December 20, 2004
Power Play: Last week the Mission Operations team at the Johns Hopkins University Applied Physics Laboratory conducted a peak power test, which determines exactly how much power MESSENGER's solar arrays can produce at a given time and position. Spacecraft team members use these data to refine their thermal and power models, as well as to make sure the arrays are in good condition and to plan events that require changes in MESSENGER's power levels (such as instrument operations).
The team ran its first peak power test in mid-September, a few weeks before MESSENGER reached its maximum distance from the Sun. They plan to conduct additional tests before MESSENGER "flips" to turn its sunshade toward the Sun next March and before it swings past Earth next August.
"In normal operation the peak power from the array is greater than the load required by the spacecraft, and MESSENGER's electronics adjust the operating voltage of the solar array to account for this," says Clark Person, MESSENGER power subsystem lead. "During these tests, we increase the loads until we reach the peak power of the arrays." They can boost the power loads by turning on secondary heaters and backup electronics, he adds.
MESSENGER continues to operate normally and in good health. Other than routine housekeeping operations, no significant events are planned through the holidays.
Stat Corner: MESSENGER is about 97.4 million miles (156.8 million kilometers) from the Sun and 27.6 million miles (44.5 million kilometers) from Earth. At that distance, the amount of time for a signal to reach the spacecraft from Earth is 2 minutes, 28 seconds. The spacecraft is moving around the Sun at 63,478 miles (102,161 kilometers) per hour. Since liftoff, MESSENGER's onboard computers have executed 20,913 commands from mission operators.