Author Topic: Space Elevator for Mars  (Read 13201 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 »

Offline 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 »

Offline 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.

Offline 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 »

Offline 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 »

Offline 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 »

Offline 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.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #20 on: 05/30/2015 06:52 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.

Quite so.

The Phobos tether portrayed above has a taper ratio of about 8 if using Kevlar with 3,600 mega pascal tensile strength and 1.44 g/cm^3 density.

Using the same material, an elevator to Mars synchronous orbit and with a balancing length above synchronous would have a taper ratio of 45.

A payload at the foot of a Phobos tether would feel a gravity only slightly less than a foot at Mars surface. But that would be mitigated by centrifugal force. It'd feel a weight of about 3 newtons per kilogram.

A payload at the foot of an elevator to synchronous would feel a weight of about 3.7 newtons per kilogram.

An elevator's volume would be average cross section area times elevator length. I will take the elevator's average cross section area as (cross section at foot + cross section at max stress)/2. This is over estimating some but I believe it is in the right ball park.

A tether's mass is density times volume.

For a full blown Mars elevator using Kevlar I get a tether mass to payload mass ratio of about 2200. For the Phobos tether I portrayed above, tether to payload mass ratio is about 90.

Offline A_M_Swallow

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Re: Space Elevator for Mars
« Reply #21 on: 05/30/2015 08:30 PM »

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.

Landing on that platform will probably be like landing on an aircraft carrier. A very tiny one because the platform mass comes off the tether's payload on a 1kg for 1kg basis.

Phobos has an elliptical orbit so the height above Mars can increase by about 200km.

There may be scope for a fun simulation here - landing on the Photos tether platform.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #22 on: 05/30/2015 09:27 PM »
Better still, you can build out incrementally.

Yes, the tether doesn't have to extend all the way to mars upper atmosphere to be useful.

One thing about tethers in the region of L1 or L2: An ion driven MTV could dock with it.

An ion driven MTV docking with Deimos is saved much of the spiral down Mars gravity well.

The Phobos and Deimos elevators share an ellipse. Going from/to Deimos tether to/from Phobos tether can take nearly zero delta V.

Dropping from a short distance beneath Phobos gives an atmosphere grazing ellipse with a periapsis speed of 3.8 km/s. Aerobraking can take this down to circular orbit moving 3.4 km/s. If Phobos is a source of propellent, much of that 3.4 could be removed. Mars EDL becomes much simpler.

Tether mass to payload ratios for attached diagram:
Deimos to Deimos drop off: 1/25
Phobos catch to Phobos: 1/18
Phobos to drop off for atmosphere grazing ellipse: 1/4

MTV could remain docked at Deimos.

Trip from Deimos tether to Phobos tether (or vice versa) takes about 8 hours so this transfer vehicle could be tiny.

The vehicle doing rendezvous/drop off with the Phobos tether foot would be a Mars ascent/descent vehicle.
« Last Edit: 05/30/2015 09:41 PM by Hop_David »

Offline A_M_Swallow

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Re: Space Elevator for Mars
« Reply #23 on: 05/31/2015 02:45 AM »
{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.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #24 on: 06/17/2015 05:56 PM »
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?

Importing an anchor mass/momentum bank for a tether to Mars orbit is an interesting idea. As mentioned in this thread, Deimos and Phobos are two existing masses already in Mars orbit.

A comet falling from the Kuiper Belt would have 10 km/s Vinf wrt to Mars. An ice ball falling from Saturn would have a nearly 8 km/s Vinf. It would take a great deal of energy and reaction mass to park these in Mars orbit.

But it may be possible to capture an asteroid to mars orbit. Similar to the Asteroid Redirect Mission but for Mars. But in Mars case you don't have a large moon that can shed up to 1 km/s Vinf. But there may be a good number of asteroids in nearly Mars like orbits.

Parking an anchor mass in a circular orbit deep in Mars gravity well would take a great deal of energy and reaction mass. Least challenging is to park it in an orbit as high as possible without the sun's influence destabilizing the rock.

If we set the orbital radius at half Hill Sphere radius, around 500,000 km, orbital period would be 125 days and speed would be about .3 km/s wrt to Mars. Synodic period wrt to Deimos would be about a day. So each day a payload could be dropped from the captured asteroid anchored tether to be caught by a Deimos tether. The drop from captured asteroid to Deimos would take nearly 50 days.

If the asteroid anchored tether were parked in a 100,000 km circular orbit, the drop to a Deimos tether would take about a week. Orbital velocity would be about .65 km/s and period would be about 12 days.

A tether relay (As I've already described between Deimos and Phobos) wouldn't require huge amounts of tether mass.

A full blown Mars elevator would need to have a tether mass 1000's of times greater than the payloads it moves (if we're using existing materials such as Kevlar).

 




Offline Hop_David

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Re: Space Elevator for Mars
« Reply #25 on: 06/17/2015 06:14 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.

I think so, yes.

Since Deimos and Phobos aren't exactly co-planar we would need some reaction mass for the rendezvous leading to a catch.

Half of the trip would be downhill (that is, in the same direction as dominant acceleration). For example the trip from Mars-Deimos L1 to Phobos drop would be downhill. If going the other direction, the trip from Mars-Phobos L2 to Deimos throw would be downhill.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #26 on: 06/19/2015 07:28 PM »
I've taken a closer look at the notion of a Phobos tether:

Phobos-Panama Canal of the Inner Solar System

Offline ilic78

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Re: Space Elevator for Mars
« Reply #27 on: 11/27/2016 02:25 PM »
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

Offline Hanelyp

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Re: Space Elevator for Mars
« Reply #28 on: 11/27/2016 11:07 PM »
Why not put a tether between Phobos and Deimos ...
I haven't run the numbers, but my gut says the forces on such a tether between those rocks would be immense.  If those moons are rubble piles with minimal self gravity they might not even hold together against such a tether.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #29 on: 11/28/2016 11:29 AM »
Why not put a tether between Phobos and Deimos

How would you capture them?

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #30 on: 12/16/2016 03:24 AM »
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

They are both very massive bodies whose speeds differ by .8 km/s. Not doable to tie them to together.

However a vertical tether could be placed at Mars synchronous orbit. There could be Zero Relative Velocity Transfer Orbit (ZRVTO) between the synchronous tether and a Deimos tether. Deimos material could be sent to the synchronous tether using very little reaction mass.

But catching material from Deimos would raise the orbit of the synchronous tether.

LIkewise there could also be ZRVTOs between the synchronous tether and a Phobos tether. But catching material from Phobos would lower the synchronous tether's orbit.

