Gravity Probe B
is emphasizing small, inexpensive science
missions, Gravity Probe B remains one of the most costly space physics
missions that has ever been undertaken.
In any case, the proposed test of relativity, critics argue, simply is
too complex for its results to be believable and the probe's tolerances
too unforgiving to perform as promised in the rigors of space.
The project's survival hung in the balance most recently last year, when
NASA suspended $50 million in project funding while a panel of a dozen
academics from the National Academy of Sciences led by Princeton Nobel
laureate Val Fitch aired misgivings about the project's scientific
When a majority of the scientists on the panel concluded that "GPB is
well worth its remaining cost to completion," NASA restored the
project's funding. Agency officials allocated $75 million in August to
keep the project moving toward its launch date.
Despite its endorsement, the panel still had many reservations about the
sheer complexity of the endeavor Stanford was undertaking.
"Nevertheless, the extraordinary experimental requirements and the
impossibility of ground tests of some critical systems at the necessary
level of accuracy introduce significant risks," the panel warned.
"A majority of the task group believes that GPB has a reasonably high
probability of achieving its design goals and completing the planned
measurements. However, based on their experience with complex
experiments on the ground, several members remain skeptical.
"The task group notes in any event, should the GPB experiment be
completed successfully but yield results different from those predicted
by general relativity, the scientific world would almost certainly not
be prepared to accept them until confirmed by a repeat mission."
The questions that dog Gravity Probe B in some instances go beyond
issues of technical competence to reflect the deep faith the scientific
community at large has invested in Einstein himself. An internal NASA