Mission One: a one way ticket to Mars?

John Creighton · 2005-08-10 22:30:24

I’m liking this idea of putting a large pond in a greenhouse to help regulate temperature. It will of course only be successful if the base is built near a large supply of water. However, I think it simplifies greenhouse construction greatly with respect to anchoring the greenhouse to ground. I always wondered if it would be difficult to transfport enough dirt to fill half the greenhouse. If water was used instead the water would just need to be piped in.

When you dig the trench to put the cylindrical greenhouse in just pour water in it instead of dirt. The water could even be piped in after the green house was already inflated. No need to go in and out of the airlock all the time. To me this seems much simpler then filling it up with dirt. I suggest that in a cylindrical greenhouse every so often there should be a valve on each side that can be opened to attach a pipe to exchange air or water between greenhouses and/or a support to support a platform above the water for people to walk on and/or grow non aqueous plants.

Perhaps also every so often there should be a section where doors or walls can be attacked to divide either the air space/end or water space. If such a section blocker was but in place then the water could be later pumped out of that section and replaced with dirt if desired. This of course would lead to issues if it was desired to remove the dirt at a later time so it may be desirable to put something between the walls and the dirt to protect the walls, should it be desirable to remove the dirt at a later time.

Rxke · 2005-08-11 01:21:13

re: UV shielding:

I once had a plastic in my hands that was blocking all but a small percentage of UV, and all but 100% transparent. So they exist, but...

Used by musea, as a retro-fit to existing buildings with historical windows (so you can't just swap those out for UV-filtering glass, heritage protection and all that...)

I'm going through my notes, but have a the datasheets are in the lab at school
There is a vast range of those films, and here come several 'but's : but only a small subset is considered good, and it's hard to find out which. And they're horribly expensive... And they don't last very long, got to be replaced every few years...

Dook · 2005-08-11 04:03:55

What about a series of domes arrayed in a circle with one almost completely dark dome (for storage) connected to one that lets in more light, and so on until you get to a dome that is clear?

The hot air from the clear dome would migrate directly to the nearby dark (cold) dome and create a natural circular air transfer, hot to cold, heating the cold dome and cooling the hot dome equally.

If a water pond were included in the clear (hot) dome and an open top water bladder in the dark (cold) dome they would also help regulate the temperature extremes.

Tubes big enough to walk through could connect them all.

GCNRevenger · 2005-08-11 08:04:27

I’m liking this idea of putting a large pond in a greenhouse to help regulate temperature. It will of course only be successful if the base is built near a large supply of water. However, I think it simplifies greenhouse construction greatly with respect to anchoring the greenhouse to ground. I always wondered if it would be difficult to transfport enough dirt to fill half the greenhouse. If water was used instead the water would just need to be piped in.
When you dig the trench to put the cylindrical greenhouse in just pour water in it instead of dirt. The water could even be piped in after the green house was already inflated. No need to go in and out of the airlock all the time. To me this seems much simpler then filling it up with dirt. I suggest that in a cylindrical greenhouse every so often there should be a valve on each side that can be opened to attach a pipe to exchange air or water between greenhouses and/or a support to support a platform above the water for people to walk on and/or grow non aqueous plants.
Perhaps also every so often there should be a section where doors or walls can be attacked to divide either the air space/end or water space. If such a section blocker was but in place then the water could be later pumped out of that section and replaced with dirt if desired. This of course would lead to issues if it was desired to remove the dirt at a later time so it may be desirable to put something between the walls and the dirt to protect the walls, should it be desirable to remove the dirt at a later time.

Anchoring? Huh? You would just tie them down with plastic rope or wire, not fill them with ballast. Filling the entire bottom of the greenhouse with water isn't such a good idea because the frozen Martian ground might freeze the water and interrupt the coolant flow. The idea is to circulate water through the greenhouses to the fish tanks, using the excess heat from the greenhouses to keep the fish tanks warm. And so if there were a dust storm/cold snap you could just heat the fish tanks and not need a seperate heating loop for the greenhouses.

Although there is some appeal to a completly passive system if the water in the floor of the greenhouse didn't freeze, it would be wonderful if the water could transport excess heat into the ground with no pumping or circulating.