However if the synchronous receives material from Phobos and Deimos in the correct proportions, it can build up a respectable momentum bank while remaining at synchronous orbit altitude. There could be several such tethers. Mars synchronous tethers might be nice intermediate steps between a Deimos and a Phobos tether. There are obvious communication uses for infrastructure in Mars synchronous orbits.They might also be good spots from which to operate tele-robots on Mars surface.

I don't think a synchronous tether extending all the way to Mars' surface is practical. For a number of reasons. I hope to write an article on a full fledged Mars beanstalk soon.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #31 on: 06/15/2017 06:01 PM »
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?

I took a look at a Zylon Mars elevator using Wolfe's spreadsheet.

For examining scenarios I had been using a safety factor of one. This is pushing Zylon to the limits of its tensile strength. The slightest nick or scrape along an elevators length would cause it to break. I don't think a sensible player would risk valuable payloads on such an elevator. Much less risk human lives.

I've been trying to go back and redo the scenarios where I include the more sensible safety factor of three as well as a safety factor of one.

Given a safety factor of one and having the Mars elevator counterweight just below Deimos, it'd take about 200 tonnes of Zylon to lift a tonne from Mars surface. This tonne would include the elevator car, the elevator's power source and engine. So the mass of the actual cargo would be much less.

The sub Deimos counterweight would need to be 1200 times the mass lifted from Mars surface.

In my opinion, a Zylon Mars elevator wouldn't be worthwhile even given the very risky safety factor of one.

Given a sensible safety factor of three, tether to payload mass ratio would be around 53,000. The counterweight would need to be 180,000 times as massive as the mass lifted from Mars surface.

The Phobos anchored elevator is still my chief interest. An upper Phobos elevator capable of flinging payloads to the Main Belt and earth wouldn't have prohibitive tether to payload mass ratio. Even with a safety factor of three. However I no longer regard as plausible a Zylon Phobos tether descending to Mars upper atmosphere. See:
Phobos upper tether
Phobos lower tether
Deimos tether

I also look at some of the different scenarios in my Physics Stack Exchange answer.

Offline Hotblack Desiato

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Re: Space Elevator for Mars
« Reply #32 on: 06/30/2017 11:01 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

How about turning the "lemon" phobos into lemonade?

Use phobos as the initial source for an orbital ring on the orbit of phobos (Birch Ring), then extend down and generate a second ring at ~100km height, which can be used to theter down to the surface.

It is challenging, and it would be actually a good idea to completely consume phobos in that process.

This way, the stationary Mars-orbit is in reach, and you can even throw things onto an escape trajectory.

Isaac Arthur did a piece on the topic orbital rings, although I'd call his ideas (interplanetary orbital rings, etc) as very advanced, even for this section of the board (yet no out of reach technologies required, no anti gravity, no warp drives, not even room temperature superconductors).


Offline Hotblack Desiato

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Re: Space Elevator for Mars
« Reply #33 on: 07/01/2017 07:12 AM »
Phobos' 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.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #34 on: 07/01/2017 02:50 PM »
Phobos' 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. That's what led Niven to write sequels to his Ringworld story. He didn't want an obviously flawed sci fi device so he added stories where the ring used stationkeeping rocket engines. And so it would be with a solid ring about a planet. There would be a constant expense to keep the ring from crashing into Mars.

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.

Your notion of using Phobos material to make a lower orbit station has merit though.

I recently revised my Phobos tether posts using a more sensible safety factor. Early versions using a safety factor of 1, I had concluded that a Phobos tether extending to Mars' upper atmosphere could be made with Zylon. But a Zylon tether that long is impractical when using a safety factor of three. See Lower Phobos Tether.

While a 5800 kilometer lower Phobos tether (Phobos to Mars upper Mars atmosphere) would take an impractical amount of Zylon, A 1,400 km tether has a nice .33 tether to payload mass ratio. This means a ten tonne Zylon tether can drop thirty tonne payloads to a periapsis just above Mars surface.

A less than 1,400 km Phobos tether could toss a payload to a tether in low Mars orbit. Given two coplanar orbital tethers there exists a ZRVTO between the two tethers. ZRVTO is short for Zero Relative Velocity Transfer Orbit.

I am thinking of examining a scenario where a low Mars orbit tether tosses stuff up to a Phobos tether as well as dropping payloads into suborbital paths to Mars surface.
« Last Edit: 07/01/2017 02:55 PM by Hop_David »

Offline Paul451

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Re: Space Elevator for Mars
« Reply #35 on: 07/02/2017 10:06 AM »
Solid 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.

Online rakaydos

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Re: Space Elevator for Mars
« Reply #36 on: 07/11/2017 01:00 AM »
Solid 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.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #37 on: 07/11/2017 09:46 AM »
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.

AIUI, for anything except the simplest structure (by necessity an equatorial ring), you need counter-rotating rings to cancel out the torque.


Offline stefan r

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Re: Space Elevator for Mars
« Reply #38 on: 07/17/2017 01:24 PM »
Phobos' 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.


Wikipedia says the Port of New Orleans handles 62 million short tons of cargo plus a million passengers. Ignoring passengers and barges they handle 5.6 x e10 kg.  Gravity on phobos is 5.81 e-4 earth.  So the lift capacity of similar cranes would be around 9.6 e14.  So just under 12 years.  Was that a complement to New Orleans workers or a claim that New Orleans is uncivilized?

Setting up the equivalent to the Port of New Orleans near mars is not a trivial project.  But if we were motivated then the whole Phobos destruction project could be done within today's children's life expectancy.   

Phobos would lose mass as you move pieces off.  So it could be done several years sooner [no need for that].  You could consume the mass from the center out.  Build most of the ring.  Then move fairly large pieces along the ring and store in bags at the equivalent to Lagrange 4/5 points. 

One of the hardest obstacles is preventing a swarm of debris.  You would need to build containers out of Phobos material or sinter dust/sand/cobbles into stackable blocks. 

Offline spacenut

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Re: Space Elevator for Mars
« Reply #39 on: 07/17/2017 01:40 PM »
Why not just build a giant space station for transfer of goods and people to Mars and then to the surface.   Large in space tugs or spacecraft wouldn't have to land, just transfer by docking with the station.  The station could be placed in GSO of Mars or at a L station.  That way it would stay put with thrusters and cargo and people could be sent directly to a fixed point on the Martian surface. 

I don't know how large this station should be, but a gateway station could be built at L2 lunar.  Then smaller rockets would ferry goods and people to and from earth to L2, then a deep space transfer ship could go between this station and the one at Mars where the space elevator may work.  An earth space elevator would, at this time, would not be practical due to distance and heavy atmosphere.  One at Mars may work. 

By the way what is the distance from the surface of Mars to GSO at Mars?

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #40 on: 07/17/2017 03:06 PM »
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.

Wikipedia says the Port of New Orleans handles 62 million short tons of cargo plus a million passengers. Ignoring passengers and barges they handle 5.6 x e10 kg.  Gravity on phobos is 5.81 e-4 earth.

