[Ed] What is with the obsession with Mars? - Page 11

3point14 · 7th December 2018, 04:07 AM

Originally Posted by GlennB

Solar power would be my bet, though, as I mentioned upthread, obtaining some of the more obscure elements could be massively difficult. Ditto nukes.

I don't think the obscure elements are required if you do it this way:

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

How effective that's likely to be at x KM further away from the sun, I have no idea. Similarly, I rally don't know if it would be easier or harder to build one of these on Mars.

smartcooky · 7th December 2018, 04:58 AM

Originally Posted by Roboramma

Not yet, but I'll look for it

Its one of the short stories in "Tales from the White Hart"

HansMustermann · 7th December 2018, 06:46 AM

Originally Posted by 3point14

I don't think the obscure elements are required if you do it this way:

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

How effective that's likely to be at x KM further away from the sun, I have no idea. Similarly, I rally don't know if it would be easier or harder to build one of these on Mars.

It's still subject to the inverse square law, so you'd get a fair bit less per square kilometre than on Earth out of it.

And then there's the usual problem with solar power. Namely that it doesn't work at night AND doesn't do much in a dust storm even during the day. And we just had a Mars dust storm that lasted for more than a month. So better have batteries that can store a month's worth of electricity for your colony.

And that's an even bigger problem for a colony than on Earth. Even skipping past importing energy and whatnot, at least you'd still have air even if you were out of power for a month somewhere. Not to mention you can get there by helicopter with the red cross or whatnot to at least make sure the people have food and water. They won't be happy, mind you, but they'll live. On Mars if you don't even have power for the MOXIE (oxygen plant) for a month, because a month-long storm plunged the surface in darkness, everyone just dies horribly.

Roboramma · 7th December 2018, 07:28 AM

Originally Posted by HansMustermann

It's still subject to the inverse square law, so you'd get a fair bit less per square kilometre than on Earth out of it.

On the other hand the Martian atmosphere is much thinner, and a significant amount of solar energy is absorbed by the Earth's atmosphere.

My VPN isn't working so I can't get on google, but it looks to me like the power/unit area at Mars should be around 1/3 of that at earth. I think (from memory) that at earth we lose about 1/2 of solar power to the atmosphere, whereas I'd guess that it's basically insignificant at Mars, in which case on the surface of both planets you'd expect similar figures for power/unit area (less on Mars but not that much). The problem of dust storms does complicate that though.

Roboramma · 7th December 2018, 07:30 AM

Originally Posted by smartcooky

Its one of the short stories in "Tales from the White Hart"

You know, I had a collection of his short stories that included some (or all) of those that I read about 15 years ago, and I think I probably read that one. Something about termites does feel familiar. I'll have to try to read some of his stuff again, though, thanks

HansMustermann · 7th December 2018, 07:45 AM

It's not as insignificant as you'd think, because of the vast amounts of dust in the atmosphere. But be that as it may, you still have the issue of storms literally plunging the surface in darkness for up to a month or two in a row.

Roboramma · 7th December 2018, 07:48 AM

Yeah, I'd be interested in actual figures for power /unit area on the surface. And certainly agreed that the dust storms cause a problem. At the very least some sort of energy storage would be necessary, but the scale here is pretty damn large.

Myriad · 7th December 2018, 08:11 AM

Originally Posted by Roboramma

Do you have any reason to think that it wouldn't be the case? I mean, what specific sorts of health problems do you think could arise from low-gravity that don't exist in zero-gravity?

If your objection is just "Well, you never no, there could be something unexpected" that's fine, but I don't put the probability very high with respect to this particular concern.

The health problems of microgravity (effectively zero gravity, as on the ISS) are lethal long-term. We've gone about as far establishing that as possible, short of leaving an astronaut in orbit long enough to actually die from it. The countermeasures (hours of exercises per day) only slow down the damage.

It's extremely likely that the health effects of fractional (e.g. Mars or lunar) gravity are less severe than those of microgravity. It's possible there are no real problems with it at all, aside from (as in the common SF trope) not being developmentally adapted to full earth gravity and so being unable to relocate there without prosthetics. But if there are other long-term effects, we don't know what will suffice to counter them (i.e. over a lifetime). A few hours a day on a tilt-a-whirl would be fairly easily manageable. Full-time on the tilt-a-whirl during pregnancy would be onerous, but hey, the survival of the species is at stake so you do what you gotta. But if you need the whole population living on the tilt-a-whirl all the time, it multiplies the cost of habitable space on the Martian surface by something like an order of magnitude.

