ASTRONOMERS have just over two weeks to stop NASA from crashing the Compton
Gamma Ray Observatory into the Pacific. They say the satellite should be good
for five or more years, but NASA has given them only until 16 February to make a
case that it can be kept safely aloft.
NASA鈥檚 plan to scuttle Compton in March follows the failure of one of the
observatory鈥檚 gyroscopes. If a second gyro fails, engineers may not be able to
control its eventual descent. And that would risk spraying an inhabited area
with debris
(快猫短视频, 22 January, p 5).
鈥淚t鈥檚 going to be a damn shame to put this thing into the ocean,鈥� says Jerry
Fishman of the NASA Marshall Space Flight Center in Alabama, principal
investigator for BATSE, an instrument aboard Compton which surveys the whole sky
for gamma-ray bursts. BATSE鈥檚 rapid detection of the bursts allows astronomers
to train other instruments on them before their afterglow fades鈥攔evealing
clues about their origin.
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NASA鈥檚 current plan is to fire six burns of Compton鈥檚 thrusters to lower it
into the atmosphere. 鈥淲e ought to be able to do a fairly precise re-entry,鈥� says
Preston Burch of the NASA Goddard Space Flight Center in Maryland.
However, engineers are racing to devise a back-up guidance system that might
allow a safe descent even if a second gyro fails鈥攁llowing the observatory
to be left in orbit. 鈥淲e could potentially use magnetometers and Sun sensors,鈥�
says Burch.
If NASA鈥檚 leaders can鈥檛 be convinced that this is safe, Fishman suggests that
Compton could be left until another gyro fails, and then be captured by a space
shuttle and returned to Earth. Other exotic plans include shuttle missions to
strap on a new gyro, or a booster that could raise the craft to an orbit so high
that it would remain aloft for thousands of years. The high cost of shuttle
launches, however, means that these ideas are unlikely to take off.