Terraforming planets/moons

[Eldan]

The same could be said for Earth.

On that note, remember to always get those funky moles checked out.

True, true. But Curiosity measured 76 mGy per year just from cosmic rays, not counting UV. (7.6 rad, for those who know that unit). I mean, that's not lethal in days or anything (that's around 5Gy if I remember correctly), but it's still... 100 full body medical Xrays per year. And that's before the planet ever gets hit by a solar flare.

And on Venus again, I mean, yes, we could give it an atmosphere and that is nice, I'm just saying that starting the terraforming process would be hard if any machine we can build would fry itself in an hour.

[Traab]

If we could terraform Mars (and to do so would take a very long time - estimates range from 1 to 100 thousand years), it would loose its atmosphere. Eventually. Of course, by the time we could do it, our tech would have advanced beyond our imaginations and we could probably keep the atmosphere maintained easily.

And if not, the atmosphere would still last for far longer than we would need it. It would last for a couple of million years before being lost again and by then it would really be a moot point. If humanity is still around in a million years we wouldn't really be needing Mars to live on anymore.

If its that slow a degradation then wouldnt we just be able to keep maintaining it?

[Frozen_Feet]

The space age has lasted for less than a century. Any talk of creating and maintaining a colony for longer than that is, at the moment, a total pipe dream.

Same goes doubly for non-planetary colonies. Last I checked, we have one experiment showing mammal embryos can develop in 0G, with all others having failed. Adult organisms fare only marginally better. Artificial gravity is theoretical at best, even spinning ships are not interesting to talk about before someone builds one.

[wumpus]

You ought to play the board game Terraforming Mars, where you play a corporation, funded by taxes, research and implement terraforming over generations. The vast majority of the cards are based on plausible, hard science fiction. Alas, it's still science fiction because transporting stuff around the solar system is currently far too expensive.

Actually transporting stuff around the solar system can be made quite cheap even with current technology. Getting it from the surface of Earth to space is another issue. Also getting things from the asteroid belt to elsewhere doesn't allow many of the available tricks.

Interplanetary transport network https://www.nasa.gov/mission_pages/g...se-071702.html
Ion propulsion (the Dawn probe had enough fuel to go from Earth to Mars 10 times) https://www.nasa.gov/centers/glenn/about/fs21grc.html
Aldrin cyclers (when you just want to go back and forth from Mars) https://en.wikipedia.org/wiki/Mars_cycler
(actually an Aldrin cycler really only makes sense for people. Cargo that doesn't need extra support would require more fuel to use the cycler).
On issue with Ion propulsion is that it takes a lot of power. Solar panels are great out to about Mars, then you better bring nuclear power. This brings its own issues, but they aren't insurmountable (especially if you use Americanium RTGs).

[Yora]

The space age has lasted for less than a century. Any talk of creating and maintaining a colony for longer than that is, at the moment, a total pipe dream.

Same goes doubly for non-planetary colonies. Last I checked, we have one experiment showing mammal embryos can develop in 0G, with all others having failed. Adult organisms fare only marginally better. Artificial gravity is theoretical at best, even spinning ships are not interesting to talk about before someone builds one.

There are people who are seemingly worried about how humanity will survive after all red dwarves have burned out and we're approaching the heat death of the universe. I don't know why, but apparently this is a serious concern for some.

The only place to live off Earth is in space. Because human bodies need gravitational pull working on it. You can get that from a planet with the size of Earth or Venus, or in rotating space stations. There is no way, nor any hypothesized physical phenomenons, that could somehow increase the gravity on a planet.
And 40% Earth gravity on Mars isn't going to be anywhere near enough. You might be able to learn to walk without falling over all the time, and with regular exercise adults might be able to maintain their muscles and circulation.
But when we're talking about coolonization, we are talking about permanent habitation and people being born and growing up there. I really don't want to imagine the effects on bone growth and motor control in children in low gravity, but I would expect severe physical disabilities without exceptions. Severe brain and nerve disorders also wouldn't surprise me a bit.