3point14 · 7th December 2018, 08:12 AM

Originally Posted by Roboramma

Yeah, I'd be interested in actual figures for power /unit area on the surface. And certainly agreed that the dust storms cause a problem. At the very least some sort of energy storage would be necessary, but the scale here is pretty damn large.

If it's practically a vacuum, does that make storing energy in a flywheel practical?

HansMustermann · 7th December 2018, 01:59 PM

Originally Posted by Myriad

The health problems of microgravity (effectively zero gravity, as on the ISS) are lethal long-term. We've gone about as far establishing that as possible, short of leaving an astronaut in orbit long enough to actually die from it. The countermeasures (hours of exercises per day) only slow down the damage.

It's extremely likely that the health effects of fractional (e.g. Mars or lunar) gravity are less severe than those of microgravity. It's possible there are no real problems with it at all, aside from (as in the common SF trope) not being developmentally adapted to full earth gravity and so being unable to relocate there without prosthetics. But if there are other long-term effects, we don't know what will suffice to counter them (i.e. over a lifetime). A few hours a day on a tilt-a-whirl would be fairly easily manageable. Full-time on the tilt-a-whirl during pregnancy would be onerous, but hey, the survival of the species is at stake so you do what you gotta. But if you need the whole population living on the tilt-a-whirl all the time, it multiplies the cost of habitable space on the Martian surface by something like an order of magnitude.

At this point, I'm not sure exactly how you envision that tilt-a-whirl, that it would be a problem. It's possible to have a centrifuge that doesn't make you puke, and still produces 1g, by basically being large and slow enough, and on Mars you don't need a full g pushing sideways, so it can be even slower.

Basically don't think the fast spinning ride with the plastic horses at the carnival, think something like the London Ferris wheel on its side.

And you don't even need to push it to a full 1g, so it can be fairly slowly rotating. For example if you can generate 3.7m/s² pushing sideways, that gets you a nice 45° sloped floor and a 5.25m/s² effective gravity on Mars. Which IMHO should be already decent enough.

And, yes, to concede your point, you probably don't even need to be on it 24/7. You could probably get away with having the work hours in lower g areas, so you don't have to put heavy industrial or scientific equipment on the centrifuge, and just have the free hours and sleep in your room on the Ferris wheel.

Roboramma · 8th December 2018, 03:41 AM

Originally Posted by Myriad

The health problems of microgravity (effectively zero gravity, as on the ISS) are lethal long-term. We've gone about as far establishing that as possible, short of leaving an astronaut in orbit long enough to actually die from it. The countermeasures (hours of exercises per day) only slow down the damage.

It's extremely likely that the health effects of fractional (e.g. Mars or lunar) gravity are less severe than those of microgravity. It's possible there are no real problems with it at all, aside from (as in the common SF trope) not being developmentally adapted to full earth gravity and so being unable to relocate there without prosthetics. But if there are other long-term effects, we don't know what will suffice to counter them (i.e. over a lifetime). A few hours a day on a tilt-a-whirl would be fairly easily manageable. Full-time on the tilt-a-whirl during pregnancy would be onerous, but hey, the survival of the species is at stake so you do what you gotta. But if you need the whole population living on the tilt-a-whirl all the time, it multiplies the cost of habitable space on the Martian surface by something like an order of magnitude.

That's all quite reasonable. I would guess that fetal development will require something quite close to 1g, though how close I won't guess. On the other hand when it comes to long term effects on adults, even if a few hours/day isn't effective, which I would also guess that it would be*, a few months on a treatment center in between stints of a few months at low-g should be (how long does it take astronauts to fully recover from a long stay on the ISS (where the problems of bone loss would be less severe per unit time)?

*Our bodies are quite good at adapting to stress, it's only the long term absense of that stress that leads to problems in living in zero-g. A few hours/day should be enough to induce that adaptive response. On the other hand it's not clear to me using sleep time would be sufficient as there's not that much load on the bones during sleep.

