New Mars Forums

It would definitely be interesting to try out some robotic mining techniques. I think hollowing out an asteroid would have to be done by robots and not by humans in very bulky and very vulnerable to damage space suits. What do you think?

What kind of energy would be required to spin up a d=500m asteroid? Let's take Golevkaas an exercise.

Golevka m = 2.1E11 kg
Radius r ~= 300m

One rocket to a point on the surface, to produce tangential thrust. Another rocket to the opposite point on the surface, to produce tangential thrust in the opposite direction. How powerful would the rockets need to be to make it do 2rpm?

First we need to calculate the target rotational energy

Erot = 0.5Iw2 = 0.5 * 0.4mr2 * w2

m = 2.1E11 kg
r = 300m
w = 2 rpm = 4pi rad / 60 sec = 1/15 pi rad/sec

Erot = 1.66E14 J = 166 000 GJ

P = 1GW power plant

t = E/P = 166 000 GJ / 1 GW = 166 000 sec =~ 1,92d

So, if my calculations are correct, a 1GW power plant could set up that rotational speed in two days. A 10MW solar array could power the sufficient rotation in 192 days, less than a year. Are my calcs in the right ballpark?

Leaving aside the debate of *whether* we should colonize free-floating space. Let's start this thread with the premise that we *wish* to build some more space stations. Maybe 10 years from now, maybe 100, maybe 1000, doesn't matter. But I just want to explore the possibilities of building habitats somewhere other than on planets, moons or asteroids.

Whenever we get to our civilization's next space station, what should it be like? What is important in the design of a space station? What sort of roles should it fill? What kind of architecture should it go for?

In my opinion, the next space station (heretofore referred to as NSS) should be built with long-term human habitability in mind. We've done the short-stay scientific research station with ISS, and it's time to go for the next step and see whether it's possible to engineer long-term habitability.

Accepting that premise (long-term human habitability) strongly suggests that we should attempt to provide artificial gravity just to be on the safe side, since we do not yet know the effects of long-term lack of gravity on habitability. And if we intend to try to implement artificial gravity, that places lower limits on the station's size. You can only implement artificial gravity on stations that are big enough.

Specifically, the g-force provided is linearly dependent on two variables. The radius of rotation, and the square of the rotations per minute. We could have a very small radius of rotation, but then the RPM (because it grows with square) would have to be insanely high. According to some studies, the highest RPM humans can tolerate long-term is 2 RPM. So if we set that 2 RPM as our parameter, we can calculate the necessary radius to establish 1g of artificial gravity, and the radius turns out to be ~224 meters. We could have a smaller radius, but then we'd have to increase RPM to intolerable levels, or we'd have to do with less than 1g of gravity. Personally, I'd rather we try for the full 1g. So, we end up establishing a lower limit of 224 meters for the radius of rotation for the NSS.

Premise 2: Minimize cost. I want to do the calculations for the very lowest limit possible, and see if the most minimal 1g space station possible is even economically doable. If the most minimal 1g space station is not economically possible, then we'll have to be stuck with things like ISS for the foreseeable future.

Accepting premise 2, cost minimization, means we want to find the shape that has the smallest surface area. The amount of surface area is directly proportional to the amount of metals (for building the superstructure) that we will need to import out of Earth's gravity well (or out of asteroids, or any source, really). The less surface area, the less raw materials we will need to build the superstructure.

To have the same gravity at each point along the walkway inside the station, that walkway will need to be the same distance from the center of rotation, i.e. the livable surface will form a circle around the center of rotation. If we include all the space inside the circle in our space station, we will create a disc-shaped station, with no ceiling. If we looked up, we'd see buildings hanging 2*224 meters above our heads. However, that is a bit of a wasteful design. Doing a torus instead, so that we cut out the center of the disc and leave it open to space, will result in surface area/amount of imported metals reduction of noticeable proportions as follows:

Parameters: Radius of rotation 230 meters. Width of habitat 20 meters.

A disc would have a surface area of 361,283m2 and a volume of 3,323,805m3.

A torus would have a surface area of 90,800m2 and a volume of 454,002m3.

As we can see, if we were to build a disc instead of a torus, we'd have to import 4 times the amount of metal, at 4 times the cost. Building a torus instead of a disc is 75% cheaper.

However, it will be a lot easier to live inside the tube if its cross-section is a square (or rectangle) instead of a circle. It would be fairly difficult to construct buildings when the "ground" isn't level. Try placing furniture in a room whose floor curves noticeably. So in the interests of ergonomy, I'm exploring the possibility of a torus that has a tube cross-section of a square instead of a circle.

A squaroidal torus of the same dimensions as the above would have a surface area of 115,611m2 and a volume of 578,053m3. That's a 27% increase from the circloidal torus. It means a 27% increase in cost. Or, conversely, at the same cost, we could have a livable area width of 15,6 meters as opposed to the 20 meter circloidal width, if we wanted to keep costs the same.

