The solar array mounted on the port side of TOPEX/Poseidon is the largest and one of the most delicate pieces of spacecraft equipment. During launch, the array was folded along the Instrument Module. After deployment, during the Assessment Phase of the mission, it expanded to 8.89 meters long and 3.30 meters wide, with a maximum power output of 3385 watts. The total power required by all instruments and systems on the spacecraft is about 1000 watts. Some of the remaining power is used to charge the three batteries aboard the spacecraft, and the remainder is margin. As the solar panels degrade over the mission lifetime, the available power will steadily decline, eating into the margin but not depriving the instruments of their required power.
During normal operations, the on-board computer turns the array to keep its face pointed at the sun. When the spacecraft is in the earth’s shadow power is supplied by the batteries.