You're wanting to move Phobos? It is Mars' gravity you want to look at, not Phobos gravity.

So the lift capacity of similar cranes would be around 9.6 e14.

And what distance do the cranes move the cargo? I would suppose From the deck of a ship to a dock. Not the same as moving Phobos thousands of kilometers. 

At any rate, the cranes of New Orleans are quite massive infrastructure. Even if your model was sound, your scenario isn't plausible.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #41 on: 07/17/2017 03:42 PM »
Solid 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.

I admire Isaac Arthur. But I am skeptical that the rings he describes would be stable. Even with an interior counter rotating ring, both parts feel the same GM/r^2. If Mars center coincides with rings' center of rotation, a decrease in r also means a decrease in ω^2 r, regardless if the inner ring is retrograde. So dipping closer to Mars means stronger gravity and weaker centrifugal force. The instability remains.

The inner and outer component of a low Mars elevator would be moving at greater than orbital speed with regard to one another. That would be more than 3.4 km/s. How far apart are the inner and outer rings? Should they come in contact with one another, the failure mode would be spectacular.

And we're talking very massive infrastructure. A low Mars orbital ring would be 23,000 kilometers in circumference. What is the mass of this ring? Isaac Arthur has been talking about megastructures that might come to pass in the distant future.

My focus has been elevator to payload mass ratios. The less ambitious Deimos  and Phobos elevator scenarios described would take tonnes to tens of tonnes infrastructure. They could happen in the 21st century.


Offline Paul451

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Re: Space Elevator for Mars
« Reply #42 on: 07/18/2017 12:12 AM »
and store in bags at the equivalent to Lagrange 4/5 points.

There's no [useful] equivalent around Mars, assuming you mean a Mars-moon Lagrange. Phobos and Deimos are too small.

(edit: pedantry)



The station could be placed in GSO of Mars or at a L station.  [...] and cargo and people could be sent directly to a fixed point on the Martian surface.

It sounds like you think that descending from GSO station to the point on the Martian surface directly under the GSO station's location is easier than descending to another point on the surface. It's not. The easiest spot would be approximately 180° away, but anywhere else along the orbital plane is pretty much the same. You do a small burn to lower your orbit a bit, drift around your orbit until you are roughly 180° from your landing site, and then do you re-orbit burn.

[It's not quite 180°, you'll hit the atmosphere first. But from GSO, with a minimum de-orbit burn, it's close enough.]
« Last Edit: 07/18/2017 12:12 AM by Paul451 »

Offline Paul451

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Re: Space Elevator for Mars
« Reply #43 on: 07/18/2017 02:29 AM »
Solid 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.
I am skeptical that the rings he describes would be stable.

Read my comment again. I wasn't arguing that they would be stable, I'm saying that they can be low enough to reach the Earth with many short cables, and those cables provide stability.

However, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.

And we're talking very massive infrastructure. A low Mars orbital ring would be 23,000 kilometers in circumference.

Much less than the length of a Mars space elevator. Or an Earth or lunar space elevator. And with much lower material requirements. (Which is what it is being compared to.)

What is the mass of this ring?

It would be interesting to know the minimum mass possible. Assuming a continuous inner-ring, so it needs to be supported by ground-cables to Earth (because of instability), the ground-cables hang from the magnetic stations, and the cables must be large enough to pull against any instability. The mag-stations need to be powerful enough to suspend themselves and the mass of the ground-cables from the inner-ring. The inner-ring needs to have enough momentum in order to hold up the mass of the magnetic-stations and the ground-cables. Knowing the mass of the ring and the rate of ring-drift gives you the force of the potential instability that the ground cables need to be able to withstand, giving you the mass of the ground-cables...

It should be possible to work out the interconnected mass dependencies and then scale down until you reach the minimum possible sized component. But I don't know how to work out the size of the ring-instability, so I don't even know where to start.

The less ambitious Deimos  and Phobos elevator scenarios described would take tonnes to tens of tonnes infrastructure. They could happen in the 21st century.

I'm a fan of the Phobos elevator. And the Phobos/Deimos transit system. Obviously an orbital ring isn't going to compete against that.

But orbital rings are intended to be a better planetary space elevator. It allows direct connection to the ground, at multiple locations, at short lengths (a few hundred km instead of tens of thousands of km, hence travel times of hours vs multiple days) and within the material strengths of realistic substances.

Around Phobos a minimum space elevator is so short there's no point building an orbital ring. Mars/Phobos L1 is lower than the radius of Phobos. Plus if you were going to build a ring around Phobos, you might as well just build it on the surface, or tunnel a linear accelerator through the centre. When you have a giant momentum bank, your options increase.

However, by the time you've extended the Phobos tether to the edge of Mars' atmosphere, and you have the volume of traffic to justify it, you're are probably within the economic range of building an orbital ring.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #44 on: 07/18/2017 02:45 AM »
However, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.

To use an example with just four stations at 90° intervals around the planet: Without the stations, the ring-particles would be in a natural circular orbit (V=Vc). Individually stable for long periods, although they would gradually drift relative to each other. If you placed the four magnetic stations in their non-orbits (V=~0), they would want to fall down (obviously). To provide them with their "statite" energy, you have each station steer ring-particles towards the next station at faster-than-orbital-velocity (V>Vc). The station bends the particle's trajectory down (& Mr. Newton lifts the station up in response) and steers it towards the next station at the same faster-that-orbital-velocity. Rinse/repeat.

That's the basic dynamic orbital ring concept, stripped to its essentials. Small variations in the trajectories of the ring-particles need to be dealt with by the capture mechanism on the stations, and hence more stations is better. (In theory, you could have just two stations exchanging a single ring-particle. But I think four and a stream of particles is easier to picture.)

But what do you do when the ring as a whole is becoming eccentric? If the particles are on a natural orbit between stations 1 & 3, they can provide no energy to station 2 and it falls, if they are on a faster-than-orbital-velocity trajectory they provide lift. So to raise or lower a station, you change the velocity of the ring-particles passing through. If you want to raise the station, tighten the bend, if you want to lower the station, soften the bend. And because the stations steer the ring-particles, the ring as a whole moves with the stations.

Hence by increasing the speed of the particles on one leg, reducing it on another, you transfer momentum around the ring, which lets you lift and lower stations (and hence the ring itself) asymmetrically; actively stabilising the ring. That varies the spacing of the ring-particles: the slower particles are on a wider, more circular orbit, hence a longer path than faster particles on a tighter, more direct trajectory; hence the spacing between particles on the slower leg is greater than on the faster leg. Which is why it won't work if you have a solid/continuous inner-ring.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #45 on: 07/18/2017 01:57 PM »
Read my comment again. I wasn't arguing that they would be stable, I'm saying that they can be low enough to reach the Earth with many short cables, and those cables provide stability.