Cookie-cutter construction is the order of the day for Mars, that you build plastic tubes with the top half exterior coated with the UV/IR reflective substance, and the lower half with Teflon for anti-abraison and soil chemical protection perhaps. Each end would be capped with a metal bulkhead or mating ring that would connect to the base airlocks or to other greenhouses. Digging machines would carve and smooth a shallow trench, and the collapsed greenhouse would be lowerd into it, the ring connected to the base, and inflated. Diggers would pile up Martian dirt about half way up the walls, and string tie-down cables over the top and anchor them with "tent pegs." External power/water hoses and wires would be connected, and the top would be coverd by retractable covers with a mirror finish on the inside to insulate during the night and concentrate sunlight in the day. The colonists would bring in pre-feb metal/plastic/glass Hydroponics or Aquaculture trays, a catwalk to walk on, and other equipment through the hatch.

GCNRevenger · 2005-08-11 08:11:31

What about a series of domes arrayed in a circle with one almost completely dark dome (for storage) connected to one that lets in more light, and so on until you get to a dome that is clear?
The hot air from the clear dome would migrate directly to the nearby dark (cold) dome and create a natural circular air transfer, hot to cold, heating the cold dome and cooling the hot dome equally.
If a water pond were included in the clear (hot) dome and an open top water bladder in the dark (cold) dome they would also help regulate the temperature extremes.
Tubes big enough to walk through could connect them all.

The whole point is to get rid of the excess heat generated by absorbed sunlight and waste heat from machinery inside the base. You can get rid of this heat in three ways, either by dumping it into the cold ground, trying to force it into the thin air, or by radiating it away into the Martian sky. It sounds like you want to get rid of the extra heat by dumping it into the ground which is in contact with the "dark" greenhouse. Since air is a lousy conductor of heat, that won't be a very efficent way to cool off the "hot" greenhouses. Although it would be an entirely passive system in theory... no natural circular air flow would be formed however, since the air would travel either direction. Using water vapor won't radically increase the flow of heat either, and will present humidity issues.

GCNRevenger · 2005-08-11 08:13:20

re: UV shielding:
I once had a plastic in my hands that was blocking all but a small percentage of UV, and all but 100% transparent. So they exist, but...
Used by musea, as a retro-fit to existing buildings with historical windows (so you can't just swap those out for UV-filtering glass, heritage protection and all that...)
I'm going through my notes, but have a the datasheets are in the lab at school
There is a vast range of those films, and here come several 'but's : but only a small subset is considered good, and it's hard to find out which. And they're horribly expensive... And they don't last very long, got to be replaced every few years...

I'm sure we could do better if we tried. There is also the fact that the degredation is accelerated by the combination of UV light and Oxygen (a really nasty combination) here on Earth, but if you block the UV light from entering the greenhouse, then there will be far less degredation since it can't reach the Oxygen to "activate" its plastic-eating properties.

Dook · 2005-08-11 08:50:23

To get a natural circular air flow the domes would be arrayed in a circle with the clear (hot) and dark (cold) domes next to each other but only connected by a small tube with one way flow direction valves. The small air flow tube should be high off the ground and angled slightly from hot to cold dome.

The cold air would have to travel all the way around, through every dome and walkway to get to the clear dome. The air flow would probably be very gentle and lose effectiveness in the morning (by then all of the air would be cold) and late evening (when all of the air would be warm) so the water bladder in the cold dome and fish pond in the warm would really be necessary.

GCNRevenger · 2005-08-11 19:18:12

"only connected by a small tube with one way flow direction valves"

Won't work. Small tubes can't move enough air, and a "one way" valve will not work for a continuous flow, which you have to have for such a tiny amount of pressure change.

Dook · 2005-08-12 04:21:47

You're so quick to criticize that you always miss the easy fix-make the tube bigger then.

But you don't have to because it will work just fine with a small tube (maybe 6'') because the air flow is going to be a gentle circulation anyway. Also with the air transfer tube being at an angle (upward from hot to cold dome) the one way valves may not even be needed.

GCNRevenger · 2005-08-12 08:14:12

I don't think that you understand the problem Dook, that you can't have a continuous circulating flow of air purely by thermal expansion.

Without pumps or fans, the air will only move until the pressure is equalized between the hot and cold regions. When you permit warm air to move into room with cold air, the air will stop when the pressure becomes equal, and so when you have opened all the valves between the hot dome and cold dome, the pressure will be equal and constant. Then, what happens when you try to complete the circut and open the next valve leading back from cold to hot around the other side of the loop?

