During July 11 to 13, 1995, a team from the NASA Lewis Research Center performed dark forward electrical testing on the Mir Cooperative Solar Array (MCSA) flight unit in the Space Station Processing Facility at the NASA Kennedy Space Center. The MCSA was jointly designed and built by the United States and Russia to supply approximately 6 kW of electricity to the Russian Mir space station (ref. 1). The primary objective of testing was to assess the overall electrical performance of the flight array after handling and shipment from Russia to NASA Kennedy. This objective was achieved without the high cost and difficulties of deploying and illuminating the MCSA as is usually done with large-area solar arrays. The data obtained provided U.S. and Russian program managers with a high level of confidence in the MCSA electrical performance prior to the array's launch on shuttle mission STS-74 in November 1995 and its deployment on Mir in May 1996.
NASA Lewis engineers developed the test hardware, test software, test procedures, and analytical software to support MCSA dark testing. The hardware and software were first verified by testing at Lewis with solar array strings available in-house. At Kennedy, MCSA dark forward testing was accomplished by applying a voltage and measuring the current. The resulting diode characteristic, or current-voltage curve, was then analyzed and compared with the nominal response expected. This procedure was repeated for each of the 12 MCSA generators. A generator consists of either 6 or 8 parallel circuits, each containing 80 solar cells connected in series. The dark forward current-voltage response of the solar cell bypass diodes was measured by reversing the polarity of the power supply,. (There is one bypass diode for each group of 10 series-connected solar cells.)
The top and bottom graphs show measured and predicted dark-forward
current-voltage curves for generator 7 solar cells and bypass
diodes, respectively. These results, which are typical for all
MCSA generators, show that pretest predictions as well as refined
posttest predictions compare very well with the experimental data.
This indicates that no substantial handling and shipment damage
was sustained by the MCSA. Major differences in the current-voltage
curves, if present, could have been attributed to various types
of array hardware damage.
Subsequently, we translated the measured MCSA dark current-voltage response into illuminated current-voltage response by factoring in solar cell series resistance and the voltage drop of test equipment and cabling. This enabled management to be fully aware, prior to launch, of the anticipated on-orbit MCSA electrical capability.
Because of the low cost of dark electrical testing and its significant
mitigation of risks, NASA Lewis is supporting the International
Space Station Program Office feasibility assessment of dark testing
the International Space Station port-side preintegrated truss
segment (P6) solar arrays.
1. Skor, M.; and Hoffman, D.J.: Mir Cooperative Solar Array. Research & Technology 1996. NASA TM-107350, 1997, pp. 153-154. Available WWW: http:/www.grc.nasa.gov/RT1996/6000/6910s.htm
Previous articleLast updated May 6, 1997
Responsible NASA Official:
Gynelle.C.Steele@nasa.gov
216-433-8258
Point of contact for NASA Glenn's Research & Technology reports:
Cynthia.L.Dreibelbis@nasa.gov
216-433-2912
SGT, Inc.
Web page curator:
Nancy.L.Obryan@nasa.gov
216-433-5793
Wyle Information Systems, LLC