I believe that cables even to a low orbit would need to be tensile rather than compressive towers. So they would not prevent a ring from dipping and suffering regions where gravity exceeds centrifugal force.

However, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.

Actively using energy to accelerate or decelerate discrete parts of an inner ring might be a way to keep the ring from spinning out of control.

And we're talking very massive infrastructure. A low Mars orbital ring would be 23,000 kilometers in circumference.

Much less than the length of a Mars space elevator. Or an Earth or lunar space elevator. And with much lower material requirements. (Which is what it is being compared to.)

In my opinion a Mars elevator would need to terminate with a counterweight below Deimos to avoid collision with that moon. Such an elevator would be about 20,000 kilometers.

And I've already said such an elevator is implausible. If made of Zylon with a safety factor of two, Zylon tether mass to payload ratio would be a little than a thousand.

I believe a lunar elevator is even less plausible than a Mars elevator. And I still haven't revised the lunar elevator scenario with a more sensible safety factor of three.  An Zylon earth elevator I don't even bother to look at.

The less ambitious Deimos  and Phobos elevator scenarios described would take tonnes to tens of tonnes infrastructure. They could happen in the 21st century.

I'm a fan of the Phobos elevator. And the Phobos/Deimos transit system. Obviously an orbital ring isn't going to compete against that.

But orbital rings are intended to be a better planetary space elevator. It allows direct connection to the ground, at multiple locations, at short lengths (a few hundred km instead of tens of thousands of km, hence travel times of hours vs multiple days) and within the material strengths of realistic substances.

I like the notion of an elevator linked to the ground. Also the notion of fast transportation from one point on the ground to another. I want it to be plausible. However I believe skepticism and some Devil's Advocacy can help solidify a sound idea. And if an idea isn't sound, the same Devil's Advocacy might prevent us from wasting time and energy on an implausible scheme

Around Phobos a minimum space elevator is so short there's no point building an orbital ring. Mars/Phobos L1 is lower than the radius of Phobos. Plus if you were going to build a ring around Phobos, you might as well just build it on the surface, or tunnel a linear accelerator through the centre. When you have a giant momentum bank, your options increase.

However, by the time you've extended the Phobos tether to the edge of Mars' atmosphere, and you have the volume of traffic to justify it, you're are probably within the economic range of building an orbital ring.

When you use a safety factor of three, a 5,800 km Zylon tether from Phobos to just above Mars atmosphere has a tether to payload mass ratio of 638. You'd need a 638 tonne elevator to accommodate a one tonne payload (which includes the elevator car as well as cargo & passengers). That makes it impractical, in my opinion. This was a painful conclusion for me as such an elevator had been one of my favorite day dreams for several years.

I still entertain the notion of a 1,400 kilometer elevator descending from Phobos. Zylon tether to payload ratio is .33. so a one tonne elevator could accommodate a three tonne payload.

A 1,400 km tether could drop payloads in a Mars orbit with an atmosphere grazing periapsis. Using repeated periapsis drag passes, aerobraking can bring this down to a low Mars orbit where the payload is moving 3.4 km/s. If the payload has propellent from Phobos, it could use that reaction mass to slow it further and Mars EDL would still be much simpler than the 6 km/s entry coming in from an earth to Mars Hohmann.

Both the 5,800 km and 1,400 km scenarios are examined in my Lower Phobos Elevator post.

Offline stefan r

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Re: Space Elevator for Mars
« Reply #46 on: 07/18/2017 10:53 PM »
and store in bags at the equivalent to Lagrange 4/5 points.

There's no [useful] equivalent around Mars, assuming you mean a Mars-moon Lagrange. Phobos and Deimos are too small.

Exactly.  The gravity becomes so small it is not relevant.  If we move mass a distance along the orbital path we do not have to worry about it returning to Phobos.  Package tape or dental floss can easily resist the force of the solar wind on a cargo container.  Saying "equivalent of L4/L5" was probably a poor choice of words.  Preventing the mass on a Phobos orbital ring from reforming a moon does not require much force.  If you lose the material you will have dangerous debris flying around for a very long time.

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.

Wikipedia says the Port of New Orleans handles 62 million short tons of cargo plus a million passengers. Ignoring passengers and barges they handle 5.6 x e10 kg.  Gravity on phobos is 5.81 e-4 earth.

You're wanting to move Phobos? It is Mars' gravity you want to look at, not Phobos gravity.

So the lift capacity of similar cranes would be around 9.6 e14.

And what distance do the cranes move the cargo? I would suppose From the deck of a ship to a dock. Not the same as moving Phobos thousands of kilometers. 

At any rate, the cranes of New Orleans are quite massive infrastructure. Even if your model was sound, your scenario isn't plausible.
Some of the containers get loaded in Shanghai and travel through the Panama canal before getting unloaded from container ships in New Orleans.  Some of the containers have a thousand kilometer trips before and after shipping.  Some of the components in the products already made ocean trips before assembly.  Of course some containers could be Huston to New Orleans.  I am not sure if they count unloading a container from a Hong Kong origin ship and reloading it onto ship heading to Boston as handling 2 containers.  On average 1000 km is probably the right order of magnitude. 

We may be confused with the words "distant future".  A dwarf elephant is "bigger" than a huge ant.  If the goal is to sustain a small research outpost then an orbital ring will not pay off its investment.  If we are talking about "how to land a human" then this entire thread becomes suspect.  Elevators and orbital rings pay off as the total volume of cargo transport increases.  Depending on context the next century could be referred to as "near future".  "Within a child's lifetime" is probably better wording. 

Elon Musk and SpaceX are talking about "a city of 1 million people" on Mars in the "next 40 to 100 years".  That requires moving a lot of mass.  It includes a lot of mass lifted out of earth's gravity well.  I guess I do not know how plausible that scenario is.  But they are throwing a lot of money and effort into it. 

I do not see a good reason to move Phobos.  An orbital ring can pass through, go above, or go below Phobos.   We could do all three without too much trouble.  Phobos has a lot of inertia so attaching a ring to it has advantages that a free flying ring would not.  A Phobos ring is also a reasonable place to construct other rings. 

The most basic orbital ring can be a thin tether like fishing line.  Tension does not need to add over thousands of kilometers. You can use spools spaced out around the ring.  Use several lines for redundancy and safety.  Pieces of the ring can be thicker chunks made out of low tensile strength material.  The problem with a single cheap thread is the launch capacity.  If most of the ring is a 50 newton fishing line then the prograde and retrograde launches have to balance within 50 newtons before the spools run out of line. 

