Hubble Presentations
Solar Array Drive Electronics Failure Investigation
Cindy Winslow / Lockheed Missiles and Space Corporation
SADE Description
- Task of SADE is to interface with the SSM for exchange of operational commands and telemetry data.
- Operate and control the SADM for the orientation of the SA and monitor the position of the arrays and the temperature of the SADM.
- SADE shall operate in the following modes
- All motors off.
- One motor on each mechanism operating simultaneously in either direction of rotation (both main or both redundant).
- One motor on one mechanism in an operating mode as above.
- Simultaneous operation of both motors in either mechanism.
Overview of Transistor Overstress Problem
- Analysis shows that transistors 2N5153 and 5154 are allowed to dissipate up to 2.2W each before reaching its junction temperature limit of 115 degrees Celsius when SADE electronics are in the maximum temperature environment of 40 degrees Celsius.
- Expected dissipations are 700mW which will be equivalent to approximately 68 degrees Celsius in vacuum.
- The transisitors T4 and T6 mounted on PCB NO.5 are allowed to dissipate 57 mW without additional means and up to 89mW with a black anodized T018 housing with 115 degrees Celsius upper junction temperature limit.
- When the transistor case is molded in an AlO2 carrier, thus connected to the PCB, the junction temperature is 75 degrees Celsius (89 mW).
Results of SADE-1 Inspection
Two transistors, T5 and T17 severely thermally stressed, conformal coating discolored and charred.
Two diodes, D8 and D10, severely thermally stressed, conformal coating discolored and charred.
Solder on connections became molten and reflowed between the two diodes.
Failed transistors gave no indication of defective construction.
All 27 boards inspected.
- Seven boards with anomaly.
- Two boards competely replaced.
The heat sink will dissipate the heat and protect the transistors.
- Same modification made to SADE-1R.
- Returned SADE did not change modifications required.
PCB 916-220 110.0A, Resolver Decoder A
- The upper right corner of the heat sink layer is partially lifted.
PCB 916-220 510.0C, Multispeed Decoder
- Dark discoloration on the lower right part of the assembly.
- Dark discoloration on contacts of PCB connector.
- Dark discoloration on lower area of solder side.
- Coating is damaged.
PCB 916-220 350.00.0C Compensation Network Filter
- Solder splashes on lower right area of assembly side.
- Six discolored points along one PCB retainer near left border on solder side.
PCB 916 220.400.00.0/1C, Sine Converter Oscillator Divider
- Dark discoloration on components on lower right side.
Motherboard 916-220 400.00.0C, PCB Retainer Guides
- Brown deposit and solder splashes in area of the slot for the oscillator board.
- Dark deposit near PCB retainer board.
Additional Reading
- Inspection report for the SADE-1, IR-SA-DO/01/F1, March 1994.
- Non-compliance report, MRB-SAR-500, March 1994.
- Minutes from SADE MRB at Dorner, 23 March 1994.
- Failure investigation of Hubble Space Telescope solar array drive electronics, ESA report 2083, March 1994.
- Metallurgy report, MGl2102, Oct. 1994.
- Visual examination and analysis of rubber compound strip and PCB side edge guide, report #2084, Aug. 1994.
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