Author Topic: SpaceX's Martian Underground  (Read 51404 times)

Offline clongton

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Re: SpaceX's Martian Underground
« Reply #60 on: 01/26/2017 07:32 pm »
It might be better to rely on a cheaper prexisting Tunnel Boring Machine, The Universe, that has already created tunnels on Mars for us!

Caves and Lavatubes likely already exist on the surface and a survey of these and their extent with human and robotic assets would be a better starting off goal. Most of these lava tubes are probably not ideal for habitation or not close to useful resources but a few probably are and with an extensive enough survey, these could be discovered.

I recently visited a lava tube, on Lanzarote Island (part of the Canary Islands). I'm not a geologist, so this was all-new for me. In case y'all have never seen one, here's my report on that.

The tunnel starts from near sea level on the east side of the island, and goes uphill about 7 KM toward the summit of "La Corona". Our tour only went a about half a KM into it, starting at "Cueva de los Verdes", but I've seen a cross-section map that shows that it's continuous for most of the way. As shown on the JPG, another attraction, "Jameos del Agua", was a non-continuous but additional section, right on the Atlantic.

The graphics that I've seen some members here post, about having multiple, half-cylinder pressure habitats within a lava tube, wouldn't have worked in the one that I visited. It wasn't wide or high enough. I didn't take any measurements, but I'd estimate that the widest point that I saw was 50-60 feet, and the highest about 40 feet. And at that widest point, the ceiling was only 20 feet. Many sections were much tighter, including places where we had to stoop to pass thru, although I'm sure that with explosives or other equipment these could have been expanded. There was one section where there were actually two levels, so perhaps such an area could have supported a structure of 100 foot in height. Some areas had strangely smooth walls, but most of the ceilings were very jagged. In many places the floor was relatively flat, but still with fist-sized or bowling-ball-sized rocks all over. Rock in-falls were common, but again, I'm sure that these could be cleared with time and effort. I would estimate that we were about 100 feet underground for most of the tour.

Again, I'm no expert on this, so I defer to any of you who are.

40 feet wide and 20 feet high for several kilometers could house a pretty significant base. You don't need a blowup structure inside except to start off with. Seal the ends then pressurize.
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Offline Lar

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Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #62 on: 01/26/2017 08:50 pm »
It might be better to rely on a cheaper prexisting Tunnel Boring Machine, The Universe, that has already created tunnels on Mars for us!

Caves and Lavatubes likely already exist on the surface and a survey of these and their extent with human and robotic assets would be a better starting off goal. Most of these lava tubes are probably not ideal for habitation or not close to useful resources but a few probably are and with an extensive enough survey, these could be discovered.

I recently visited a lava tube, on Lanzarote Island (part of the Canary Islands). I'm not a geologist, so this was all-new for me. In case y'all have never seen one, here's my report on that.

The tunnel starts from near sea level on the east side of the island, and goes uphill about 7 KM toward the summit of "La Corona". Our tour only went a about half a KM into it, starting at "Cueva de los Verdes", but I've seen a cross-section map that shows that it's continuous for most of the way. As shown on the JPG, another attraction, "Jameos del Agua", was a non-continuous but additional section, right on the Atlantic.

The graphics that I've seen some members here post, about having multiple, half-cylinder pressure habitats within a lava tube, wouldn't have worked in the one that I visited. It wasn't wide or high enough. I didn't take any measurements, but I'd estimate that the widest point that I saw was 50-60 feet, and the highest about 40 feet. And at that widest point, the ceiling was only 20 feet. Many sections were much tighter, including places where we had to stoop to pass thru, although I'm sure that with explosives or other equipment these could have been expanded. There was one section where there were actually two levels, so perhaps such an area could have supported a structure of 100 foot in height. Some areas had strangely smooth walls, but most of the ceilings were very jagged. In many places the floor was relatively flat, but still with fist-sized or bowling-ball-sized rocks all over. Rock in-falls were common, but again, I'm sure that these could be cleared with time and effort. I would estimate that we were about 100 feet underground for most of the tour.

Again, I'm no expert on this, so I defer to any of you who are.

40 feet wide and 20 feet high for several kilometers could house a pretty significant base. You don't need a blowup structure inside except to start off with. Seal the ends then pressurize.

Totally agree! However . . .

You want a glassified tunnel surface to prevent zillions of small air leaks and act as its own pressure vessel.  Glass forced into cracks also acts as anchors to provide mechanical support for the walls and ceilings

I would think that a better idea would be to have a whole bunch of relatively small modules, which could be linked together, ad hoc. That would allow the arriving astronauts to set things up as the physical dimension limits allowed, and yet still use the lava tube for protection.