HansMustermann · 8th December 2018, 07:27 AM

Well, in my imaginary scenario they'd spend more like 16 hours a day on the centrifuge. Which would presumably involve at the very least some walking around and sitting, even if someone absolutely can't be convinced to spend some time on a treadmill or ergonomic bike. It's only when they have to do their job that they'd be in microgravity, and that mainly because some things can't be put on the centrifuge (e.g., maintaining the solar panels outside would still be microgravity) and some I really don't want to for cost reasons (e.g., it would take an insanely reinforced centrifuge to hold a nuclear reactor at 1g.)

So anyway, you'd spend some 8 hours or so in low g, then have 16 hours or so to recuperate in more acceptable g.

IMHO it should be enough to keep people at least reasonably healthy. With the caveat that I'm no doctor, so MHO doesn't have to count for much.

fuelair · 8th December 2018, 10:03 AM

Originally Posted by erwinl

Just leave Matt Damon.

It's the Princesses of Mars that need rescuing!

Read the books, watch the movies (if you can find them now...……)...

HansMustermann · 8th December 2018, 10:14 AM

Originally Posted by 3point14

If it's practically a vacuum, does that make storing energy in a flywheel practical?

Well, you'd still have friction in the bearing, especially if the dust can get into it. Which, if it's not somehow sealed off, it will.

But let's do some maths there. You know me, I'm like math's little bitch. I keep coming back for more.

So let's say our whole colony needs only 1MW worth of power on the average. Which is actually very very Spartan, especially if you want to have 160 humans so they can at the very least have enough genetic diversity for a backup.

Let's say you want to hold power for a month. (Again, I'm going low. There have been recent storms that lasted a lot longer.)

so 1MW x 86400 s/day x 30 days = 2592000 MJ = 2.6 TJ

that's how much energy you'd have to store in the flywheel.

Now, that's pure kinetic energy. Assuming an ideal flywheel where the mass is all concentrated at the edge (or the vast majority of it, anyway) you need mv² to be a little over 5*10¹². So if we have a flywheel weighing 5000 TONS, its edge would have to be going at 1000m/s. You can plug in your own desired radius to get the RPM, but the edge is going at nearly mach 3 in any case. A bit more if it's a less ideal flywheel.

I'm thinking though that if you make it too large, the tensile strength of steel (or really ANY material you're using) isn't going to cut it.

Edit: the same applies, btw, if you have 5000 tons worth of lighter wheels. If you have 5000 flywheels, weighing 1 ton each, well, you still get the edge going at nearly mach 3 for each of them.

3point14 · 8th December 2018, 10:31 AM

That's an awful lot of flywheel.

Thank you for the maths!

Myriad · 8th December 2018, 11:27 AM

Originally Posted by 3point14

That's an awful lot of flywheel.

Yeah, but we can solve the power storage and the artificial gravity problems together! A rotating habitat with a rim mass of 50,000 tons (including contents) and a diameter of 150 meters (about the size and mass of a large modern stadium) would only need a rim speed of about 32 m/s to store your 2.6 TJ. That would be about 2/3 g centripetal acceleration, or a resultant of about .76 g. You get about 70,000 square meters of living and working space.

Of course, you'd lose your artificial gravity temporarily when you have to draw down significant amounts of that reserve power (but you'd only do that in emergencies, surely), and your habitat will seem a bit tilted until you can rev it up again.

HansMustermann · 8th December 2018, 11:59 AM

Hmm, I like that idea. Though I think 50,000 tons is a bit much. That's the weight of a bloody battleship.

HansMustermann · 8th December 2018, 12:07 PM

Hmm... could you please run the maths past me, though? When I do it in my head, it ends up about 2 orders of magnitude too short for 2.6TJ. Of course my maths could be wrong, but I'd like to learn where I went wrong with it.

Myriad · 8th December 2018, 12:23 PM

Never mind, I think I made a calculation error. It needs 10x more energy.

For instance, 4x the radius, 2x the rim speed (so 1/2 the rpm), and 2.5x the mass.

ETA: No, even that's not enough; I was even farther off.

HansMustermann · 8th December 2018, 02:33 PM

Ah. Well, for once I'm sorry to have been right. I was starting to like your centrifuge doubling as a flywheel idea.

HansMustermann · 10th December 2018, 05:18 AM

BTW, just to make it clear, just beacause the number is big, it doesn't mean it's impossible to store it. Just not in a flywheel. About 5000 tons of li-ion batteries should just about store that much. And would only cost about half a billion for the batteries, and a fair bit more for the transport.

