Author Topic: Space Elevator for Mars  (Read 30619 times)

Offline 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.)

Online 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.

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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.)

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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.

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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.

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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 »

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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?

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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 »

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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.

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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 »

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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.

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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
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline LMT

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Re: Space Elevator for Mars
« Reply #69 on: 11/11/2017 09:21 PM »
Integrating new SpaceX spacecraft into the Omaha Trail:  quantifying efficiencies and radiation protection, in conference at the British Interplanetary Society.

Press release Nov. 7.

Dr. Lades presented new Mars Lift feasibility details, plus our estimates of Omaha Trail efficiency and radiation shielding for new (2017) SpaceX designs. 

Highlights:

- Number of Earth launches for cargo cut 71%.

- Number of Earth launches for crew cut 83%.

- Solar flare proton flux cut 90%+, eliminating dedicated solar flare shelter.



Omaha Trail, crew flight staging. Deimos propellant and water shielding.


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Re: Space Elevator for Mars
« Reply #70 on: 11/12/2017 06:03 PM »
Integrating new SpaceX spacecraft into the Omaha Trail:  quantifying efficiencies and radiation protection, in conference at the British Interplanetary Society.

Press release Nov. 7.

Dr. Lades presented new Mars Lift feasibility details, plus our estimates of Omaha Trail efficiency and radiation shielding for new (2017) SpaceX designs. 

Highlights:

- Number of Earth launches for cargo cut 71%.

- Number of Earth launches for crew cut 83%.

- Solar flare proton flux cut 90%+, eliminating dedicated solar flare shelter.
...

Omaha Trail, crew flight staging. Deimos propellant and water shielding.
So many problems with your claims. First of all, the benefits aren't even real benefits. There is no "dedicated solar flare shelter" because SpaceX is just using the supplies that would be onboard anyway as shielding. You aren't particularly clear on how you cut proton flux by 90%, but that would basically involve heavy shielding everywhere, wasting much of the carrying capacity.

Your reduction in Earth launches is pointless, because the Earth launches are relatively cheap, you are ignoring the costs of getting those extra ships you are using as tankers there to start with, and the much more limited lifetime of ships used for interplanetary transfer due to heat shield ablation. Plus there are other problems, since it does not seem like your propellant amounts would work out. You have 3 ships leave Deimos, spend fuel on a trans-Earth injection, more fuel to capture at Earth (even with aerocapture) transfer fuel from one of them to the crew ship, by magic then have all 3 of these ships full again so they can do a full trans-Mars Injection and then capture/landing. This is even worse given that the only way SpaceX is keeping their landing propellant cool is by having the outer tanks empty during interplanetary cruise.

Offline LMT

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Re: Space Elevator for Mars
« Reply #71 on: 11/13/2017 12:48 AM »
First of all, the benefits aren't even real benefits. There is no "dedicated solar flare shelter" because SpaceX is just using the supplies that would be onboard anyway as shielding.

?  No, absent additional shielding a dedicated shelter space is needed.  Hence the R&D of SR2S, etc.  Likewise Omaha Trail shielding. 

That's why SpaceX included a dedicated shelter space in the new spacecraft design

Why did you think otherwise?

You aren't particularly clear on how you cut proton flux by 90%, but that would basically involve heavy shielding everywhere, wasting much of the carrying capacity.

It's a 130-ton water shield from Deimos.  What's unclear? 

As for "carrying capacity", ascent cargo payload limit applies during ascent.  It has no bearing in transit.

Your reduction in Earth launches is pointless, because the Earth launches are relatively cheap, you are ignoring the costs of getting those extra ships you are using as tankers there to start with

Extra ships?  No, fewer because less propellant is used. 

Also it's far cheaper to build and operate a fleet of, say, 25 giant boosters than a fleet of 100.  That itself is justification, though of course the Omaha Trail would offer other benefits.

it does not seem like your propellant amounts would work out

Did you calculate something?  With Omaha Trail facilities, the numbers add up.

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Re: Space Elevator for Mars
« Reply #72 on: 11/13/2017 03:02 AM »
First of all, the benefits aren't even real benefits. There is no "dedicated solar flare shelter" because SpaceX is just using the supplies that would be onboard anyway as shielding.

?  No, absent additional shielding a dedicated shelter space is needed.  Hence the R&D of SR2S, etc.  Likewise Omaha Trail shielding. 

That's why SpaceX included a dedicated shelter space in the new spacecraft design

Why did you think otherwise?
Solar storm shelter is not a dedicated area, and the shielding comes from supplies that are carried anyway. Try actually reading my post before you respond next time.

You aren't particularly clear on how you cut proton flux by 90%, but that would basically involve heavy shielding everywhere, wasting much of the carrying capacity.

It's a 130-ton water shield from Deimos.  What's unclear? 

As for "carrying capacity", ascent cargo payload limit applies during ascent.  It has no bearing in transit.
You should go research the rocket equation, weight matters a lot when leaving LEO, not just during ascent to LEO. You won't get to "in transit," because it takes delta V to leave Earth and go to Mars, and you will lose a lot a delta V due to the unnecessary extra weight.

Your reduction in Earth launches is pointless, because the Earth launches are relatively cheap, you are ignoring the costs of getting those extra ships you are using as tankers there to start with

Extra ships?  No, fewer because less propellant is used. 

Also it's far cheaper to build and operate a fleet of, say, 25 giant boosters than a fleet of 100.  That itself is justification, though of course the Omaha Trail would offer other benefits.
You clearly have not actually understood SpaceX's plans. Their fleet of boosters will probably be < 10 without your changes (unless they get that point-to-point use case going). Also, your plan involves ships leaving Deimos, but you have made no mention of how they got there to begin with. These ships can be used many fewer times due to the heat shield ablation from aerocapture, and you need multiple in parallel, compared to the single ship that can be reused many times refueling from Earth.

it does not seem like your propellant amounts would work out

Did you calculate something?  With Omaha Trail facilities, the numbers add up.
Yes I calculated something. Assuming you somehow have 3 ships leave Deimos starting with full fuel Lets call this amount of fuel 3. They will spend some amount of fuel that we can call X departing for Earth and then capturing at Earth. You then have a total of 3-X fuel. Unfortunately to send 3 ships back to Mars from LEO (without the excess weight from your unnecessary radiation shield), you need a total fuel of 3 full ships. Since 3-X < 3 you do not have enough fuel.

Offline LMT

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Re: Space Elevator for Mars
« Reply #73 on: 11/13/2017 05:03 AM »
Solar storm shelter is not a dedicated area, and the shielding comes from supplies that are carried anyway. Try actually reading my post before you respond next time.

It's dedicated.  Musk said as much.  It's "a small part of the ship," and noted in presentation. 

You clearly have not actually understood SpaceX's plans. Their fleet of boosters will probably be < 10

Booster ratio is invariant.  Musk's intention (2016) was "1,000 or more spaceships" per window.  With 2017 resizing that payload needs ~2,000 ships and ~12,000 booster launches.  A single-digit fleet couldn't do that.

Did Musk explicitly abandon the intention?  I hadn't heard.

You should go research the rocket equation

No, that's wrong and inappropriate.

I calculated something. Assuming you somehow have 3 ships leave Deimos starting with full fuel Lets call this amount of fuel 3. They will spend some amount of fuel that we can call X departing for Earth and then capturing at Earth. You then have a total of 3-X fuel. Unfortunately to send 3 ships back to Mars from LEO (without the excess weight from your unnecessary radiation shield), you need a total fuel of 3 full ships. Since 3-X < 3 you do not have enough fuel.

That's not the rocket equation.

Cutting [X], that's kinda what Omaha Trail facilities are intended for.  Maybe you can find improvements.

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Re: Space Elevator for Mars
« Reply #74 on: 11/13/2017 10:02 AM »
Solar storm shelter is not a dedicated area, and the shielding comes from supplies that are carried anyway. Try actually reading my post before you respond next time.

It's dedicated.  Musk said as much.  It's "a small part of the ship," and noted in presentation.
Small does not mean dedicated. My post already explained why it can't be considered dedicated.

You clearly have not actually understood SpaceX's plans. Their fleet of boosters will probably be < 10

Booster ratio is invariant.  Musk's intention (2016) was "1,000 or more spaceships" per window.  With 2017 resizing that payload needs ~2,000 ships and ~12,000 booster launches.  A single-digit fleet couldn't do that.

Did Musk explicitly abandon the intention?  I hadn't heard.
That you for the continued evidence that you haven't read SpaceX's plans. In terms of passenger count, the number of ships hasn't changed, they still plan to fit around 100 passengers per ship, so there is no doubling of ships sent. Each booster is expected to be good for 1000 uses, which means a single digit number of boosters can launch 6000 times. Though they will probably

You should go research the rocket equation

No, that's wrong and inappropriate.
Wait, you are saying the rocket equation is wrong? No seriously, the rocket equation states that contrary to your previous post, the mass of what you are trying to move matters a lot for on orbit maneuvers. It is not a hard equation to understand if you bother to look it up.

I calculated something. Assuming you somehow have 3 ships leave Deimos starting with full fuel Lets call this amount of fuel 3. They will spend some amount of fuel that we can call X departing for Earth and then capturing at Earth. You then have a total of 3-X fuel. Unfortunately to send 3 ships back to Mars from LEO (without the excess weight from your unnecessary radiation shield), you need a total fuel of 3 full ships. Since 3-X < 3 you do not have enough fuel.

That's not the rocket equation.

Cutting [X], that's kinda what Omaha Trail facilities are intended for.  Maybe you can find improvements.
I never said that was the rocket equation, it makes it even easier by making use of the fact that SpaceX engineers already calculated that capabilities of their vehicle. Rather than redo the calculations with incomplete information, I can simply recognize that X is a positive number, and nothing you do can ever make it 0, which is what would be needed for your architecture to work.

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Re: Space Elevator for Mars
« Reply #75 on: 11/13/2017 12:18 PM »
Wait, you are saying the rocket equation is wrong? No seriously, the rocket equation states that contrary to your previous post, the mass of what you are trying to move matters a lot for on orbit maneuvers. It is not a hard equation to understand if you bother to look it up.

No, telling people to "look it up" is wrong and inappropriate.  And you're not using it yourself.  You should use it.

--

No Tankers

Notably, one of the benefits of the Omaha Trail proposal is that cargo flights can be launched without dedicated tanker ships. 

No tankers at all.  Just returning cargo ships.

This could be especially beneficial to the construction phase of SpaceX's Mars City, which could take decades.  The work might go 10x faster at Omaha Crater, but still, it's a benefit.



Cargo flight staging. Deimos propellant. Mars Lift space elevator in gold.

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Re: Space Elevator for Mars
« Reply #76 on: 11/13/2017 02:46 PM »
Wait, you are saying the rocket equation is wrong? No seriously, the rocket equation states that contrary to your previous post, the mass of what you are trying to move matters a lot for on orbit maneuvers. It is not a hard equation to understand if you bother to look it up.

No, telling people to "look it up" is wrong and inappropriate.  And you're not using it yourself.  You should use it.
The only thing inappropriate is that you are trying to propose changes to an architecture created by experienced engineers when you apparently don't understand the most basic of equations governing rockets, and that you refuse to even do basic research on your own.
 
