Right thesis, wrong facts
Posted by aogTuesday, 04 February 2003 at 21:56 TrackBack Ping URL
Orin Judd quotes Greg Easterbrook on the Shuttle. Rand Simberg hits the high points of the problems in a more recent article, so I'll just respond to the points in the cited quote.

I agree with Mr. Easterbrook's main thesis but he overstates his case. His iteration of physical conditions is highly misleading. Although Rand Simberg has already taken his shot, allow me to attach Easterbrook's claims that you quoted.

  1. Rockets were built as throw away not because "the forces of space flight twist and sizzle machines into scrap" but because recovery is very hard and expensive. I fly model rockets myself and the recovery systems are far harder than any other part of building and flying. And one notes that in all the flights the SSME's haven't had problems (and in fact the trickiest bit of technology is those is the cryogenic pump which doesn't even notice that it's flying). So Easterbrook's claim that the engine "is impractical to use again even if you can get it back" is clearly false on its face.
  2. The comment that "During ascent, the shuttle must withstand 3 Gs of stress" is laughable. I've got rockets made out of paper and balsa that can handle 10 G's of stress. I've got another model made of somewhat stronger stuff that handle FIFTY (50) G's on takeoff.
  3. As for temperature, it's true that re-entry is tough (notice - the problem is in the recovery of the rocket). However, as we discussed earlier concerning solar power satellites, in Earth orbit the equilibrium temperature from solar radiation is about 270K or roughly the freezing point of water.
  4. Finally, the dead stick landing is a bit sticky, but modern avionics should find that not too difficult. There are other designs that provide powered landings. But Easterbrook is closer here than elsewhere because recovery is in fact a hard problem.
Easterbrook's main point, that the Shuttle has been overhyped, under performing and over budget from day one is dead on. I've heard the $500 million per flight, although some claim it's closer to $800 million. But the point of my tirade is that this that NASA hasn't failed because of the inherent difficulties but for other reasons.
Comments — Formatting by Textile
pj Wednesday, 05 February 2003 at 12:29

Heh. I might add that expressing force in terms of “G’s” of acceleration, rather than the product of mass and acceleration, leaves vague how large the stress is. When I go running, the force on my shoes is 3*(my mass)*(1 G) (walking of course is (my mass)*(1 G)). But because my sneakers weigh so little, this force is actually around (sneaker mass)*(500 G). Of course, it’s not the shuttle, but the people, who have trouble with high G’s on takeoff — and the reason is that we have fluids and vessels carrying them, and high G’s interfere with the motion of our blood.

I like the idea of endowed bounties for private space conquests — e.g. $500 mn each for the first 3 manned trips to orbit using distinct technologies, $500 mn each for the first 3 unmanned trips to orbit using distinct technologies and meeting some limited variable cost per kg to orbit, $20 bn for a manned visit to Mars and return. It seems to me this, plus a military space program that uses private contractors, is all the government needs to do.

Annoying Old Guy Wednesday, 05 February 2003 at 15:21

Yes, but Easterbrook talks about how a 3g stress makes building the Shuttle difficult.

But you should see the MachBuster (sadly out of production now). It’s about 30cm long and 3cm in diameter, takes off at over 50g up to Mach 1.2. You can’t watch it take off - it starts to move and then it’s just gone leaving nothing but a streak of smoke. You can see one of my other rockets in flight at http://thought-mesh.net.

I’d much prefer that NASA just say “we’ll pay $1000/lb to orbit for at least 500,000 pounds per year for 10 years. Here’s a sample 5000 lb mass. Call us when it’s in orbit.”

End of Discussion