Just, well, hope the batteries don't blow up, like li-ion occasionally does, or you'll be able to see the resulting crater from Earth

Myriad · 10th December 2018, 06:45 AM

Does anyone remember the old "solar power satellite" concept?

Such a thing might work better for Mars than for earth. For instance if the transmitted microwave power went off target, the colonists would still be safe due to the same radiation shielding that was protecting them from all the other radiation.

(But would a dust storm block the surface power reception? If so, they're of course no better off than if the panels themselves were on the surface.)

To be able to maintain it themselves, the colonists would need to maintain a space flight capability. But with Mars gravity, that might not be much more difficult than maintaining all the other technology they would need.

HansMustermann · 10th December 2018, 07:15 AM

Bingo. The problem is that when there's a dust storm, you literally can't see the sun for all the dust. I don't expect a satellite to do much better there.

GlennB · 10th December 2018, 09:41 AM

And whatever panels you use might need some built-in wipers. There will never be any rain to wash off the accumulated dust. There are cleaning event^WPs, but you might not want to rely on them.

Down here in Greece we quite often get saharan dust blowing in. It can make my car undriveable unless I use the screen washers.

Belz... · 10th December 2018, 09:56 AM

Originally Posted by HansMustermann

Bingo. The problem is that when there's a dust storm, you literally can't see the sun for all the dust. I don't expect a satellite to do much better there.

I'm sure the Icarus from Die Another Day can break through. Can't speak to the safety of anyone it targets, however.

HansMustermann · 10th December 2018, 10:08 AM

Originally Posted by GlennB

And whatever panels you use might need some built-in wipers. There will never be any rain to wash off the accumulated dust. There are cleaning event^WPs, but you might not want to rely on them.

Down here in Greece we quite often get saharan dust blowing in. It can make my car undriveable unless I use the screen washers.

Well, just as long as you don't end up polishing those panels an opaque white, while rubbing the dust on them with the wipers. I know at least the moon dust it's not the rounded particles of dust on Earth, but some rather jagged rock fragments. I'm sure some of the dust on Mars has been around the block often enough to have gotten rounded, but anything from recent enough impacts AND anything from humans digging a bunker there, has got to be the jagged kind.

autumn1971 · 15th December 2018, 09:03 AM

Originally Posted by Belz...

I'm sure the Icarus from Die Another Day can break through. Can't speak to the safety of anyone it targets, however.

I was thinking of “Real Genius,” which was both funny on purpose and more realistic.

Belz... · Today, 03:19 AM

Originally Posted by autumn1971

I was thinking of “Real Genius,” which was both funny on purpose and more realistic.

Yeah, that was a pretty fun movie.

7th December 2018, 04:07 AM	#401
3point14 Pi Join Date: Nov 2005 Posts: 16,308	Originally Posted by GlennB Solar power would be my bet, though, as I mentioned upthread, obtaining some of the more obscure elements could be massively difficult. Ditto nukes. I don't think the obscure elements are required if you do it this way: https://en.wikipedia.org/wiki/Concentrated_solar_power How effective that's likely to be at x KM further away from the sun, I have no idea. Similarly, I rally don't know if it would be easier or harder to build one of these on Mars.
3point14 Pi Join Date: Nov 2005 Posts: 16,308	__________________ Up the River!

7th December 2018, 04:58 AM	#402
smartcooky Philosopher Join Date: Oct 2012 Location: Nelson, New Zealand Posts: 9,702	Originally Posted by Roboramma Not yet, but I'll look for it Its one of the short stories in "Tales from the White Hart"
	__________________ _{As democracy is perfected, the office represents, more and more closely, the inner soul of the people. We move toward a lofty ideal. On some great and glorious day the plain folks of the land will reach their heart's desire at last, and the White House will be adorned by a downright moron. - Henry Louis Mencken - Baltimore Evening Sun, July 26, 1920}

