Wednesday, March 22, 2006

Crackpots and Rocket Science

There's been an uptick in talk of space elevators. Here's Rand Simberg going at it. I get annoyed when I read this stuff, and lately I've been trying to figure out what it is about space elevators that I find so alarming. Unfortunately I have figured it out and don't like the answer.

I'll get the tedious bit out of the way first.

  • Space elevators from anywhere in the Earth's atmosphere are not going to be built for a very long time, certainly not in my lifetime, probably not ever. In short, they require engineering miracles (cheap large scale carbon nanotubes and megawatt lasers), and they do not have realistic return-on-investment (a proposed $5 billion elevator would lift one 8-ton cargo per week. 5% interest and 5% maintenance is about $10 million per week, or $625 per pound lifted, and does not include the cost of actually lifting the cargo).

  • And, should the above engineering miracles occur, they would enable other ways of getting to space that would be better than an elevator. You could, for instance, build a fully reusable single-stage-to-orbit rocket from large-scale carbon nanotubes that would certainly be cheaper than an elevator. All sorts of things from la-la land are possible if you make unreasonable assumptions. It's sort of like trying to figure out if a Tyrannosaurus Rex could win a fight with King Kong....

  • Back to the bit that alarms me.

    Much of the breathless discussion of elevators is conducted by the same folks who discuss something quite important to me: cheap rocket launches. These people are clearly unable to sanely evaluate engineering propositions. In short, they are dreamers or crackpots.

    (An aside: researchers who are developing carbon nanotube materials are most definitely not crackpots. That's R&D, which is a great thing. It's common for folks working on new materials to suggest outlandish uses. That's fun and harmless so long as they concentrate at their day job which is figuring out how to make the material in the first place. CNT materials, if developed, are likely to be as popular as carbon fiber is today, and find all sorts of good uses.)

    Anyway, here's the bit I don't like at all: how is someone who does not know a thing about engineering (my mom, for instance) supposed to tell the difference between me and one of the aforementioned crackpots? I'm working on an upcoming post which will suggest that hot water first stages and a little aerodynamic lift could cut LEO launch prices by a factor of about 2. Like the aforementioned folks, I don't work in this industry, and am unlikely to. My suggestions are unlikely to be picked up by others in the industry. Why am I burning my valuable time on this stuff?

    The answer is that I find the engineering entertaining, and I post the bits that I do because I think they might be entertaining to a small group of people who I don't bump into day-to-day. Part of the entertainment is the thought that if I noticed something really useful, I'd act on it. But it's just a thought. I like to think I have a reasonably good sense of the difficulty of making technical progress in a few fields, this one included. Frankly, I decline to make the big investment here (i.e. change careers) because I think the difficulty is too high. It is rocket science, after all.

    1 comment:

    1. Just a 'small' point;
      Not being an engineer (mechanic, says my job description :o) either, but having followed Space Elevator 'theory' for awhile.
      (Let's face it, I've followed EVERY new idea for GTO travel at some point)
      I need to ask 'why' your assuming that the lasers would be so 'hard' to do? My understanding is we've had megawatt laser cability for a while now, just no real need for them. Most of the research on laser launch has focused on 'pulse' lasers while little has been said about the power of the easier to produce 'beam' type.

      I'd attended a Laser Launch panel given by Jodin Kare where he showed that instead of focusing on huge 'monolithic' lasers such as are suggested in the orginal Space Elevator proposal, or most laser launch system proposals, smaller, moduler laser systems would be cheaper, easier to maintain, and very near term.

      While I still see the 'hesitation' over cheap/mass-produced carbon nanotubes themselves, the lasers don't and haven't seemed a problem.

      Of course I should note, that I (frankly) don't see any 'single' method bringing launch costs down, nor any single system being 'the' GTO system either.