With any object other than Venus and Mars in the solar system, the effects would even be much worse.

And regarding adding greenhouse gases to Titan: Methane is a extremely powerful greenhouse gas. And it already exists on Titan. There are methane clouds, methane rain, methane, river, and methane lakes. I don't think adding more greenhouses gases would help.

[gomipile]

There is no way, nor any hypothesized physical phenomenons, that could somehow increase the gravity on a planet.

We do it all the time. With centrifuges. Granted, making a large centrifuge that can be lived in would be a engineering challenge, but I think it could be done. After all, we already have large rooms that roll on bearings for long periods of time in the form of trains. Something as reliable as a train that provides 1g net acceleration should be good enough.

Sure, it'd be expensive-ish at first, but maybe we'll only need them part of the time, too, given further research. We might find out that full Earth gravity is only necessary 100% of the time during pregnancy and the first "n" years of life, etc.

We might even find out that 1g isn't the healthiest value of gravity to live at long term. If the "best" value turns out to be lower than 1g, then the centrifuge houses will be cheaper to build and maintain.

[halfeye]

We do it all the time. With centrifuges. Granted, making a large centrifuge that can be lived in would be a engineering challenge, but I think it could be done. After all, we already have large rooms that roll on bearings for long periods of time in the form of trains. Something as reliable as a train that provides 1g net acceleration should be good enough.

The problem with large centrifuges in space is that they must constantly be under 1g of strain. The bigger they get, the more massive they become, and the more strain (in terms of tons) there is on them. It's the same reason elephants can't fly, things increase in mass by the cube as their linear dimensions increase. A small centrifuge (say the size of the wheel in a hamster cage) would be adequately strong and relatively light, but it would have to rotate very fast (but nothing like impossibly fast) to generate 1g.

[Lord Torath]

The larger the radius of the cylinder, the slower it needs to rotate to generate 1 G of acceleration at its outer surface (okay the inside of its outer surface). Plus, we build structures to resist 1 G of acceleration literally all the time. Most of them resist 1 G of compression, rather than tension, but it's still not a major engineering challenge.

[Xyril]

True, true. But Curiosity measured 76 mGy per year just from cosmic rays, not counting UV. (7.6 rad, for those who know that unit). I mean, that's not lethal in days or anything (that's around 5Gy if I remember correctly), but it's still... 100 full body medical Xrays per year. And that's before the planet ever gets hit by a solar flare.

Sorry, I was just making a joke. I don't want you to think I was dismissing your point, which is certainly an issue we wouldn't be able to ignore on any serious venture to Titan.

And on Venus again, I mean, yes, we could give it an atmosphere and that is nice, I'm just saying that starting the terraforming process would be hard if any machine we can build would fry itself in an hour.

That's certainly true, but I don't really think it would be something done on the surface. If machinery of some sort would be required, it would probably have to be deployed to float/orbit in the marginally-less-hellish zone. However, even if it weren't impractical to do so, I don't think the terraforming of Venus would start with some sort of mechanical system at the surface. Instead, we would probably have to pretty much drop chemicals into the atmosphere to start nudging the atmospheric chemistry back in the right direction--maybe with carbon sequestration on a massive scale. Alternatively, we could alter the energy balance of the system, maybe direct enough radiation towards Venus to strip away some of the atmosphere, or deploy satellites in orbit that can deflect most of the solar energy away from the planet. I'm just spitballing here: Maybe whatever practical solutions we engineer will be hampered by the challenge of getting delivery devices to work near the surface, but it seems just as likely that won't need to get anywhere near the surface, at least in the early stages.

[halfeye]

The larger the radius of the cylinder, the slower it needs to rotate to generate 1 G of acceleration at its outer surface (okay the inside of its outer surface).

It's slower, but the whole point is it still generates a constant 1g, and there's nothing else to take the strain.

Plus, we build structures to resist 1 G of acceleration literally all the time. Most of them resist 1 G of compression, rather than tension, but it's still not a major engineering challenge.