With a Phobos ring you can use a magnetic rail line to launch prograde and retrograde near phobos.  A few hundred kilometers mass driver track could catch/launch shuttles from the surface, launch shuttles to earth, and function as a landing strip for incoming spacecraft.  The momentum from a landing ship will not cause a huge change in Phobos's momentum.  So the far side of the ring do not need to spool out much fishing line to compensate. 

An active support orbital ring is a bit bigger and more complicated but requires much lower technology than much of the Mars mission.

From an infrastructure standpoint orbital rings have a lot of advantages.  Mars does not have an ocean so none of Earth's shipping will be possible.  A rail line circling Mars is already a huge expense.  A rail or road only makes sense if it is part of a transportation network.  An active support orbital ring can bypass all of the long distance road and rail. 

The entirety of "city on Mars" or "million colonists on Mars" may be implausible.  But if we start with that assumption then the orbital ring may be one of the easier paths.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #47 on: 07/19/2017 12:23 AM »
Some of the containers get loaded in Shanghai and travel through the Panama canal before getting unloaded from container ships in New Orleans.  Some of the containers have a thousand kilometer trips before and after shipping.  Some of the components in the products already made ocean trips before assembly.  Of course some containers could be Huston to New Orleans.

So you're not just talking about the cranes at the New Orleans harbor. You are also talking about all the ships that move between New Orleans and points throughout the planet. You're also talking about the Panama Canal which is rather massive.

Also a ship traveling on the Atlantic has different fuel requirements than a tug moving stuff to different orbits. Delta V to move a mass from Phobos to Low Mars Orbit is about 1.2 km/s. By my arithmetic it would take about 3.1e15 kilograms of hydrogen/oxygen bipropellent. The world's annual production of oil was about 77,500,000 barrels per years as of 2014. That comes to about 4.4e12 kg of oil.

So the hydrogen/oxygen bipropellent to move Phobos would need to mass about 700 times as much as the world's annual oil production.



What is the mass of the infrastructure you imagine?

This is an important factor that people seem to want to ignore.


Offline Paul451

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Re: Space Elevator for Mars
« Reply #48 on: 07/19/2017 12:30 AM »
Read my comment again. I wasn't arguing that they would be stable, I'm saying that they can be low enough to reach the Earth with many short cables, and those cables provide stability.
I believe that cables even to a low orbit would need to be tensile rather than compressive towers. So they would not prevent a ring from dipping and suffering regions where gravity exceeds centrifugal force.

For the ring to drift off-centre (so that one side brushes the planet), as one side lowers, the other side is lifted. If (tensile) ground-cables prevent that side from lifting, the ring itself prevents the other side from dipping.

However, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.
Actively using energy to accelerate or decelerate discrete parts of an inner ring might be a way to keep the ring from spinning out of control.

The whole structure is active, that's the whole point. It only works because the mag-stations are guiding the inner-ring (even if you completely enclose the inner-ring(s), the mag system is still always on.) Actively changing the orientation of the ring would simply be a variation within that continuous process.

[BTW I might be wrong about my interpretation of how a non-grounded ring is stabilised. I'm going from fragments of what I've read, but its always pop.science stuff, I haven't tried to dig up any genuine scientific papers.]

Offline stefan r

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Re: Space Elevator for Mars
« Reply #49 on: 07/21/2017 04:10 AM »
Some of the containers get loaded in Shanghai and travel through the Panama canal before getting unloaded from container ships in New Orleans.  Some of the containers have a thousand kilometer trips before and after shipping.  Some of the components in the products already made ocean trips before assembly.  Of course some containers could be Huston to New Orleans.

So you're not just talking about the cranes at the New Orleans harbor. You are also talking about all the ships that move between New Orleans and points throughout the planet. You're also talking about the Panama Canal which is rather massive.

Also a ship traveling on the Atlantic has different fuel requirements than a tug moving stuff to different orbits. Delta V to move a mass from Phobos to Low Mars Orbit is about 1.2 km/s. By my arithmetic it would take about 3.1e15 kilograms of hydrogen/oxygen bipropellent. The world's annual production of oil was about 77,500,000 barrels per years as of 2014. That comes to about 4.4e12 kg of oil.

So the hydrogen/oxygen bipropellent to move Phobos would need to mass about 700 times as much as the world's annual oil production.



What is the mass of the infrastructure you imagine?

This is an important factor that people seem to want to ignore.

I was expecting the converse.  Build the station at Phobos.  Take your numbers: 3.1e15 kg of oxy/hydrogen.  It is readily available as momentum.  Phobos may be much more valuable than the petro because we can use the momentum both ways.  Incoming craft add momentum out going craft drain it. 

If we are dealing with 1 million colonists then a lot of numbers get large.  For instance SpaceX would be transporting 3 to 5 million meters of live human small intestine.  That is 5 to 8% of the length of an orbital ring.  A typical house in the USA has more than 60 meters of pipe.  Count hot, cold, drainage.  The Martians will also have some sort of farms.  Farms in the midwest have drainage lines every 3 meters.  Hydroponics would use more pipe.

I am not sure of the minimum mass needed.  The orbital ring is not excessive.
« Last Edit: 07/22/2017 01:18 AM by stefan r »

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #50 on: 08/07/2017 03:42 PM »
Read my comment again. I wasn't arguing that they would be stable, I'm saying that they can be low enough to reach the Earth with many short cables, and those cables provide stability.
I believe that cables even to a low orbit would need to be tensile rather than compressive towers. So they would not prevent a ring from dipping and suffering regions where gravity exceeds centrifugal force.

For the ring to drift off-centre (so that one side brushes the planet), as one side lowers, the other side is lifted. If (tensile) ground-cables prevent that side from lifting, the ring itself prevents the other side from dipping.

However, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.
Actively using energy to accelerate or decelerate discrete parts of an inner ring might be a way to keep the ring from spinning out of control.

The whole structure is active, that's the whole point. It only works because the mag-stations are guiding the inner-ring (even if you completely enclose the inner-ring(s), the mag system is still always on.) Actively changing the orientation of the ring would simply be a variation within that continuous process.

[BTW I might be wrong about my interpretation of how a non-grounded ring is stabilised. I'm going from fragments of what I've read, but its always pop.science stuff, I haven't tried to dig up any genuine scientific papers.]

A low Mars orbital ring would be around 20,000 km in length. A low earth orbital ring about 40,000 km. They would not be as narrow as an elevator tether. So a large cross sectional area and thus larger chance of impact from a meteoroid or piece of orbital debris.

I attached a sketch of a piece of debris puncturing the walls and putting material in the path of the elements providing centrifugal lift. When the element strikes the debris in it's path it will itself turn into an expanding blob of debris further damaging the walls around the elements.

These guys are moving faster than something in a normal low earth or low Mars orbit. LEO orbital period is about an hour and a half. LMO is about two hours. In less than two hours after an impact all the rapidly moving elements will have reached the impact site.

