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The Cal Team

September 9, 1999 ::

Members of the Cal Team
Photo: CXC

It's 11:00 a.m., time for the Calibration (Cal) Team's daily meeting to assess the state and performance of the Chandra X-ray Observatory. Before launch, separate components of the observatory were thoroughly tested in various laboratories -- the telescope at NASA's Marshall Space Flight Center in Huntsville, Alabama, and the spacecraft at the TRW Space and Electronics Group's (now NGST) space park in Redondo Beach, California.

The tests were designed to simulate as closely as possible the sound and fury of launch, and the cold, empty severity of space. The Cal Team worked long hours during these pre-launch tests to understand the performance of the telescope under known conditions, to compare the predicted performance of mirrors and detectors with the test measurements.

Members of the Cal Team
Photo: CXC

Now that Chandra has launched, they have moved on to their next and final phase -- the six to eight week in-orbit calibration phase, where they compare the performance of Chandra in space with what they expected from the testing on the ground, and with what previous observations of cosmic sources have shown. The expected and the real are never the same. Launch, the out-gassing of water vapor from epoxy or other materials, the hazardous trips through the radiation belts for ten hours every two and a half days, the bursts of high-energy particles released by solar flares, an unexpected bug in a computer program. It's like driving a car in a simulator, and then getting behind the wheel of a car with its own eccentricities and driving on a road with potholes,shadows, rain, snow, eighteen-wheelers, and bugs on the windshield.

The Cal Team's job is to sort all this out, literally on the fly, as a dozen or more of them pack into the Tea Room at the Harvard-Smithsonian Center for Astrophysics. Christine Jones, the Cal Team leader, starts the meetings off by saying hello to her colleagues that are patched in remotely from MIT and Marshall Space Flight Center.

Members of the Cal Team
Photo: CXC

"This was a more or less quiet day except for the almost safe mode," she reports, referring to a minor glitch when the star tracker used to orient the observatory got confused.

Larry David comments on the numbers on the sensitivity of the detectors, and the new results on the gratings. Brian McNamara comments on the point response function and wonders about the aspect -- how well do they know where Chandra is looking? Herman Marshall of MIT breaks in over the phone to mention a memo that addresses the situation. A graph is laid on the table and everyone huddles around to look at it and assess its meaning. Today, the puzzle is quickly resolved. But on any given day, there are new challenges and new puzzles, some trivial, some not. The latter may require a change in the observing plans to test out a hypothesis.

"You never know what each day will bring," Jones comments. "Life is complicated, and so is Chandra."

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Sep 27 Mirror Man

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