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 An Interview with
Dr. Harvey Tananbaum, Director
Chandra X-Ray Center
August 26, 1997
Q: A lot has happened in the last twelve
months.
HT: It has been the busiest year so far for the ASC. The AXAF team
successfully completed the calibration of the telescope, the two
objective grating assemblies, and the two focal plane science
instruments. TRW*, the prime contractor for AXAF, was responsible
for the overall test and Marshall (NASA's Marshall Space Flight
Center in Huntsville, AL) was responsible for building the testing
facility. The SAO Mission Support Team, under separate contract to
MSFC, built special detectors used to test the telescope. The ASC
was set up as the hub for planning of the calibration. The ASC and
the MSFC Project Scientist team, with the help of the Science
Instrument teams, listed the tests to be made, scheduled them, and
then evaluated the test results in near real-time. The testing
itself was an intense effort. We literally had thousands of tests
to make and a limited time in which to do them. We kept the XRCF
(the X-ray Calibration Facility at Marshall Space Flight Center)
running 24 hours a day, 7 days a week.
Q: What were some of the high points of the
calibration?
HT: One of the high points, probably the high point, was first
light. Around the th ird week of December, we pumped the air out of
the vacuum chamber and waited a few hours until we were sure all
the contaminants had been cleared out of the chamber. By this time
it was well after midnight. We woke up a few of the team members
who had been with the project a long time so they could share the
experience with us. Then we opened the covers to the mirrors and
exposed them to X-rays for the first time. We adjusted the focus
and there it was, a nice sharp image, just like we had predicted.
It was a very exciting time.
Q: Did the tests reveal things you didn't
expect?
HT: Nothing major, and that is very good news. Because of the
testing we know we have the best X-ray mirrors ever made, and the
most sensitive X-ray detectors. Of course there were many things we
learned about the performance of the telescope that we couldn't
have learned any other way. For example, the upper and lower parts
of the mirror are not centered exactly alike, so the efficiency of
the upper part is about ten percent greater than the lower part.
Because of calibration, we now understand that effect and can
correct for it. Otherwise, every image we made would have been off
by a few percent and we wouldn't have known it.
Q: Were there any major crises?
HT: The most significant crisis was of a personal nature after the
testing had been completed, when Martin Weisskopf (the AXAF Project
Scientist at Marshall Space Flight Center) had a heart attack. This
followed a very intense and stressful five-month test period.
Fortunately, Martin is now fully recovered and even back to his
daily basketball game.
Q: The testing must have been exhausting for
everyone, given the round-the-clock schedule and the complexity of
the job.
HT: In one way it was. In my case for example, I would often work
here (at the Harvard-Smithsonian Center for Astrophysics) Monday
through Thursday, catch the plane to Huntsville in time for the
three-to-midnight shift, work that shift through Sunday night and
fly back to Cambridge. In another way though, it was an
exhilarating and energizing process, seeing it all come together
and actually work, so you didn't realize how hard you were working.
All in all it was a very satisfying experience, seeing how all the
different groups learned to work together --- TRW, Marshall Project
Science, the science instrument teams and the ASC. It built up a
camaraderie that will stand us in good stead in the year ahead as
we integrate the telescope and science instruments with the
spacecraft and get ready for launch, which is about a year
away.
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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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