Author Topic: Envisioning Amazing Martian Habitats  (Read 259254 times)

Offline biosehnsucht

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Re: Envisioning Amazing Martian Habitats
« Reply #1480 on: 03/09/2018 09:06 PM »
If the power fails, the cables would fall down, right? Probably bad for any structure underneath (but at least it's not a falling orbital elevator). Can you use Lorentz forces to pull them into position initially, then reinforce them after the fact with supports? Don't need to be supports holding them in exact shape, just such that if power fails they don't fall down totally, if they sag some between supports that's fine until the power is back, I'd assume.

What sort of strain occurs at the outer edges where they are anchored to the ground/structure? Is it trying to pull itself from the structure due to Lorentz forces, or does it act more like a solid dome structure sitting on top of walls, held down by gravity? I'm guessing the cables are in the open Martian atmosphere, not themselves a solid pressurized space, so we don't have to worry about buoyancy ripping them off their moorings, just balancing gravity / mass of the structure and Lorentz forces (and any anti-sag/collapse reinforcements to protect against power loss).

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #1481 on: 03/09/2018 09:33 PM »
If the power fails, the cables would fall down, right?

They're superconductors, so the power cables themselves need no power supply once charged.

The kW power is just for refrigerant replenishment.  If that power system failed, you'd shunt some of the stored power out of the cables into the refrigeration system, as backup.  If that situation persisted for several days, the cables would eventually settle toward the ground, as Lorentz force very slowly decreases.

What sort of strain occurs at the outer edges where they are anchored to the ground/structure? Is it trying to pull itself from the structure due to Lorentz forces, or does it act more like a solid dome structure sitting on top of walls, held down by gravity?

Actually the current would just be calibrated to balance net upward Lorentz force against the weight of primary cable (red), when in operation 1.5 km above the return cable.  With balancing, the primary cable exerts only small horizontal force on the anchor pylon. 

The return cable (purple), would experience downward Lorentz force + weight.  As in our original Omaha Field proposal, light suspension cabling would hold the return cable horizontal.  Anchor pylons would support the suspension cabling.

I'm guessing the cables are in the open Martian atmosphere, not themselves a solid pressurized space, so we don't have to worry about buoyancy ripping them off their moorings, just balancing gravity / mass of the structure and Lorentz forces (and any anti-sag/collapse reinforcements to protect against power loss).

Well, cables would have a tiny vacuum insulation space, but no significant buoyancy, no.  And yes, a balancing of forces and the low cable unit mass should keep the architecture manageable. 
« Last Edit: 03/13/2018 01:12 AM by LMT »

Offline Paul451

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Re: Envisioning Amazing Martian Habitats
« Reply #1482 on: 03/09/2018 11:41 PM »
If the power fails, the cables would fall down, right?
They're superconductors, so the power cables themselves need no power supply once charged.

"Power failure" generally means a failure of the active, not the drain.

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #1483 on: 03/10/2018 04:28 PM »
https://www.alibaba.com/product-detail/2-Generation-High-Temperature-Superconductor-tape_50013334401.html
I find it amusing it's now off-the-shelf.

Test Sites

Off-the-shelf is good.  Superconductor cable tech is generally mature, used daily for example at fusion research centers.  So it may be that a demo of an Omaha Field on Earth, while not trivial, isn't very interesting.  Perhaps the interesting test would be lunar.

Rationale:

Polar craters are candidate sites for a first lunar base.  Shoemaker, for example.  It seems to have a little ice as per the neutron count; maybe enough ice in spots for ISRU experiments like LOX production.



A polar network of PV panels can have overlapping illumination to supply power continually, as from the 6 peaks marked on Bussey et al. 2010.



Shoemaker is in continual shade.  It's deep enough to keep Omaha Field cables in continual shade as well, to minimize refrigeration requirement.  Here a small site of, say, 10 km2, could be protected from cosmic rays by the Omaha Field, and using little power or LOX, all well within capability of even the smallest base infrastructure.

