Attitude Control System Electronics
The EO-1 spacecraft went into an anomalous state on 9-14-01 . The Attitude Control Electronics (ACE) went into a hung (latch-up) state. Later, following some actions by the ACS team, EO-1 went into safehold. As a result, 7 Data Collection Events (DCE’s) were lost involving all three instruments and also an additional 3 DCE’s were affected in the Hyperion portion of those DCE’s that were lost.
The team concluded that the ACE lost power despite the fact that the status display for the ACE indicated that the power to the ACE was nominal. After extensive deliberation about possible causes, it was decided that there are two electronic parts which could have caused the anomaly. One of the parts is a DC/DC converter from Interpoint and the other part is a solid state power controller (SSPC) from DDC. A teleconference was held with both vendors, led by Amri Henrnandez of the Power Systems Branch supported by many of the salient members of the Anomaly Resolution team members. A brief summary of the findings after the meeting is as follows.
- Interpoint: The EO-1 ACE Low Voltage Power Controller (LVPC) uses a MHF+2805S to provide +5v power to the digital electronics in the ACE. It also provides drive power to the low current +28v switched services in the LVPC. The internal control logic for this converter is mostly analog and it does not include an integrated controller. After walking through the design schematic with Interpoint engineers, it was agreed that a latched event is not likely to happen due to the implementation of the control circuitry. A credible failure of the part is most likely to be permanent. After the ACE power was rebooted all signals returned to nominal with no signs of degradation.
- DDC: The EO-1 Power Subsystem Electronics (PSE) uses a RP-21015DO-602, Solid State Power Controller (SSPC), to distribute power to the ACE.
As a result of the findings, it was decided that the most likely cause of the anomaly was a Single Event Upset on the SSPC that resulted in the ACE going into a latch-up state. It was also noted that there are many of these SSPC’s on EO-1 and that adequate contingencies should be established to assure that any future occurrences are covered.
A summary of actions taken, as a result of the meetings to address the EO-1 Attitude Control Electronics (ACE) anomaly, was that three new Telemetry and Statistic Monitors (TSM’s) were added and one TSM was modified. There were approximately five contingency flow diagrams that were modified also.
A full accounting of this anomaly is contained in the Anomaly Resolution Report for ACE Anomaly dated 11/18/01.