7th December 2018, 06:46 AM	#403
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Originally Posted by 3point14 I don't think the obscure elements are required if you do it this way: https://en.wikipedia.org/wiki/Concentrated_solar_power How effective that's likely to be at x KM further away from the sun, I have no idea. Similarly, I rally don't know if it would be easier or harder to build one of these on Mars. It's still subject to the inverse square law, so you'd get a fair bit less per square kilometre than on Earth out of it. And then there's the usual problem with solar power. Namely that it doesn't work at night AND doesn't do much in a dust storm even during the day. And we just had a Mars dust storm that lasted for more than a month. So better have batteries that can store a month's worth of electricity for your colony. And that's an even bigger problem for a colony than on Earth. Even skipping past importing energy and whatnot, at least you'd still have air even if you were out of power for a month somewhere. Not to mention you can get there by helicopter with the red cross or whatnot to at least make sure the people have food and water. They won't be happy, mind you, but they'll live. On Mars if you don't even have power for the MOXIE (oxygen plant) for a month, because a month-long storm plunged the surface in darkness, everyone just dies horribly.
	__________________ Which part of "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" don't you understand? Last edited by HansMustermann; 7th December 2018 at 06:47 AM.

7th December 2018, 07:28 AM	#404
Roboramma Penultimate Amazing Join Date: Feb 2005 Location: Shanghai Posts: 11,434	Originally Posted by HansMustermann It's still subject to the inverse square law, so you'd get a fair bit less per square kilometre than on Earth out of it. On the other hand the Martian atmosphere is much thinner, and a significant amount of solar energy is absorbed by the Earth's atmosphere. My VPN isn't working so I can't get on google, but it looks to me like the power/unit area at Mars should be around 1/3 of that at earth. I think (from memory) that at earth we lose about 1/2 of solar power to the atmosphere, whereas I'd guess that it's basically insignificant at Mars, in which case on the surface of both planets you'd expect similar figures for power/unit area (less on Mars but not that much). The problem of dust storms does complicate that though.
	__________________ "... when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together." Isaac Asimov

7th December 2018, 07:30 AM	#405
Roboramma Penultimate Amazing Join Date: Feb 2005 Location: Shanghai Posts: 11,434	Originally Posted by smartcooky Its one of the short stories in "Tales from the White Hart" You know, I had a collection of his short stories that included some (or all) of those that I read about 15 years ago, and I think I probably read that one. Something about termites does feel familiar. I'll have to try to read some of his stuff again, though, thanks
	__________________ "... when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together." Isaac Asimov

7th December 2018, 07:45 AM	#406
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	It's not as insignificant as you'd think, because of the vast amounts of dust in the atmosphere. But be that as it may, you still have the issue of storms literally plunging the surface in darkness for up to a month or two in a row.
	__________________ Which part of "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" don't you understand?

7th December 2018, 07:48 AM	#407
Roboramma Penultimate Amazing Join Date: Feb 2005 Location: Shanghai Posts: 11,434	Yeah, I'd be interested in actual figures for power /unit area on the surface. And certainly agreed that the dust storms cause a problem. At the very least some sort of energy storage would be necessary, but the scale here is pretty damn large.
	__________________ "... when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together." Isaac Asimov

7th December 2018, 08:11 AM	#408
Myriad Hyperthetical TLA Winner Join Date: Nov 2006 Location: A pocket paradise between the sewage treatment plant and the railroad Posts: 14,267	Originally Posted by Roboramma Do you have any reason to think that it wouldn't be the case? I mean, what specific sorts of health problems do you think could arise from low-gravity that don't exist in zero-gravity? If your objection is just "Well, you never no, there could be something unexpected" that's fine, but I don't put the probability very high with respect to this particular concern. The health problems of microgravity (effectively zero gravity, as on the ISS) are lethal long-term. We've gone about as far establishing that as possible, short of leaving an astronaut in orbit long enough to actually die from it. The countermeasures (hours of exercises per day) only slow down the damage. It's extremely likely that the health effects of fractional (e.g. Mars or lunar) gravity are less severe than those of microgravity. It's possible there are no real problems with it at all, aside from (as in the common SF trope) not being developmentally adapted to full earth gravity and so being unable to relocate there without prosthetics. But if there are other long-term effects, we don't know what will suffice to counter them (i.e. over a lifetime). A few hours a day on a tilt-a-whirl would be fairly easily manageable. Full-time on the tilt-a-whirl during pregnancy would be onerous, but hey, the survival of the species is at stake so you do what you gotta. But if you need the whole population living on the tilt-a-whirl all the time, it multiplies the cost of habitable space on the Martian surface by something like an order of magnitude.
	__________________ A zømbie once bit my sister...

