Solar array with ESD protection

Details Solar array with ESD protection Solar array with ESD protection

1999-03-12

2001-06-05

Jackson, Stephen W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Load shunting by fault responsive means

C361S018000, C361S111000, C361S118000

Reexamination Certificate

active

06243243

ABSTRACT:

TECHNICAL FIELD
The present invention relates to solar panels, and more particularly, to a circuit to protect solar panels from electrostatic discharge (ESD) particularly for use with a satellite.
BACKGROUND ART
Solar arrays are used to power satellites in space. The solar arrays are used to power the spacecraft payload as well as charge batteries onboard the satellite. Recently, on-orbit solar array power losses have been observed. These power losses have been attributed to electrostatic discharge (ESD) induced arcing. It has been found that the ESD induced arcing is enhanced by the power available from the solar array circuit. On most satellites, there is a high ratio of insulating to conductive materials that are exposed to sunlight. During a geomagnetic storm, electrical potentials on the spacecraft can reach several kilovolts.
Solar arrays have cover glass that protects the individual solar cells beneath it. The cover glass is isolated from the spacecraft structure because of its high resistivity. The isolation allows the glass to charge less negative due to photo emission. The result is a net positive voltage differential between the cover glass and solar array substrate over time. At differential voltages of between 500 and 1500 volts, ESD may occur. The ESD manifests itself in plasma that spreads out over adjacent cover glasses. The positively charged cover glass absorbs negative charge from the neutral plasma and induces a transient displacement current in the solar cell circuits below. The displacement current can flow to spacecraft ground, which is electrically at the opposite end of the solar cell circuit.
If sufficient plasma is generated at the original ESD site, and there are solar cells with large potential differences between them nearby, the plasma can generate a low impedance path for current from the solar cell circuit to flow. If the current flow through the plasma persists, it can pyrolize the solar array substrate and permanently short the circuit. This may result in permanent power loss for the spacecraft.
SUMMARY OF THE INVENTION
It is, therefore, one object of the invention to provide a solar cell array circuit that prevents power loss due to electrostatic discharge.
In one aspect of the invention, a satellite system has a spacecraft payload and a solar array having a plurality of solar panels electrically coupled to the payload. The spacecraft ground terminal and the solar array are coupled together through a directional high impedance device that only increases the impedance to ground for the displacement current but keeps the impedance low for the usual low current, thereby reducing the potential for a sustained discharge.
One advantage of the invention is that this circuit may be used in place of, or in addition to, other electrical protections used on a spacecraft.


REFERENCES:
patent: 4691159 (1987-09-01), Ahrens et al.
patent: 5594313 (1997-01-01), Takeda

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