Nothing! Since the pressure is equal to that of the "hot" dome, no air will flow. You can't have a continuous flow this way, because the pressure will quickly equalize and the flow will stop. And say you abandoned continuous flow and closed valves between hot/cold and let the hot dome pressure increase and cold decrease so you could repeat the sequential flow? No good either, since if you drain the air out of the hot dome at its maximum temperature during the day, then that will also be its maximum pressure, and the flow will again stop. Continuous or sequential flow, you won't get much air movement any which way since the pressure difference in the first place is so small, because what air there is won't expand or contract over the small temperature difference between the hot and cold domes.

And letting the air rise up hill? What are you talking about? The cold air will contract and sink right back down either direction equally, so you won't get any circular flow either. It won't be gentle, it will be zero.

John Creighton · 2005-08-12 10:13:02

If you had a cold green house besides a warm green surly you could open the door between the warm and cold greenhouse to cool the warm greenhouse down just like you can open a window in a house to cool a house down during the night. As for trying to improve the circulation perhaps you could try connecting the warm to the cool greenhouse at one end on the ceiling and one end on the floor so that the hot air would tend to flow out one side of the greenhouse and the cool air would tend to flow out the other side.

Fledi · 2005-08-12 10:32:11

That would help but there will have to be ventilators if natural flow is insufficient to exchange the air between different areas. This is because you will want to get the CO2 out of the living quarters and to the green houses even with mechanical aid if a natural flow isn't enough.
Alternatively one could try to filter out the CO2 and release it into the atmosphere near the living quarters and let some stream into the greenhouses. It might be too difficult to separate the small amount of CO2 to bother with though.

Still, it is not sure that air circulation alone will also be enough to exchange the heat, too, we need a design for a specific base and look into this matter with the whole system in mind, not just a part of it.

GCNRevenger · 2005-08-12 10:42:00

No, because this isn't like opening a window, there is a fixed amount of air inside and not an unlimited supply of cold air you can just draw in from outside. If the two greenhouses are connected, the air between greenhouses will not have a signifigant heat-flow or any special heat-rejecting properties. Remember: you have to aproach the thermal situation from a "total" prespective, it doesn't matter how much air your circulate if all the greenhouses absorb more heat then they lose in total. Thats all there is to it.

And besides, think, think about it... dark greenhouses? I mean come on, what a worthless waste of limited/expensive plastic & metal!

John Creighton · 2005-08-12 11:02:40

No, because this isn't like opening a window, there is a fixed amount of air inside and not an unlimited supply of cold air you can just draw in from outside. If the two greenhouses are connected, the air between greenhouses will not have a signifigant heat-flow or any special heat-rejecting properties. Remember: you have to aproach the thermal situation from a "total" prespective, it doesn't matter how much air your circulate if all the greenhouses absorb more heat then they lose in total. Thats all there is to it.
And besides, think, think about it... dark greenhouses? I mean come on, what a worthless waste of limited/expensive plastic & metal!

We, in theory we could make the dark greenhouse as big as needed, provided the plastic could be produced cheaply enough. Anyway, why do you assume the dark greenhouse will absorb more heat then it gives off? Doesn't the soil on the ground at the equator not get much above –20 degrees Celsius and aren’t the Martian winds 200 miles per hour? Also couldn't you design the material to make the walls out of for the dark greenhouse that is a good thermal conductor, reflects visible light and is transparent to infra red light? As for uses perhaps it could serve as a giant walk in fridge.

GCNRevenger · 2005-08-12 12:20:11

No substance on Mars, except perhaps water, CO2, and regolith, will be so cheap that you could afford to waste it on applications with such little bennefit. Sure we could make vast, huge "Dark" greenhouses as heat sinks, but how big do they have to be? Since most of that volume will be wasted, what good is it? The whole idea of a dark greenhouse is a pretty bad idea. Sure you could cover the thing with aluminum foil to keep it dark and cooler inside, but if its not much colder then it isn't an efficent way to cool anything, since you would need so many of them.

Don't go getting the idea you can use the dark greenhouses for anything very useful either, that since they will not be able to dump much heat if any at all, putting anything that makes heat in them will severely impact their effectiveness. Lighting, machinery, and even people generate signifigant amounts of heat that you would ultimatly go into making the "clear" greenhouses hot.

