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Responsible Parties: Page Content: William H. Kinard Page Construction: Thomas H. See

A wide variety of electrical and electronic systems and hardware were used on LDEF. NASA provided certain guidelines and design review requirements, but success or failure of the individual experiments was the responsiblity of the individual Principal Investigators.

Conclusions reached by the Systems SIG 1992 study included: (1) most of the anomalies associated with related Electrical Power Systems (EPS) hardware (batteries, relays, solar cells, solar array materials, etc.) flown on LDEF were design limitations and were not component or materials failures; (2) major emphasis must be placed on atomic oxygen protections; and (3) the synergistic effects of contamination/atomic oxygen/ultraviolet/thermal cycling environment place the emphasis on contamination control.

Results from analysis of LDEF solar cells continue to show the robustness of covered silicon and gallium-arsenide cells in low-inclination LEO environments. LDEF provided valuable knowledge concerning the viability of using various solar cells and solar-cell encapsulants (adhesives and coverglass materials). Coverglass materials such as ceria-doped microsheet and fused silica withstood the environment exceptionally well. Measureable degradation of some widely used anti-reflection coatings was observed. Results from some low-cost materials such as silicone, Teflon^®, and polyimide indicated that these materials will require additional research before full-scale replacement of the conventional encapsulants (fused-silica coverglass and DC 93500 adhesive) is justified. Solar-cell performance degradation due to the deposition of contamination on the surfaces was also well documented. Results continued to show that cells covered with polymer-type materials exhibited higher cell performance degradation than cells mounted with more conventional glass covers. In addition, the glass covers appeared to provide additional protection against incident micrometoroids or debris.

Micrometeoroid and debris impacts will continue to be a significant solar cell performance degradation mechanism. The vast majority of meteoroid and debris impactors were typically of small size and high energy, but their impacts resulted in minimal electrical degradation.

The LDEF results have verified the selection of solar-cells/solar-array materials planned for use on the International Space Station (ISS). Although the exact type of silicon solar cell planned for use on the ISS was not flown on LDEF, similar silicon cells performed well, and the wrap-through contacts should avoid the problems that some of the wrap-around cells had on LDEF. Copper interconnects were a good choice because they will not be eroded in the same way as exposed silver interconnects.

A concept for a large area space-based phased array antenna was evaluated on LDEF's space end. In addition to passively exposing potential antenna materials, the experiment was designed to study the issue of the interaction between high voltage and LEO plasma with the active electronic components including a high-voltage power supply, timing control circuitry, and a memory system. This was accomplished by recording discharges initiated across high-voltage electrodes. Very few discharge events were recoded with only one 3 kV discharge and eleven 1.5 kV discharges being recorded during the active data collection (day 32 to day 243). There was no evidence of any single-event upsets and there was no charring of the Kapton or other damage visible at the electrode gaps. Creep measurements of the Kapton and glass Kapton showed little or no significant differences between flight specimens and the ground-control specimens. As was expected, the exposed Kapton surfaces were degraded by the space-end atomic oxygen environment.

Electrical/mechanical relays continue to be a design concern. Two of the most significant LDEF active system failures involved relay failures. The Interstellar Gas Experiment was one of the more complex experiments on LDEF, with seven "cameras" located on four trays. Each camera contained five copper-beryllium foil plattens, which were to sequentially rotate out of their exposed position at pre-determined intervals. This experiment was never initiated due to a failure of the experiment's master initiate relay. The Thermal Control Surfaces Experiment recorded on-orbit optical properties of various thermal-control coatings using a four-track Magnetic Tape Module. The latching relay which switched track sets failed to operate when switching from track 3 to track 4. Consequently, portions of the early flight data on track 1 were overwritten and lost.

The Experiment Initiate System (EIS) provided the initiate signal to the active experiments which directed them to turn on their power and begin their operational programs. Post-flight inspection and testing, using the original ground support equipment, showed the condition of the EIS to be nominal.

NASA supplied seven Experiment Power and Data Systems (EPDS) to record on-orbit generated data. All EPDS units were similar, consisting of a Data Processor and Control Assembly (DPCA), a tape recorder (the Magnetic Tape Module), and two LiSO₂ batteries, all of which were attached to a mounting plate designed to fit into the backside of the experiment tray. The EPDS components were not directly exposed to the exterior environment, being protected by their mounting plate and by external thermal shields. Although simple compared with today's data systems, the EPDS contained many elements common to most such systems, including various control and "handshake" lines, programmable data formats and timing, and a data storage system. EPDS electronic components were procured to MIL-SPEC-883, Class B standards, and were not rescreened prior to installation. Data analysis and post-flight functional testing showed that all EPDS functioned normally during and after the LDEF flight.

Three different types of batteries were used on LDEF: lithium-sulfur-dioxide (LiSO₂), lithium carbon monofluoride (LiCF) and nickel-cadmium (NiCd) batteries. NASA provided a total of 92 LiSO₂ batteries that were used to power all but three of the active experiments flown on LDEF. Ten LiCF batteries were used by the two active NASA MSFC experiments. One NiCd battery, continuously charged by a four-array panel of solar cells, was used to power an active experiment from NASA GSFC. A loss of overcharge protection resulted in the development of internal pressures which caused bulging of the NiCD cell cases. However, post-flight testing showed that the battery still has the capability to provide output current in excess of the cell manufacturer's rated capacity of 12.0 ampere-hours. All the LiCF and LiSO₂ batteries met or exceeded expected lifetimes.

Pyrotechnic devices, flown on Experiment AO038, were successfully fired during post-retrieval ground testing.

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