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We Are Getting Photons !!!

August 26, 1999 ::

Chandra X-ray Observatory & photons
Illustration of X-ray photons entering the telescope The photons are reflected at grazing angles and focused onto an electronic detector to make an image of a cosmic source. See the Quick Time movie
Illustration: CXC
Big time space science has its drawbacks. Long, long waits, sometimes for decade, sometimes longer, before your project finally gets to fly. Bruising political battles in which your instrument can get bumped off the bird. And the ever present shadow of catastrophic failure, from which there is no recovery.

Why then do it? The answer was there for anyone to see at the Chandra Center on August 12. It was on any of dozens of faces that would not quit smiling. Faces that, during the past three weeks, you would have sworn would break if you had asked them to smile as they endured two scrubbed launches, one harrowing successful launch that was almost aborted, two boosting burns with a type of rocket that had malfunctioned four months earlier, five more burns with a new propulsion system, and the remote opening of four doors whose failure could have terminated or seriously damaged the mission.
Scientists deep in concentration Scientists deep in concentration at the OCC.
Photo: CXC

The telescope's Sunshade door had opened, and Fred Wojtalik, Chandra project manager from Marshall, was ready to celebrate. Not yet, replied Craig Staresinich, TRW's (now NGST's) Chandra project manager, and Martin Weisskopf, Chandra project scientist from Marshall.

They pulled off their headphones, got up from the monitors in the Action Room and rushed into the TST (Technical Support Team room), and crowded into the claustrophobic ACIS detector room. There, Gordon Garmire of Penn State, the principal investigator for the Advanced CCD Imaging Spectrometer (ACIS), was peering over the shoulder of his wife Audrey as she tapped on the keys of her computer and brought up a screen showing the response of ACIS.

"We are getting photons," Garmire announced breathlessly.

Photons from where?

"This is better than good,"
- Rob Cameron, from the Harvard-Smithsonian commented as the aspect camera locked onto guide stars.
"Mostly background," he cautioned, as a buzz started among the onlookers. "But if the gyros hold us still long enough, we will probably see something."

Out in the TST room, Staresinich reported, "We're controlling our gyros okay, but we still don't know where we are."

The aspect camera, another vital piece of equipment on Chandra, was recording the positions of stars and comparing them with the positions of billions of stars in the guide star catalog to find out exactly where Chandra was pointing.

"We have locked," Tom Aldcroft of Harvard-Smithsonian announced from his console.

"So have we!" Rob Cameron, also from Harvard-Smithsonian, yelled from another computer.

Staresinich looked over Cameron's shoulder and inquired, "This is good, isn't it?"

"This is better than good," Cameron replied.

Back in the ACIS room, George Chartas reported that they had found a source -- 67 photons so far--from somewhere out there in the direction of the south ecliptic pole.

"Audrey, have you named it yet?" asked Harvey Tananbaum. Tananbaum, now director of the Chandra X-ray Center, had 23 years earlier, submitted with Riccardo Giacconi a proposal for the telescope that would become the Chandra X-ray Observatory.

About that time Leon van Speybroeck walked into the room. Van Speybroeck has been designing and overseeing the construction of X-ray mirrors longer than anyone on the planet. He is the Chandra Telescope Scientist, which means, as the title suggests, that he played a major role in the design and construction of Chandra's mirrors. He was here this afternoon to see if the last twenty years of work on Chandra had been worth it, or if they were flying around with a "bucket of broken glass" as he put it.

The image on the screen was a little smeared.

"How big is that image?" someone asked.

"About three arc seconds, but it's off-axis." Meaning that the source was slightly off to the side of where the telescope was looking

"How big should it be, Leon?"
Chandra scientists smiling
Smiling Scientists at the OCC.
Photo: CXC

"How far off axis are we?" he asked.

"About three arc minutes."

"Then the source should have a size of about three arc seconds," van Speybroeck said with a broad grin. "We've got good mirrors."

"Come on, Leon, they're great mirrors," said Martin Weisskopf, Chandra project scientist from Marshall Space Flight Center. "And, that's the first source they've ever seen. Leon X-1!"

"Yeah, Leon X-1!" the group agreed.

Van Speybroeck was still smiling when we left the room about an hour later.

"It's a good start," he acknowledged. "Not a bad start at all."

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    Disclaimer: This material is being kept online for historical purposes. Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. Visit for current information.

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