And I will say it again, you cannot focus on the thermal mechanisms of a single greenhouse, that the whole colony's heat flux has to be balenced. You can move heat from one place to another in the colony, but as long as there is more total heat entering the colony - clear greenhouse, dark greenhouse, buried HABs or whatever - then there is leaving it, then the colony as a whole will eventually overheat. This is alot like a ship full of holes; you can move water around to keep from drowning in a particular compartment, but if you aren't bailing out the ship as fast as water is flooding in, you'll eventually drown the denizens of some of the compartments anyway.

Temperatures of the soil and the Martian air aren't very relevent, the only real question is what colony buildings absorb or lose a particular amount of heat and how. The Martian air, even when blowing at 200mph, has only the same cooling potential as the faintest of breeze on Earth because it is so thin; the Martian air is actually a great insulator. The ground, though it may be pretty cold, is not that good of a conductor of heat either. It doesn't matter if its -20C or -200C, the only relevent quesiton is how much heat it draws away and how quickly. Plastic that the greenhouses will undoubtably be made of are generally pretty poor conductors of heat too, especially if they are thick enough to not be easily punctured.

Dark greenhouses can't be used for as a refrigerator since they will be pumped full of hot greenhouse air during the day, they can't be used for housing or workshops since they generate heat or get too cold and night, and can't really be used for anything except storing things that aren't sensitive to heat/humidity swings.

John Creighton · 2005-08-12 12:40:42

No substance on Mars, except perhaps water, CO2, and regolith, will be so cheap that you could afford to waste it on applications with such little bennefit. Sure we could make vast, huge "Dark" greenhouses as heat sinks, but how big do they have to be? Since most of that volume will be wasted, what good is it? The whole idea of a dark greenhouse is a pretty bad idea. Sure you could cover the thing with aluminum foil to keep it dark and cooler inside, but if its not much colder then it isn't an efficent way to cool anything, since you would need so many of them.
Don't go getting the idea you can use the dark greenhouses for anything very useful either, that since they will not be able to dump much heat if any at all, putting anything that makes heat in them will severely impact their effectiveness. Lighting, machinery, and even people generate signifigant amounts of heat that you would ultimatly go into making the "clear" greenhouses hot.
And I will say it again, you cannot focus on the thermal mechanisms of a single greenhouse, that the whole colony's heat flux has to be balenced. You can move heat from one place to another in the colony, but as long as there is more total heat entering the colony - clear greenhouse, dark greenhouse, buried HABs or whatever - then there is leaving it, then the colony as a whole will eventually overheat. This is alot like a ship full of holes in every compartment; you can move water around to keep from drowning in a particular compartment, but if you aren't bailing out the ship as fast as water is flooding in, you'll eventually sink (cook to death) anyway.
Temperatures of the soil and the Martian air aren't very relevent, the only real question is what colony buildings absorb or lose a particular amount of heat and how. The Martian air, even when blowing at 200mph, has only the same cooling potential as the faintest of breeze on Earth because it is so thin; the Martian air is actually a great insulator. The ground, though it may be pretty cold, is not that good of a conductor of heat either. It doesn't matter if its -20C or -200C, the only relevent quesiton is how much heat it draws away and how quickly. Plastic that the greenhouses will undoubtably be made of are generally pretty poor conductors of heat too, especially if they are thick enough to not be easily punctured.
Dark greenhouses can't be used for as a refrigerator since they will be pumped full of hot greenhouse air during the day, they can't be used for housing or workshops since they generate heat or get too cold and night, and can't really be used for anything except storing things that aren't sensitive to heat/humidity swings.

Aluminium is probably not the best material to use because at typical earth temperatures it absorbs more heat then it emits through thermal radiation. Also it is probably is not transparent to IR radiation since it is electrically conductive. As for plastics Mylar is considered an insulator and if the outside of it can be kept at Martian air temperatures and the inside is 30 degrees Celsius then if the Mylar was 1 cm think and 1/pi of it was perpendicular to the sun then the Mylar would let twice the heat conduct though it as is absorbed by the sun. So if we could devise a better conductor that would be strong enough if it was 1 cm thick I am not yet convinced it won't work. Must do more math.

As for plastic being cheap or expensive I was under the impression that you could make plastics from the Martian air. But perhaps the cost to make those plastics is well above the cost required to keep the greenhouse cool. However, there is something reassuring about a colony that doesn't need to depend on machines.