For simplicity of building stuff inside the torus, I am going with a squaroidal cross-section even though it will mean a slightly increased cost (or reduced width). So we've determined the shape the space station should be. It's going to be an approximately 230m radius torus which means 1445m long habitat. You make a morning jog through the hab, when you get back to your starting point, you'll know you've jogged nearly 1.5km. This'll be a more impressive jog distance when we build a 2g space station.

I'm going to refine and minimize the dimensions of the cross-section now. To avoid bumping our heads, we don't need the ceiling to be much higher than 2.5 meters or so. However, we might like to have more headroom than that simply for air circulation and the feeling of openness, to avoid any claustrophobic kinds of feelings. I would personally suggest a ceiling height of 5m -- a nice, good headroom without going nuts with open "sky". But, perhaps, while we're doing an exercise in minimalization, I should tone that down a bit. I'll go with a 3m ceiling.

As for the width of the habitat, I think there needs to be a transit system running through the length of the hab, a "road" as it were. Since the hab will be too small for vehicles of any kind (except perhaps bicycles) this pretty much means the road will take approximately a human's width, perhaps a little more for comfort.  Let's give the road a 2m width, that will be enough for one-direction traffic, and enough space to dodge another person as well if they're coming from the opposite direction. So the road alone will require 2m of width for the hab. The rest of the width for the hab is all about the widest item to be included in the station. If the station will have a nuclear reactor 50m wide, then the hab will need to be 52m wide altogether. If the biggest item to be accommodated is a 2m bed, then we could build a hab only 4m wide. I would say that 4m width is probably as small as a hab could be possibly constructed. It would probably require much more, but I'd say 4 is the minimum.

So, now we have a hab that is 4m wide, 3m high to the ceiling, and 1445m long. Now that we know the width, we can calculate that the rotational radius (from center of rotation to center of hab) is 226m (224m to the inner surface of the hab + 2m to the center of hab). With these parameters, let's re-do our calculations.

Rotational radius: 226m
Disc hab width: 4m
Torus hab width: 4m
Rectanguloidal torus hab width: 4m
Rectanguloidal torus hab height: 3m

Disc A = 326,600m2 V = 641,860m3
Torus A = 17,844m2 V = 17,844m3
Rectanguloidal torus A = 19880m2 V = 17040m3

By these figures we can see that by rectangularizing the cross-section of the hab, we increased the surface area, but actually decreased the amount of livable space (volume) from the torus. Compared to the torus, we have 111% the surface area (and thus cost of materials importation) but only 95% the volume. If we were to pull the ceiling down to 2m, we could reduce these figures to 95% and 64% of the torus. If we'd increase the ceiling to 4m (same as width, thus a squaroidal cross-section instead of rectanguloidal) we'd have 127% the area and 127% the volume. 5m ceiling would have 143% the area and 159% the volume. As we can see from these numbers, the higher the ceiling goes, the more dominant the volume becomes. If the hab height is less than width, we have more area than volume. If the hab height is equal to width, area and volume are equal. If the hab height is more than width, then the volume starts to exceed area. In any case, let's move on with the final figures for our hab.

Rotational radius: 226m
Rectanguloidal torus hab width: 4m
Rectanguloidal torus hab height: 3m
Rectanguloidal torus hab length: 1420m
Rectanguloidal torus surface area: 19880m2
Rectanguloidal torus interior volume: 17040m3

For comparison, ISS interior volume is approximately 1000m3, so this would have the interior space of 17 ISSes.

Next, I'm going to calculate the cost of getting the raw materials into GEO. I don't know what kind of material and thickness ISS walls are constructed of, so I could use help to refine those numbers. I have guessed the below numbers:

Wall thickness: 0,01m (10cm)
Wall volume: 0,01m*19880m2 = 199m3
Wall density: 2700kg/m3 (aluminum)
Superstructure mass: 536,760kg

Now, we have a huge torus built, but we still need to fill it with an atmosphere. Let's go with a simple 80/20 N/O mix. So, we multiply the volume by 80% and multiply that with nitrogen density, do the same with oxygen.

Nitrogen mass: 17,054kg
Oxygen mass: 4,870kg

Adding all of those together, we get

Total mass (superstructure + interior atmosphere): 558,684kg
Price to GEO: 20,000$/kg
Price to GEO: 11,173,672,331 $ = approx. 11 billion

And that's just for transporting the raw materials, not including obtaining the raw materials, building them into modules, manpower, or anything else. I could use some help with estimating those figures.

If oriented optimally towards the sun, the station's surfaces would present a 5680m2 catchment area (4m width * 1420 m length) for solar rays. If the entire surface were to be covered with space-rated solar panels (1kg = 1m2 = 300W) it could produce 1.7MW while adding 5680kg to the station weight. (Covering the entire station area, including the central gap, with a disc of solar panels, would produce approx. 49 MW and would weigh 163 tons.) At $2.50/Watt, it would add 4.26 million dollars to the station's cost to include that 1.7MW power plant.

More thoughts to come...