The elevators to the ring as well as much of the ring structure would fall to the planet surface. There would also be an impressive debris cloud that would remain in orbit for some time.
« Last Edit: 08/07/2017 03:46 PM by Hop_David »

Offline stefan r

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Re: Space Elevator for Mars
« Reply #51 on: 08/07/2017 05:05 PM »


These guys are moving faster than something in a normal low earth or low Mars orbit. LEO orbital period is about an hour and a half. LMO is about two hours. In less than two hours after an impact all the rapidly moving elements will have reached the impact site.

The elevators to the ring as well as much of the ring structure would fall to the planet surface. There would also be an impressive debris cloud that would remain in orbit for some time.

There are multiple models of orbital rings.  Would be nice if more specific terms could were common.  Your drawing looks like one of the active support structure.  And parts of your ring are co-rotating with the planet's surface. 

Active support structures are not commonly available so it is hard to evaluate risks.  Suppose you have 10 or 100 conduit tubes and a matching set of wire/pellets.  Broken pieces of the co-rotating conduit would fall promptly or dangle.  Most of the 20,000 km of wire-pellets could switch to an alternate conduit.  Many km of wire would fly through the punctured section but they are moving at exit velocities.  (of course 100 wires means 2 orders of magnitude increase in minimum mass).

Meteor damage is not trivial.  Compare to a meteor puncturing a tank of chemical rocket fuel.  Most of the debris from an exploding storage depot will remain in mars orbit because it was at rest in low mars orbit before the explosion.  A supply line for 1 million Mars residents will contain a lot of dangerous energy and momentum.  Not simple to calculate which option is most dangerous.  Depends on a lot of variables.

An "orbital ring" can be actually orbital.  The active support exists only to stabilize the orbit and to cancel launch/landing momentum.  A meteor does not change anything except splash form the impact site.  Most of the ring could be fishing line.  Reels would be spread around the ring.  A Hoyt tether design would allow a comet to fly through without seriously effecting business as usual.  With an orbiting orbital ring you still need mass drivers, tethers, and/or rockets.  You could think of the (orbiting)orbital ring as a complex tether. 

Offline Paul451

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Re: Space Elevator for Mars
« Reply #52 on: 08/07/2017 10:47 PM »


The projectiles are guided by the magnetic rings, in your drawing they would be the sections connected to the ground-cables. Between, the projectiles are free-flying. The meteors achieve nothing. See below.

If you take out a mag-section, the projectiles in that section will continue on their super-orbital trajectory, missing the next mag-section and flying off into deep space. However, once the damage is detected, the previous mag-section would change its deflection angle and re-aim the following projectiles for the next intact section. The system as a whole wouldn't fail, although you'll need to re-inject new projectiles to make up for the loss.

Once you get to the point where the entire ring is enclosed (which means continuous mag-sections all the way round) then any strike would hit a mag-ring, but by the time you get to that point, you're talking a massive level of development and inevitably many redundancies and safety systems; at the very least, with so many mag-rings, each deflection would be so slight that losing a mag-ring or seven would still leave the projectiles within the target area of the remaining mag-rings. (Otherwise, how do you take rings off-line for maintenance.)

Offline Asteroza

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Re: Space Elevator for Mars
« Reply #53 on: 08/08/2017 01:37 AM »
Aren't some active full ring systems predicated on very small projectiles (grain of sand or less) with a fairly generous vacuum tube area? Penetration events, if not very catastrophic, aren't going to make much of a tube debris cloud, and would basically sandblast any accident debris to dust while accelerating it down the tube right? Eventually debris dust would line the tube upper surface past the penetration site due to splatter because it can't be magnetically directed too right?

Offline stefan r

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Re: Space Elevator for Mars
« Reply #54 on: 08/08/2017 08:41 PM »
Aren't some active full ring systems predicated on very small projectiles (grain of sand or less) with a fairly generous vacuum tube area? Penetration events, if not very catastrophic, aren't going to make much of a tube debris cloud, and would basically sandblast any accident debris to dust while accelerating it down the tube right? Eventually debris dust would line the tube upper surface past the penetration site due to splatter because it can't be magnetically directed too right?

The energy and momentum can be independent of size and shape.  106 spherical grains with millimeter diameter have the same momentum as 109 spherical grains with diameter 0.1 millimeter.  A single wire with 1.0mm diameter and 750 m length also has the same mass, momentum and energy. 

My impression was that wire shaped particles are easier to work with and can overlap.  The particle model is used to counter concerns about stretching. 

Offline Dao Angkan

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Re: Space Elevator for Mars
« Reply #55 on: 08/12/2017 08:35 PM »
With regards to a Phobos tether;

Phobos L1 Operational Tether Experiment (PHLOTE)



Quote
A sensor package that “floats” just above the surface of Phobos, suspended by a tether from a small spacecraft operating at the Mars/Phobos Lagrange 1 (L1) Point would offer exciting opportunities for science (SMD), for human exploration (HEOMD) and for advancements in space technology (STMD). Detailed information on the Martian moon Phobos is limited even though it is considered an important destination for near term human exploration. A PHLOTE spacecraft would perform fixed point station keeping at the Mars/Phobos L1 point to allow a tethered sensor package to “float” just above the moon’s surface and also park instruments on the surface for in situ science measurements. This can include ground penetrating radar for subsurface composition measurements to determine how thick the layer of fine grained regolith is for future landings. Other key instruments would be dosimeters for understanding the radiation environments for future human missions, cameras, and a spectrometer for surface mineral analysis. If deployed after a human landing, a PHLOTE spacecraft could provide a constant “eye in the sky” for ground controllers to monitor mission deployments and operational activities. The PHLOTE mission concept has only now become feasible due to recent technology advances, many of which have been supported by NASA’s STMD. Key technologies that make this mission concept feasible include: The Navigation Doppler Lidar (NDL) Sensor for the providing precise spacecraft position and rate knowledge relative to Phobos. This high precision is needed to maintain position at the L1 point; Carbon Nanotube (CNT) braided yarns for a structurally strong tether that doubles as a power and data conduit, Ultralightweight solar arrays, and highly efficient electrospray micro-propulsion thrusters for long term “hover mode” station keeping.

The Martian Moon Phobos offers a key waypoint toward enabling human surface landings on Mars. In particular Stickney Crater, which always faces Mars due to Phobos’ synchronous rotation, provides an excellent stepping stone destination as a precursor to a human Mars landing. There is very limited information on the composition and the environments at Stickney Crater on Phobos. Since Phobos has a composition similar to carbonaceous chondrite meteorites, it is believed that it could provide minerals that can be used for In Situ Resource Utilization (ISRU) to recover key elements such as Oxygen for use as return trip propellant. The mission concept below would answer many of these questions as well as provide TRL advancement in key technology areas for human exploration.

