Marginal Utility

by Tom Bozzo

To: Corndog

From: Tom

Re: Insulation on cryogenic fuel tanks

Get those steel-toed boots ready...

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Billmon has an interesting perspective from a stint working as a writer for the commission that investigated the Challenger accident, and doesn't feel good about the Discovery launch plans either. Meanwhile, even members of the CAIB are saying that the concerns are overblown:

Dr. Logsdon, a member of the independent board that investigated the Columbia disaster, said, "Prior to Columbia, we flew 113 times with foam apparently falling off without it hurting us."

At the time, he said, NASA did not understand the problem.

"Now that we are aware of it and have learned about it," he said, "it's more reasonable to fly with falling foam, because we at least understand the issue better."

Now we are "aware" of the problem, we just don't know exactly how to fix it. In any event, from one total vehicle loss and at least one near-hit in 114 tries, the observed instance of the latter occurring after a round of remedial work, you might conclude that they were sitting on something like a 1% failure risk, and the rolls of 0 (*) and 1 on 2d10 — improbable, but not vanishingly so given the consequences — came up in not-unexpected time.

As failures of human decision-making go, get-there-itis is demonstrably dangerous. Most of the time, you get away with it. I remember, back in the days before the fortress cockpit, listening to the pilot and copilot of a flight to Madison that had already been diverted to Green Bay plot a departure around a thunderstorm just off the windward end of the runway: that was an exciting climbout. Other times, you don't. The problem is when the successes make you irrationally optimistic.

Godspeed, Discovery.

This isn't to say that it isn't an improvement that there's a plan B for the Discovery's crew in the event Michael Griffin's luck is bad. And Billmon is almost surely correct that the PR calculus is such that the White House probably isn't pushing the launch schedule. On the other hand, if Bush really were the decider-in-chief, you might think he'd strongly suggest that NASA brass consider whether the taxpayer's interest is served by building an orbital monument to bureaucratic learning processes that has a price tag (in expected value) of some tens of millions of dollars. Can you imagine Bush volunteering such a question? Right.

Addendum: The launch appears to have been successful, pending the on-orbit inspections, though as the NY Times noted:

About 2 minutes 47 seconds into the ascent, an onboard camera showed numerous pieces of unspecified debris appearing to fall away from the shuttle's external tank. They fluttered away and did not appear to strike the shuttle orbiter, the part of the craft where the astronauts ride.

This is much later in the ascent than the foam strike that led to the Columbia disaster. There, deceleration of the foam chunk due to atmospheric drag combined with the acceleration of the vehicle led to the high-velocity strike. At sufficiently high altitudes (and thus thin air), debris shedding is much less dangerous as any strikes would be at lower relative velocities.

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(Previous Marginal Utility posts on the Bush space "vision" here, here, here, here, here, here, here, here, and here.)