7th December 2018, 08:12 AM	#409
3point14 Pi Join Date: Nov 2005 Posts: 16,308	Originally Posted by Roboramma Yeah, I'd be interested in actual figures for power /unit area on the surface. And certainly agreed that the dust storms cause a problem. At the very least some sort of energy storage would be necessary, but the scale here is pretty damn large. If it's practically a vacuum, does that make storing energy in a flywheel practical?
3point14 Pi Join Date: Nov 2005 Posts: 16,308	__________________ Up the River!

7th December 2018, 01:59 PM	#410
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Originally Posted by Myriad The health problems of microgravity (effectively zero gravity, as on the ISS) are lethal long-term. We've gone about as far establishing that as possible, short of leaving an astronaut in orbit long enough to actually die from it. The countermeasures (hours of exercises per day) only slow down the damage. It's extremely likely that the health effects of fractional (e.g. Mars or lunar) gravity are less severe than those of microgravity. It's possible there are no real problems with it at all, aside from (as in the common SF trope) not being developmentally adapted to full earth gravity and so being unable to relocate there without prosthetics. But if there are other long-term effects, we don't know what will suffice to counter them (i.e. over a lifetime). A few hours a day on a tilt-a-whirl would be fairly easily manageable. Full-time on the tilt-a-whirl during pregnancy would be onerous, but hey, the survival of the species is at stake so you do what you gotta. But if you need the whole population living on the tilt-a-whirl all the time, it multiplies the cost of habitable space on the Martian surface by something like an order of magnitude. At this point, I'm not sure exactly how you envision that tilt-a-whirl, that it would be a problem. It's possible to have a centrifuge that doesn't make you puke, and still produces 1g, by basically being large and slow enough, and on Mars you don't need a full g pushing sideways, so it can be even slower. Basically don't think the fast spinning ride with the plastic horses at the carnival, think something like the London Ferris wheel on its side. And you don't even need to push it to a full 1g, so it can be fairly slowly rotating. For example if you can generate 3.7m/s² pushing sideways, that gets you a nice 45° sloped floor and a 5.25m/s² effective gravity on Mars. Which IMHO should be already decent enough. And, yes, to concede your point, you probably don't even need to be on it 24/7. You could probably get away with having the work hours in lower g areas, so you don't have to put heavy industrial or scientific equipment on the centrifuge, and just have the free hours and sleep in your room on the Ferris wheel.
	__________________ Which part of "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" don't you understand?

8th December 2018, 03:41 AM	#411
Roboramma Penultimate Amazing Join Date: Feb 2005 Location: Shanghai Posts: 11,434	Originally Posted by Myriad The health problems of microgravity (effectively zero gravity, as on the ISS) are lethal long-term. We've gone about as far establishing that as possible, short of leaving an astronaut in orbit long enough to actually die from it. The countermeasures (hours of exercises per day) only slow down the damage. It's extremely likely that the health effects of fractional (e.g. Mars or lunar) gravity are less severe than those of microgravity. It's possible there are no real problems with it at all, aside from (as in the common SF trope) not being developmentally adapted to full earth gravity and so being unable to relocate there without prosthetics. But if there are other long-term effects, we don't know what will suffice to counter them (i.e. over a lifetime). A few hours a day on a tilt-a-whirl would be fairly easily manageable. Full-time on the tilt-a-whirl during pregnancy would be onerous, but hey, the survival of the species is at stake so you do what you gotta. But if you need the whole population living on the tilt-a-whirl all the time, it multiplies the cost of habitable space on the Martian surface by something like an order of magnitude. That's all quite reasonable. I would guess that fetal development will require something quite close to 1g, though how close I won't guess. On the other hand when it comes to long term effects on adults, even if a few hours/day isn't effective, which I would also guess that it would be, a few months on a treatment center in between stints of a few months at low-g should be (how long does it take astronauts to fully recover from a long stay on the ISS (where the problems of bone loss would be less severe per unit time)? Our bodies are quite good at adapting to stress, it's only the long term absense of that stress that leads to problems in living in zero-g. A few hours/day should be enough to induce that adaptive response. On the other hand it's not clear to me using sleep time would be sufficient as there's not that much load on the bones during sleep.
	__________________ "... when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together." Isaac Asimov