This mission concept is a synthesis of new technologies that would provide a unique platform for multiple sensors directed at Phobos as well as Mars. Since the Mars/Phobos L1 point is only ~3.1 km from the surface of Phobos, the PHLOTE tether length only needs to be a few kilometers long. A tether configuration with its Center of Gravity at the Mars/Phobos L1 point can place a sensor package on the moon’s surface or float it just above. Due to Phobos’ very low gravity, the tether will be under very low tensile loads.

Using a longer tether, this concept can be similarly used for other missions such as Mars/Deimos or at the Pluto/Charon L1 point where both bodies are tidally locked which means a PHLOTE spacecraft with a much longer tether could descend into Pluto’s tenuous atmosphere and sample its chemistry at all elevations unlike a traditional probe.
If selected, a feasibility study for the Phobos L1 Operational Tether Experiment (PHLOTE) mission would be performed that will define the PHLOTE mission, determine the technology needs and assess the technology readiness. The study would also model the system, identify risks, as well as explore new science opportunities that could be done with this unique sensor platform.

And a similar lunar tether;

NASA Studies Tethered CubeSat Mission to Study Lunar Swirls



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NASA’s Planetary Science Deep Space SmallSat Studies, or PSDS3, program recently selected a team at the Goddard Space Flight Center in Greenbelt, Maryland, to further develop a mission concept called the Bi-sat Observations of the Lunar Atmosphere above Swirls, or BOLAS. The study, led by Goddard Principal Investigator Timothy Stubbs, could lead to the first tethered planetary CubeSat mission, Stubbs said.

“This is an exciting concept,” said Michael Collier, a BOLAS co-investigator who has studied tether-based missions for gathering difficult-to-obtain lunar measurements since 2015. “Candidly, I think it’s groundbreaking. Tethered satellites are a very natural approach for targeting lunar science.”

As currently conceived, the mission would involve two 12-unit CubeSats, whose individual units would measure just four inches on a side. Once the pair reached a low-maintenance, quasi-stable orbit about 62 miles above the Moon’s surface, the two, connected by a 112-mile-long thin tether, would separate. The top satellite would climb 118 miles above the surface, while the lower, nearly identical twin would plunge to an altitude of about six miles above the surface.

“The tension in the tether keeps the CubeSats in vertical alignment as they orbit,” Stubbs said. “The configuration, with the center-of-mass in a quasi-stable orbit, should enable the lower CubeSat to fly for long durations at low altitudes.”

So, is it necessary to keep the tethers extended at all times putting them at risk of micrometeorite damage, or could we just reel the tethers in and out when needed from close to L1? This would also eliminate the need for specialised tether climbing and power equipment, it would all be powered from the L1 station. An extra thick tether could be used for the permanently exposed 3.1km Phobos - L1 tether, but this would not be used for transportation, simply tethering the L1 station. The "winched tethers" could be thinner, with spare spools kept on the L1 station in case of any damage to the existing tethers.

Any flaws with this?

(not to scale);


Offline A_M_Swallow

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Re: Space Elevator for Mars
« Reply #56 on: 08/13/2017 01:10 PM »
That looks like the deployment method proposed for an Earth space elevator. For asteroids an alternative was to land the whole lot on the asteroid, dig in and fire the ribbon into space. Has this option been considered?

A 2 stage launch may be needed for the L1 equipment.

Offline stefan r

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Re: Space Elevator for Mars
« Reply #57 on: 08/14/2017 09:10 PM »
That looks like the deployment method proposed for an Earth space elevator. For asteroids an alternative was to land the whole lot on the asteroid, dig in and fire the ribbon into space. Has this option been considered?

A 2 stage launch may be needed for the L1 equipment.

Ancient workers used clay bricks to make grain silos more than 10 meters high.  With gravity 1/2000 a structure made with equivalent material can be built to the Lagrange points.  Standard intermodal shipping containers can also be stacked over 10 meters on Earth's surface. 

A challenge on Phobos will be to prevent things from flying around.  A typical cork in a champagne bottle could be popped into orbit around Mars.  A good table tennis (ping pong) match would also send balls out of Phobos's gravity well.  It becomes dangerous if corks or ping pong balls are accelerated by the solar wind and return through Phobos's orbit around Mars in an elliptical path.  Even if the cork remains in a circular orbit it could endanger a ship flying to or from Mars' surface and ships using a gravity assist.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #58 on: 08/14/2017 10:26 PM »
Pedantry, because it's one of those things that always bugs me:


For a tether, the part in circular orbit is not at the centre-of-mass. Because centripetal acceleration is linear to distance, but gravitational acceleration is to the square, the balance point of the forces on a tether (and hence its orbit) is below the centre-of-mass.

(Hence "COM orbit" (for a free flying object) would be an eccentric orbit (or even escape velocity) with periapsis at the COM's altitude.)

Online Phil Stooke

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Re: Space Elevator for Mars
« Reply #59 on: 08/14/2017 10:54 PM »
"Stickney Crater, which always faces Mars due to Phobos’ synchronous rotation,"

(from the post about PHLOTE, above)

Just to make sure nobody is misled by this statement, Stickney is visible from Mars but it's not at the sub-Mars point as the illustration seems to suggest.  It is about 60 degrees west of the sub-Mars point.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #60 on: 08/15/2017 04:15 PM »
Ancient workers used clay bricks to make grain silos more than 10 meters high.  With gravity 1/2000 a structure made with equivalent material can be built to the Lagrange points.

{laughs} That's a hilarious image.

An unfired, hand pressed clay brick has a crush strength of around 15kg/m² and a course height of around 100mm. At Phobos surface gravity (but completely ignoring the reduction of gravity with height) that lets you build a structure 170km tall. Which is way beyond the Phobos/Mars L1 point.

On Phobos, you can build a brick staircase to orbit.

Offline LMT

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Re: Space Elevator for Mars - Dr. Lades' Mars Lift
« Reply #61 on: 09/24/2017 01:36 PM »
Dr. Martin Lades has now solved the longstanding MSE problem of Phobos/tether collision.  His numerical analysis of an off-equator tether has determined that a reasonable tether design can passively avoid Phobos. 

In one example, an MSE base station just 13 degrees off the equator has a tether curve that clears Phobos.  No active tether management is required.

Our Omaha Trail press release here.

« Last Edit: 09/24/2017 01:37 PM by LMT »

Offline Asteroza

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Re: Space Elevator for Mars - Dr. Lades' Mars Lift
« Reply #62 on: 09/25/2017 11:13 PM »
Dr. Martin Lades has now solved the longstanding MSE problem of Phobos/tether collision.  His numerical analysis of an off-equator tether has determined that a reasonable tether design can passively avoid Phobos. 

