Transterrestrial Musings

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I don't like to nitpick, but your thesis reads as follows.

Step 1: buy diamonds
Step 2: ???
Step 3: launch operational space elevator

Nowhere do you explain the engineering required to fabricate this 90Mcarat diamond, or how many millenia it would take to grow it. An exercise for the reader I suppose...

Posted by at July 23, 2007 04:26 PM

Hehe, Space Elevator Ltd. a wholly owned subsidiary of Underpants Gnomes Inc.
We have multiple operating "space elevators" in the book I'm writing at the moment. Six on Earth, two on Luna and one on Titan. A couple temporary systems deployed on various moons and or asteroids as needed....I can dream, can't I?

Posted by TBinSTL at July 23, 2007 05:16 PM

A lunar space elevator could be built with stuff I can buy off the shelf at West Marine (Kevlar & Spectra)

Well okay there is some hyperbole there, but not much.

Posted by Bill White at July 23, 2007 06:57 PM

No, the materials are off the shelf. There would be some billions in engineering but it's perfectly buildable now. You could also use M5, it's a little stronger although I don't know how it holds up to UV.

What we're missing is the 1000 tonne Sea Dragon vehicle to lift it, and a big nuclear powered tug to bring back an asteroid counterweight.

Posted by Adrasteia at July 24, 2007 05:20 AM

A rotating tether may be more practical for the moon. The end can dip quite close to the surface, releasing payloads that can then descend and decelerate with modest terminal delta V.

Since polar orbits always pass over each pole on each orbit, this could work well with a polar lunar base.

Posted by Paul Dietz at July 24, 2007 05:38 AM

Long before these unobtanium materials will allow a space elevator, the same materials will make SSTO possible. SSTO is largely a matter of getting a high enough mass fraction, and super-strength materials should make that part easy.

The original notion behind X-33/VentureStar was, hey, we have light weight carbon composites, the SSTO problem is now easy, or at least much easier when you were using aluminum (Space Shuttle).

Jerry Pournelle still thinks SSTO is possible here and now based on the DC-X type configuration and the Air Force Have Region studies of lighweight structures. The problem with all of these systems from space elevator down to SSTO to Shuttle-derived launcher to Elon Musk is the chicken-and-egg problem of development cost vs size of market. We build an SSTO now, and the development cost may not even be much more than a mega airliner like the A380, but at the current market, amortizing the development cost will make launch expensive which will in turn keep the launch market small.

Speculation about space elevators is fine because if we are to be a space-faring and space resource using society, we will eventually need to reach that point. But I really don't think space elevators will leap-frog the progression of rocket technology and the development of markets for orbiting payloads because whatever supermaterials would help the elevator will also help rockets a lot.

Posted by Paul Milenkovic at July 24, 2007 08:45 AM

Anonymous: Step 2: Make a bunch of diamond rods short enough to fit in a heavy launch rocket at the right taper. The diamonds can be grown via standard CVD processes. Articulate them and interlock them at the ends like a chain. Build in the right taper. Shoot it up to GEO. Start unfolding. Basically, see Edwards except use diamonds instead of nanotubes.

Paul M: OK, build a SSTO RLV out of CVD diamonds.

Posted by Sam Dinkin at July 24, 2007 10:15 AM

The problem with diamond rockets is that diamonds, because they are carbon, burn at around 1000C.
Diamonds are also extremely effective thermal conductors which would create design problems as well for both rockets and space elevators.

Given Diamond’s behavior under ultraviolet light the space elevator should fluoresce beautifully. The color depends on the composition of the diamond, but it will be seen, that is for sure.

You will need to be sure trace elements like Boron are left out. The have a tendency to turn diamonds into semi-conductors. In fact one of the non-destructive tests for a blue diamond is its ability to complete an electric circuit as a semi-conductor. The would make for an interesting effect as the space elevator travels through the Earth's magnetic field.