GCNRevenger · 2005-08-12 12:58:43

Are you sure about the IR transparency? Aluminum-coated Kapton is the insulation of choice to keep large space-based cryogenic tanks cold without going to too much trouble.

The assumption that a Mylar layer can be kept at the same temperature as outside air is a pretty big assumption, and one that is pretty unlikly given the hotter, thicker air inside. Unfortunatly too, there aren't many plastics with good thermal conductivity. Your figure for the amount of heat rejected is pretty big too, are you calculating the amount of heat lost to the thin atmosphere (in which case I wonder if you used Earth pressure instead of Martian in error) or by radiation (which does not take into account the insulating qualities of the Martian atmosphere, though this would be a small error).

As long as you aren't making a fluoropolymer or much polyamide/imide/aramide (nylon, teflon, kevlar), then all the atoms you need to make plastics are available on Mars in easy-to-get quantity. The trouble about making polymers is the amount of chemistry that has to be done to make them from raw CO2 and H2O, which is quite extensive. Hence, the polymer factory will be limited in its capacity due to its complexity, so you cannot afford to waste it.

Having a colony which doesn't depend on active machinery would be nice, but it really isn't practical to have this ability for any length of time. Sure a safety margin of a few hours or days before dangerous conditions arise would be a good thing, but at a certain point you just have to trust in the machinery not to fail. Airplanes, nuclear power plants, medical life support equipment, and many other systems that we literally bet lives on use active systems are relied upon today, and so too will Martians.

John Creighton · 2005-08-12 13:41:22

Are you sure about the IR transparency? Aluminum-coated Kapton is the insulation of choice to keep large space-based cryogenic tanks cold without going to too much trouble.

If you are using it as insulation you would want it to block or reflect right. Metals create a boundary in terms of elect conductivity which helps reflect infrared radiation. Works better at lower wavelengths and that is why waveguides are made out of metal.

The assumption that a Mylar layer can be kept at the same temperature as outside air is a pretty big assumption, and one that is pretty unlikely given the hotter, thicker air inside.

I agree but you got to start somewhere and I plan to develop the model further however, I believe in starting with the simplest possible model and building up from there. It provides a check on the more complex models and once the answers start to get close enough together you know you’ve included enough factors. I have presented more models I plan to develop here:
http://www.newmars.com/wiki/index.php/T … greenhouse
Also using simple models that only depend on a few factors lets you get a feel of what factors are significant one you start building more complex models.

Unfortunatly too, there aren't many plastics with good thermal conductivity. Your figure for the amount of heat rejected is pretty big too, are you calculating the amount of heat lost to the thin atmosphere (in which case I wonder if you used Earth pressure instead of Martian in error) or by radiation (which does not take into account the insulating qualities of the Martian atmosphere, though this would be a small error).

Clearly I assumed the atmosphere could take the heat away quick enough to keep the outside wall cold and I understand that this may not be the case. Perhaps if overheating is really the problem, the solution is to let only let in the visible light frequencies into the greenhouse that the plants need and make the greenhouses as transparent to IR light as possible.

If heat rejection is still a problem we will still need some way of dumping it whether we pump the heat into hotter greenhouses or metal radiators. As for plastics being used to transmit heat, what about a composite material perhaps metal disks helped together by plastic.

Having a colony which doesn't depend on active machinery would be nice, but it really isn't practical to have this ability for any length of time. Sure a safety margin of a few hours or days before dangerous conditions arise would be a good thing, but at a certain point you just have to trust in the machinery not to fail. Airplanes, nuclear power plants, medical life support equipment, and many other systems that we literally bet lives on use active systems are relied upon today, and so too will Martians.

Well, I suppose we can only try and see if in the end of the day it was worth the price.

GCNRevenger · 2005-08-12 16:00:48

I know that gold is used as a material to make infrared mirrors, and there are other inorganics that reflect IR but not visible. You must also balence the shape of the greenhouse that not too much light is blocked, which we have to maximize on Mars. I am already assuming that such a coating would be employed to help keep the greenhouses cool in the likly event that RobertDyck's quote about the heat flux is correct.

Simple models are a good starting point, but if you miss any major sources of heat flux, then they aren't much good.