I am using the rocket equation in the very post that you quoted. I draw a very basic conclusion from it that you previously denied:
As for "carrying capacity", ascent cargo payload limit applies during ascent.  It has no bearing in transit.
Which is wrong, because the cargo mass has a major impact on available delta V.
« Last Edit: 11/13/2017 03:00 PM by meberbs »

Offline LMT

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Re: Space Elevator for Mars
« Reply #77 on: 11/15/2017 06:14 AM »
Wait, you are saying the rocket equation is wrong? No seriously, the rocket equation states that contrary to your previous post, the mass of what you are trying to move matters a lot for on orbit maneuvers. It is not a hard equation to understand if you bother to look it up.

No, telling people to "look it up" is wrong and inappropriate.  And you're not using it yourself.  You should use it.
The only thing inappropriate is that you are trying to propose changes to an architecture created by experienced engineers when you apparently don't understand the most basic of equations governing rockets, and that you refuse to even do basic research on your own.
 
I am using the rocket equation in the very post that you quoted. I draw a very basic conclusion from it that you previously denied:
As for "carrying capacity", ascent cargo payload limit applies during ascent.  It has no bearing in transit.
Which is wrong, because the cargo mass has a major impact on available delta V.

That's a confused post.  Calculate some particular delta-v, flare shielding, or other quantity you imagine contentious, and try a comparison.

--

Potential Improvements

Results for the Mars Lift and the greater Omaha Trail are of course preliminary, and many improvements are conceivable, even now.  NSF posters might have useful suggestions.  Some areas to explore:

Tether specific strength:

In August ISEC noted the highest confirmed specific strength in a macroscopic carbon material:  a CNT film checking in at 5.2 MYuri.  But that result was published in 2016, and much research is presently targeting higher specific strengths.  Has a higher specific strength been reported recently?

Removing ice from the tether:

A Mars Lift tether can accumulate water ice and dry ice, which must be removed for safe rappeller passage.  One approach is Joule heating: a CNT tether circuit is established in the terminal 100 km, and its resistance melts or sublimates ice.  Electrical power on the order of 100 kW could warm the tether to clear 1 mm of water ice and an extra 1 cm of dry ice over 10 minutes.  What are some other plausible methods for ice removal?

Online meberbs

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Re: Space Elevator for Mars
« Reply #78 on: 11/15/2017 07:19 AM »
Wait, you are saying the rocket equation is wrong? No seriously, the rocket equation states that contrary to your previous post, the mass of what you are trying to move matters a lot for on orbit maneuvers. It is not a hard equation to understand if you bother to look it up.

No, telling people to "look it up" is wrong and inappropriate.  And you're not using it yourself.  You should use it.
The only thing inappropriate is that you are trying to propose changes to an architecture created by experienced engineers when you apparently don't understand the most basic of equations governing rockets, and that you refuse to even do basic research on your own.
 
I am using the rocket equation in the very post that you quoted. I draw a very basic conclusion from it that you previously denied:
As for "carrying capacity", ascent cargo payload limit applies during ascent.  It has no bearing in transit.
Which is wrong, because the cargo mass has a major impact on available delta V.

That's a confused post.  Calculate some particular delta-v, flare shielding, or other quantity you imagine contentious, and try a comparison.
Exact calculations aren't necessary to know that 130 tons of extra cargo mass would greatly reduce the available delta V. You on the other hand made the nonsensical claim that this has no effect. After I have pointed out repeatedly how wrong this is, you simply refuse to accept this plain fact and offer nothing in the form of counterargument. You are the one who seems to be confused.

Offline LMT

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Re: Space Elevator for Mars
« Reply #79 on: 11/25/2017 02:44 AM »
You are the one who seems to be confused.

you apparently don't understand the most basic of equations governing rockets, and that you refuse to even do basic research on your own

Anyone calculating Omaha Trail efficiencies would use the rocket equation repeatedly, across many possible flight configurations, and with gravity losses where appropriate, as we did. 

You might have asked, nicely.

Dr. Lades appreciates that work, and all our work.  Hence his ongoing collaboration.  --  You're not going to accuse an ISEC Director of being confused etc... are you?  If not, you've reached the end of that mess.  You should just apologize for the misunderstanding.

« Last Edit: 11/25/2017 02:50 AM by LMT »

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Re: Space Elevator for Mars
« Reply #80 on: 11/25/2017 05:18 AM »
Dr. Lades [...] You're not going to accuse an ISEC Director of being confused etc... are you?

Hard to say. The only Martin Lades I've seen involved in Space activities is an AI researcher in pattern recognition and neural networks; which doesn't seem related to to any special expertise in orbital mechanics.

And the page on ISEC about their "Martin Lades" reads, in full:

"Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit."

...making it a little difficult to profile the guy.

Your appeal-to-authority seems a little weak. If you've done the analysis, why not answer Meberbs questions instead hiding behind someone else?

Offline stefan r

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Re: Space Elevator for Mars
« Reply #81 on: 11/28/2017 10:41 AM »
...What are some other plausible methods for ice removal?

Tether climbers use some sort of motor.  The motor needs a heat sink. 

A descending vehicle could simply slide.  Similar to snow removal from roads. Without sliding, compression could still liquefy water ice.  The grip pressure will be high.

Fullerenes are hydrophobic.  Is there reason to believe ice would collect?

Offline Paul451

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Re: Space Elevator for Mars
« Reply #82 on: 11/28/2017 11:57 AM »
Fullerenes are hydrophobic.  Is there reason to believe ice would collect?

Hydrophobic surfaces don't prevent frost build up. There are surfaces that can, but they are all structural, harder to produce and wouldn't stand up to wear from the climber.

Offline stefan r

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Re: Space Elevator for Mars
« Reply #83 on: 12/03/2017 02:17 AM »
...What are some other plausible methods for ice removal?

You could pluck it like a guitar string.  That would increase tension but when the climber is off the tether an increase should be manageable.   Could pull the tether below the pad where the tether is attached and then snap release back to normal.  That would keep all tension in one dimension. 

Some descending "climbers" could release and use parachutes/wings.  Time on the tether is tedious and prevents climbers from going up.  Releasing early on a descent allows direct delivery to locations far away from the tether pad(s).  A sudden release should send a wave down the tether.  Ice would detach due to inertia. A descending vehicle should be bending the tether with Coriolis forces.  The letting go wave would have both a vertical stretch component and a horizontal component.

I have not tested the efficiency of ice removal from guitar strings.  I believe all of the musicians I know would be offended if I asked for permission to test. 

Offline LMT

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Re: Space Elevator for Mars
« Reply #84 on: 12/05/2017 05:55 AM »
Dr. Lades [...] You're not going to accuse an ISEC Director of being confused etc... are you?

Hard to say. The only Martin Lades I've seen involved in Space activities is an AI researcher in pattern recognition and neural networks; which doesn't seem related to to any special expertise in orbital mechanics.

And the page on ISEC about their "Martin Lades" reads, in full:

"Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit."

...making it a little difficult to profile the guy.

Your appeal-to-authority seems a little weak. If you've done the analysis, why not answer Meberbs questions instead hiding behind someone else?

Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask. 

And of course ISEC Director and research physicist Dr. Lades knows orbital mechanics well enough to mark our rocket equations -- is the difficulty of the Phobos/tether collision problem underappreciated?  Anyway, some c.v info.   

His current research on CNTs gives him insight into the achievement of space elevator tethers.   Notably, his Mars Lift tether is more easily achieved than an Earth tether or lunar tether.  Comparatively very short and light, and unpowered, the Mars Lift presents a first opportunity.  Implementation sets a technical basis for greater space elevators, at Mars and elsewhere. 

Maybe some thread participants would want to explore the possibilities.

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Re: Space Elevator for Mars
« Reply #85 on: 12/05/2017 02:27 PM »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.

So why not answer Meberbs question instead of vague appeals to authority?

And of course ISEC Director and research physicist Dr. Lades knows orbital mechanics well enough to mark our rocket equations

So show your/his work. Why is that so difficult? Why should it take two pages of comments to get you to just show your work?

is the difficulty of the Phobos/tether collision problem underappreciated?

Off-equator tethers is an old concept, Lades didn't come up with that. (And I'm not accusing him of taking credit for that.) His own calculations of the minimum off-equator angle necessary to avoid Phobos are just geometry, not orbital mechanics.

Online meberbs

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Re: Space Elevator for Mars
« Reply #86 on: 12/05/2017 04:37 PM »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask.

You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta V the implicit question for you to answer was for you to either accept that your statement was wrong, or to do math to justify your statement.

Discussing who did your proposal is irrelevant, because your statement was still wrong even if you had von Braun himself working for you.

Either way, you need to show your work for your architecture including what assumptions you made. Currently you have a spacecraft spending fuel for an Earth transfer, losing propellant during the transfer, spending fuel to arrive at Earth and rendezvous with another identical ship, and somehow fully fuel that other ship while reserving enough propellant to land on Earth. This self evidently leads to the ship needing to carry more fuel than fits in its tanks.

Since you don't seem to acknowledge the existence of questions if there is no question mark let me rephrase:

Do you acknowledge that your statement that adding 130 tons of dead weight/cargo to a spacecraft on orbit has no effect on performance is wrong? If not why?

Can you provide an explanation of your architecture using numbers to justify your claimed performance?

Offline LMT

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Re: Space Elevator for Mars
« Reply #87 on: 12/19/2017 08:33 PM »
is the difficulty of the Phobos/tether collision problem underappreciated?

Off-equator tethers is an old concept, Lades didn't come up with that. (And I'm not accusing him of taking credit for that.) His own calculations of the minimum off-equator angle necessary to avoid Phobos are just geometry, not orbital mechanics.

You're "not accusing" Dr. Lades of anything.  OK.  Nb:  no reason to accuse us of anything, either; you should clean that text.  ::) 

--

But really, imagining Dr. Lades' tether solution as "just geometry" is a severe underappreciation of the difficulty.  To find a solution, the space elevator feasibility condition must be satisfied and the off-equator tether shape equation must be solved, altogether within parameters set by Mars and Phobos, including osculation.   

Not "just geometry". 

Dr. Lades' BIS deck on the feasibility condition and our joint BIS deck on the Omaha Trail give some Mars Lift physics. 

--

Connection

CNT fiber is a plausible material for a Mars Lift tether.  ITS can deliver tether from Earth in 150-ton segments. 

These segments would be connected at the Arestation.  Ideal connections would be low-mass and fully automated.  The Tethers Unlimited SpiderFab spinneret might be modified for such purpose, but there are other possibilities to consider.  Has anyone at NSF explored the challenge of tether segment connection?

Offline LMT

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Re: Space Elevator for Mars
« Reply #88 on: 12/19/2017 08:40 PM »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask.
You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta V

Never said any such thing, obviously.  You should quote people fairly, and you really should apologize for the misunderstanding that fed your accusations here.

