Status 27 January 2000
The Terra solid-state recorder (SSR) has been reset by turning it
off and back on again. This has restored the capability for
recording engineering data, but software that was in place before
the power was cycled needs to be reloaded before recording of
science data can be resumed. This is expected to happen by this
weekend.
Upload of the MISR flight software and transition to science mode
are currently scheduled for Saturday, but there is a good chance
that the SSR activities could push this to Sunday. Preparations to
insure that our Science Computing Facility at JPL is ready to
receive and display MISR data (along with Superbowl XXXIV coverage)
are progressing well.
The performance of the spacecraft cooling system that supports the
ASTER thermal-infrared (TIR) instrument has improved significantly.
Spacecraft engineers have obtained a better understanding of the
operational behavior of the control system, and some additional
checkouts are planned for the next few days. Turn-on of the TIR
instrument could occur as early as Monday.
Checkout of the spacecraft propulsion system using two series of
1-second test burns was scheduled for today. During the first burn
attempt this morning, a yaw rate measurement exceeded a threshold
level, which caused the fault detection software to put the
spacecraft in "safe" mode. The problem was quickly traced to an
incorrect value for the threshold. As of this afternoon, the
spacecraft has been brought out of safe mode and the test burns have
been rescheduled for tomorrow. This may cause a 20-second
engineering burn, now scheduled for Monday, to slip by a day or two.
Following that, the overall ascent maneuver plan calls for six burns
per day--three 30-second burns occurring within a span of about 10
minutes, followed several hours later by another cluster of three
30-second burns. The cumulative burn time to get to orbit is 1800
seconds, and should consume 39 kilograms of hydrazine fuel. Final
orbit is expected to be achieved around February 12.
The spacecraft safing event that occurred earlier today resulted in
automatic safing of MISR (and the other instruments) as well. MISR
responded properly, and the cameras and optical bench heaters turned
off. Within two hours of the safing event, the optical bench cooled
from 26 degrees to 20 degrees Centigrade, and the cooling trend is
continuing. ("Replacement" heaters will keep the instrument from
getting too cold.) This unplanned event has effectively given us a
head start on the cool-down which would have occurred when the
commands to load the flight software are sent, so we have opted
simply to remain in safe mode for the next few days.
Many of these hiccups the spacecraft has experienced are typical of
early mission activations. In general, Terra and MISR are handling
all that is happening very well.
You can see earlier status reports by checking the "News" link of the MISR
web site at http://www-misr.jpl.nasa.gov.
David Diner
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