The biggest structural problem with diamonds is that their atomic matrix makes them very sensitive to fractures along one of the planes of the carbon atoms. This is the basis for the diamond cutting industry. One could imagine what a small piece of debris could do if it hit the space elevator at just right angle… You would probably need to encase the diamond elevator in some material to protect it.

Posted by Thomas Matula at July 24, 2007 11:16 AM

The would make for an interesting effect as the space elevator travels through the Earth's magnetic field.

Since the conductor would be corotating with the planet, there would be no induced electric field, so no current would flow (think about it: if you could get such a current, you would violate conservation of energy and/or angular momentum).

You could get some electric fields from fluctuations in the magnetic field induced by turbulence in the solar wind flow, however.

Posted by Paul Dietz at July 24, 2007 11:22 AM

Atomic oxygen exposure has been demonstrated to reduce Kevlar strength by about 30% per year so that’s out. I suspect that diamond would fare better, but energies are high (~6eV) and oxygen does love carbon now doesn’t it. I hate when the real world ruins my fantasies.

Posted by brian d at July 24, 2007 01:51 PM

Paul, you wrote

My take is that the further you get away from Earth the less likely the fields are corrotating with Earth. Some cable designs would even stick out of the magnetosphere at times. Those designs would pass through areas of relatively strong magnetic fields that aren't corrotating with Earth.

Posted by Karl Hallowell at July 24, 2007 02:17 PM

Sam, the present growth rate for CVD diamond is maybe 10 microns per hour. How long are you going to make your cable sections? Even a 1 meter section would take 10 years to grow, and would still leave you with 50 million joints in your cable.

Posted by Carl Pham at July 24, 2007 04:13 PM

*cough* I'll just point out that Earth's magnetic field isn't static in the first place (that goes for both strenght and position).

It's happening gradually all the time and doesn't violate anything at all.

Posted by Habitat Hermit at July 24, 2007 06:48 PM

Hi All,

Actually these problems are not just limited to diamond. Its likely they apply to other materials as well. And give the nature of carbon may well apply to carbon nanotubes as well.

Also, in terms of the diamond spaceship. There is some research being done on using a thin film of diamonds, in a process called Chemical Vapor Deposition, to protect surfaces from wear and evenly distribute heat. So although we may not see a diamond spacehip in the future we may well see a diamond coated one :-)

Posted by Thomas Matula at July 24, 2007 10:49 PM

It's happening gradually all the time and doesn't violate anything at all.

There are fairly rapid changes in the magnetic field due to buffeting by the solar wind, which I mentioned.

There are also slow changes due to internal processes in the Earth, which would be utterly negligible for the purposes of this discussion.

The point from the other poster about the magnetosphere at large distances not necessarily co-rotating is a good one. This becomes true for magnetized bodies even in the absence of a solar wind if you go out far enough -- the magnetic field can't be rotating faster than the speed of light (example: pulsars). Before that, if there's a plasma trapped in the magnetic field, eventually the kinetic energy of the plasma approaches the magnetic energy of the field, and things also get distorted.

Posted by Paul Dietz at July 25, 2007 09:18 AM

Not sure I got your point there Paul Dietz, what was it?

Posted by Habitat Hermit at July 25, 2007 01:41 PM

If space elevators cost $25,000/kg and space delivery after the elevator's up cost $10-$800/kg,

Sam, expendable rocket launches *already* cost $10-800/kg *after* you have a rocket built, checked out, and on the pad, needing nothing more than propellant.

That's a meaningless figure because in the real world, capital and labor costs count just as much as energy costs.

You can't ignore the construction costs of a space elevator any more than you can ignore the cost of building and prepping a rocket.

Tom -- The nose of the Shuttle is already made of reinforced carbon-carbon. Obviously, it does not burn up. Note that a space elevator could not be built out of pure carbon nanotubes; it would have to be some sort of composite like the Shuttle nose. You need a matrix to hold the nanotubes together.

Composite materials might be built with diamond, too are are probably more likely in the near term than single-crystal diamonds thousands of kilometers in size. (Scaling up current fabrication techniques to those sizes would be nontrivial, to say the least.)