Would you like to see estimates of the transit delta-v and mass possible for an ITS craft on the Omaha Trail? 
« Last Edit: 12/19/2017 08:58 PM by LMT »

Offline Lar

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Re: Space Elevator for Mars
« Reply #89 on: 12/20/2017 01:25 AM »
sterile. Stop it. Don't bring this bickering here.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline Paul451

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Re: Space Elevator for Mars
« Reply #90 on: 12/20/2017 01:36 AM »
.

I've PM'd you previously with a suggestion about how you might change the way you are approaching this site and potentially get your Lake Matthew thread unlocked. You ignored the PM and seem to be doubling down on this.

It's your concept, so show your work instead of demanding that others do work for you. I don't think the mods would have a problem with that.
« Last Edit: 12/20/2017 10:13 AM by Paul451 »

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Re: Space Elevator for Mars
« Reply #91 on: 12/20/2017 06:47 AM »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask.
You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta V

Never said any such thing, obviously.  You should quote people fairly, and you really should apologize for the misunderstanding that fed your accusations here.
This is an exact quote below, you said that this adding 130 tons would have "no bearing" on available payload in transit. (Note that I said carrying capacity, not ascent cargo limit. Not really much difference either way, because this system will be designed by SpaceX such that one load of fuel = sending one full ascent load from LEO to Mars.)
You aren't particularly clear on how you cut proton flux by 90%, but that would basically involve heavy shielding everywhere, wasting much of the carrying capacity.

It's a 130-ton water shield from Deimos.  What's unclear? 

As for "carrying capacity", ascent cargo payload limit applies during ascent.  It has no bearing in transit.

Would you like to see estimates of the transit delta-v and mass possible for an ITS craft on the Omaha Trail?
Paul451 and I have repeatedly asked you to provide numbers. If you actually answered questions and provided numbers, you wouldn't be upsetting the mods.

Offline LMT

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Re: Space Elevator for Mars
« Reply #92 on: 12/20/2017 05:50 PM »
Ah, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.

Delta-v Example:  DRL & Gravity Assist

If used efficiently, tethered systems at Mars, such as Deimos Dock, Deimos Rail Launcher (DRL) and Mars Lift could improve flight efficiency significantly. 

Example:  M/E transit with the Omaha Trail's proposed DRL.

Here 0.94 km/s DRL delta-v launches to Mars periapsis, and gravity assist.  At periapsis a small burn of 1.55 km/s gives approximate transfer to Earth.  This is a Mars perihelion transfer; near aphelion, the burn delta-v is less, ~0.8 km/s.

Options:  The Deimos Dock propellant load could be minimized for minimum periapsis delta-v, or else maximized for greater delta-v or greater payload.








The example GMAT script:

--

%  Contact:  [email protected]
%
%  Example Script:  Deimos Rail Launcher (DRL) on Omaha Trail
%
%  Sequence:  DRL EM launch, propagate to Mars periapsis, periapsis burn, propagate approximately to Earth intercept.
%
%  Links:
%  Sept 18 2017:  http://www.lakematthew.com/press/press-release-september-18-2017/
%  Nov 7 2017:  http://www.lakematthew.com/press/press-release-november-7-2017/
%
%----------------------------------------
%---------- User-Defined Celestial Bodies
%----------------------------------------

Create Moon Deimos;
GMAT Deimos.NAIFId = 402;
GMAT Deimos.SpiceFrameId = 'IAU_DEIMOS';
GMAT Deimos.OrbitSpiceKernelName = {'C:\Program Files (x86)\GMAT\R2016a\data\planetary_ephem\spk\mar097.bsp'};
GMAT Deimos.OrbitColor = Tan;
GMAT Deimos.TargetColor = DarkGray;
GMAT Deimos.EquatorialRadius = 7.5;
GMAT Deimos.Flattening = 0.3066666666666666;
GMAT Deimos.Mu = 0.0001588174;
GMAT Deimos.PosVelSource = 'SPICE';
GMAT Deimos.CentralBody = 'Mars';
GMAT Deimos.RotationDataSource = 'IAUSimplified';
GMAT Deimos.OrientationEpoch = 28990;
GMAT Deimos.SpinAxisRAConstant = 0;
GMAT Deimos.SpinAxisRARate = -0.641;
GMAT Deimos.SpinAxisDECConstant = 90;
GMAT Deimos.SpinAxisDECRate = -0.5570000000000001;
GMAT Deimos.RotationConstant = 190.147;
GMAT Deimos.RotationRate = 360.9856235;
GMAT Deimos.TextureMapFileName = 'GenericCelestialBody.jpg';
GMAT Deimos.3DModelFile = '';
GMAT Deimos.3DModelOffsetX = 0;
GMAT Deimos.3DModelOffsetY = 0;
GMAT Deimos.3DModelOffsetZ = 0;
GMAT Deimos.3DModelRotationX = 0;
GMAT Deimos.3DModelRotationY = 0;
GMAT Deimos.3DModelRotationZ = 0;
GMAT Deimos.3DModelScale = 10;

%----------------------------------------
%---------- Spacecraft
%----------------------------------------

Create Spacecraft OmahaTrailSpacecraft;
GMAT OmahaTrailSpacecraft.DateFormat = TAIModJulian;
GMAT OmahaTrailSpacecraft.Epoch = '28990';
GMAT OmahaTrailSpacecraft.CoordinateSystem = MarsMJ2000Eq;
GMAT OmahaTrailSpacecraft.DisplayStateType = Keplerian;

% Approximately Match Deimos
GMAT OmahaTrailSpacecraft.SMA = 23458.17634980082;
GMAT OmahaTrailSpacecraft.ECC = 0.0003144182911521799;
GMAT OmahaTrailSpacecraft.INC = 37.0000000000051;
GMAT OmahaTrailSpacecraft.RAAN = 43.99999999998535;
GMAT OmahaTrailSpacecraft.AOP = 193.1409087306092;
GMAT OmahaTrailSpacecraft.TA = 64.99999997766069;
GMAT OmahaTrailSpacecraft.DryMass = 850;
GMAT OmahaTrailSpacecraft.Cd = 2.2;
GMAT OmahaTrailSpacecraft.Cr = 1.8;
GMAT OmahaTrailSpacecraft.DragArea = 15;
GMAT OmahaTrailSpacecraft.SRPArea = 1;
GMAT OmahaTrailSpacecraft.NAIFId = -10032001;
GMAT OmahaTrailSpacecraft.NAIFIdReferenceFrame = -9032001;
GMAT OmahaTrailSpacecraft.OrbitColor = Red;
GMAT OmahaTrailSpacecraft.TargetColor = Teal;
GMAT OmahaTrailSpacecraft.EstimationStateType = 'Cartesian';
GMAT OmahaTrailSpacecraft.OrbitErrorCovariance = [ 1e+070 0 0 0 0 0 ; 0 1e+070 0 0 0 0 ; 0 0 1e+070 0 0 0 ; 0 0 0 1e+070 0 0 ; 0 0 0 0 1e+070 0 ; 0 0 0 0 0 1e+070 ];
GMAT OmahaTrailSpacecraft.CdSigma = 1e+070;
GMAT OmahaTrailSpacecraft.CrSigma = 1e+070;
GMAT OmahaTrailSpacecraft.Id = 'SatId';
GMAT OmahaTrailSpacecraft.Attitude = CoordinateSystemFixed;
GMAT OmahaTrailSpacecraft.SPADSRPScaleFactor = 1;
GMAT OmahaTrailSpacecraft.ModelFile = 'aura.3ds';
GMAT OmahaTrailSpacecraft.ModelOffsetX = 0;
GMAT OmahaTrailSpacecraft.ModelOffsetY = 0;
GMAT OmahaTrailSpacecraft.ModelOffsetZ = 0;
GMAT OmahaTrailSpacecraft.ModelRotationX = 0;
GMAT OmahaTrailSpacecraft.ModelRotationY = 0;
GMAT OmahaTrailSpacecraft.ModelRotationZ = 0;
GMAT OmahaTrailSpacecraft.ModelScale = 1;
GMAT OmahaTrailSpacecraft.AttitudeDisplayStateType = 'Quaternion';
GMAT OmahaTrailSpacecraft.AttitudeRateDisplayStateType = 'AngularVelocity';
GMAT OmahaTrailSpacecraft.AttitudeCoordinateSystem = EarthMJ2000Eq;
GMAT OmahaTrailSpacecraft.EulerAngleSequence = '321';

%----------------------------------------
%---------- Formation
%----------------------------------------

Create Formation OTS;
GMAT OTS.Add = {OmahaTrailSpacecraft};

%----------------------------------------
%---------- ForceModels
%----------------------------------------

Create ForceModel MarsProp_ForceModel;
GMAT MarsProp_ForceModel.CentralBody = Mars;
GMAT MarsProp_ForceModel.PointMasses = {Mars, Sun};
GMAT MarsProp_ForceModel.Drag = None;
GMAT MarsProp_ForceModel.SRP = Off;
GMAT MarsProp_ForceModel.RelativisticCorrection = Off;
GMAT MarsProp_ForceModel.ErrorControl = RSSStep;

Create ForceModel EarthProp_ForceModel;
GMAT EarthProp_ForceModel.CentralBody = Earth;
GMAT EarthProp_ForceModel.PointMasses = {Earth};
GMAT EarthProp_ForceModel.Drag = None;
GMAT EarthProp_ForceModel.SRP = Off;
GMAT EarthProp_ForceModel.RelativisticCorrection = Off;
GMAT EarthProp_ForceModel.ErrorControl = RSSStep;

Create ForceModel SunProp_ForceModel;
GMAT SunProp_ForceModel.CentralBody = Sun;
GMAT SunProp_ForceModel.PointMasses = {Sun, Earth, Luna};
GMAT SunProp_ForceModel.Drag = None;
GMAT SunProp_ForceModel.SRP = Off;
GMAT SunProp_ForceModel.RelativisticCorrection = Off;
GMAT SunProp_ForceModel.ErrorControl = RSSStep;

%----------------------------------------
%---------- Propagators
%----------------------------------------

Create Propagator MarsProp;
GMAT MarsProp.FM = MarsProp_ForceModel;
GMAT MarsProp.Type = RungeKutta89;
GMAT MarsProp.InitialStepSize = 60;
GMAT MarsProp.Accuracy = 1e-012;
GMAT MarsProp.MinStep = 0.001;
GMAT MarsProp.MaxStep = 2700;
GMAT MarsProp.MaxStepAttempts = 50;
GMAT MarsProp.StopIfAccuracyIsViolated = true;

Create Propagator EarthProp;
GMAT EarthProp.FM = EarthProp_ForceModel;
GMAT EarthProp.Type = RungeKutta89;
GMAT EarthProp.InitialStepSize = 60;
GMAT EarthProp.Accuracy = 1e-012;
GMAT EarthProp.MinStep = 0.001;
GMAT EarthProp.MaxStep = 86400;
GMAT EarthProp.MaxStepAttempts = 50;
GMAT EarthProp.StopIfAccuracyIsViolated = true;

Create Propagator SunProp;
GMAT SunProp.FM = SunProp_ForceModel;
GMAT SunProp.Type = RungeKutta89;
GMAT SunProp.InitialStepSize = 60;
GMAT SunProp.Accuracy = 9.999999999999999e-012;
GMAT SunProp.MinStep = 0.001;
GMAT SunProp.MaxStep = 160000;
GMAT SunProp.MaxStepAttempts = 50;
GMAT SunProp.StopIfAccuracyIsViolated = true;

