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Power Distribution Unit Tests

Following installation, an APL engineer tests the power distribution unit (PDU) on the STEREO “A" observatory—the one that will be placed ahead of Earth in its orbit around the sun. (The PDU is the black box with red cap in the foreground.) The PDU, which is installed on both STEREO observatories, distributes power to all spacecraft systems. It also provides power to devices aboard each spacecraft used to separate the two observatories from each other after their launch into space, and deployment of both spacecraft's solar arrays.

Aside from the battery, the PDU is the largest electronics unit on each spacecraft. However, it's small enough to fill a backpack, and weighs approximately 30 pounds.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory