Hubble Space Telescope Status Report
On June 15, 2009 at approximately 2:51 a.m. EDT, the HST Science
Instrument Command and Data Handler (SI C&DH), installed during the
recently completed servicing mission, began to send unexpected "zero"
readings to the on-board HST 486 computer. Seconds later, the
computer sent commands to put the SI C&DH and the HST science
instruments into safe mode.
Because of the SI C&DH's anomalous condition no science instrument
telemetry was being reported, and Power Distribution Unit (PDU)
currents and voltages provided the only indication of science
instrument status. These data indicated that the Science Instruments
had not transitioned to their safe states indicating that none of
them had received the HST486's safing commands. Engineers quickly
concluded that the SI C&DH was neither receiving or forwarding
commands nor processing telemetry. Other than these components, all
HST spacecraft systems were nominal throughout and after the event.
Beginning at 2:50 pm, attempts to send commands to the HST payload via
the SI C&DH interface used for ground commanding were unsuccessful.
As planned, the next step taken was to power-cycle the SI C&DH that
is, to turn it off and then on again. The power cycle succeeded just
before 4 pm, restoring fixed-format telemetry from all payload
elements. This telemetry indicated that each of the science
instruments was in the state to which it had been commanded prior to
the SI C&DH anomaly.
Subsequently each science instrument was commanded into its safe mode
by HST's flight controllers.
Around 8 pm Monday evening, Hubble engineers recovered the SI C&DH to
'normal mode.' The science instruments will remain in their safe
configurations while investigation of Monday's anomaly continues.
Hubble engineers are assessing the risk posture of the science
instruments from potential future reoccurrences of this anomaly.
An Anomaly Review Board (ARB) will be convened to further evaluate the
anomaly and make recommendations to the HST Program. We are presently
looking at approximately a one-week delay to our planned Servicing
Mission Observatory Verification (SMOV) activities.
The Observatory as a whole, including the new and repaired
instruments, is in excellent shape and activities not requiring
the use of the SI C&DH (Gyro and FGS calibrations for instance) are