Of late I've been toying with the idea of a fission reactor providing power for a plasma or ion thruster type engine. The real make-or-break for whether fission reactors are feasible for interstellar transportation comes from their weight. I've been able to find data on the power output, but not so much on the weight of fission reactors. I have been specifically looking at fission reactors designed to operate on vehicles, such as:

OK-150 and OK-900 are used on icebreakers and produce 90 and 171 MW respectively.

K48 used on French nuclear submarines and produces 48 MW.

S6G used on US nuclear submarines and produces 165 MW.

I just haven't been able to find any data at all about reactors' physical dimensions (how much room they require) and how much they weigh. These are rather make-or-break things, so I'd be very interested if anybody could give any ballpark figures.

So we should just bend over, spread our buttocks, and accept whatever the planet decides to throw at us? With that mentality, we'd still be living nomadic existence, because building houses is reclaiming land from nature to our use.

So I guess we shouldn't try to restore the Aral Sea, we should just accept that the planet "wants" it to be a barren wasteland now.

We shouldn't try to restore the Sahara, we should just accept that the planet "wants" it to be a barren wasteland now.

Do we have the "right" to irrigate land that became desert in the last 5 years, in an attempt to restore it to bloom? If not, that's basically a mentality of "bending over and letting the planet do as it will". If yes, then do we have the "right" to irrigate the land that became desert in the last 50 years? 500 years? 5000 years? Where does the limit go? If we go back far enough, Sahara wasn't desert. We have the "right" to turn back the clock by 5 years, but not 50,000? Where does the line go, and who has the right to decide where the line goes?

Because rocket technology is not yet as mature as balloon technology is. You cannot discredit the safety of balloon technology by dragging in another tech and saying, "look how unsafe this entirely unrelated technology is!"

Livable temperature. Livable pressure. Easy access to oxygen, carbon and nitrogen. On a space station, every single kilogram of oxygen or nitrogen (or anything else) that you need will need to be imported for a high price out of a gravity well. If you want to "live off the land", it's usually smart to pick a land that actually *has* some resources. The livable temperature and pressure of Venus mean that systems failures will have much less drastic results. Having a space station suddenly exposed to absolute zero vacuum due to hull breach will do a lot more damage than having a cloud city suddenly exposed to 50C temperature and 1 bar pressure due to hull breach.

"Adding water" is even more complex than importing hydrogen, because "adding water" is importing hydrogen *and* oxygen.

And Venus doesn't really need any more oxygen, so importing water rather than importing only the hydrogen seems to be a waste of resources. We don't need to import any more oxygen.

Only at certain altitudes, which we can avoid.

Oh I see, you're going for the "designers are idiots because that's the only way I can come up with a far-fetched disaster scenario so I can doomsay".

Any *intelligent* designer will include redundancies, so any *one* problem won't end up crashing the float.

You could also say that "one problem and a terrestrial hot air balloon falls to the ground from 1km altitude". You know what? People still go up in terrestrial hot air balloons. When's the last time you've heard of a balloon accident on Earth? Here's a hint: they're very rare. You know why? Because this is proven, well understood technology that our civilization has mastered to a *very* high level.

The only real problem with terrestrial zeppelins was hydrogen use (Hindenburg), but since hydrogen would not be used on Venus, even that problem is eliminated.

This is very well understood, mastered, functional technology. Humans can do balloons *very* well.

Fine, fine, if you want to nitpick, I can provide...

Tesla

Go diss him.

http://news.nationalgeographic.com/news … water.html

Not that I'm aware of. It can be terraformed perfectly fine where it is. If you want to reduce the solar constant, a solar shade makes FAR more sense, as it is a LOT less work, than moving around a planet-size mass for 0.3 AU.

If we don't have an active civilization on Earth or Venus, we've got worse problems than maintaining Venus' temperature.

Personally I think messing around with Venus' orbit isn't something we should do...next thing we'll know, we'll have sent the Earth spiralling into the Sun...the slightest miscalculation in moving Earth's nearest planetary neighbor could have DISASTROUS results. It's a risk I'd rather not take. Venus can be terraformed without moving it anyway, so I don't see a lot of added benefit to messing around with its orbit.

I disagree on this point. I think in order for us to have the expertise and know-how to build fully self-sustaining bases *far* away, we need to first get the technology perfected. We should perfect the art of building fully closed cycle ecosystems *near* Earth first where help is quickly available, before sending people to Mars to try to implement a closed ecosystem. Space also provides the most clinical environment to build those experiments in, without interference from planetary environments. Would we want to perform the first lung transplant in the world in a surgically clean room or in a battlefield? The first advances, the steps forward, will need to be perfected in a sterile environment, before starting to apply them to a wide variety of environments.

Because of these two reasons 1) relative nearness while perfecting the technology and 2) relative sterility while perfecting the technology, I believe that it will make more sense to try to build larger orbital stations before building bases on other celestial bodies.

Once we're good and skilled at creating closed ecosystems, and can create pretty good closed cycles, *then* it's time to head further away when we feel secure in our ability to provide the *basics* of survival.