NASA MESSENGER Status Report 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.

Scholars Wanted: Think you have a good idea of what we’ll learn from
the first
mission to orbit Mercury? If you’re a high school senior, tell us
in a short essay — and maybe earn a MESSENGER scholarship! Visit
the MESSENGER Web site at
http://messenger.jhuapl.edu/scholarship/index.html for details.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and
Ranging) is a scientific investigation of the planet Mercury, and
the first NASA mission designed to orbit the planet closest to the
Sun. Dr. Sean C. Solomon, of the Carnegie Institution of Washington,
leads the mission as principal investigator. The Johns Hopkins
University Applied Physics Laboratory in Laurel, Maryland, built and
operates the MESSENGER spacecraft and manages the Discovery-class
mission for NASA.