 06:39 PM »
But dangle a cord of the other side of Phobos
You'd need a counter-weight on the end of that cord.

No. You only use a counter-weight to shorten the length of tether needed beyond the balance point (beyond GEO/L1/etc). The L1/L2 points for Phobos are less than 4km from its surface, whereas the tether lengths being talked about are thousands of km long. So there will be vastly more tether mass beyond the L1/L2 point than is required to keep the tether taut; no additional counter-mass is required.

How would you dock with the end of the ribbon and keep it stable if it cannot be anchored to the ground?
The closest approximation to docking to the end of the ribbon I can think of is an in-flight refuelling.

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.

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