If you really could seal the the whole tube, as you suggest, that would be outstanding, but perhaps we should plan for something less ambitious at the beginning.

I'm uploading a few pix from my trip to the two sites on Lanzarote. Perhaps you all will find these instructive. The first 6 are from the long tube, which extends most of the way to the summit. The last one is from the place on the Atlantic, which is non-continuous with the rest of the lava tube. It is has cave-ins on both ends, with a shallow pond of collected rainwater inside of it.

« Last Edit: 01/26/2017 09:40 pm by pobermanns »

Offline guckyfan

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Re: SpaceX's Martian Underground
« Reply #63 on: 01/27/2017 09:37 am »
I would think that a better idea would be to have a whole bunch of relatively small modules, which could be linked together, ad hoc. That would allow the arriving astronauts to set things up as the physical dimension limits allowed, and yet still use the lava tube for protection.

In that case the lava tube would only provide radiation shielding. The habitats would still need to withstand the full habitat pressure. Not needing structural strength in habitats because the cave provides it is the main advantage over manufactured habitats.

Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #64 on: 01/27/2017 03:43 pm »
You want a glassified tunnel surface to prevent zillions of small air leaks and act as its own pressure vessel.  Glass forced into cracks also acts as anchors to provide mechanical support for the walls and ceilings

I'm uploading a few pix from my trip to the two sites on Lanzarote. Perhaps you all will find these instructive. The first 6 are from the long tube, which extends most of the way to the summit. The last one is from the place on the Atlantic, which is non-continuous with the rest of the lava tube. It is has cave-ins on both ends, with a shallow pond of collected rainwater inside of it.

Gorgeous photos.  They illustrate perfectly why lava tubes won't be used IMHO.  You'd have no idea about the mechanical strength and stability of the tube, and their wildly varying shapes and ragged edges would force you to tunnel through the tunnel to get some sort of standardized diameter- which you would then have to reinforce.

All of this would be done in a hard vacuum over months or years with materials brought from Earth, and they'd be small tools too because of shipping constraints.

So much safer, cheaper, and easier to use an electric TBM or welding subterrene and make a new tunnel, then only ship an airlock door, which you mount to the sealed walls.  You're already going to have to send up a huge powerplant, so it's not your limiting constraint.  The ITS diameter and mass to Mars is your limiting constraint.

And I haven't even broached the subject of longevity.  A glassified tunnel would exist for eons.  Anything less will not.  If we're serious about colonizing Mars with anything less than complete terraforming, then we need to think on the time scales of civilizations, not decades.

I'm not going to venture an opinion on drilling methods, 'cause I know less than zero about such things.

I also don't know how to judge the stability of caves, tunnels or lava tubes, but I will mention that this tube has been there for about 4000 years, so perhaps it's already done whatever collapsing that it was going to do. From what I've read, the volcanos on Mars are much older, so I would also guess that they're stabilized.

Fun fact: in centuries past, the inhabitants used to hide in this tunnel when pirates showed up, seeking people to abduct and sell in North Africa as slaves.

Offline guckyfan

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Re: SpaceX's Martian Underground
« Reply #65 on: 01/27/2017 04:02 pm »
We do know these lava tubes exist, because some have caved in and we can look into them through the holes.

Using them may well be a good idea long term. But I would want geologists do very thorough surveys. It will also be a major undertaking. I understand the ones we know of are huge and making them airtight will be a huge undertaking. Worth it if we want to build a city with plenty of space for a million people, but not something we can do early. Unless we find much smaller ones.

Offline Robotbeat

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Re: SpaceX's Martian Underground
« Reply #66 on: 01/27/2017 04:16 pm »
I think trying to make them air tight might not be worth it. Probably just using it as extra shelter from radiation and temperature swings. Maybe if you find a big one that is strong, you can pressurize it to 1-2psi  with outside air (in case it's leaky) as a double layer of safety for the habs. That'd mean a positive-pressure oxygen mask and/or helmet would work but you could have far better dexterity since the limbs wouldn't need to be pressurized.
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Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #67 on: 01/27/2017 04:43 pm »
Something else that I've been wondering about, for a lava tube or a drilled tunnel, would be heating. If we used a separate habitat inside of such a cave, it would be easier to keep the temperature inside the hab comfortable. If we just sealed the whole thing, it would take quite a while before the surrounding rock warmed up enough so that it wasn't a cold sink. I've never been any good at thermo calculations, but perhaps someone else knows how to model this problem.

Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #68 on: 01/27/2017 05:53 pm »
I think trying to make them air tight might not be worth it. Probably just using it as extra shelter from radiation and temperature swings. Maybe if you find a big one that is strong, you can pressurize it to 1-2psi  with outside air (in case it's leaky) as a double layer of safety for the habs. That'd mean a positive-pressure oxygen mask and/or helmet would work but you could have far better dexterity since the limbs wouldn't need to be pressurized.

I've been think exactly the same thing about having a double-pressure vessel. However, I'd really want much higher ambient pressure in the cave. I've personally used a version of positive-pressure breathing on a few flights in Navy jet aircraft - and that was only with about 4 psia @ 30,000 feet, and it was fatiguing. True positive-pressure breathing - at 50,000 feet and above - is known to be highly conducive to hyperventilation and hypoxia, followed by unconsciousness. If it were possible to get up to about 7-8 psi, that would be a good thing.

As you say, having a double pressure system could also be a safety feature. If somehow a habitat breached, those inside could scramble to grab an emergency O2 mask, just like all airline pax have available. And this could also mean that the habitat would have less stringent construction specs.

And your points about this resulting in less restrictive suits sound really good.
« Last Edit: 01/27/2017 06:07 pm by pobermanns »

Offline Robotbeat

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Re: SpaceX's Martian Underground
« Reply #69 on: 01/27/2017 06:06 pm »
Were you using pure oxygen in your positive pressure device?

The Apollo suits were 3.5psi, without positive pressure breathing. They used pure O2.

Some people climb Everest without oxygen. That's a partial pressure of just 1psi oxygen. Twice that is adaptable for pure oxygen, and if you add another 1psi of positive pressure (or some other method like blood doping), I think performance should be more than acceptable.
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Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #70 on: 01/27/2017 06:25 pm »
Were you using pure oxygen in your positive pressure device?

The Apollo suits were 3.5psi, without positive pressure breathing. They used pure O2.

Some people climb Everest without oxygen. That's a partial pressure of just 1psi oxygen. Twice that is adaptable for pure oxygen, and if you add another 1psi of positive pressure (or some other method like blood doping), I think performance should be more than acceptable.

Yes, it was 100% O2, derived from an onboard LOX converter. It has to be, so as to keep your blood-oxygen level above 90% at the lower ambient pressures.

Note that all of the Apollo guys were former Navy/Air Force jet pilots, and thus very used to this regimen. I was mostly a helicopter guy, so although I'd been thru the pressure chamber multiple times for qualification, flying with my friends in the back seat was my only experience with this.

The problem with positive-pressure breathing is that it inverts the normal breathing cycle that people use. Normally, we use muscles to inhale, but exhalation happens by simply relaxing. With PP breathing, the system pushes air into your lungs, so that's easy, but you have to push to exhale. Your exhalation muscles aren't as strong as those you use to inhale. This means that your next breath will come immediately after you stop pushing out, which is how you can get into the spiral of hyperventilation. This can quickly lead to hypocapnia - too low CO2. Quoting Wikipedia,

"Because the brain stem regulates breathing by monitoring the level of blood CO2, hypocapnia can suppress breathing to the point of blackout from cerebral hypoxia."

As for the point about mountain climbers, it is also the case that most people are not so adapted, and would suffer altitude sickness from it. When I personally went thru the pressure chamber - at a simulated altitude of 30,000 feet - I lost consciousness after about 30 seconds. So, I guess that I'll never climb Mt. Everest - or go to Mars. The fact that I'm now 66 might also have something to do with that.
« Last Edit: 01/27/2017 06:30 pm by pobermanns »

Offline Robotbeat

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Re: SpaceX's Martian Underground
« Reply #71 on: 01/27/2017 06:28 pm »
Except you adapt fairly quickly to higher altitudes, but it still takes weeks or months, you shouldn't compare your experience of just going from sea level to low pressure in minutes or hours. People who live at high altitudes have adapted to this. On Mars, you'll likely have lower pressures, so it'll be like living in Breckenridge or Leadville at 10000ft, then going hiking or skiing at 13000-14000ft.
« Last Edit: 01/27/2017 06:33 pm by Robotbeat »
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Offline rsdavis9

Re: SpaceX's Martian Underground
« Reply #72 on: 01/27/2017 06:30 pm »
So is .2 atm @ 100% o2 the same as 1 atm @ 20% o2.
1. The same for fire propagation?
2. It should be the same for human breathing and health?
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Offline Robotbeat

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Re: SpaceX's Martian Underground
« Reply #73 on: 01/27/2017 06:36 pm »
No to the first.

You need buffer gas in a hab to help reduce fire risk (to carry away heat from a fire).