The ones that are similar in specification are bridges. Sometimes bridges fail, it's often not a big problem, because not many people are on them at the time, and there's time to get off. There won't necessarily be anywhere safe to go from a space station. People have built some nice, impressive bridges, the old ones tend to be heavy stone structures, which is fine, because they are solid and the main threat is typically water. We really don't want the equivalent of a humpback bridge in space.

[Lord Torath]

The ones that are similar in specification are bridges. Sometimes bridges fail, it's often not a big problem, because not many people are on them at the time, and there's time to get off. There won't necessarily be anywhere safe to go from a space station. People have built some nice, impressive bridges, the old ones tend to be heavy stone structures, which is fine, because they are solid and the main threat is typically water. We really don't want the equivalent of a humpback bridge in space.

All that is required is a different set of specifications. We can do the math to determine the involved loads, and design accordingly. This is easy-peasy. Wind loads (the cause of "Galloping Girdie"'s demise) are non-existent in outer space. We will certainly still need to take harmonics and vibrations into account, design for atmosphere retention (pressure vessel), and design for interactions with visiting spacecraft, but again, these are all things we can do. It's feasible with current materials. We can even design for micrometeorites. The structural requirements of space stations are easy (relatively). We can even design fail-safe mechanisms for when things do go wrong. The question isn't if we can design and build a safe space station. It's a question of cost vs benefit.

[zlefin]

by the time we're able to do serious space colonization/terraforming, or shortly thereafter, there's a good chance we'll have bioengineering capabilities advanced enough to adjust life forms to work in different gravities.

[Leewei]

We do it all the time. With centrifuges.

In 0G, this would be needed. In 0.4G, there's an easier solution: suit up with additional 100-150% mass.

[gomipile]

In 0G, this would be needed. In 0.4G, there's an easier solution: suit up with additional 100-150% mass.

That doesn't address the health of organs and body parts that aren't load bearing. Is there a weight training regimen that can be handed to a developing fetus to make it develop the same as it would in 1G?

(edit: If it turns out that more g force than locally available is necessary for fetal development after future research.)

[Knaight]

Venus is theoretically possible if we ignore resources - but if we start considering resources things look grimmer. Currently our state of the art terraforming technology is failing to reduce atmospheric CO₂ concentrations by 200 ppm on Earth, where there's no need to put stuff in space. Venus meanwhile would need 965,000 ppm reduction in CO₂, and that's without getting into how much thicker the atmosphere is. Sure, there's no need to counteract other industry but that's a far smaller concern than going through space is.

[Tvtyrant]

I think it is almost a given at this point that we aren't going anywhere unless some miraculous new scientific theory finds a way around the current issue (IE gravity and fuel.) Every rocket we send up is using irreplaceable fuel from a dwindling pool that has to be shared with everyone else's needs, and the amount we can send up is tiny.

If we invent anti-gravity or manage to invent a material capable of making a space elevator, great. Otherwise we are spending billions to support a few hundred people in space, not a great prospect with climate change happening right now.

[halfeye]

I think it is almost a given at this point that we aren't going anywhere unless some miraculous new scientific theory finds a way around the current issue (IE gravity and fuel.) Every rocket we send up is using irreplaceable fuel from a dwindling pool that has to be shared with everyone else's needs, and the amount we can send up is tiny.

I don't know what the fuel bill for an Atlantic Crossing by jet aircraft is, but I wouldn't be surprised if it was more than a shuttle launch used to use. Rockets burn a lot of fuel fast, but they don't burn it for very long.

[gomipile]

Every rocket we send up is using irreplaceable fuel from a dwindling pool that has to be shared with everyone else's needs, and the amount we can send up is tiny.

We don't always use liquid hydrogen fuel, but we have used a lot of hydrogen fueled rockets and we could again if necessary. Hydrogen is hardly what I'd call "irreplaceable."

[Traab]

Cant we just bring back the nuke powered rockets?

