DATE OF INCIDENT: August 3, 2004 @ 16:38 GMT (12:38 PM EDT)

LOCATION OF INCIDENT: HST Space Telescope Imaging Spectrograph (STIS)

DESCRIPTION OF INCIDENT – Updated 8-6-04:

On August 3, 2004 @ 16:38 GMT (12:38 PM EDT) the Space Telescope Imaging Spectrograph (STIS) suspended after suffering a failed command echo check between the Control Section (CS) of the STIS Main Electronics Box (MEB) and the Multi-Anode Micro-channel Array (MAMA) Control Electronics (MCE).

Accompanying the Suspend was an anomalous rapid rise in the STIS input current of approximately 1A just prior to the Suspend entry. Additionally, a voltage dropout of the Main Electronics Box (MEB)/Support Electronics +5 Volt power converter occurred approximately 43 minutes prior to the Suspend. Further investigation has now revealed a probable failure mechanism linking these anomaly signatures. Accordingly, it is now believed that STIS’s mechanism functions are inoperable and unrecoverable. Because STIS has been single-string in its electronics since May 2001, it can no longer be used for science observations.

With support from the +5 Volt power converter manufacturer (Interpoint), investigators have duplicated the power converter failure under loading conditions nearly identical to that seen onorbit. The incipient failure is believed to have been in an inductor within the power converter, which failed during the orbit night preceding the Suspend. The inductor failure caused the power converter +5 volt output to drop to zero volts, as seen in telemetry. Following this dropout the converter remained relatively stable until entry into orbit day, after which slight (and nominal) increases in its input voltage caused its current draw to rapidly rise.

The large and rapid current draw resulted in the 1A increase in STIS input current noted in telemetry just prior to the Suspend.

Additionally, current limiter logic within the electronics card housing the power converter responded by reducing the supply voltage, which in turn caused a reduction in voltage to the MAMA Control Electronics (MCE). This, in turn, is believed to have caused the interface communications failure with the Control Section and the subsequent Suspend action. The MAMA detectors are believed to have been unharmed by this sequence of events since they were not active (no high voltage on) when the anomaly occurred.

The highly probable consequence of this scenario is the total failure of the MEB/Support Electronics +5V power converter. Since this component is essential to the operation of all of the 8 mechanisms within the instrument (including shutters), its demise renders those mechanisms inoperable. A re-configuration to the Side 1 electronics (current operations are on Side 2) is not possible. (The Side 1 electronics failed in May 2001.)

The instrument remains in Suspend mode. The Project will convene a follow-up meeting on August 6, 2004 to continue the review and analysis of data and to discuss a forward plan.

IMPACT ON PROGRAM/PROJECT AND SCHEDULE:

The STIS science program timeline was interrupted when Suspend mode was entered. The Project and Space Telescope Science Institute will cease scheduling STIS science. Alternate observations from other instruments will replace STIS observations. All other HST science instruments are functioning nominally.

CORRECTIVE ACTION:

The corrective actions to be taken are as follows: Continue investigations and develop a plan to confirm the proposed failure mechanism. Ball Aerospace, GSFC AETD, Interpoint, ST ScI, and HST Program personnel are actively participating in the investigation. Assess the pros and cons of leaving the STIS in Suspend mode versus Safe Mode, pending performance of possible tests.

Form a Failure Review Board to perform a thorough investigation of the anomaly.

REPORT FILED BY:

John Gainsborough/Operations Manager/Code 441
Mike Prior/Observatory Systems Manager/Code 441