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An Interview with
Dr. Harvey Tananbaum on the Chandra Launch Delays
February 11, 1999, in Cambridge, MA.
After staying on schedule for an August 28, 1998 launch date for
five years, the launch of the Chandra X-ray Observatory has slipped
several times. We talked to Dr. Harvey Tananbaum, Director of the
Chandra X-ray Observatory Center about these delays.
Q: When did you first realize that the
Chandra Observatory would not be launched on the originally
scheduled date?
TANANBAUM: In the Fall of 1997, TRW*
encountered problems with the software they had developed to test
the spacecraft. In spite of added manpower, incentives, and a
reorganization of the management, these problems caused a slip in
schedule to a December 3, 1998 launch date.
Q: We talked to TRW and other Chandra
officials in April of 1998, and they were confident they would make
the December ‘98 launch date. What happened?
TANANBAUM: Several things. In June of
‘98, during the course of a routine test, the door to one of
the science instruments, the CCD Imaging Spectrometer, failed to
open. It stuck and a fail-safe disk within the wax actuator burst,
so the actuator could not open the door. Exactly why the door stuck
was never determined. Most people believe that the O-ring seal on
the door stuck, and the problem was compounded because we tried to
open the door cold, which would not have happened in orbit. The
testing could not find the reason for sticking. They ruled out
every possibility. You would have concluded from the tests that the
door must have opened!
Q: What has been done to ensure that
this problem doesn't recur in orbit?
TANANBAUM: The mechanism that opens the
door has been rebuilt and modified, and the door will be opened
gradually to prevent the safety disk from bursting even if the
O-ring sticks a little. In addition, the door will be opened at a
warmer temperature.
Q: Were other problems cropping up at
this time?
TANANBAUM: Yes. More software delays,
related to safe mode testing. For example, you want to keep the
telescope from pointing to the Sun in event of a failure, or keep
the solar panels pointed toward the Sun. Software is used to
simulate a failure, for example a gyro failure, and then the
onboard software is supposed to solve the problems that may arise
from this failure. All the software needed for this activity turned
out to be more complicated than expected. The net effect of the
software and the door problems was that the launch slipped to
January 23, 1999.
Q: Then in October the launch date
slipped again.
TANANBAUM: Yes, this was just before the
spacecraft was due to be shipped to Kennedy Space Center to prepare
for launch. The safe mode testing still wasn't complete and there
was a problem with some electrical switching boxes that switch
power on and off between various components of the spacecraft. In
addition, some timing synchronization problems cropped up in the
interface unit which handles communications between the onboard
computers and other parts of the spacecraft. NASA's Associate
Administrator for Space Science, Ed Weiler, decided that these
problem should be fixed at TRW rather than at Kennedy. This pushed
the launch back until April15. Everything was fixed ahead of
schedule. TRW got ready to ship in early January and then other
problems surfaced.
Q: What were the nature of these
problems?
TANANBAUM: They were discovered while
testing another satellite built by TRW. This satellite has some of
the same components as Chandra. Small printed circuits boards were
found to be faulty. It turns out that Chandra has 129 of these
boards. Fortunately only four required replacement. New boards were
fabricated at the subcontractor, B. F. Goodrich. Two of the boards
have been installed in their unit and are undergoing testing at
Goodrich. The other two boards will be installed in their unit
soon. After testing, all the boards will be re-installed in Chandra
at Kennedy Space Center in early March. In the meantime the
observatory was put in a protective bag and shipped to Kennedy
Space Center on February 4.
Q: Do these delays pose any danger to
the instruments or other components?
TANANBAUM: The major worry is
contamination, which is why Chandra was put in a protective bag,
and why all the work on it is done in a clean room.
Q: What is the anticipated launch
date?
TANANBAUM: We are now working toward a
July 9 launch.
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*In December 2002, TRW was aquired by Northrop Grumman and is now a part of Northrop Grumman Science Technology.
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