Posted by Edward Wright at July 25, 2007 04:52 PM

Another problem is Sam's expected cost reductions for diamond crystals. Even if the hoped-for cost reductions appear, production facilities that are designed for relatively tiny industrial crystals are unlikely to be capable of producing a huge single-crystal space elevator. So, the cost reductions may not apply.

Posted by Edward Wright at July 25, 2007 05:07 PM

Make a bunch of diamond rods short enough to fit in a heavy launch rocket at the right taper.

Finding rods that are "short enough" is unlikely to be the problem. What's the longest diamond rod currently available off the shelf? Or likely to be in the future?

The diamonds can be grown via standard CVD processes. Articulate them and interlock them at the ends like a chain.

Standard CVD processes are designed to produce crystals of a few carets. Connecting trillions of small diamonds into a single cable would be a nontrivial task.

Then there's the matter of the locking mechanism. As the saying goes, a chain is only as strong as its weakest link.

Posted by Edward Wright at July 25, 2007 05:21 PM

Not sure I got your point there Paul Dietz, what was it?

That your comment doesn't actually invalidate anything I wrote in that earlier comment. If your comment wasn't intended to be a disagreement, then my response wasn't necessary.

Posted by Paul Dietz at July 26, 2007 11:19 AM

Ed, once you have built the elevator, optimizing it is about marginal cost especially when talking about internal operations. If building extra elevator costs $X of fixed costs and $25,000/kg of marginal costs, it still makes sense to build more ballast and less elevator even if the fully capitalized cost of the first 18 tons up the elevator is $25,000/kg. At the end of the day doing you would have spent $450 million to build one elevator and $100 million to build the second or $450 million to build one elevator and $450 million to build the second if you use average costs and decide that you should not modify the design of the second elevator.

As for EELV's being cost competitive, they are only $10-$800/kg for a few kilos because their fixed costs only buys a limited capacity, not 5000kg/day. Granted, demand is a few kilos just today, but part of that is because we are charging average costs and not marginal costs for service.

Re: manufacturing problems. They are moot. Imagine trying to go to Congress to ask for an 18 ton diamond.

Posted by Sam Dinkin at July 26, 2007 12:14 PM

The tiny diamonds are already being quoted for $3/carat=$15/gram. CVD is a standard chip industry technique. A thin film (which is what you get when you want .25 kg/km) is very easy for them.

But nitpicking misses the point. Instead of trying to argue why it won't work and is uneconomic, argue why your solution is better. The objections have fallen mostly into the development category. It's possible to use conventional semiconductor techniques to grow a solid diamond crystal ring interlocking with another ring.

Use the diamond elevator to show why nanotubes are worse (not available at any price). Use the diamond elevator to highlight the non-incremental approach inherent in an elevator.

It is a carbon-man (aka straw man). What do you see when you look into the sky?

Posted by Sam Dinkin at July 26, 2007 02:13 PM

Ed, once you have built the elevator, optimizing it is about marginal cost

Since you haven't built a space elevator, optimizing it is not just about marginal cost. That's the classic "sunk cost fallacy."

As for EELV's being cost competitive, they are only $10-$800/kg for a few kilos because their fixed costs only buys a limited capacity, not 5000kg/day.

5000 kg/day is also a limited capacity; it's simply a bigger limit. Nor does it appear achievable. According to Brad Edwards, the space elevator would carry a 13-ton payload. Since the roundtrip time to geosynch is about two weeks, that gives you a capacity of about 1000 kg/day, not 5000.

At the end of the day doing you would have spent $450 million to build one elevator and $100 million to build the second.

Yes, and the first space elevator was going to be completed in 2010, according to the Spaceward Foundation. At Las Cruces, their test vehicles achieved an altitude of only 55 meters.

The fact that they're offering a $1-million prize purse for a level of performance significantly less than that of an Estes rocket suggests that rockets might not be quite as terrible as they say.

Posted by Edward Wright at July 26, 2007 04:34 PM

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