%----------------------------------------
%---------- Burns
%----------------------------------------

% DRL EM Launch to Mars Periapsis
Create ImpulsiveBurn TOI;
GMAT TOI.CoordinateSystem = Local;
GMAT TOI.Origin = Mars;
GMAT TOI.Axes = VNB;
GMAT TOI.Element1 = 0;
GMAT TOI.Element2 = 0;
GMAT TOI.Element3 = 0.94;
GMAT TOI.DecrementMass = false;
GMAT TOI.Isp = 382;
GMAT TOI.GravitationalAccel = 9.810000000000001;

% Mars Periapsis Burn to Approximate Earth Intercept
Create ImpulsiveBurn EarthTxfr;
GMAT EarthTxfr.CoordinateSystem = Local;
GMAT EarthTxfr.Origin = Mars;
GMAT EarthTxfr.Axes = VNB;
GMAT EarthTxfr.Element1 = -1.55;
GMAT EarthTxfr.Element2 = 0;
GMAT EarthTxfr.Element3 = 0;
GMAT EarthTxfr.DecrementMass = false;
GMAT EarthTxfr.Isp = 382;
GMAT EarthTxfr.GravitationalAccel = 9.810000000000001;

%----------------------------------------
%---------- Coordinate Systems
%----------------------------------------

Create CoordinateSystem MarsMJ2000Eq;
GMAT MarsMJ2000Eq.Origin = Mars;
GMAT MarsMJ2000Eq.Axes = MJ2000Eq;

Create CoordinateSystem SunMJ2kEc;
GMAT SunMJ2kEc.Origin = Sun;
GMAT SunMJ2kEc.Axes = MJ2000Ec;

Create CoordinateSystem SunMJ2kEq;
GMAT SunMJ2kEq.Origin = Sun;
GMAT SunMJ2kEq.Axes = MJ2000Eq;

Create CoordinateSystem EarthSunRot;
GMAT EarthSunRot.Origin = Earth;
GMAT EarthSunRot.Axes = ObjectReferenced;
GMAT EarthSunRot.XAxis = R;
GMAT EarthSunRot.ZAxis = N;
GMAT EarthSunRot.Primary = Sun;
GMAT EarthSunRot.Secondary = Earth;

%----------------------------------------
%---------- Solvers
%----------------------------------------

Create DifferentialCorrector TOIDC;
GMAT TOIDC.ShowProgress = true;
GMAT TOIDC.ReportStyle = Normal;
GMAT TOIDC.ReportFile = 'DifferentialCorrectorTOIDC.data';
GMAT TOIDC.MaximumIterations = 25;
GMAT TOIDC.DerivativeMethod = ForwardDifference;
GMAT TOIDC.Algorithm = NewtonRaphson;

%----------------------------------------
%---------- Subscribers
%----------------------------------------

Create OrbitView MarsMJ2KView;
GMAT MarsMJ2KView.SolverIterations = None;
GMAT MarsMJ2KView.UpperLeft = [ 0 0.3382899628252788 ];
GMAT MarsMJ2KView.Size = [ 0.7997630331753555 0.8463444857496902 ];
GMAT MarsMJ2KView.RelativeZOrder = 15;
GMAT MarsMJ2KView.Maximized = true;
GMAT MarsMJ2KView.Add = {OmahaTrailSpacecraft, Sun, Earth, Mars, Deimos};
GMAT MarsMJ2KView.CoordinateSystem = MarsMJ2000Eq;
GMAT MarsMJ2KView.DrawObject = [ true true true true ];
GMAT MarsMJ2KView.DataCollectFrequency = 1;
GMAT MarsMJ2KView.UpdatePlotFrequency = 50;
GMAT MarsMJ2KView.NumPointsToRedraw = 0;
GMAT MarsMJ2KView.ShowPlot = true;
GMAT MarsMJ2KView.ShowLabels = true;
GMAT MarsMJ2KView.ViewPointReference = Mars;
GMAT MarsMJ2KView.ViewPointVector = [ 20000 -5000 20000 ];
GMAT MarsMJ2KView.ViewDirection = Mars;
GMAT MarsMJ2KView.ViewScaleFactor = 2;
GMAT MarsMJ2KView.ViewUpCoordinateSystem = MarsMJ2000Eq;
GMAT MarsMJ2KView.ViewUpAxis = Z;
GMAT MarsMJ2KView.EclipticPlane = Off;
GMAT MarsMJ2KView.XYPlane = On;
GMAT MarsMJ2KView.WireFrame = Off;
GMAT MarsMJ2KView.Axes = On;
GMAT MarsMJ2KView.Grid = Off;
GMAT MarsMJ2KView.SunLine = Off;
GMAT MarsMJ2KView.UseInitialView = On;
GMAT MarsMJ2KView.StarCount = 7000;
GMAT MarsMJ2KView.EnableStars = On;
GMAT MarsMJ2KView.EnableConstellations = Off;

Create OrbitView EclipticView;
GMAT EclipticView.SolverIterations = Current;
GMAT EclipticView.UpperLeft = [ 0 0 ];
GMAT EclipticView.Size = [ 0.7997630331753555 0.8463444857496902  ];
GMAT EclipticView.RelativeZOrder = 17;
GMAT EclipticView.Maximized = true;
GMAT EclipticView.Add = {OmahaTrailSpacecraft, Sun, Earth, Mars};
GMAT EclipticView.CoordinateSystem = SunMJ2kEq;
GMAT EclipticView.DrawObject = [ true true true true ];
GMAT EclipticView.DataCollectFrequency = 10;
GMAT EclipticView.UpdatePlotFrequency = 200;
GMAT EclipticView.NumPointsToRedraw = 0;
GMAT EclipticView.ShowPlot = true;
GMAT EclipticView.ShowLabels = true;
GMAT EclipticView.ViewPointReference = Sun;
GMAT EclipticView.ViewPointVector = [ 0 0 600000000 ];
GMAT EclipticView.ViewDirection = Sun;
GMAT EclipticView.ViewScaleFactor = 1;
GMAT EclipticView.ViewUpCoordinateSystem = SunMJ2kEq;
GMAT EclipticView.ViewUpAxis = Z;
GMAT EclipticView.EclipticPlane = Off;
GMAT EclipticView.XYPlane = On;
GMAT EclipticView.WireFrame = Off;
GMAT EclipticView.Axes = On;
GMAT EclipticView.Grid = Off;
GMAT EclipticView.SunLine = Off;
GMAT EclipticView.UseInitialView = On;
GMAT EclipticView.StarCount = 7000;
GMAT EclipticView.EnableStars = On;
GMAT EclipticView.EnableConstellations = Off;

%----------------------------------------
%---------- Mission Sequence
%----------------------------------------

BeginMissionSequence;
Maneuver BackProp TOI(OmahaTrailSpacecraft);
Propagate 'Propagate to Mars Periapsis' MarsProp(OTS) {OmahaTrailSpacecraft.Mars.Periapsis};
Maneuver BackProp EarthTxfr(OmahaTrailSpacecraft);
Propagate 'Propagate to Approximate Earth Intercept' MarsProp(OTS) {OmahaTrailSpacecraft.ElapsedDays = 195};





« Last Edit: 12/20/2017 06:47 PM by LMT »

Offline Lar

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Re: Space Elevator for Mars
« Reply #93 on: 12/20/2017 08:02 PM »
Code like that usually is just given as a text file attachment rather than pasted in en masse, but that's a nit.

I applaud showing your work this way. Keep it up. There is a reason that everyone is urging you to show your numbers, show your calculations, show your work in general... you're the one making claims, you get to back them up. You do NOT get to push any work onto those challenging your calculations.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Online meberbs

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Re: Space Elevator for Mars
« Reply #94 on: 12/21/2017 12:26 AM »
Ah, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.

Delta-v Example:  DRL & Gravity Assist

If used efficiently, tethered systems at Mars, such as Deimos Dock, Deimos Rail Launcher (DRL) and Mars Lift could improve flight efficiency significantly. 

Example:  M/E transit with the Omaha Trail's proposed DRL.

Here 0.94 km/s DRL delta-v launches to Mars periapsis, and gravity assist.  At periapsis a small burn of 1.55 km/s gives approximate transfer to Earth.  This is a Mars perihelion transfer; near aphelion, the burn delta-v is less, ~0.8 km/s.

Options:  The Deimos Dock propellant load could be minimized for minimum periapsis delta-v, or else maximized for greater delta-v or greater payload.
Thank you, that gives some numbers to work with.

First a couple notes about your numbers:
Quote
GMAT OmahaTrailSpacecraft.DryMass = 850;
...
GMAT EarthTxfr.DecrementMass = false;
GMAT EarthTxfr.Isp = 382;
Spacecraft mass is 85 tons dry (85000 kg), plus cargo (to compare with SpaceX's architecture  apples to apples, 50 tons return to Earth)
Isp of raptor vacuum is 375.
Neither of these matter, because you are telling the sim to ignore fuel consumption.

This is fine, but now you need to apply the rocket equation to determine fuel consumption. I'll do it for you this time to demonstrate the magnitude of the fuel consumed.

You would use 26.7% of your fuel for a 1 km/s delta v (towards the low end of the range you listed.) For the 1.55 km/s delta V, you would use 38.6% of your fuel, calling this a "small" delta-V does not seem accurate.

You would then lose fuel in transit to Earth (boil off), spend fuel during earth capture and rendezvous with another ship. Your architecture expects you to then fully fuel that other ship for it to transfer to Mars while still reserving propellant to land on Earth. This is clearly impossible because of how much fuel is spent just leaving Mars.

You also appear to be using a roughly Hohmann transfer, compared to the fast transfers that SpaceX plans on.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #95 on: 01/01/2018 09:49 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.

Happy to see you point this out. Acceleration gradient isn't symmetrical about the balance point's circular orbit. It always makes me gnash my teeth when I hear people say it'd take a 36,000 km length above geosynchronous orbit to balance the 36,000 km length below. (Actually it'd take about a 100,000 km length).

But acceleration gradient gets more symmetrical as you get closer to the balance point's circular orbit. I attached a pic of acceleration gradient. You can see the top of the "hill" is less lopsided.

In the case of the two lunar cube sats, the upper and lower points are only separated by 180 kilometers.

Let's say the ends of this tether each mass a tonne. If the balance point's circular orbit is at 100 kilometers altitude the cube sat 90 kilometers below this orbit would exert a downward force of 2.25 newtons and the upper end 90 kilometers above the circular orbit would exert an upward force of 2.04 newtons.

In the case of that proposed lunar mission, the balance point is very close to the COM. It is a forgivable approximation. Still, I wish they hadn't given it that label, it helps to perpetuate a popular misconception.
« Last Edit: 01/01/2018 09:52 PM by Hop_David »

Offline Nilof

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Re: Space Elevator for Mars
« Reply #96 on: 01/02/2018 02:46 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.

You can tether an orbital ring to the surface to make it stable, since it can be built just above the atmosphere. The point where the tethers to the ground attach can be used to exchange momentum with the body it orbits. That's something that Niven's ringworld couldn't do.

