Chandra status report for Sunday at 6 p.m. EDT
NASA Marshall Space Flight Center Release for Sunday, July 25, 1999 6:00 p.m. EDT
The Chandra X-ray observatory continues
its mission of discovery as preparations
continue for the second burn of Chandra’s
Integral Propulsion System.
The Flight Operations Team in Cambridge,
Mass., has worked during the past 12
hours to position the spacecraft for
the burn that is expected to occur at 9:47 EDT
tonight.
The team has commanded Chandra through
two additional Earth sensor scans.
These routine maneuvers are conducted
to determine the spacecraft’s attitude in
relationship to the Earth. Sensors on
Chandra scan the Earth and detect the edges of
the planet. The data is used to compare
which direction the spacecraft "thinks" it's
pointing with its actual attitude. Ground
controllers then use the information to update
the spacecraft's knowledge of its position.
Chandra’s perigee is 740 miles or 1,192
kilometers and the apogee, or highest orbit
point, is 44,781 miles or 72,067 kilometers.
The first burn of the Integral Propulsion
System occurred at 9:11 p.m., Saturday
July 24.
Tonight, Chandra’s primary liquid apogee
engines are scheduled to burn for 11
minutes and 13 seconds. After the firing
perigee is expected to be 2,142 miles, or
3,448 kilometers. The apogee will remain
unchanged at 44,782 miles or 72,069
kilometers.
The first two burns are at apogee because
that is the most efficient use of fuel in
raising the spacecraft’s perigee.
After tonight’s burn the Flight Operations
Team will conduct another Earth sensor
scan as Chandra moves from apogee toward
its new perigee. They will also turn on
the vacuum monitor and take additional
readings. The monitor reads pressure inside
the optical bench of Chandra’s High
Resolution Camera.
The team will also commission the Electron
Proton Helium Instrument. The unit
detects levels of radiation in space,
similar to radiation belts surrounding the Earth. It
has the capability to shut down the
telescope’s science instruments for self-protection
if radiation levels are too high.
Editor’s Note: NASA’s Marshall Space
Flight Center in Huntsville, Ala., manages
the Chandra X-ray Observatory for NASA’s
Office of Space Science, NASA
Headquarters, Washington, D.C. The Smithsonian
Astrophysical Observatory in
Cambridge, Mass., manages the Chandra
science program and controls the
observatory for NASA. TRW Space and
Electronics Group of Redondo Beach,
Calif., leads the contractor team that
built Chandra.