Because most required tech is mature, in some cases off-the-shelf, a system could be designed and constructed in advance of a lunar base initiative, even a rapidly-advancing one.  Deployment would be concurrent with the first temporary residency.  Should the system suffer failure, temporary residents would not incur a great radiation dose, as they return to Earth soon anyway.  Of course you'd want to learn from failures and perfect the system prior to long-term residency.

And no one has to live underground.

Q:  What are the most mature and applicable lunar hardware designs available today?  e.g., designs for lunar LOX plants, suspension-cable systems, and lightweight pylons.  Such designs can extend the initial thought experiment, or factor into some future Mars design.

Refs:

Bussey, D. B. J., McGovern, J. A., Spudis, P. D., Neish, C. D., Noda, H., Ishihara, Y., & Sørensen, S. A. (2010). Illumination conditions of the south pole of the Moon derived using Kaguya topography. Icarus, 208(2), 558-564.

Wright, E. LEND Looks for Water at the South Pole (2013).  NASA/Goddard Space Flight Center.

--

Addendum on Power and Communication:

A smaller, separate magnetostatic system might serve quite different infrastructure roles in this lunar scenario, providing continuous power and continuous line-of-sight communication with Earth

Solar panels at Connecting Ridge site CR1 in Vanoutryve et al. 2010 (marked up above with red circle in lower left quadrant, and also marked as "B" down below) can have continuous illumination if raised at least 20 m above the surface.  Uninterrupted line-of-sight with Earth would require that the communication platform be raised about 3 km.  Ideally one system would meet both requirements at that site, or at another elevated site analyzed by Vanoutryve et al.

Both requirements might be met with a two-cable magnetostatic system.  Lorentz force draws the two primary cables together and can raise them to 3 km height.  Opposite-facing solar panels could be suspended from the cables to create a pair of PV "walls" for continuous power.  A line-of-sight communication platform would be mounted at apex. 

If the solar panels were designed with reflective backing, they could provide a sunshield to the suspended cables, to cool them and perhaps keep LOX refrigerant requirement manageable.  Room temperature keeps superconductor refrigeration manageable on Earth, so perhaps here as well, if LOX production is robust.

Also, in this system the return cables would be simplified as straight cables, without solenoids, because surface magnetic flux density is not an issue at this uninhabited infrastructure site.



Refs:

Vanoutryve, B., De Rosa, D., Fisackerly, R., Houdou, B., Carpenter, J., Philippe, C., ... & Gardini, B. (2010). An analysis of illumination and communication conditions near lunar south pole based on Kaguya Data. 7th, 10.
« Last Edit: 03/11/2018 05:33 AM by LMT »

Offline biosehnsucht

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Re: Envisioning Amazing Martian Habitats
« Reply #1484 on: 03/12/2018 09:29 PM »
That's very interesting, if the failure mode due to loss of power is just a gradual settling, might not do any damage to structures below.

Though I'd still think some kind of basic support would be good in case of some kind of damage that stops the superconducting flow ?

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #1485 on: 03/13/2018 12:53 AM »
That's very interesting, if the failure mode due to loss of power is just a gradual settling, might not do any damage to structures below.

Right.  It's a reversal of deployment. 

One method:  In deployment each primary cable is initially wrapped around a tensioned spool system at the pylons.  As deployment begins superconducting current increases.  Lorentz force exceeds weight and spool tension, so that the primary cable spools out toward operational height.  When you lose power, or just want to lower the cable for maintenance, you decrease superconducting current and Lorentz force, so that tension slowly wraps the cable around the spool again.

Though I'd still think some kind of basic support would be good in case of some kind of damage that stops the superconducting flow ?

To manage superconductor failure, quench protection would be expected, but cable redundancy also protects the system.  For example the ENEA-TRATOS cable design has five independent tape stacks, for five independent currents.  If one tape stack overheats, its current is shunted to the quench protector, and the other four tape stacks continue to operate. 

