Chandra status report for Saturday at 6 a.m. EDT

      Marshall Space Flight Center Status Report for Saturday, July 24, 6:00 a.m. EDT

      Closing in on its first full day in space, the Chandra X-ray Observatory is performing
      normally as controllers in Cambridge, Mass., continue activation and checkout of the
      spacecraft. The observatory is in excellent condition and all systems are functioning
      as expected.

      During the last 12 hours, the team activated Chandra's High Resolution Camera for
      initial checkouts that verified it is in good condition. The camera is one of a pair of
      science instruments located at the narrow end of the telescope cone. It will record
      X-ray images, giving scientists an unequaled look at violent, high-temperature
      occurrences like the death of stars or colliding galaxies. When used with the Chandra
      mirrors, the camera will collect images that reveal detail as small as one-half arc
      second -- equivalent to the ability to read a newspaper at a distance of one-half mile.

      Also, the Chandra Flight Operations Team conducted a dry run for the first firing of
      the spacecraft's Integral Propulsion System. During the practice exercise, the team
      checked out hardware, software and procedures that will be used in the engine
      firings that will boost Chandra to its working orbit.

      The Integral Propulsion System has a redundant set of two 105-pound-thrust liquid
      apogee engines that perform orbit adjustment burns. The engines are fueled by
      hydrazine and nitrogen tetroxide.

      During the practice session, controllers turned on the Liquid Apogee Engine injection
      heaters, commanded Chandra through two maneuvers and then into a burn attitude.
      All systems performed normally during the three-hour procedure.

      The dry run prepared the team and the spacecraft for the first firing of Chandra's
      Integral Propulsion System at approximately 9:16 EDT tonight. Five firings of the
      system's liquid apogee engines are planned over the next few days as Chandra
      climbs toward its final orbit.

      Chandra is moving around the Earth in an elliptical orbit with its perigee, or lowest
      point, at 206 miles (329 kilometers) and its apogee, or highest point at 45,041 miles
      (72,065 kilometers). Following the first Integral Propulsion System burn, the new
      perigee is expected to be 750 miles (1,200 kilometers) and the new apogee is
      expected to be 45,014 miles (72,023 kilometers). Chandra's new orbit duration will
      be 24 hours, 38 minutes, slightly longer than its current orbit of 24 hours, 17 minutes.
      At perigee, Chandra is traveling approximately 23,500 miles per hour (10.47
      kilometers per second). After tonight's five-minute burn, the spacecraft velocity at
      perigee will be about 22,000 miles per hour (9.8 kilometers per second.)

      One of the recurring procedures that will help Chandra controllers position the
      spacecraft for the engine firings is an Earth sensor scan. Early today, the team
      initiated activities for the first such scan, scheduled to begin about 7:30 a.m. EDT and
      last approximately one hour. Using Earth sensor mirrors, a sensor on Chandra scans
      the Earth and detects 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. During the transfer orbit phase of the mission, Earth sensor scans will be
      performed twice during each orbit of the Earth -- once on the way "up" to apogee
      and again on the way "down" to perigee.

      During the next 12 hours, the control team's focus will be on the upcoming burn. A
      second Earth sensor scan is scheduled to begin shortly before noon EDT and last
      about four hours.

      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.