Chandra :: Chronicles :: First Safe, Then Spectacular

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First Safe, Then Spectacular

August 26, 1999 ::

Chandra X-ray image of Quasar PKS 0637-752

After the Sunshade door opened and let the first cosmic X-rays shine into the Chandra Observatory, the calibration team began to test out the observatory. They moved it around, looked at sources on axis, then off-axis, and shifted the detector, the Advanced CCD Imaging Spectrometer, (ACIS), a few fractions of a millimeter at a time, searching for focus.

The serendipitous discovery of a cosmic X-ray jet in one of the test sources, a quasar called PKS 0637-752 that is billions of light years away gave the Chandra team confidence that they were close to focus. It seemed only a short time before they would point toward Cassiopeia A, the target for the first significant image made at the focus. Video crews were scheduled to cover the anticipated event on Tuesday, August 17. Then came a reminder that this is, after all, space science.

An artist's illustration of the Chandra X-ray Observatory in orbit
Illustration: NGST

"We've had a major hiccup." It was Harvey Tananbaum, director of the Smithsonian Observatory's Chandra Center, calling to say that Chandra had gone into safe mode.

"A load (a series of commands radioed up to the spacecraft) put two incompatible maneuvers back to back," he continued. "The spacecraft didn't like it and went into safe mode."

In safe mode, as Steve Murray of Harvard-Smithsonian and one of Chandra's principal investigators explained, the instruments are powered down, the spacecraft points so that its solar panels get maximum Sunlight, and the mirrors point away from the Earth or the Sun.

"Recovery will be done very carefully," Tananbaum emphasized. "It could take six hours, it could take forty-eight."

As it turned out, it took around thirty hours. By Thursday, Chandra was out of safe mode. The mood in the Action Room was relaxed, the scientists making small talk and Tananbaum checking on his beloved Red Sox from time to time. Around 8 p.m., the command was made to slew toward Cassiopeia A, the remnant of an exploded star. The small talk stopped and all eyes went to the monitor, looking for a sign that the aspect cameras would lock on guide stars.

CXC Manager Roger Brissenden & CXC Director Harvey Tananbaum at the OCC
Photo: CXC

"Three stars. That will hold it!" Tananbaum exclaimed, as the "flags" on the monitor lit up.

"We're there! A full set of flags!" shouted Roger Brissenden, manager of the CXC.

The monitors were quickly abandoned as the scientists rushed out of the Action Room, into the Technical Support Team room, past the rows of computer monitors with engineers and scientists staring intently at the screen, and into the tiny ACIS room that had been the scene of so much excitement when the first light came in.

"How long before we get an image?"

"About forty minutes," replied Mark Bautz, MIT member of the ACIS team.

The group dispersed for a while, moving over to the snack room to get a bite to eat, or into a nearby office to check on their e-mail or make a call with their cell phones. At 8:40 p.m. the room was full again. The photons were beginning to stream in at the rate of about 300 per second.

Supernova Remnant Cassiopeia A: The Chandra X-ray Observatory's First Light

Then, there it was! A gorgeous, dramatic image of the remains of a star that exploded ten thousand light years away. In half an hour they were looking at the best X-ray image ever made of a cosmic object.

"Awesome!"

"Spectacular!"

"What's that in the middle?"

What indeed? Closer inspection showed a tiny bright dot in the middle of the remnant. Was it real? Yes. Was it the long sought neutron star or black hole that was produced in the explosion that created Cas A?

Right now it is impossible to tell. Chandra will soon look at Cas A again for a much longer time as part of the Chandra's scientific observing program. After this data has been analyzed, we should know the answer.

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