Result:  Lorentz force decreases by only 1/5, and the cable remains suspended.

--

A loss of all five tape stacks would of course drop the cable.   (And of course you wouldn't place an important structure right on a cable drop path.)

One method to manage:  Increase spool take-up speed to match.  Under lunar gravity a dropped cable would need 43 seconds to fall 1.5 km, so high-speed take-up during fall should be feasible.  When the remaining taut cable reaches pylon top, adjust the spool tension to allow a small play-out that gives a constant deceleration.   When the cable's fall is arrested, lock the spool. 

--

Of course many methods of cable management are conceivable.  What methods might be better?
« Last Edit: 03/13/2018 01:11 AM by LMT »

Offline speedevil

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Re: Envisioning Amazing Martian Habitats
« Reply #1486 on: 03/13/2018 01:36 AM »
Of course many methods of cable management are conceivable.  What methods might be better?
Don't insulate the cable stacks from each other?
Or provide shorting bridges very regularly?


Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #1487 on: 03/13/2018 02:59 PM »
Of course many methods of cable management are conceivable.  What methods might be better?
Don't insulate the cable stacks from each other?
Or provide shorting bridges very regularly?

Hmm.  Are you thinking of some in-cable quench protection method, perhaps?  But wouldn't the stack contacts also remove redundancy, by spreading hotspots across tape stacks?  Can you expand a bit?  Thanks.

Offline speedevil

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Re: Envisioning Amazing Martian Habitats
« Reply #1488 on: 03/13/2018 03:13 PM »
Of course many methods of cable management are conceivable.  What methods might be better?
Don't insulate the cable stacks from each other?
Or provide shorting bridges very regularly?

Hmm.  Are you thinking of some in-cable quench protection method, perhaps?  But wouldn't the stack contacts also remove redundancy, by spreading hotspots across tape stacks?  Can you expand a bit?  Thanks.

If your cable is in one enclosure with one thermal environment, heat from a quenched strand is going to be shared across all strands, so if you've got enough heat to make a hotspot spread, then it risks spreading across the whole cable.

If however, the strands are tied together electrically occasionally, what happens instead is as that as one spot quenches, the current is immediately taken up by the other strands, and there is no generated heat, as there is no current flow in the cable that's gone resistive, leading to the possibility that it can become superconducting again if there was some transitory issue.

I need to think about this properly and read the above paper in more depth.

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #1489 on: 03/16/2018 08:26 PM »
Of course many methods of cable management are conceivable.  What methods might be better?
Don't insulate the cable stacks from each other?
Or provide shorting bridges very regularly?

Hmm.  Are you thinking of some in-cable quench protection method, perhaps?  But wouldn't the stack contacts also remove redundancy, by spreading hotspots across tape stacks?  Can you expand a bit?  Thanks.

If your cable is in one enclosure with one thermal environment, heat from a quenched strand is going to be shared across all strands, so if you've got enough heat to make a hotspot spread, then it risks spreading across the whole cable.

If however, the strands are tied together electrically occasionally, what happens instead is as that as one spot quenches, the current is immediately taken up by the other strands, and there is no generated heat, as there is no current flow in the cable that's gone resistive, leading to the possibility that it can become superconducting again if there was some transitory issue.

I need to think about this properly and read the above paper in more depth.

Cold Steel

I was just thinking you'd want to isolate the hotspot within the originating tape stack, for safety.  The selection of cable core material could do that.  For example, looking at that ENEA-TRATOS design, if you replace their aluminum core with austenitic stainless steel, you get a core having much lower thermal conductivity than the tape stacks.  Result:  the core is a relative thermal insulator, isolating a hotspot within its originating tape stack.

