SPACE: Economic Benefit of Manned Space Stations (fwd)

Eugene Leitl (
Thu, 29 Jul 1999 22:49:45 -0700 (PDT)

Robert J. Bradbury writes:

> The basic strategy is to construct an exponentially growing array
> of solar collectors that beam the power back down onto Mercury.

Oh, I realize that. It is just that Mercury already receives quite a lot of radiation. Even if you increase the amount if incoming power by one order of magnitude (doubtful the more delicate structures can survive it), does it really allow the dismanting process to complete in just 11 d? You must be hiding at least a few big envelopes back there.

> You could vaporize the planet completely, but I favor a strategy

Vaporization is sure easy, but I do not see a way to recapture the material quantitatively. The point is not destruction, the point is retaining the bulk of the material (especially volatiles) for constructive purposes.

> of using mass drivers to hurl selected materials into space over
> the entire surface of the planet. It requires nanotechnology mass
> doubling times to be done in 11 days. The surface temperature

I grant you nanotechnology, but this does not address the maximum tolerable energy flux on planetary body's surface.

> on the sun-facing side of Mercury is below the operating temperature
> of diamondoid materials. How harsh the environment gets depends
> entirely on how efficiently you can convert the incoming energy
> from its "beamed" form (e.g. light, microwaves, etc.) into the
> form(s) you need for mining/mass-drivers activities. I believe

You could carry off some energy as hot cargo, but how much can you carry off with mass launchers? These coils get awful hot after a while.

> that Eric has pointed out in Nanosystems that some of these
> conversions can be quite efficient.
> There are two constraints on the speed:
> (a) How thin you can make the solar collectors in space.
> (b) How long it takes you to position the solar collectors on the
> far side of the sun.

I don't think these are relevant questions. The bottleneck is obviously elsewhere.

> There may be an additional constraint when you get to the point
> where the amount of power being delivered to the planet exceeds
> any possible cooling technologies. At that point you either have

Yes, and it is a very stringent constraint indeed. Either you have numbers I am unaware of, or you're glossing over the issue.

> to go the vaporization route, or perhaps expand the planetary surface
> area [as you point out, perhaps unintentionally, via diamondoid
> beanstalks :-)].

It was most assuredly intentional. It is difficult to envision more efficient launch mechanisms than launching from top of beanstalks (and a large beanstalk sees mostly 4 K space, not Mercury surface, and, well, some of Sun's), Mercury is probably small enough for them (and doesn't have an atmosphere).

> > Once the stuff is in space, and more or less dispersed, anything is
> > cheap. The hard part is getting a massive planetary body dispersed
> > without rendering it unusable. How do you do that?
> Mass drivers or condensation of a gas at various distances from the
> source. You never render material unusable unless you let it

How do you intercept a ~Mt/s stream of evaporated planet? (Or Gt/s, don't know how much mass Mercury has divided by 10^6 s).

> "escape". Most of the techniques for moving materials around in
> space were worked out in detail in the late '70's for Space Manufacturing,
> Lunar Colonization & O'Neill's colonies. The self-replicating
> factories were worked out in NASA's Advanced Automation for Space
> Missions study (and then forgotten...).

You're telling us little new so far. I was hoping to see some actual back-of-the envelopes.

> Last year I asked Robert Freitas (one of the authors on the NASA
> study), what the advantages were for nanotech based self-replicating
> factories vs. the macro-scale versions envisioned in the NASA study?
> He gave a rather succinct answer that summed up the basic reason
> nanoscale manufacture trumps macroscale -- "The parts count is lower".
> You only need ~10-15 part-types (i.e. elements) for most nanoscale
> manufacturing. What needs to be done is the updating of all of
> old designs for macro-scale self-replicating factories and
> mass-drivers to nanotech based designs. There *might* be
> difficulties if some essiential element happens to be in short
> supply on Mercury (though I expect substitutions could occur).
> > I would like to see an easy way of translating power into such a
> > coordinated activity as planet dismantlement.
> The easiest approach is to vaporize the planet and condense it.

How do you duct it? How do you trap it?

> I suspect however, that this approach wastes energy (and therefore
> takes longer). Much better is to dismantle the planet bit-by-bit

Energy is cheap, very cheap. A 0.1 um metal foil would reflect ~95% of incoming radiation. One needs to tranform the planet into a fleet of solar sailers which try to keep the original body in focus. The higher the initial insolation the faster the initial growth. Difficult to do that trick with Pluto.

> and only launch into space those materials you absolutely need
> there. I believe that if you do this cleverly, you may be able
> to recapture some of the energy used to get the material out of
> the gravity well either to "recast" the materials into useful
> forms or provide the deltaV required to move the materials into
> more useful orbits.

Once again, energy is not a problem. The Sun produces sufficient amounts of power that it is difficult to get enough material to make the computers -- and then there is lots of fusable hydrogen out there in the Oort.

> The basic approach I've developed works with the asteroids too but
> I think it takes longer because the solar insolation is lower at
> most asteroid orbital distances.

Asteroids are fundamentally much easier, because the volume/surface ratio and absolute gravitation are not an issue. There is even no need to launch, just transfer material to the rim, which flattens things and increases surface along with launching mirrors/building rectenna arrays/microwave beamers. The only minus is that most of them reside beyond Mars' orbit, but that just delays the matters somewhat if you have to start from a microgram seed.

> If you are really interested in the nuts & bolts, I've got rough
> draft paper at:
> Constructive comments would be welcomed.

Thanks for the earl, going there.

> I've also got a C program that does a "brute force" simulation of
> a planetary disassembly using exponentially growing energy availability

I am not sure how you can integrate the multiple factors of surface increase into one simulation. Lot's of orbiting mirrors will sure produce lots of evaporating planet smoke....

> if anyone wants to tinker with it. If anyone is good with graphics
> adding "visual" output would make this a great toy. It takes apart
> the small planets quite quickly, while Jupiter takes many CPU hours.
> Of course, IMHO, simulating taking apart Jupiter *has* to be a better
> use of excess CPU cycles compared to certain *other* recently discussed
> uses of such resources...
> Robert

P.S. I do not seem to be able to reach Max/Natasha. Does anybody have their phone# at hand?