With that said, Mars is so much smaller than Earth that the advantages of an orbital ring don't make a lot of sense. You can use aerobraking to land, and for going up, building a mass driver on one of Mars's giant volcanoes makes more sense. The top of Olympus Mons is close enough to a vacuum, with a pressure more than two orders of magnitude lower than the pressure at the exit of the proposed Startram.

With that said, a good Mars SSTO should have a payload fraction on the order of 50% so *shrugs*. There's not that much point in using launch assists. Mars orbit delta-v is in the range where chemical propulsion comes reasonably close to the optimal energy efficiency for delivering things to orbit, and Mars SSTO's can be built with way more margin than Earth-based launchers.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #97 on: 01/02/2018 06:13 PM »
You can tether an orbital ring to the surface to make it stable, since it can be built just above the atmosphere.

If the rotor (the super-orbiting ring) is fully enclosed and evacuated, you could actually build it inside the atmosphere.

With that said, Mars is so much smaller than Earth that the advantages of an orbital ring don't make a lot of sense.

Not for Mars. Certainly not with a large anchor mass so conveniently close to the planet. The tether length/mass from Phobos leaves any orbital ring, or mass accelerator, or other launch/entry assist system for dead. And can drop the delta-v for launch down to below 1km/s.

OTOH, once orbital rings were a standard technology, proven around the Earth and the moon, it's likely that a Mars colony would say "Me too". They make everything so much easier. I don't need to drive my car to work, but it's much more convenient.

Offline Nilof

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Re: Space Elevator for Mars
« Reply #98 on: 01/02/2018 09:05 PM »
Orbital rings are not a form of space launch by themselves. They are just a convenient platform to build a mass driver above the atmosphere. You still need to build some kind of accelerator on your orbital ring. The top of Olympus Mons happens to give you a nice platform with an atmospheric pressure comparable to Earths atmosphere at 60 km altitude, without having to build your own.


As for space tethers, several of the posts here seem to overstate the utility of a tidally locked tether. In an earlier space elevator thread, I made some computations for a climber and came to the conclusion that trying to climb a space elevator with chemical energy is strictly less efficient than getting to orbit with a chemical rocket. So space elevators and tidally locked tethers in general require a dedicated remotely-powered climber vehicle with good performance to outperform chemical.

It would be more efficient to use a rotating tether in order to do the tethered equivalent of a gravity assist to steal orbital energy from Phobos.
« Last Edit: 01/03/2018 01:32 AM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline LMT

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Re: Space Elevator for Mars
« Reply #99 on: 01/03/2018 01:42 AM »
As for space tethers, several of the posts here seem to overstate the utility of a tidally locked tether. In an earlier space elevator thread, I made some computations for a climber and came to the conclusion that a space elevator with chemical energy is strictly less efficient than getting to orbit with a chemical rocket. So space elevators and tidally locked tethers in general require a dedicated remotely-powered climber vehicle with good performance to outperform chemical.

Climber & Rappeller Utility

Yes, a climber would need something other than chemical energy.  Even HVDC power lines are inefficient and unsuitable over MSE distances.  It may be that areosync PV + a superconducting tether power line will be needed, to power an MSE climber system with performance superior to Mars launch.

A cargo descent rappeller is more efficient than a climber:  it uses 0 kW.  :)  And it does so while saving the tremendous energy that would otherwise be devoted to propellant manufacture on Mars, for the cargo ship's surface launch. 

There's utility in that, yes?

It would be more efficient to use a rotating tether in order to do the tethered equivalent of a gravity assist to steal orbital energy from Phobos.

Centripetal Tethers & Rail Launchers

Dr. Lades looked at a locked Phobos L1 (lower) tether for cargo delivery, as in slides 46-47, but couldn't find an economic case.  As for an upper tether, of course David did his own analysis; e.g., a 6155 km tether for Earth return of small masses. 

If David's centripetal launch tether were feasible on Phobos, it would also be feasible on Deimos, and at least as useful.  And as David noted, "...parking at Deimos would save a lot of time and delta V." 

One would deploy this tether from a Deimos base station much as the DRL was itself deployed.  (tether added at lower right)



The 1 AU centripetal tether would give delta-v to Earth only slightly greater than that of the DRL, and it would launch a smaller mass.  Would this be enough to justify construction?  Maybe not.  But Deimos is envisioned as a proving ground, so perhaps this first centripetal tether could serve as proof-of-concept: a precursor to even stronger and longer tethers for greater launches, to the asteroid belt and beyond. 

Conceivably a greater Deimos centripetal tether could be scaled to accommodate ITS mass, for extension of the Omaha Trail.  To that end we can note also that helical coil launchers are bidirectional, accelerating in either direction by design.  So one might reduce the centripetal tether's very great tension by incorporating this tether within a new DRL; one having shorter length than a stand-alone tether.  This DRL would launch not inward toward Mars, but outward.  Here the DRL acceleration and centripetal acceleration would be additive, and cumulatively very great, if all forces can be managed.

Q:  Might the synergy between DRL acceleration and centripetal acceleration be a key to efficient and rapid transit from Mars to, say, Callisto?

Q:  How might a rotator be usefully incorporated, if at all?

« Last Edit: 01/03/2018 02:17 AM by LMT »

Offline Nilof

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Re: Space Elevator for Mars
« Reply #100 on: 01/03/2018 03:15 AM »
Quote
Climber & Rappeller Utility

Yes, a climber would need something other than chemical energy.  Even HVDC power lines are inefficient and unsuitable over MSE distances.  It may be that areosync PV + a superconducting tether power line will be needed, to power an MSE climber system with performance superior to Mars launch.

A cargo descent rappeller is more efficient than a climber:  it uses 0 kW.  :)  And it does so while saving the tremendous energy that would otherwise be devoted to propellant manufacture on Mars, for the cargo ship's surface launch.

There's utility in that, yes?

Mars surface to mars escape is 5.2 km/s. Mars surface to the foot of a 1400 lower phobos tether is 4.1 km/s. Going from Mars surface to Phobos the traditional way takes 5 km/s.

You need the really ambitious versions of the lower Phobos tether to gain a substantial benefit from the rest of the system compared to just burning from LMO with an Oberth benefits. Otherwise, you just spent most of your delta-v alternative cost budget to get to Phobos, and you save a few hundred m/s of delta-b budget at best.

So it really boils down to Mars SSTO vs Mars suborbital vehicle + beamed power climber hybrid vs mass driver.

I think a more likely use for a Rapeller could be with a 1400 km tether to drop cargo to LMO in order to build infrastructure there.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline LMT

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Re: Space Elevator for Mars
« Reply #101 on: 01/03/2018 04:43 AM »
I think a more likely use for a Rapeller could be with a 1400 km tether to drop cargo to LMO in order to build infrastructure there.

As regards the rappeller, it's used more effectively on the Mars Lift as given.  Dropping off cargo at Arestation and rappelling it to Mars obviates the need for suborbital transfer craft launch and landing, and the associated propellant manufacture on Mars.  It's not hard to make the business case for Omaha Trail cargo, vis-a-vis the upper/lower tethered system. 

--

And yes, the budget required to reach a Phobos tether from Mars, for transit in either direction, is considerable.  It does seem to consume the desired savings of the upper/lower tethered system.  Also some practical issues of Phobos cargo delivery were noted in Dr. Lades' talk.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #102 on: 01/03/2018 03:20 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.

Okay so we've eliminated the enclosing ring continuously accelerating the projectiles

Then the projectiles flying at faster than orbital velocity would not be flying a nice circular orbit from one platform to another. You would have to aim the ricochet to hit the next platform. See illustration below

Holding the platforms aloft by continuously ricocheting machine gun bullets poses some engineering challenges. How far apart are the platforms? What precision is needed in directing the ricochets?

I can imagine some spectacular failure modes with this scheme as well.
« Last Edit: 01/03/2018 03:22 PM by Hop_David »

Offline Paul451

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Re: Space Elevator for Mars
« Reply #103 on: 01/03/2018 06:46 PM »
Okay so we've eliminated the enclosing ring continuously accelerating the projectiles
Then the projectiles flying at faster than orbital velocity would not be flying a nice circular orbit from one platform to another.
You would have to aim the ricochet to hit the next platform.

You might want to read up on orbital rings, you seem to be thinking of it as a passive tube. The concept is that the particles are magnetically accelerated (not "ricocheted") faster than orbital velocity. It's like a launch-loop, but around the entire world. It wouldn't work if the particles were just in a natural circular orbit. The centripetal acceleration of the particles keeps the useful structure aloft.

My point was that if you damage one of the magnetic guides, the others would need to redirect to compensate. But they'll need to do that anyway whenever parts of the system is under maintenance. And I suspect they'll be constantly doing that based on the natural variability in the ring anyway.

But explaining how it works is off-topic for this thread, especially zombied from back in August. If you want to dig around, there might be an existing thread in Advanced Concepts that would be more appropriately re-animated.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #104 on: 01/03/2018 08:43 PM »
It wouldn't work if the particles were just in a natural circular orbit.

That was my point. You had altered my illustration of a continuous circular ring. You removed the ring  but left the projectiles still sailing nicely along circular paths from one platform to another.

But the paths would look more like straight lines.

So rather than constant acceleration along a circular ring, you'd have discreet, abrupt accelerations at the corners of a large polygon.

Below I drew the projectiles being magnetically redirected from one platform to another.

My objections remain.

It would take very precise aiming to send a projectile from one platform to another thousands of kilometers away. The projectile would have to hit the exact center of the platform or it would set the platform spinning instead of halting and reversing it's downward fall.

In the case of earth based platforms 60 degrees apart and approximating the hyperbolic paths as straight lines, the change in vertical velocity component would be about the same the projectile speed. How fast are the projectiles moving? 10 km/s? 16 km/s? That's a very drastic velocity change in a very short time. How many g's would the projectile endure? How many g's to the platform? The pusher plate in the boom boom Orion vehicle comes to mind.

But explaining how it works is off-topic for this thread, especially zombied from back in August. If you want to dig around, there might be an existing thread in Advanced Concepts that would be more appropriately re-animated.

Isaac Arthur's scheme was off topic back in August as well (in my opinion). But I address the August arguments because Nilof just responded to them within the past few days. If you like, you can open a new thread on Isaac Arthur's orbital rings.

Offline LMT

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Re: Space Elevator for Mars
« Reply #105 on: 01/05/2018 06:27 AM »
No Tankers

Notably, one of the benefits of the Omaha Trail proposal is that cargo flights can be launched without dedicated tanker ships. 

No tankers at all.  Just returning cargo ships.

This could be especially beneficial to the construction phase of SpaceX's Mars City, which could take decades.  The work might go 10x faster at Omaha Crater, but still, it's a benefit.



Cargo flight staging. Deimos propellant. Mars Lift space elevator in gold.

Depot

That slide didn't garner comment, but it shows on-orbit depot use, an ambition at SpaceX and elsewhere.

Quote from: Elon Musk
By establishing a propellant depot in the asteroid belt or one of the moons of Jupiter, you can make flights from Mars to Jupiter, no problem.