[Xyril]

Venus is theoretically possible if we ignore resources - but if we start considering resources things look grimmer. Currently our state of the art terraforming technology is failing to reduce atmospheric CO₂ concentrations by 200 ppm on Earth, where there's no need to put stuff in space. Venus meanwhile would need 965,000 ppm reduction in CO₂, and that's without getting into how much thicker the atmosphere is. Sure, there's no need to counteract other industry but that's a far smaller concern than going through space is.

That's true, but that's pretty much why I feel Venus is the best bet: All of the other options would also require resources beyond what our economy could support, but calling them "theoretically possible" even is tenuous at best. Venus requires an unlimited bank account and probably substantial evolutionary advances in science and technology; Mars requires the same, except the necessary advancement would be nothing short of revolutionary steps.

It's slower, but the whole point is it still generates a constant 1g, and there's nothing else to take the strain.

It's been a long time since solid mechanics, but isn't pretty much every suspension bridge on Earth under a constant 1g strain?

If we're talking about a giant bicycle wheel type deal, where all the spokes are effectively the only thing imposing the necessary centripetal force on all of the rotating bits, and you're transferring the collective force of g times all that mass onto a small structure near the center, I can see how that would get bad, quickly. However, if you literally have a cylinder being put into a spin by reaction thrusters, then the structure imposing the needed centripetal force on one differential chunk of cylinder is the next differential chunk of cylinder. Again, a long time since solid mechanics, so I don't know if that force will be the equivalent of 1g on that differential mass, or several times g on that mass, but I don't think it would be more than an order of magnitude. In terms of materials science, I think we can already handle those sorts of stresses: Jet engines, for example, probably experience hundreds of gs worth of stress, and they're manufactured to last thousands of hours without failing. Steam turbines probably experience slightly lower stresses, but they run for years. Because their geometry is constrained by fluid dynamics, they're probably not as mechanically robust as they could be if we took the exact same material and just made a solid cylinder out of it.

[Excession]

I think it is almost a given at this point that we aren't going anywhere unless some miraculous new scientific theory finds a way around the current issue (IE gravity and fuel.) Every rocket we send up is using irreplaceable fuel from a dwindling pool that has to be shared with everyone else's needs, and the amount we can send up is tiny.

Rocket fuel does not need to be made from fossil fuels. The next generation of engines from both SpaceX and Blue Origin will both run on liquid oxygen and liquid methane, which can be made from solar power, water, and CO₂. Methane is also nice because it burns a little cooler and cleaner than kerosene so the engines are easier to reuse, and can be used to pressurise the tank as it empties rather than carrying helium to do that. Compared to hydrogen it's smaller and easier to handle; hydrogen tends to leak through metal tanks. Plus you can make it on Mars.

[LordEntrails]

It's been a long time since solid mechanics, but isn't pretty much every suspension bridge on Earth under a constant 1g strain?

If we're talking about a giant bicycle wheel type deal, where all the spokes are effectively the only thing imposing the necessary centripetal force on all of the rotating bits, and you're transferring the collective force of g times all that mass onto a small structure near the center,....

Yea, nope. It's dynamics you need to worry about.

Assuming a spinning "wheel" type station, like '2001: Space Odyssey" the hub is only under tension. And almost all materials are much stronger in tension than compression. Plus tension does not have any failure modes like buckling, etc.

As Lord Torath stated, the design and materials for a station with a revolving wheel is not challenging. Materials under 1g of tensile strain is not that big a deal. We do it all the time. For reference, a station with the target 1g diameter of 1000 meters only has to revolve at about 1.3 RPM. We really are not talking high speed.

Think of it this way, take a yoyo on a string and spin it around. How often does that string break? Pretty rare unless you have mistreated that string. Now, replace that string with braided steel wire, or carbon nano-tubes. Or with a redundant structure of multiple load bearing members. And, note that when you are spinning that yoyo around, you are probably subjecting it to 6 or 8gs, not 1.

[halfeye]

It's been a long time since solid mechanics, but isn't pretty much every suspension bridge on Earth under a constant 1g strain?

Yes, but the straining lines/bars are connected to the pillars, which are supported by the ground, and in compression.