I reiterate though, you must consider the heat flux of all the greenhouses at all different temperatures and probobly the whole pressurized volume of the colony. If the colony is absorbing too much heat, then you can't pump it into a "hot" greenhouse very well, since it would get too hot and nothing would live in there. I hope that putting (salted?) water in the bottom of the greenhouse would transfer enough heat from the air into the cold ground (water conducts heat MUCH better then air) to keep the air cool while retaining enough heat to keep the air warm in the night, moderating the temperature.

Plan B would be to connect the greenhouses by a series of "waterways" that would passively convey heat to a central "pond" which would act to moderate the temperature in the greenhouses, plus passively reoxygenate the water with the high surface area.

Plan C would be to force said water via hoses and pumps into greenhouses, and either using open-air "spillways" or sealed metal radiators to achieve thermal transfer.

Plan D, if its STILL not enough, then active mechanical cooling/heating would be called for, where a coolant (likly a water/antifreeze mixture) would be pumped into air conditioners in the greenhouses and to a centralized "heat pump" outside operated by electricity, either with a chinmey-effect or forced air radiator or through looped pipes buried in the cold regolith. If forced air heat transfer inside the greenhouse was an acceptable risk, then this method would be the easiest to construct, albeit the most energy hungry of the active systems. It would not be subject to water supply contamination issues either.

As far as increasing the thermal conductivity of the polymer without ruining its optical or mechanical properties, I don't think that is happening. Polymers are pretty much by nature lousy heat conductors, and if you add a dopant to them, their optical properties suffer badly.

Relying on machinery for a Mars colony is going to be a fact of life. Backup supplies of bottled oxygen and CO2 sorbants, freezedried food, drinking water, and emergency heaters would probobly provide a few days of life support, but active systems on some level, probobly a pretty signifigant level, are a must.

idiom · 2005-08-12 18:10:39

After you have taken corings around your base, could you insert long heat exchangers into the holes?

srmeaney · 2005-08-12 18:30:45

After you have taken corings around your base, could you insert long heat exchangers into the holes?

You could, but you would constantly need to repair and clean them. The heat dissapation leaves would be collecting water from the surrounding permafrost and everytime it shut off and on you get ice expanding and contracting between your metal leaves.

After a while they would need new ones. The old ones would be stuck in the Mars equivelent of Concrete so you would need new holes all the time.

Heat exchangers in the Permafrost (or is that dehydrated permafrost) might be an interesting way to produce convection in the "soil". Might even get stuff to the surface.

Its a real pity we cant trigger planet wide volcanic activity on Mars. It might be useful in churning up Minerals from the core and boiling the Permafrost.

idiom · 2005-08-12 18:47:34

Couldn't it simply be a metal tube, say 100 metres long? With a plastic tube running inside. If you kept the outer surface circular, to match the diameter of the hole then it could be easily removed when cold for replacement.

And you might not need to shut it down, just slow it down at night. You might need to reclaim heat at night depending on how finely balanced the heat situation is.

GCNRevenger · 2005-08-12 21:10:18

The whole point is to try and avoid needing to do anything external or requiring pumping to keep the greenhouse temperatures moderated, right? Adding external measures like heat pipes into the ground would require either plumbing/pumping or punching holes in the plastic walls.

If we had to go with active cooling, dumping the heat radiatively into the Martian air might be safer if you want to avoid problems with permafrost melting, even though it might be harder... How much harder I am not sure, but perhaps very hard due to the low temperature of the coolant.

srmeaney · 2005-08-16 19:48:57

Dumping the heat into the surrounding air might be interesting. You get a thermal pulse once a day comming from the Mars habitat sites. Convecting upward through the atmosphere very slowly (maybe all day) due to the low pressure. Any ice or water forming in the cooling thermal cell would snow/rain on your greenhouse every night. Might even get ice build up.

SpaceNut · 2011-11-29 20:24:25

Wow 2005 last post but here is a bump...

Putting Scientists on Mars in Permanent Colonies

Eminent physicist Paul Davies has a proposal for you: a one-way ticket to the Red Planet. As it’s typically conceived, a round-trip Mars mission would take about two years and cost at least $80 billion. But you could cut 80 percent of the expense, Davies says, by nixing the return and initiating a permanent Mars colony. The hard part, he says, isn’t subsisting in a hostile environment millions of miles from home but changing the Space Shuttle-era culture of timidity.

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