Quote from: Charles Miller
...produce propellant [from water in the lunar soil]. You’d put that in a propellant depot in lunar orbit to allow humans to go anywhere in the solar system.

Here the depot is at Deimos, with propellant shuttled to LEO.  Typical #s, allowing notional 55 t propellant reserves:

(1) Burn 397 t of 1008 t propellant after DRL, for transit and LEO circularization.

(2) Launch cargo to LEO.

(3) Transfer 540 t in LEO.

(4) Burn 16 t for EDL.

(5) Burn 540 t for transit and Mars Lift Arestation circularization.

Option:  To double payload, (1) is performed with 1066 t propellant load, twice, filling tanks in (3).  A second Earth launch transfers the second cargo.  With full tanks (5) delivers 300 t to Arestation.

All is done without an Earth tanker fleet, tanker booster fleet, and their propellant.  Cost savings would follow efficiency. 
« Last Edit: 01/08/2018 01:21 AM by LMT »

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Re: Space Elevator for Mars
« Reply #106 on: 01/05/2018 02:49 PM »
That slide didn't garner comment, but it shows in-orbit depot use, an ambition at SpaceX and elsewhere.
False. My previous post was directly discussing that slide. Your claims in it are wrong, and the claimed numbers you just provided make this easy to show.

Here the depot is at Deimos, with propellant shuttled to LEO.  Typical #s, allowing notional 55 t propellant reserves:

(1) Burn 397 t of 1008 t propellant after DRL, for transit and LEO circularization.
Not sure why you are limiting yourself to 1008 t instead of the 1100 that constitutes a full load of the tanks.
Also, I get that to just do the 1.55 km/s burn to get on an Earth trajectory it would take 399 t with your claimed propellant load and the 50 t cargo needed for this architecture to be compared to SpaceX's.

This does not include losses in transit or LEO circularization.

(2) Launch cargo to LEO.

(3) Transfer 540 t in LEO.

This allows you 4.385 km/s delta-v in total. (Cargo is 150 tons for direct comparison of course) Typically LEO to MTO takes 4.3 km/s on its own, and that is not for fast transfers. If you want to get straight back to Deimos like you show, you would need to burn the same 0.94 km/s to circularize at Deimos that the rail launcher gave you on the way out, and that is assuming you accurately hit the aerocapature, getting into the exact desired capture orbit and have very accurate timing of the transfer as well.

(4) Burn 16 t for EDL.
I'm curious where you got this number, I don't think anyone outside SpaceX has a good idea how much fuel is needed forth this on BFR, there are too many unknowns.

Option:  To double payload, (1) is performed with 1066 t propellant load, twice, filling tanks in (3).  A second Earth launch transfers the second cargo.  With full tanks (5) delivers 300 t to Arestation.
Not going to bother with this since it  obviously just has larger problems than the first plan.

Note that the extra 92 tons I mentioned that you could start with would also cause an extra 25 t to be lost in the initial burn from Earth, and then with the losses in transit and LEO circularization, this will not come close to rescuing your plan.

All is done without an Earth tanker fleet, tanker booster fleet, and their propellant.  Cost savings would follow efficiency.
SpaceX is planning to fully fill up the ship's fuel before departing for Mars. They aren't doing this for no reason, so it should be obvious that your plan to only half fuel the ship will not work. None of the claimed benefits would emerge.
« Last Edit: 01/05/2018 02:50 PM by meberbs »

Offline LMT

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Re: Space Elevator for Mars
« Reply #107 on: 01/06/2018 09:01 PM »
Cargo Depot Redo

False. My previous post was directly discussing that slide.

Your architecture expects you to then fully fuel that other ship for it to transfer to Mars

compare with SpaceX's architecture  apples to apples, 50 tons return to Earth

No, you didn't mention the slide, and your text is not consistent with that flight plan.

There's no need to "fully fuel" cargo ships in LEO.  That's required only for crewed missions, where delta-v must be maximized.  Different flight plan.

Also there's no cargo on the return flight.  These cargo ships never land on Mars.  So unless you assume a booming market for Deimos cinder block at Home Depot, return cargo is naturally 0 t.

To discuss a particular flight plan, paste the image and reference the numbered steps; that'll keep your text clear.

Not sure why you are limiting yourself to 1008 t

Because that's the minimum needed.  We add more for options, such as doubled payload.

to just do the 1.55 km/s burn to get on an Earth trajectory it would take 399 t with your claimed propellant load and the 50 t cargo needed for this architecture to be compared to SpaceX's.

This does not include losses in transit or LEO circularization.

As we noted previously, perihelion requires ~1.55 km/s, aphelion requires ~0.8 km/s.  "Typical" #s are intermediate, not the extremes.  For example, 1.16 km/s.   

Then we tacked on 0.5 km/s for circularization.  (Your 0.94 km/s reasoning isn't right, and typical #s are smaller.)

As for losses, long-duration tankage scenarios expect some ZBOT method.  Any further loss would get some of the 92 t left at Deimos.

I'm curious where you got this number, [Burn 16 t for EDL.]

ITS drops 99%+ of KE aerodynamically, leaving only a landing burn.  We used a 40 s hover.

I don't think anyone outside SpaceX has a good idea how much fuel is needed forth this on BFR

"Fuel"?  "Propellant".  :)  Redo the cargo flight plan to see how the numbers improve.

Online meberbs

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Re: Space Elevator for Mars
« Reply #108 on: 01/06/2018 11:32 PM »
No, you didn't mention the slide, and your text is not consistent with that flight plan.
I shouldn't have to explicitly mention the slide, it should be obvious that is what I was discussing, and it follows your mission plan exactly, other than pointing out that you have entirely insufficient fuel. 

There's no need to "fully fuel" cargo ships in LEO.  That's required only for crewed missions, where delta-v must be maximized.  Different flight plan.
Wrong, please read the numbers in the post I just made again. You do not have anywhere near enough fuel for what you are proposing. I suggest you actually think about the fact that SpaceX is not planning to use fewer tankers for cargo vs. crew flights and why this is their plan.

Also there's no cargo on the return flight.
Wrong, look at SpaceX's architecture again.

These cargo ships never land on Mars.  So unless you assume a booming market for Deimos cinder block at Home Depot, return cargo is naturally 0 t.
Your architecture still involves transport capability from Mars surface, no reason cargo could only come from Deimos.

Not sure why you are limiting yourself to 1008 t

Because that's the minimum needed.  We add more for options, such as doubled payload.
Except as I showed it is nowhere near enough. Doubled payload would fail even with full tanks.

to just do the 1.55 km/s burn to get on an Earth trajectory it would take 399 t with your claimed propellant load and the 50 t cargo needed for this architecture to be compared to SpaceX's.

This does not include losses in transit or LEO circularization.

As we noted previously, perihelion requires ~1.55 km/s, aphelion requires ~0.8 km/s.  "Typical" #s are intermediate, not the extremes.  For example, 1.16 km/s.
Your architecture is basically useless unless it works every window, not just when you get an easy window. You need to plan for the worst case.

Then we tacked on 0.5 km/s for circularization.  (Your 0.94 km/s reasoning isn't right, and typical #s are smaller.)
The 0.5 km/s should be conservative for circularization at Earth after aerocapture, however as my calculation showed, you actually allowed less than 0 km/s for this.

The 0.94 number has nothing to do with the LEO circularization, and everything to do with the fact that you used 0.94 km/s to get from Deimos to an elliptical orbit with a periapsis close to Mars. In the best case scenario, that is also the orbit you would end up in after an aerocapture maneuver (actually you would need a lower periapsis to be deep enough in the atmosphere, but that just makes things worse for you). Circularizing that elliptical orbit to match Deimos takes exactly the same delta-v as entering that orbit from Deimos took in the other direction.

As for losses, long-duration tankage scenarios expect some ZBOT method.  Any further loss would get some of the 92 t left at Deimos.
Unfortunately for you, SpaceX is not using ZBOT, and their method of reducing boil off is to vent the outer tanks for greatly improved insulation. You can't do this, since you need the fuel that is in the outer tanks.

I'm curious where you got this number, [Burn 16 t for EDL.]

ITS drops 99%+ of KE aerodynamically, leaving only a landing burn.  We used a 40 s hover.
99% KE is for direct landing on Mars from MTO. Your use of it in this case is simply ignoring the deorbit burn entirely. It also isn't a number that is necessarily very exact. The 40s hover that you guessed doesn't mean much on its own. It depends on how many engines at what throttle.

Redo the cargo flight plan to see how the numbers improve.
No, you redo the numbers without using assumptions that contradict your architecture, and without assuming best case transfer windows, and without ignoring the fuel needed to circularize at Deimos.

Offline LMT

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Re: Space Elevator for Mars
« Reply #109 on: 01/10/2018 06:41 AM »
No, you didn't mention the slide, and your text is not consistent with that flight plan.
I shouldn't have to explicitly mention the slide, it should be obvious that is what I was discussing, and it follows your mission plan exactly, other than pointing out that you have entirely insufficient fuel.

Not at all.  The given, specific cargo flight plan has no requirements or assumptions for full LEO tanks or 50 t return cargo -- and of course in this flight plan there's no Mars landing for a 50-t cargo pickup anyway. 

So our mass and delta-v numbers work as given, with corresponding efficiency improvements over SpaceX baseline.  The numbers shouldn't be very surprising, especially given the familiarity of the route and spacecraft.

Then we tacked on 0.5 km/s for circularization.  (Your 0.94 km/s reasoning isn't right, and typical #s are smaller.)
The 0.94 number has nothing to do with the LEO circularization, and everything to do with the fact that you used 0.94 km/s to get from Deimos to an elliptical orbit with a periapsis close to Mars. In the best case scenario, that is also the orbit you would end up in after an aerocapture maneuver (actually you would need a lower periapsis to be deep enough in the atmosphere, but that just makes things worse for you). Circularizing that elliptical orbit to match Deimos takes exactly the same delta-v as entering that orbit from Deimos took in the other direction.

That reasoning is quite wrong.  The delta-v coming off the DRL by no means sets the delta-v for aerocapture circularization. 

For one thing, the DRL launch vector is certainly not the most efficient for lowering periapsis; so it's not the delta-v that one must "take".  That's easy to see with the example GMAT script: tweak the DRL VNB to reach the same periapsis using much less than 0.94 km/s delta-v.

Example vectors:

GMAT TOI.Element1 = 0.5;
GMAT TOI.Element2 = 0;
GMAT TOI.Element3 = 0.5; 

GMAT TOI.Element1 = 0.64;
GMAT TOI.Element2 = 0;
GMAT TOI.Element3 = 0;

Second, the mission literature shows you what's actually needed for circularization.  In one Lockheed Martin flight plan the spacecraft changes plane and circularizes to Deimos with a pair of burns totaling 607 m/s delta-v.



In an ITS cargo plan MOI is aerocapture, with aerodynamic plane change.  This removes propulsive plane change, lowering the burns for Arestation down toward 0.5 km/s.

But the rocket equation and orbit changes are, by themselves, OT.  Focus should be on possibilities for the Mars Space Elevator and related tether systems.