In one example, an MSE base station just 13 degrees off the equator has a tether curve that clears Phobos.  No active tether management is required.

Our Omaha Trail press release here.




Off-axis elevators are certainly an interesting solution and provide continuous ops, rather than a two step Deimos/Phobos tether pair with central coast phase.

The coilgun launcher above Deimos near Deimos L2 is not very clear in this design, nor are the advantages relative to just jumping off the counterweight at the appropriate time. Guess we have to wait for the full paper/presentation?

Offline LMT

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Re: Space Elevator for Mars - Dr. Lades' Mars Lift
« Reply #63 on: 09/25/2017 11:52 PM »
Dr. Martin Lades has now solved the longstanding MSE problem of Phobos/tether collision.  His numerical analysis of an off-equator tether has determined that a reasonable tether design can passively avoid Phobos. 

In one example, an MSE base station just 13 degrees off the equator has a tether curve that clears Phobos.  No active tether management is required.

Our Omaha Trail press release here.




Off-axis elevators are certainly an interesting solution and provide continuous ops, rather than a two step Deimos/Phobos tether pair with central coast phase.

The coilgun launcher above Deimos near Deimos L2 is not very clear in this design, nor are the advantages relative to just jumping off the counterweight at the appropriate time. Guess we have to wait for the full paper/presentation?

Yes, his off-equator solution allows for continuous operation.  Moreover, having a base station at 13 degrees latitude allows the tether to retain nearly all of its strength for vehicle support.

As for Deimos, there is of course the option for spacecraft to depart the L1 "Deimos Dock" via rocket propulsion, but one would like to avoid that expenditure if possible.  A tethered superconducting helical coil electromagnetic launcher could fit the bill, if extended through L2 with sufficient length and power to get craft to Mars, or to cloud-skimming periapsis for Earth-return.  Luckily 1 km/s is the requirement in either case; a speed that's relatively modest, compared to the orbital-launch speeds floated elsewhere. 

And yes, one might extend the Deimos Rail Launch tethers further for drop-launch outward, but that loses the gravity-assist of Mars periapsis, and increases tension.

One might extend the simpler Mars Lift tether to drop-launch from that tether instead, but that requires more tension and also more infrastructure to manage the dynamics; especially collision-avoidance tech, to dodge Deimos.  As they are, Omaha Trail tethers passively avoid both moons, and each other, continuously.

A possible DRL extension:  one might combine methods in a second deployment by attaching a long, simple tether to the counterweight of the shorter, more complex DRL tethers.  Craft bound for Mars launch via DRL.  Other craft drop-launch from the attached tether.  However DRL tethers would require reinforcement or replacement to manage the greater tension.

We give some of the reasoning, tech, numbers and references in the conference presentation attached to the press release.  Feel free to ask about things not shown in presentation.
« Last Edit: 09/26/2017 01:12 AM by LMT »

Offline Asteroza

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Re: Space Elevator for Mars
« Reply #64 on: 09/26/2017 08:21 AM »
Ah, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.

The structural arrangement baseline for the coilgun relative to the L2 tether would be interesting to see, along with the Deimos L1 dock arrangement considering the no capstan rule.

Offline LMT

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Re: Space Elevator for Mars
« Reply #65 on: 09/26/2017 11:31 AM »
Ah, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.

Right.

The structural arrangement baseline for the coilgun relative to the L2 tether would be interesting to see, along with the Deimos L1 dock arrangement considering the no capstan rule.

re: L1 Deimos Dock

Deimos Dock is needed only as a transfer station for propellant and water.   There's no need for cargo transfer.   The only "climber" envisioned would be a low-speed inspection/repair vehicle.  Capstaning is therefore allowable on the Deimos Dock tether.  However it doesn't seem necessary.  Pressure from paired wheels should be adequate, on a straight tether, as in Pearson 2005.

re: DRL through L2

Presentation slides 36-38 are just intended as conversation starters, with a suggested approach for adaptation of Engel's helical coil launcher.  (Engel 2004, Engel et al. 2015.)  A few notes:

Whereas Engel's high-acceleration projectile launcher requires a thick fixed-box construction, the low acceleration (0.5 m/s2) of the DRL should allow a light tethered construction.  The stator can be a skinny, flexible coiled tube of high-temperature superconductor.  HVDC power can be delivered by thin outrigger tethers.

In slide 37 the redundant stator pair is shown in red.  Each stator is flanked by a pair of HVDC tethers in white.  Two additional pairs of tethers in white are added at the periphery.  They serve, notionally, only to provide extra power line repulsion force, to balance repulsive forces on the load-bearing tethers and keep the wires roughly in parallel for easy passage of platform Lorentz tubes.

Engel has demonstrated record-setting launch efficiency by cooling the armature in liquid nitrogen, to cut electrical resistance.  At Deimos LOX would substitute.  Full efficiency would be obtained by cooling both armature and stator to high-temperature superconducting range with LOX.  A LOX dewar would travel with the armature.  The stator is however stationary by definition.  One would deploy the flexible stator hollow, filling it with LOX from Deimos base station prior to launch.
« Last Edit: 09/27/2017 01:04 AM by LMT »

Online Phil Stooke

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Re: Space Elevator for Mars
« Reply #66 on: 09/26/2017 11:38 AM »
Very interesting - just one minor point.  The 'Taylor Oner' you credit with the Deimos image is really Tayfun Oner.

Offline LMT

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Re: Space Elevator for Mars
« Reply #67 on: 09/26/2017 01:47 PM »
Very interesting - just one minor point.  The 'Taylor Oner' you credit with the Deimos image is really Tayfun Oner.

Fixed, thanks.  Interesting for us as well.

It was especially interesting to see how far CNT materials have now advanced toward the required Mars Lift specific strength.  Dr. Lades analyzed Mars Lift tethers at 7-13 MYuri, and CNT film is reported from 2016 at 5.2 MYuri  (J. Knapman, from Xu et al. 2016:  9.6 GPa / 1.85 g/cc.) So specific strength is getting there, apparently.  It justifies consideration of a Mars Lift system proposal for 2036 timeframe, don't you think?

Offline whitelancer64

Re: Space Elevator for Mars
« Reply #68 on: 09/26/2017 02:06 PM »
Ancient workers used clay bricks to make grain silos more than 10 meters high.  With gravity 1/2000 a structure made with equivalent material can be built to the Lagrange points.

{laughs} That's a hilarious image.

An unfired, hand pressed clay brick has a crush strength of around 15kg/m² and a course height of around 100mm. At Phobos surface gravity (but completely ignoring the reduction of gravity with height) that lets you build a structure 170km tall. Which is way beyond the Phobos/Mars L1 point.

On Phobos, you can build a brick staircase to orbit.

This is the kind of trivia that I wish were common knowledge :p
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