Power subsystem design and early mission performance

The power subsystem for the Near Earth Asteroid Rendezvous (NEAR) spacecraft is a direct energy transfer system with an Eagle Picher Industries Super nickel-cadmium battery and fixed solar panels populated with solar cells of gallium arsenide on germanium. Power is controlled by digital and analog sequential shunts. During the mission the distance from the Sun varies significantly, causing large variations in solar array power and temperature. To minimize solar array size, the solar array and power system electronics were designed to allow operation at voltages both greater than and less than the array's maximum power voltage. The power system design emphasizes reliability with low weight and volume. Analyses verified subsystem capabilities over the varied mission environment, and early mission flight data indicate that performance is consistent with analysis models.