Solar array passive functional tests

Abstract

Passive functional tests are required to monitor the health of Mars Pathfinder solar arrays. To accomplish this, a Solar Array Ground Support Equipment Testbed (SAGSET) was proposed with five passive tests to be performed in sequence: positive and negative bus isolation from substrate; solar array string isolation from substrate; string blocking diode forward conduction; string blocking diode reverse leakage; and dark forward IV (DFIV) curves of the solar array strings. It was established that the DFIV test could not easily discriminate a good cell string from a damaged cell string. String capacitance measurements proved to be a superior alternative. Both the DFIV and capacitance tests suffer from one basic problem-the impact of a loss of cell area in one cell is reduced by the remaining series cells in the string. However, tests showed a factor of 4.6 temperature sensitivity advantage and a factor of 18 to 22 cell area loss sensitivity advantage for capacitance measurements. Using these findings, the SAGSFT was reconfigured to have seven passive tests. The DFIV test was deleted and three tests were added: solar array string continuity; string parallel capacitance; and string series capacitance. All of these passive solar array tests were successfully computerized using the SAGSET. The capacitance is measured as a component of both a series and parallel network which includes resistance as the other component. The series capacitance test impedance angle may prove to be as useful as the capacitance measurement. Problems usually encountered with cracked cells are not easily identified by any type of passive testing so a visual inspection of an array is still recommended.