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Re: Space Elevator for Mars
« Reply #110 on: 01/10/2018 08:41 AM »
Not at all.  The given, specific cargo flight plan has no requirements or assumptions for full LEO tanks or 50 t return cargo -- and of course in this flight plan there's no Mars landing for a 50-t cargo pickup anyway. 
50 tons return cargo is part of the SpaceX baseline you claim to be comparing to, you can't just throw out capability and claim your system is equivalent but more efficient.

Full LEO tanks isn't an assumption, it is a fact of what SpaceX has presented as their plan.

So our mass and delta-v numbers work as given, with corresponding efficiency improvements over SpaceX baseline.  The numbers shouldn't be very surprising, especially given the familiarity of the route and spacecraft.
No, your numbers don't work. You have simply ignored most of what I wrote, and have made no attempt to do things like update your numbers to account for worst case transfer windows.

Then we tacked on 0.5 km/s for circularization.  (Your 0.94 km/s reasoning isn't right, and typical #s are smaller.)
The 0.94 number has nothing to do with the LEO circularization, and everything to do with the fact that you used 0.94 km/s to get from Deimos to an elliptical orbit with a periapsis close to Mars. In the best case scenario, that is also the orbit you would end up in after an aerocapture maneuver (actually you would need a lower periapsis to be deep enough in the atmosphere, but that just makes things worse for you). Circularizing that elliptical orbit to match Deimos takes exactly the same delta-v as entering that orbit from Deimos took in the other direction.

That reasoning is quite wrong.  The delta-v coming off the DRL by no means sets the delta-v for aerocapture circularization. 

For one thing, the DRL launch vector is certainly not the most efficient for lowering periapsis; so it's not the delta-v that one must "take".  That's easy to see with the example GMAT script: tweak the DRL VNB to reach the same periapsis using much less than 0.94 km/s delta-v.

...

Second, the mission literature shows you what's actually needed for circularization.  In one Lockheed Martin flight plan the spacecraft changes plane and circularizes to Deimos with a pair of burns totaling 607 m/s delta-v.
I just used the number you provided for simplicity, assuming that you had bothered to orient the vector in close to optimal direction. I figured that a maneuver like in the picture you posted could reduce the delta-V some, but the order of magnitude is still the same. As I showed you barely have enough fuel transferred to get to MTO from LEO (using your number for transferred fuel rather than a corrected value.) You would have less than 100 m/s remaining in a typical case, so it doesn't matter whether you need 600 or 900 m/s for the last step, my point remains the same.

But the rocket equation and orbit changes are, by themselves, OT.  Focus should be on possibilities for the Mars Space Elevator and related tether systems.
You brought up your plan for supposedly improving on the BFR system using your tether architecture for Deimos-Mars transport. Pointing out that your numbers don't add up is on topic if your architecture is. (And if not your architecture can be split off into a separate topic.)

You have simply ignored multiple of the points I made about the flaws in your plan and analysis. I have stuck to ones provable with straightforward numbers, no point in bringing up the others when you can't recognize these.

Offline stefan r

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Re: Space Elevator for Mars
« Reply #111 on: 01/10/2018 08:41 PM »

(1) Burn 397 t of 1008 t propellant after DRL, for transit and LEO circularization.


Why LEO circularized?  The shuttle already has a tether attachment.  Seems like a waste of momentum. 

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Re: Space Elevator for Mars
« Reply #112 on: 01/12/2018 04:25 AM »
I just used the [DRL] number you provided for simplicity, assuming that you had bothered to orient the vector in close to optimal direction.

?  The DRL vector isn't remotely "close to optimal direction", obviously.  You don't seem to understand VNB impulse.  You might "look it up," as you put it.  OT here.

The given, specific cargo flight plan has no requirements or assumptions for full LEO tanks or 50 t return cargo -- and of course in this flight plan there's no Mars landing for a 50-t cargo pickup anyway. 
50 tons return cargo is part of the SpaceX baseline you claim to be comparing to, you can't just throw out capability and claim your system is equivalent but more efficient.

Full LEO tanks isn't an assumption, it is a fact of what SpaceX has presented as their plan.

Oh, it's fair comparison because equivalent and properly calculated.  Same ship, same cargo, out and back, with and without Omaha Trail infrastructure.  "150 out / 0 back" is naturally the baseline ITS requirement.   

Each variation on cargo and crewed flights is calculated and compared separately.  We don't mix willy-nilly.

--

SpaceX hasn't proposed an Omaha Trail themselves.  But if tomorrow SpaceX proposed it under their own logo, I'm pretty sure no one would say, "But this isn't the plan!  They can't claim this is more efficient!"  More likely folks would brainstorm ways to deliver tunnel-boring machines and Tesla Roadsters by elevator.  ;)

Quote from: Rob Manning, Universe Today
"Mars is really begging for a space elevator," said Manning. "I think it has great potential. That would solve a lot of problems, and Mars would be an excellent platform to try it."

Online meberbs

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Re: Space Elevator for Mars
« Reply #113 on: 01/12/2018 06:45 AM »
I just used the [DRL] number you provided for simplicity, assuming that you had bothered to orient the vector in close to optimal direction.

?  The DRL vector isn't remotely "close to optimal direction", obviously.  You don't seem to understand VNB impulse.  You might "look it up," as you put it.  OT here.

I already said why I was wrong and why it doesn't matter, but let me rephrase since you seem to have not read my post.

I didn't bother looking at what vector you used in what frame, so the issue has nothing to do with my understanding of the frame. The 940 m/s seemed to be (and is, your next post showed that in a practical example, the answer is around 600 m/s) the correct order of magnitude, so I took the path of not doing more math, since my experience told me that the number was in the correct ballpark.

The real issue that you are failing to address is that you don't have the available delta V for any of these trajectories.

The given, specific cargo flight plan has no requirements or assumptions for full LEO tanks or 50 t return cargo -- and of course in this flight plan there's no Mars landing for a 50-t cargo pickup anyway. 
50 tons return cargo is part of the SpaceX baseline you claim to be comparing to, you can't just throw out capability and claim your system is equivalent but more efficient.

Full LEO tanks isn't an assumption, it is a fact of what SpaceX has presented as their plan.

Oh, it's fair comparison because equivalent and properly calculated.  Same ship, same cargo, out and back, with and without Omaha Trail infrastructure.  "150 out / 0 back" is naturally the baseline ITS requirement.   
Only if you ignore SpaceX's stated cargo return capability, so no that is not the baseline. When you are comparing to SpaceX the baseline is what SpaceX stated, 150 out and 50 back, not something you made up.

Maybe you didn't understand their presentation, they are using basically the same ship for cargo or crew the capability is the same either way.

SpaceX hasn't proposed an Omaha Trail themselves.  But if tomorrow SpaceX proposed it under their own logo, I'm pretty sure no one would say, "But this isn't the plan!  They can't claim this is more efficient!"  More likely folks would brainstorm ways to deliver tunnel-boring machines and Tesla Roadsters by elevator.
SpaceX wouldn't propose what you have themselves because the numbers don't work out. If they did people would add up the numbers and point out that fact. (This has already happened on this site, notably in L2 when people added up some numbers and determined the BFR rocket dimensions did not make sense. It turns out one of the numbers was out of date or miscommunicated, and their prediction came close to the actual dimension)

Quote from: Rob Manning, Universe Today
"Mars is really begging for a space elevator," said Manning. "I think it has great potential. That would solve a lot of problems, and Mars would be an excellent platform to try it."
Mars could be a great location for a space elevator, but your proposed use of it in combination with BFR simply does not work the way you claim it does.

Please stop ignoring all of the problems I have pointed out.

Offline alexterrell

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Re: Space Elevator for Mars
« Reply #114 on: 01/28/2018 07:16 PM »
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.


If you wanted to move Phobos to a higher orbit, you would build an elevator to near Mars, and lower a substantial fraction of Phobos' mass to a release point. I'm not sure what the Coriolis force would do dynamically to the cable though.

As it's lowered, Phobos would rise up. If it's released as small particles, they descend harmlessly to the surface.

Still a huge amount of mass to move - perhaps enough to build a O'Neil type cylinder inside Phobos. Or perhaps it';; be needed to prevent Phobos disintegration if a lot of material is being exported in other direction. (Either towards escape, or to build MSO colonies and mirrors) 

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Re: Space Elevator for Mars
« Reply #115 on: 03/06/2018 03:27 AM »
The real issue that you are failing to address is that you don't have the available delta V

No, our very first thread presentation gave the novel propellant and delta-v numbers for the Omaha Trail.  Anyone could plug those numbers into the rocket equation, to compare against famous Earth/Mars baseline, and verify.  That much is easy.

You, Paul451 and Lar imagined otherwise, and ignored the presentation numbers. 

--

The Pendulum

If we want to drive the bus, we have to gas it up.  And if we want to justify a LEO propellant depot, we have to deliver propellant to LEO with great efficiency.  The most efficient system wins, all things being equal.

A DRL improves the efficiency of Deimos ISRU by increasing the delivered propellant load, but DRL benefit is limited by the Deimos / L2 tether launch geometry.  A DRL delta-v above 1 km/s intercepts Mars; course correction is needed, requiring propulsive maneuver at Mars, and reducing delivered load.  This caps net efficiency. 

An EM DRL delta-v of 1.9 km/s could, if vectored optimally, execute Earth-return without rocket propulsion.  Getting that vector is the first trick. 

GMAT modeling indicates that the 1.9 km/s DRL launch must be angled about 15 degrees off the Deimos / L2 line in order to pass above Mars and intercept Earth. 

How to get the 15-degree launch angle?

The DRL terminates at a counterweight.  Tapping the counterweight sets up an oscillation.  It's visually similar to a pendulum, but it differs in that varying gravitational and centripetal accelerations act on the counterweight and tether.  We can view the system as a "quasi-pendulum". 

Goal:

If this quasi-pendulum can be designed to give an oscillation period that's in resonance with Deimos' orbit, the launch window can be scheduled at the top of the pendular swing, where the tether's angle is at maximum.  The angle (swing amplitude) required for Earth-return is about 15 degrees.

Method:

A 2-D physical simulation of the Mars/Deimos system was used, with DRL tether and counterweight.  Properties of the tether, counterweight and perturbation force were systematically adjusted, to produce a table of quasi-pendulum oscillations.  The table was examined for useful swing amplitudes and swing/orbit resonances.

Result:

A DRL tether with length of 2500 km responds to a 60 m/s transverse perturbation of the counterweight by entering a quasi-pendulum oscillation having amplitude of 15 degrees.  This is the required Earth-return angle, and the 2500-km length is more than adequate for gentle DRL acceleration producing the required 1.9 km/s delta-v.



Oscillation period is about 20 hours.  This sets a 3:2 resonance with Deimos' 30.3-hour orbit.

In consequence, the DRL is aligned for Earth-launch every 2 Deimos days.  That is, the launch window opens every 60.6 hours.

Each pair of ITS tankers launching on the pendular DRL aerobrakes at Earth with tanks full.  This represents a nearly ideal efficiency of delivery to the LEO depot.

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Re: Space Elevator for Mars
« Reply #116 on: 03/06/2018 02:20 PM »
The real issue that you are failing to address is that you don't have the available delta V

No, our very first thread presentation gave the novel propellant and delta-v numbers for the Omaha Trail.  Anyone could plug those numbers into the rocket equation, to compare against famous Earth/Mars baseline, and verify.  That much is easy.