But in a spacesuit, you don't have many ignition sources, and you can control the environment easier. So pure O2 isn't a problem for a suit or mask.
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Re: SpaceX's Martian Underground
« Reply #74 on: 01/27/2017 06:38 pm »
Except you adapt fairly quickly to higher altitudes, but it still takes weeks or months, you shouldn't compare your experience of just going from sea level to low pressure in minutes or hours. People who live at high altitudes have adapted to this. On Mars, you'll likely have lower pressures, so it'll be like living in Breckenridge or Aspen at 10000ft, then going hiking or skiing at 13000-14000ft.

Well, I'd have to hear a medical professional verify that before I believe the "fairly quickly" part of this. And if it were true, why is true that people who are real mountain climbers suffer from "altitude sickness"? Personally, I do not believe this.

Obviously, people who are born in Bolivia or Colorado develop tolerance to this. So does this mean that we would only recruit people for Mars who were born at high altitudes?

Offline Robotbeat

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Re: SpaceX's Martian Underground
« Reply #75 on: 01/27/2017 06:48 pm »
It's not perfect adaption. As you go higher and higher, it's harder and harder. But this is the reason why people who attempt Mount Everest stay at the base camp for a while before starting the real climb. You have to give your body time to adapt. And you don't have to be born some place to take advantage of it. Merely living there a while can do it.

Over the longer term, many generations, you get actual genetic adaptations. The Tibetans are a classic example, who adapted to the high altitudes (15000 ft... The average altitude of the whole country is higher than any peak in Colorado) after splitting off from their low altitude cousins just 2750 years ago. Gene therapy can probably accelerate this and help regular people adapt, too. And so there's a long-term reason to make your habs low-pressure: to develop adaptations (natural and artificial) to prepare Martians for the early days of terraforming when pressures will be very low.

I can tell a lot of people have misconceptions about high altitudes. Maybe we have people who live in Denver (Lockheed, etc) design the habs so we don't get this low lander bias in the design. :)

« Last Edit: 01/27/2017 06:56 pm by Robotbeat »
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Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #76 on: 01/27/2017 07:14 pm »
So is .2 atm @ 100% o2 the same as 1 atm @ 20% o2?

Referencing the Navy Flight Surgeons Manual ( http://www.med.navy.mil/sites/nmotc/nami/academics/Documents/FlightSurgeonsManual.pdf), 33,700 feet MSL yields the same blood O2 saturation level, when on 100% O2, as when breathing normally at sea level. That's about 4 psia.

I don't know what the partial pressure of oxygen would be at .2 ATM, nor what the equivalent altitude would be, but I'm sure that a full-pressure suit would be mandatory.
« Last Edit: 01/27/2017 07:29 pm by pobermanns »

Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #77 on: 01/27/2017 07:26 pm »
It's not perfect adaption. As you go higher and higher, it's harder and harder. But this is the reason why people who attempt Mount Everest stay at the base camp for a while before starting the real climb. You have to give your body time to adapt. And you don't have to be born some place to take advantage of it. Merely living there a while can do it.

Over the longer term, many generations, you get actual genetic adaptations. The Tibetans are a classic example, who adapted to the high altitudes (15000 ft... The average altitude of the whole country is higher than any peak in Colorado) after splitting off from their low altitude cousins just 2750 years ago. Gene therapy can probably accelerate this and help regular people adapt, too. And so there's a long-term reason to make your habs low-pressure: to develop adaptations (natural and artificial) to prepare Martians for the early days of terraforming when pressures will be very low.

I can tell a lot of people have misconceptions about high altitudes. Maybe we have people who live in Denver (Lockheed, etc) design the habs so we don't get this low lander bias in the design. :)

I have respected your opinions on many previous posts, but in this case I think that you are wrong. Personal experience tells me that these are dangerous assumptions.

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Re: SpaceX's Martian Underground
« Reply #78 on: 01/27/2017 07:31 pm »
I think we've had this discussion before. More than once. Some intrepid reader pointing to threads where this happened might reduce how stale this seems.
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Offline envy887

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Re: SpaceX's Martian Underground
« Reply #79 on: 01/27/2017 07:38 pm »
So is .2 atm @ 100% o2 the same as 1 atm @ 20% o2?

Referencing the Navy Flight Surgeons Manual ( http://www.med.navy.mil/sites/nmotc/nami/academics/Documents/FlightSurgeonsManual.pdf), 33,700 feet MSL yields the same blood O2 saturation level, when on 100% O2, as when breathing normally at sea level. That's about 4 psis.

I don't know what the partial pressure of oxygen would be at .2 ATM, nor that the equivalent altitude would be, but I'm sure that a full-pressure suit would be mandatory.

0.2 atm is 20 kPa or 2.9 psi. It's the standard air pressure at 41,000 feet, and a full pressure suit is not critical, according to page 1-21 of that manual.

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