If we're talking about a giant bicycle wheel type deal, where all the spokes are effectively the only thing imposing the necessary centripetal force on all of the rotating bits, and you're transferring the collective force of g times all that mass onto a small structure near the center, I can see how that would get bad, quickly.

So we have no central piece, just bars going past each other. We probably want something near the centre, but there's no reason it has to bear all the tension.

The thing about the suspension bridges is that they're always being maintained, painted, etc. It's very much more difficult to do routine maintenance in space.

If there's a hotel just above LEO, then it probably ought to be in freefall, that's what the tourists will be there for after all, the ISS shows that can be done.

I'm not sure that the never ending suspension bridge in space is impossible, but I do think it will be very difficult. Suspension bridges are carefully designed long before they are built, they're not something it's easy to do even down on Earth. I think there needs to be temporary living capacity nearby so that if it fails there's somewhere to go, even if that is weightless.

Aircraft are made with a limited number of flying hours intended for them, they go up, the come down, they are maintained and refueled before they go up again. The bridge to infinity will be built in space, and it will stay up, with no maintenance until it breaks.

Jet engines, for example, probably experience hundreds of gs worth of stress, and they're manufactured to last thousands of hours without failing.

Now. The first ones to fly in combat had service lives on average of twenty hours.

Steam turbines probably experience slightly lower stresses, but they run for years. Because their geometry is constrained by fluid dynamics, they're probably not as mechanically robust as they could be if we took the exact same material and just made a solid cylinder out of it.

Until we're smelting asteroids, every bit of usable metal in space is going to come from Earth. A solid steed cylinder with a 1000 meter diameter 10 feet thick would weigh what? It would certainly be immensely strong, but it would be so massive, where would all that metal come from.

[factotum]

Yes, but the straining lines/bars are connected to the pillars, which are supported by the ground, and in compression.

That's irrelevant. In a spinning space station the support cables would be connected to a central hub rather than the support towers. so as long as *that* can support the weight (and they don't pull a howler like the Hyatt Regency walkway collapse) you're fine. Oh, as for your comment about old bridges all being big stone ones, there were some proto-suspension bridges built in Bhutan in 1433, the last of which didn't collapse until 2004--and it was washed away by floodwaters, it didn't fall down of its own accord.

[Frozen_Feet]

Re: "Terraforming Titan"

Titan's atmosphere is full of methane and its general chemical composition is simimar to primordial Earth. It has been theorized that Titan could warm up and become life-bearing on its own...

... after the Sun turns into a red giant.

Beyond that, it's just too far from a heat source to become sustainably Earth-like.

---

Re: "spinning spaceships"

The engineering challenges are not in making something that can spin for long periods of time, they are in getting all the crap up in space and then making the spinning thing livable. The biggest challenges are related to the fact that terrestrial life has been shown to fare really poorly in space, much more poorly than was expected when spinning ships were first thought up.

That's why I say it's not interesting to talk about before someone builds one. We need genuine experimental data on terrestrial life living on such things for extended periods. Before that, we risk falling into "spherical cows in a vacuum" type of deal.

[factotum]

I think it's impractical to move all the stuff required to build one of these things into orbit, which is why we need to be looking at asteroid repositioning and mining--e.g. mine the materials up there. This is itself a massive undertaking, but IMHO it's the real starting point for any sort of space habitat.

[Knaight]

That's true, but that's pretty much why I feel Venus is the best bet: All of the other options would also require resources beyond what our economy could support, but calling them "theoretically possible" even is tenuous at best. Venus requires an unlimited bank account and probably substantial evolutionary advances in science and technology; Mars requires the same, except the necessary advancement would be nothing short of revolutionary steps.

You'll get no argument from me here - Venus is better than any planet besides Earth, hands down. It's just worth noting that Venus is still far, far beyond current technology or even anything that's closer to a projection than an optimistic far future assumption. It's a monumental task compared to the tiny one of getting Earth back on track, which we're failing miserably at.