You, Paul451 and Lar imagined otherwise, and ignored the presentation numbers. 
That presentation is obviously from before IAC 2017, so the numbers in it are inconsistent to begin with.

We have plugged the numbers in for you in this thread. They do not add up even ignoring things like boil off.

An EM DRL delta-v of 1.9 km/s could, if vectored optimally, execute Earth-return without rocket propulsion.  Getting that vector is the first trick. 
Just to be clear here, you are proposing a 2500km 370 km long rail launcher connected to a 2500km teather, which will have to support itself under variable gravity gradients. This could only support 1 launch every 2.5 days, so a maximum of about 25 launches assuming a 2 month window. (Feel free to show the calculations if you think you could squeeze more in than that per alignment, remembering that you need to calculate dV needed for worst case Mars-Earth alignments)

By the time there is resources at Mars for a project on that scale, we will want more than 30 BFS per year of combined cargo and crew.

There is still the problem that even if this does allow you to leave Mars with no spent propellant, you still haven't even taken a guess at how much boil off will occur.

Edit: calculated it and realized that you weren't talking about the launcher itself being 2500km long, it would "only" be 370 km for 0.5 g acceleration

Added: It is good that you are working on ideas to fix the problems that you had previously with your plan, but you would have more credibility doing so if you actually acknowledged the existence of the problems, rather than dismissing them with an irrelevant reference. As it is, your history of making best (or near-best) case assumptions makes me question if the 1.9 km/s would even work for all transfer windows, and what kind of transfer times it allows.
« Last Edit: 03/06/2018 04:48 PM by meberbs »

Offline LMT

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Re: Space Elevator for Mars
« Reply #117 on: 03/07/2018 04:22 AM »
This could only support 1 launch every 2.5 days, so a maximum of about 25 launches assuming a 2 month window...
By the time there is resources at Mars for a project on that scale, we will want more than 30 BFS per year of combined cargo and crew.

?  The DRL is always shown with paired launches, for balance; it's twice the launch rate you imagined. 

That's the rate for one pendular DRL -- and there's no cosmic limit of one.

i.e., roll out another.   ::)

--

Steam Engine

The envisioned pendular DRL delivers full tanks to Earth aerobrake.  However some propellant is used after aerobrake, for final orbit circularization to LEO depot. 

Q:  Can even that small burn be eliminated, to achieve perfect delivery efficiency?

Consider cargo flights: 



On the Omaha Trail, return flights (1) load methalox at Deimos Dock.  As cargo ships unload only at Arestation (5), they have no return cargo.

However one cargo can be loaded at Deimos Dock:  water. 

Water can act as a safe supplemental propellant.  A tiny water resistojet can be integrated into the water piping, to give a supplemental steam impulse.

Quantifying the challenge:  it's circularization from low aerobrake elliptical orbit down to LEO depot, using a "steam engine":

- Delta-v:  500 m/s

- ISP: 200 s

- Mass without water:  1185 t

Can an ITS cargo ship load enough water to do the job, and achieve perfect delivery efficiency?  We plug numbers into the rocket equation and find...


Online meberbs

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Re: Space Elevator for Mars
« Reply #118 on: 03/07/2018 06:00 AM »
This could only support 1 launch every 2.5 days, so a maximum of about 25 launches assuming a 2 month window...
By the time there is resources at Mars for a project on that scale, we will want more than 30 BFS per year of combined cargo and crew.

?  The DRL is always shown with paired launches, for balance; it's twice the launch rate you imagined. 
See slide 37 of the presentation you just linked. I can see now how you may have intended that to be 2 perspectives, with both being dual launch, but I never would have guessed that based on the BFR not being rotated in the images. I haven't seen you state with words that it is always dual launches before now. You can't expect people to magically get that knowledge from simplistic sketches.

That's the rate for one pendular DRL -- and there's no cosmic limit of one.

i.e., roll out another.   ::)
It is a major infrastructure project to just build 1. That part of the infrastructure needing to be duplicated for additional launch rates has a notable impact on your design feasibility.

The envisioned pendular DRL delivers full tanks to Earth aerobrake.
It doesn't matter what you envision, reality says that you will have lost significant propellant to boil off, and will lose quite a bit more before the propellant gets used. BFS does not have ZBOT, and it does not even have low boil off except when the outer tanks are empty.

As cargo ships unload only at Arestation (5), they have no return cargo.
As I said before, return cargo is part of the SpaceX architecture you are comparing to. If you want a fair comparison you don't get to eliminate that.

Offline LMT

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Re: Space Elevator for Mars
« Reply #119 on: 03/07/2018 06:36 PM »
I haven't seen you state with words that it is always dual launches before now.

The pairing is sensible and illustrated clearly in presentation, even with power and energy numbers to quantify launch of the tanker pair.  That's easy to see, and it's reiterated on this very page, viz:

Quote from: LMT
Each pair of ITS tankers launching on the pendular DRL aerobrakes at Earth...

--

We have plugged the numbers in for you in this thread. They do not add up

"We" have?  :)  No, you haven't demonstrated, because our numbers are ok.  Also you've struggled with spaceflight basics here, meberbs.  So don't repeat an untrue statement, but make corrections before moving forward.

--

Quote from: LMT
Can an ITS cargo ship load enough water to do the job, and achieve perfect delivery efficiency?  We plug numbers into the rocket equation and find...

344 t. 

And yes.

--

Hop_David, haven't heard from you.  You know tethers.  Got any rope tricks we might try, out on the Trail?



Online meberbs

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Re: Space Elevator for Mars
« Reply #120 on: 03/07/2018 07:18 PM »
We have plugged the numbers in for you in this thread. They do not add up

"We" have?  :)  No, you haven't demonstrated, because our numbers are ok.  Also you've struggled with spaceflight basics here, meberbs.  So don't repeat an untrue statement, but make corrections before moving forward.
You are the one making untrue claims and who has struggled with basics.

As a reminder of recent posts:
(2) Launch cargo to LEO.

(3) Transfer 540 t in LEO.

This allows you 4.385 km/s delta-v in total. (Cargo is 150 tons for direct comparison of course) Typically LEO to MTO takes 4.3 km/s on its own, and that is not for fast transfers. If you want to get straight back to Deimos like you show, you would need to burn the same 0.94 km/s to circularize at Deimos that the rail launcher gave you on the way out, and that is assuming you accurately hit the aerocapature, getting into the exact desired capture orbit and have very accurate timing of the transfer as well.
And then in the same chain:
That reasoning is quite wrong.  The delta-v coming off the DRL by no means sets the delta-v for aerocapture circularization. 

For one thing, the DRL launch vector is certainly not the most efficient for lowering periapsis; so it's not the delta-v that one must "take".  That's easy to see with the example GMAT script: tweak the DRL VNB to reach the same periapsis using much less than 0.94 km/s delta-v.

...

Second, the mission literature shows you what's actually needed for circularization.  In one Lockheed Martin flight plan the spacecraft changes plane and circularizes to Deimos with a pair of burns totaling 607 m/s delta-v.
I just used the number you provided for simplicity, assuming that you had bothered to orient the vector in close to optimal direction. I figured that a maneuver like in the picture you posted could reduce the delta-V some, but the order of magnitude is still the same. As I showed you barely have enough fuel transferred to get to MTO from LEO (using your number for transferred fuel rather than a corrected value.) You would have less than 100 m/s remaining in a typical case, so it doesn't matter whether you need 600 or 900 m/s for the last step, my point remains the same.

That chain shows me admitting to a bad assumption on my part, accepting your correction that insertion would only require about 600 m/s rather than 900 m/s. At the same time it shows you ignoring my point that you only would have 85 m/s available (typical, not even worst case), which is clearly less than either number for insertion at Mars.

I made a correction to my statement, you have yet to admit to any mistakes, I just provided one out of multiple examples of your mistakes that have been pointed out.

Offline LMT

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Re: Space Elevator for Mars
« Reply #121 on: 03/08/2018 08:19 PM »
Perfect Pendular Pitch

The DRL has a free plane of pendular oscillation.  This is useful for maintaining delivery efficiency. 

Method:

Like a true pendulum, the DRL quasi-pendulum's oscillation begins with perturbation of the weight.  Perturbation force vector is arbitrary, free; not restricted to the plane of Deimos' orbit.  Dial in the angle and magnitude, and tap.

Result:

Launch vector can be set for heliocentric trajectory in the ecliptic plane.

Tankers need no propulsive burn for inclination change, irrespective of planetary alignment.

Therefore tankers maintain excellent, even perfect, delivery efficiency.  Anytime, every time.
« Last Edit: 03/09/2018 02:36 AM by LMT »

Offline LMT

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Re: Space Elevator for Mars
« Reply #122 on: 03/09/2018 03:21 AM »
That presentation is obviously from before IAC 2017, so the numbers in it are inconsistent to begin with.

You didn't check those numbers, or even note them, so you can't make a claim, and shouldn't.  The numbers in both presentations are internally consistent; they were calculated with the version of ITS contemporaneous, as should be expected.

--

Your Base

Where to site the first Mars Elevator base station?  Some considerations in context of the Omaha Trail's Mars Lift:

With off-equator elevators, the feasible payload fraction decreases as the base station latitude and tether-angle increase (angle being measured from vertical at base).  Payload fraction follows angle cosine.

Example sites are given in Dr. Lades' Mars Lift analysis.  Two candidate base station sites were considered, to anchor a relatively strong tether having specific strength of 13.3 MYuri.



Pinnacle Station is at 12.65 degrees S.  Tether angle is 20 degrees, so payload fraction is 94%.



Elevator Peak is at 18.0 degrees S.  Tether angle is 28 degrees, so payload fraction is 88%.

Payload drops quickly from that point.  30 degrees latitude approaches the maximum practical limit.  The minimum limit is set by the need to avoid Phobos; this minimum latitude may be as high as 10 degrees.  Therefore the useful range of latitudes for the Mars Lift base station may be roughly 10-30 degrees.

Pinnacle Station was considered for the interesting geological history of Morava Valles.  Elevator Peak was considered for its great elevation (6200 m).  Many other sites could serve as well as these.

Q:  What are some other sites deserving consideration? 

What other sites between 10 and 30 degrees latitude have important histories, intriguing properties or resources that recommend themselves for an elevator base station? 

One consideration:  The first base station would be a prime logistics hub.  The surrounding region would therefore be positioned for the first extensive scientific study.  Great scientific prospects are therefore a +1 for a candidate site.

One other consideration:  Dr. Lades presently feels that an off-equator tether is most readily affixed to its base station by ground transit.  That is, by lowering the tether to the equator, capturing it on a weighted mobile platform, and then "driving" the platform to the off-equator site.  Therefore a site that is readily accessible by "off-road vehicle" is +1.  Giant chasms, dust bowls and sarlacci are -1.  Google Mars perspective views might help with notional route planning.

We'll keep interesting sites in mind as we calculate options for the next Omaha Trail presentation.


« Last Edit: 03/10/2018 06:15 PM by LMT »

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