--

And yes, the quench protector would quickly remove current and prevent further heating in the warmed tape stack.  However if the cause of the hotspot were not obviously an eddy current transient, I think you'd want to lower the cable for inspection before firing up that specific circuit again.  If a physical defect were the cause, it would likely be located within that one tape stack.

--

Incidentally, stainless steel also has exceptional and maximized fracture toughness at those cryogenic temperatures.  Implication:  stainless steel enables safe use of high cable tension, as for example in the (hopefully very unlikely) emergency of free-fall cable arrest.

Refs:

Bonura, M., & Senatore, C. (2015). Transverse thermal conductivity of REBCO coated conductors. IEEE Transactions on Applied Superconductivity, 25(3), 1-4.

Duthil, P. (2015). Material properties at low temperature. arXiv preprint arXiv:1501.07100.
« Last Edit: 03/16/2018 08:28 PM by LMT »

Online jpo234

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You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Online jpo234

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You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Online KelvinZero

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Re: Envisioning Amazing Martian Habitats
« Reply #1492 on: 09/03/2018 07:53 AM »
One of my hobby horses is that although terraforming is hard, oceanforming is easy. All over the solarsystem there are icy worlds (and mars has ice caps 4km thick) and if we buried ourselves in them our waste heat would trivially begin building ocean environments with all the basics for life: pressure, temperature between freezing and boiling, radiation protection.

(Some worlds already have oceans of course but the point is it is not important. Our waste heat will create them anyway. There is no cost, in fact a way of disposing arbitrary amounts of waste heat is a convenience)

If we mastered self sufficient lifestyles under water on earth then these might translate easily to the rest of the solar system.

Im not sure if this clip is the most relevant, but it is very pretty.



(edit: wrong clip)
« Last Edit: 09/03/2018 07:54 AM by KelvinZero »

Offline aero

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Re: Envisioning Amazing Martian Habitats
« Reply #1493 on: 09/06/2018 11:16 PM »
I was just wondering if anyone has a good handle on the lapse rate of the atmosphere and the temperature profile of the upper crust on Mars.

The reason is that evacuated caverns deep down may be doable if the temperature and atmospheric pressure provide any advantage to using such caverns in which to construct facilities. Reaching ~5psi pressure would be a significant benefit allowing survival with only an oxygen mask for breathing.

Another way of asking the question above is, "What would the atmospheric pressure at the bottom of a 30 km deep shaft on Mars?" And what would the rock temperature be at the bottom of a 30 km deep shaft on Mars?" Then substitute your best guess at a practical depth and use that instead of 30 km in these questions. I have used "shaft" as in "elevator shaft" which could be used for both surface access and cooling atmosphere flow.
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Online KelvinZero

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Re: Envisioning Amazing Martian Habitats
« Reply #1494 on: 09/06/2018 11:27 PM »
I did a search and found this calculation by RobotBeat:

Excavating a portion of Hellas Planitia deep enough that the surface pressure is above the Armstrong Limit.
« Last Edit: 09/06/2018 11:31 PM by KelvinZero »

Offline aero

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Re: Envisioning Amazing Martian Habitats
« Reply #1495 on: 09/07/2018 01:24 AM »
I did a search and found this calculation by RobotBeat:

Excavating a portion of Hellas Planitia deep enough that the surface pressure is above the Armstrong Limit.

https://forum.nasaspaceflight.com/index.php?topic=22046.msg608359#msg608359

That was an interesting read, evacuating an open pit but the idea here is an elevator shaft down to depth. Atmospheric pressure would increase down a shaft just the same as down an open pit. Robobeat calculates about 18 km deep below Hellas basin to get enough pressure but doesn't consider the natural temperature of the rock at that depth. On Earth, rock temperature goes up quickly with depth and I don't think Mars is totally dead. I don't know what the temperature gradient is though.

A shaft would be easier to dig, easier to seal against collapse and equally useful to transfer human-generated heat from the facility at the bottom. It all depends on what the actual rock temperature is at depth. And of course, the lack of something much better being developed before digging such a shaft becomes doable in the future. It seems to me that something better should come along.

