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This article originally published in
Then there’s the nightmarish "Gravity Probe B Error Tree" to consider.
That’s a poster that shows 177 boxes representing factors that could affect
GP-B’s final measurements. On a mission where a random gas molecule in the
instrument or too much sloshing of the liquid helium could queer the whole thing,
the tolerances for each of those 177 factors must be excruciatingly fine to
guarantee valid results. Says science mission project manager Jeremy Kasdin,
whose office displays the poster, "The idea is to make sure we’ve tracked
all the errors, understand them, and can drive them down." But always there
is the overarching question: What if the gyroscopes get rocked by a disturbance no
one had foreseen?
Everitt has obviously fielded this question before. He fairly leaps to the board
in his office and launches into an hour-long lecture on the checks, cross-checks,
and redundancies built into GP-B, as well as the years he and his colleagues have
spent considering the possible effects of everything from cosmic rays to
micrometeoroids--at the end of which he say, "So I’ve really just given you
flavors, rather than a detailed argument of why I think the results of this
experiment will be very believable."
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