8th December 2018, 07:27 AM	#412
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Well, in my imaginary scenario they'd spend more like 16 hours a day on the centrifuge. Which would presumably involve at the very least some walking around and sitting, even if someone absolutely can't be convinced to spend some time on a treadmill or ergonomic bike. It's only when they have to do their job that they'd be in microgravity, and that mainly because some things can't be put on the centrifuge (e.g., maintaining the solar panels outside would still be microgravity) and some I really don't want to for cost reasons (e.g., it would take an insanely reinforced centrifuge to hold a nuclear reactor at 1g.) So anyway, you'd spend some 8 hours or so in low g, then have 16 hours or so to recuperate in more acceptable g. IMHO it should be enough to keep people at least reasonably healthy. With the caveat that I'm no doctor, so MHO doesn't have to count for much.
	__________________ Which part of "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" don't you understand?

8th December 2018, 10:03 AM	#413
fuelair Cythraul Enfys Join Date: May 2006 Posts: 57,930	Originally Posted by erwinl Just leave Matt Damon. It's the Princesses of Mars that need rescuing! Read the books, watch the movies (if you can find them now...……)...
fuelair Cythraul Enfys Join Date: May 2006 Posts: 57,930	__________________ There is no problem so great that it cannot be fixed by small explosives carefully placed. Wash this space! We fight for the Lady Babylon!!!

8th December 2018, 10:14 AM	#414
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Originally Posted by 3point14 If it's practically a vacuum, does that make storing energy in a flywheel practical? Well, you'd still have friction in the bearing, especially if the dust can get into it. Which, if it's not somehow sealed off, it will. But let's do some maths there. You know me, I'm like math's little bitch. I keep coming back for more. So let's say our whole colony needs only 1MW worth of power on the average. Which is actually very very Spartan, especially if you want to have 160 humans so they can at the very least have enough genetic diversity for a backup. Let's say you want to hold power for a month. (Again, I'm going low. There have been recent storms that lasted a lot longer.) so 1MW x 86400 s/day x 30 days = 2592000 MJ = 2.6 TJ that's how much energy you'd have to store in the flywheel. Now, that's pure kinetic energy. Assuming an ideal flywheel where the mass is all concentrated at the edge (or the vast majority of it, anyway) you need mv² to be a little over 5*10¹². So if we have a flywheel weighing 5000 TONS, its edge would have to be going at 1000m/s. You can plug in your own desired radius to get the RPM, but the edge is going at nearly mach 3 in any case. A bit more if it's a less ideal flywheel. I'm thinking though that if you make it too large, the tensile strength of steel (or really ANY material you're using) isn't going to cut it. Edit: the same applies, btw, if you have 5000 tons worth of lighter wheels. If you have 5000 flywheels, weighing 1 ton each, well, you still get the edge going at nearly mach 3 for each of them.
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8th December 2018, 10:31 AM	#415
3point14 Pi Join Date: Nov 2005 Posts: 16,308	That's an awful lot of flywheel. Thank you for the maths!
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8th December 2018, 11:27 AM	#416
Myriad Hyperthetical TLA Winner Join Date: Nov 2006 Location: A pocket paradise between the sewage treatment plant and the railroad Posts: 14,267	Originally Posted by 3point14 That's an awful lot of flywheel. Yeah, but we can solve the power storage and the artificial gravity problems together! A rotating habitat with a rim mass of 50,000 tons (including contents) and a diameter of 150 meters (about the size and mass of a large modern stadium) would only need a rim speed of about 32 m/s to store your 2.6 TJ. That would be about 2/3 g centripetal acceleration, or a resultant of about .76 g. You get about 70,000 square meters of living and working space. Of course, you'd lose your artificial gravity temporarily when you have to draw down significant amounts of that reserve power (but you'd only do that in emergencies, surely), and your habitat will seem a bit tilted until you can rev it up again.
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8th December 2018, 11:59 AM	#417
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Hmm, I like that idea. Though I think 50,000 tons is a bit much. That's the weight of a bloody battleship.
	__________________ Which part of "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" don't you understand?