[Kato]

Okay, serious serious question : if we had a way to keep Venus from receiving any solar heat / radiation, what would happen?
Blind intuition would be since it's basically at equilibrium right now, it'd cool by à decent amount pretty fast, even given her high albedo. Putting time scales aside, what would happen ? The clouds should cool and rain increase, cooling the surface. But my gut tells me there's so much internal heat this would still take a long time to get anywhere comfortable. And then... We have oceans of sulfuric acid and CO2? Doesn't seem too nice but I guess it's a start if we can regulate how much solar rays reach it afterwards.

[halfeye]

That's irrelevant. In a spinning space station the support cables would be connected to a central hub rather than the support towers. so as long as *that* can support the weight (and they don't pull a howler like the Hyatt Regency walkway collapse) you're fine.

There would be no reason to have tension in the central hub, that would make that the obvious failure point, and there's no need for it. I am really not convinced that this is an easy thing to build. It's presumably intended to last for tens of years, there is no easy way to do maintenance on it, and it will be in constant tension. Aircraft are built with an intended life time of thousands or lately tens of thousands of flight hours, that'll be gone in months. What does for aircraft is the changes in stress and strain, this thing will suffer variations in stress and strain due to heating, it will be sitting in sunlight most of the time, sometimes it will pass through the shadow of the Earth, sometimes it will turn over as the Earth moves around the Sun.

Oh, as for your comment about old bridges all being big stone ones, there were some proto-suspension bridges built in Bhutan in 1433, the last of which didn't collapse until 2004--and it was washed away by floodwaters, it didn't fall down of its own accord.

That's not old. I was thinking of the old road humpback bridges (not that they're necessarily that old, one I remember being over a railway track), the single span ones, they're typically quite small, and very massive for what they are, but not big at all.

I think it's impractical to move all the stuff required to build one of these things into orbit, which is why we need to be looking at asteroid repositioning and mining--e.g. mine the materials up there. This is itself a massive undertaking, but IMHO it's the real starting point for any sort of space habitat.

Yes, we need to be doing that as soon as possible, but it's probably not going to be that soon unfortunately.

Okay, serious serious question : if we had a way to keep Venus from receiving any solar heat / radiation, what would happen?
Blind intuition would be since it's basically at equilibrium right now, it'd cool by à decent amount pretty fast, even given her high albedo. Putting time scales aside, what would happen ? The clouds should cool and rain increase, cooling the surface. But my gut tells me there's so much internal heat this would still take a long time to get anywhere comfortable. And then... We have oceans of sulfuric acid and CO2? Doesn't seem too nice but I guess it's a start if we can regulate how much solar rays reach it afterwards.

We need to check first that there's nothing exotic living on Venus as it currently is. We can make machines to survive the temperature and pressure, it would be difficult, but iron is still solid at that temperature so it could be done.

The temperature variation at the poles of Earth is all due to incoming solar radiation.

I am pretty sure that with sunlight totally blocked you would see Venus drop at least 30 degrees Celcius per Earth year, quite possibly a lot more than that. Once the temperature is down below the boiling point of water, you can parachute in some sulphur eating bacteria and selected ordinary plants, desert adapted ones if there's really very little water. I'm not sure how much water there is present on Venus, people sometimes say none, but there's sulfuric acid, which is H2S04, so there's some water in that. The clouds are sulfuric acid, so they won't rain or will rain acid. The ph will be very much on the acidic end of the scale, CO2 is acid too.

[gomipile]

Okay, serious serious question : if we had a way to keep Venus from receiving any solar heat / radiation, what would happen?
Blind intuition would be since it's basically at equilibrium right now, it'd cool by à decent amount pretty fast, even given her high albedo. Putting time scales aside, what would happen ? The clouds should cool and rain increase, cooling the surface. But my gut tells me there's so much internal heat this would still take a long time to get anywhere comfortable. And then... We have oceans of sulfuric acid and CO2? Doesn't seem too nice but I guess it's a start if we can regulate how much solar rays reach it afterwards.

High albedo slows cooling as well as heating. Black bodies are perfect radiators as well as perfect absorbers, and the reverse holds for reflective objects.