Edit Add:
KelvinZero's idea, posted elsewhere, of just filling the elevator shaft with water would be easier. Just make the shaft a little oversized then convert the elevator car to a bathysphere with watertight seals around the lower exit door. That is, the lower exit would be a water lock, like an airlock only working underwater instead of in a vacuum. This system would hold atmospheric pressure as long as the cavern with facilities at the bottom was deep enough so that the overburden could prevent a blowout.
« Last Edit: 09/07/2018 04:50 AM by aero »
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Offline Paul451

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Re: Envisioning Amazing Martian Habitats
« Reply #1496 on: 09/07/2018 02:25 PM »
Robobeat calculates about 18 km deep below Hellas basin to get enough pressure but doesn't consider the natural temperature of the rock at that depth. On Earth, rock temperature goes up quickly with depth and I don't think Mars is totally dead. I don't know what the temperature gradient is though.

The googles says 8℃/km. So ~140-150℃ above surface temp at Hellas. Not good.

But if you're able to afford to dig a great big, multi-km deep hole. Sealing a fail-safe roof across a much shallower shaft seems pretty basic.

KelvinZero's idea, posted elsewhere, of just filling the elevator shaft with water would be easier.

Given that ~26m of water gives one atm of downward pressure, it's not only easier, it's not even in the same league as digging a multi-km shaft.



As an aside, the vapour pressure from water alone is almost the same as Mars' atmospheric pressure. Ie, at that pressure of water-vapour, boil-off stops. Note: Of water vapour. Doesn't help you outside, since it's a partial-pressure thing. However, if you merely stop the exchange of water-vapour and Mars air, by having an unpressurised door, you won't lose water from the water-lock once it hits vapour pressure. Hence ideally, the water temperature would be kept at the level needed to reduce the vapour pressure to ambient Mars air pressure. But in most places, that's around or just below freezing. (610pa at 0℃, 870pa at 5℃) So in practice, you'd want a low-pressure capable door. Say max difference 1 kpa. I assume you'd also have both an outer and inner door each capable of maintaining a full 1atm difference, as backup for failure elsewhere. But the water-lock lets you keep the inner-hatch open, and the water-vapour atmosphere in a low-pressure outer room lets you keep the outer hatch open. You only need a low-pressure door.

Assuming you aren't struggling for every drop of water (or you wouldn't have considered a water-lock), then you don't need to worry about losing a little water-vapour when you open the low-pressure door. Similarly, you don't need to pump it down into an air-tank, you just vent the door before opening. Depending on how fast the boil-off is from the water-lock when at ambient Mars pressure, you might even be able to leave the door unpressurised during the multi-hours long EVA. Just close it to stop the free exchange of water-vapour and Mars air, but leave the vents open.

If that low-pressure door fails, the only danger is the faster boil-off of water in the water-lock. Long, long time to repair it, to close the outer emergency hatch, or to close the inner hatch.

convert the elevator car to a bathysphere

Hardly a "bathysphere". By definition, the highest desirable pressure difference is 1atm.

Offline rakaydos

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Re: Envisioning Amazing Martian Habitats
« Reply #1497 on: 09/07/2018 04:46 PM »
I remember some older concepts that used certian oils that remain liquid at mars surface pressure for vapor locks. Is that a better option that water?

Offline Lar

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Re: Envisioning Amazing Martian Habitats
« Reply #1498 on: 09/07/2018 05:01 PM »
If you have a robust ISRU infrastructure including complex hydrocarbon synthesis, yes... otherwise you have to import all the oil so no (presumably)
"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 nacnud

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Re: Envisioning Amazing Martian Habitats
« Reply #1499 on: 09/07/2018 05:23 PM »
Maybe just float a small amount of oil on top of the water to stop it evaporating.