8th December 2018, 12:07 PM	#418
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Hmm... could you please run the maths past me, though? When I do it in my head, it ends up about 2 orders of magnitude too short for 2.6TJ. Of course my maths could be wrong, but I'd like to learn where I went wrong with it.
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8th December 2018, 12:23 PM	#419
Myriad Hyperthetical TLA Winner Join Date: Nov 2006 Location: A pocket paradise between the sewage treatment plant and the railroad Posts: 14,267	Never mind, I think I made a calculation error. It needs 10x more energy. For instance, 4x the radius, 2x the rim speed (so 1/2 the rpm), and 2.5x the mass. ETA: No, even that's not enough; I was even farther off.
	__________________ A zømbie once bit my sister... Last edited by Myriad; 8th December 2018 at 12:31 PM.

8th December 2018, 02:33 PM	#420
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Ah. Well, for once I'm sorry to have been right. I was starting to like your centrifuge doubling as a flywheel idea.
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10th December 2018, 05:18 AM	#421
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	BTW, just to make it clear, just beacause the number is big, it doesn't mean it's impossible to store it. Just not in a flywheel. About 5000 tons of li-ion batteries should just about store that much. And would only cost about half a billion for the batteries, and a fair bit more for the transport. Just, well, hope the batteries don't blow up, like li-ion occasionally does, or you'll be able to see the resulting crater from Earth
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10th December 2018, 06:45 AM	#422
Myriad Hyperthetical TLA Winner Join Date: Nov 2006 Location: A pocket paradise between the sewage treatment plant and the railroad Posts: 14,267	Does anyone remember the old "solar power satellite" concept? Such a thing might work better for Mars than for earth. For instance if the transmitted microwave power went off target, the colonists would still be safe due to the same radiation shielding that was protecting them from all the other radiation. (But would a dust storm block the surface power reception? If so, they're of course no better off than if the panels themselves were on the surface.) To be able to maintain it themselves, the colonists would need to maintain a space flight capability. But with Mars gravity, that might not be much more difficult than maintaining all the other technology they would need.
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10th December 2018, 07:15 AM	#423
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Bingo. The problem is that when there's a dust storm, you literally can't see the sun for all the dust. I don't expect a satellite to do much better there.
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10th December 2018, 09:41 AM	#424
GlennB Loggerheaded, earth-vexing fustilarian Join Date: Sep 2006 Location: Arcadia, Greece Posts: 23,831	And whatever panels you use might need some built-in wipers. There will never be any rain to wash off the accumulated dust. There are cleaning event^WPs, but you might not want to rely on them. Down here in Greece we quite often get saharan dust blowing in. It can make my car undriveable unless I use the screen washers.
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10th December 2018, 09:56 AM	#425
Belz... Fiend God Join Date: Oct 2005 Location: In the details Posts: 76,593	Originally Posted by HansMustermann Bingo. The problem is that when there's a dust storm, you literally can't see the sun for all the dust. I don't expect a satellite to do much better there. I'm sure the Icarus from Die Another Day can break through. Can't speak to the safety of anyone it targets, however.
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10th December 2018, 10:08 AM	#426
HansMustermann Penultimate Amazing Join Date: Mar 2009 Posts: 14,325	Originally Posted by GlennB And whatever panels you use might need some built-in wipers. There will never be any rain to wash off the accumulated dust. There are cleaning event^WPs, but you might not want to rely on them. Down here in Greece we quite often get saharan dust blowing in. It can make my car undriveable unless I use the screen washers. Well, just as long as you don't end up polishing those panels an opaque white, while rubbing the dust on them with the wipers. I know at least the moon dust it's not the rounded particles of dust on Earth, but some rather jagged rock fragments. I'm sure some of the dust on Mars has been around the block often enough to have gotten rounded, but anything from recent enough impacts AND anything from humans digging a bunker there, has got to be the jagged kind.
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15th December 2018, 09:03 AM	#427
autumn1971 Master Poster Join Date: Jan 2007 Posts: 2,504	Originally Posted by Belz... I'm sure the Icarus from Die Another Day can break through. Can't speak to the safety of anyone it targets, however. I was thinking of “Real Genius,” which was both funny on purpose and more realistic.
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Today, 03:19 AM	#428
Belz... Fiend God Join Date: Oct 2005 Location: In the details Posts: 76,593	Originally Posted by autumn1971 I was thinking of “Real Genius,” which was both funny on purpose and more realistic. Yeah, that was a pretty fun movie.
	__________________ Master of the Shining Darkness "My views are nonsense. So what?" - BobTheCoward