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.