| RISKS-LIST: RISKS-FORUM Digest Thursday 16 August 1990 Volume 10 : Issue 21
FORUM ON RISKS TO THE PUBLIC IN COMPUTERS AND RELATED SYSTEMS
ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator
Contents:
Space Shuttle O-Rings NOT the real problem (S. Klein)
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Date: Sun, 12 Aug 90 15:55:01 -0700
From: sklein@cdp.uucp
Subject: Space Shuttle O-Rings NOT the real problem
[Starkly excerpted by PGN from selections from SKlein]
There is much more to the article excerpted below, which appeared in Washington
CityPaper, a weekly muckraking free newspaper distributed in and around the
Washington, DC area. The article was written by Greg Kitsock, August 10th
issue (Volume 10, No 32?). Washington City Paper at 724 9th Street NW, 5th
floor, Washington, DC 20001. Phone (202) 628-6528. They can also be reached
at MCI Mail 384-9327.
Bent Out of Shape:
Four years and millions of dollars after Challenger, NASA thinks it's got the
shuttle's glitches all straightened out. But engineer Ali AbuTaha insists
there are a fatal few that NASA missed.
Ali AbuTaha, an engineer with 20-years of aerospace experience traces the
Challenger disaster--and future disasters if his warnings aren't heeded--to a
radical change in launch procedures that was mandated by NASA officials just
prior to the shuttle's maiden voyage in 1981. That change in launch
procedures, says AbuTaha, has subjected every mission to liftoff forces far
exceeding the hardware's safety margins.
[There is a fascinating bit about the torque while revving to full throttle
before takeoff, because of the asymmetry with respect to the boosters,
producing a motion known as `twang', and AbuTaha's analysis of the
situation.]
"The Rogers Commission was not oblivious to shuttle "twang." But it
rejected the idea that twang had anything to do with the Challenger disaster.
Page 54 of the first volume of the commission's report states, 'The resultant
total bending moment experienced by [the Challenger] was 291 x 10^6
inch-pounds, which is within the design's allowable limit of 347 x 10^6
inch-pounds.' However, on Page 1,351 of Volume 5 of the report, the commission
cites the same figure, written as '291,000,000,' as the bending moment for the
_right_ solid booster only. The effect on the entire assembly, argues AbuTaha,
should be the combined bending moments of both boosters. Multiply by two, and
you arrive at the maximum force that AbuTaha calculated.
"This figure is 70 percent greater than the design's allowable limit,
as cited in the Rogers report. And every shuttle mission up to the
Challenger explosion (and possibly afterward) has experienced this force.
'This is the kind of error that catches up with you,' warns AbuTaha.
"Not only does this miscalculation explain the shuttle disaster that
killed seven astronauts and set our space program back nearly three years, as
AbuTaha suggests, it also reveals the source of the mysterious malfunctions
that have plagued the shuttle program since its first launch in 1981, from
tiles knocked off and booster segments warped to satellites that inexplicably
failed to work."
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