A New Pair of Glasses
by: Holly Nordquist
From Research/Penn State, Vol. 20, no. 3 (September, 1999)

t was a time of great elation," reminisces Gordon Garmire. He quietly breaks into a grin. Fourteen years ago, he and his team of 17 scientists received word that their CCD Imaging Spectrometer would be one of four scientific instruments on NASA's Advanced X-ray Astrophysics Facility, or AXAF, the premiere x-ray telescope of the next century. Forty labs had competed for those four spots. Garmire's team, including five Penn State astronomers, had beaten the likes of Harvard and Lockheed Martin.

Astronomer Gordon Garmire, whose team designed Chandra's CCD imaging spectrometer. (Photo: M. Scott Johnson)

Yet ever since NASA awarded them the contract back in 1985, they have struggled and stressed to solve problems with their instrument. "Things don't always work as you expect them to," says Garmire, his grin fading. "Teamwork really comes into play when you have problems."

Teamwork really came into play when the entire AXAF program was almost eliminated in 1992. The scientists had to redesign the spacecraft to cost much less, yet still try to maintain the incredible image capability they had originally proposed.

Garmire sits down at a cherry table that matches the cherry desk piled with scientific papers in his large corner office. Behind the desk is a blackboard scribbled with equations. He begins to explain that "AXAF will look at x-ray objects that we've looked at before, but with more clarity." Once in orbit, he says, the telescope will produce x-ray images ten times sharper than ever before seen. "AXAF will operate like a new pair of glasses."

The telescope stands 35 feet tall, with a 10-foot-wide waist. It is powered by sunlight absorbed through delicate solar panels jutting out from both sides of the spacecraft, like arms. The head is a door which, at a scientist's command, will open to let x-rays in to pass through the body, which houses the mirror system. The barrel-shaped mirrors will direct the x-ray photons (packets of light) to a central focal point, located at the spacecraft's feet, where the scientific instruments wait to record their presence. It is these instruments that will produce the extraordinary new images—images of a different universe than the one we look at each night. They will picture a violent universe, where the temperatures reach into the millions of degrees. They will reveal new secrets about super-dense neutron stars, black holes, and the expanding gas clouds of exploding stars.

Those first images will—Garmire hopes—provide another time of great elation for his team.

armire built his first telescope when he was eleven. He bought a kit for an optical telescope from Edmund Scientific and read astronomy books to learn how to grind the glass for its mirrors. Each cloudless night, he set his telescope up in the backyard of his parents' house just south of Portland, Oregon. The night sky was free of bright city lights, allowing for a crisp, clear view of the stars. He began to take pictures of the mysterious wonders in the night sky, and dreamed of becoming an astronomer.

Artist's rendition of the Chandra X-ray Observatory in orbit. (Courtesy: NASA)

He soon realized that it wouldn't be easy to make a living. "You needed a position at a university or observatory, and I felt that such positions were highly competed for," says Garmire, so he turned his focus towards chemistry and physics instead. Yet he began graduate school in physics at the Massachusetts Institute of Technology in 1959, just after the launch of Sputnik. Sputnik had shown astronomers they could have a better vantage point from which to study the universe: space. The Earth's atmosphere acts as a sponge, absorbing most light with wavelengths smaller than optical light so that it never reaches ground-based telescopes. To study these forms of light—x-ray light or even shorter gamma-ray light—astronomers needed to get beyond the atmosphere, and Sputnik provided a way.

Not surprisingly, Garmire was soon immersed in this new "space astronomy." At about the same time he began his graduate studies, MIT started a program to search the sky for gamma-rays. Garmire used his physics background to assist with building the first gamma-ray telescope to be flown in space—Explorer 11. Later, he spent a summer working at American Science and Engineering, working on systems to detect x-rays coming from distant stars and galaxies. The next fall Garmire, along with faculty and other graduate students, began developing an x-ray astronomy group at MIT, which flew x-ray-recording sounding rockets with scientists at American Science and Engineering. Although these rockets broke through the atmosphere for only a few minutes, it was long enough for their detectors to intercept x-rays and record their presence.

After receiving his doctorate from MIT in 1962, Garmire worked at MIT as a staff scientist until 1964, when he became an assistant professor. In 1966, he moved to the California Institute of Technology as a senior fellow, becoming part of the faculty in 1968. There, he began his research on Charged Coupled Devices, a kind of light-gathering chip, at the time being studied by a group at NASA's Jet Propulsion Laboratory (JPL) near the Caltech campus A CCD chip is made of silicon and looks like a miniature solar panel. It has far greater sensitivity than other x-ray detectors. By picking up many more x-ray photons, it increases the precision of the image.

The JPL group was developing these chips for the Hubble Space Telescope, an optical telescope that would be launched into space in the early 1990s. "I started working with the JPL group to show that you could use x-rays as a diagnostic tool to improve CCD performance—and we did, in fact, improve them," Garmire says. "Each x-ray that goes into a CCD chip puts in a fixed amount of charge. You can analyze what happens to that charge as it moves through the chip. This allowed us to diagnose any problems in the process of moving the charge." If less charge were to come out of a chip than went in, for instance, they would know that the chip isn't operating correctly. While doing this research, however, Garmire saw the potential for using CCD chips as x-ray detectors themselves—"and that's what we started doing, just before I came to Penn State in 1980. It was easy to divide one CCD chip into much smaller components. The greater the number of these smaller components, the better the resolution of the image," he explains.

Garmire's instrument on AXAF includes ten of these CCD chips, each one roughly an inch across. Each chip is further divided into 1,048,576 smaller squares or pixels, making a grid. The ten chips are set on a beryllium plate: six arranged in a horizontal row with the remaining four arranged as a square, next to them.

The pixels on each chip absorb and collect the charge from the incoming x-ray, the number of x-rays passing through each pixel per second measuring the brightness of the source. The variation in the amount of x-rays each pixel collects is then translated by a computer into a gray scale, to produce high-resolution images.The amount of charge collected determines the energy of the x-ray—its wavelength. By recognizing spectral features at specific wavelengths, astronomers can determine the chemical composition of the x-ray source. So Garmire's instrument has two capabilities: imaging and spectroscopic. Astronomers will be able both to make detailed images of x-ray objects and to study their chemical make-up and temperature.

e began the original proposal for AXAF in 1977—a time when the word telescope conjured up feelings of animosity in many legislators, because previous telescopes had exceeded their original budgets by hundreds of millions of dollars," says Garmire. "So we decided to call our x-ray telescope a facility. I guess we fooled someone, because AXAF was approved." At the time, the plan was to launch the telescope by the mid-1980s. "But the administrator at NASA dragged his feet a bit and the call for experiments didn't occur until 1983"—so the launch of the telescope was delayed. Garmire and a team of scientists from Penn State, MIT, and JPL submitted the proposal for a CCD imaging spectrometer, incorporating the devices he had designed at Caltech.

It was a long two years before Garmire's proposal was accepted. When it was, "This was exciting because we were a part of the core science. AXAF is the most advanced and challenging project in high-energy astrophysics. There was a lot of competition to get an experiment on the observatory."

The NASA mission patch for the Space Shuttle flight that carried Chandra aloft. (Courtesy: NASA)

The other three science instruments NASA accepted were a high-resolution x-ray camera that would operate in conjunction with Garmire's instrument to produce images, a Bragg Crystal spectrometer, to split the incoming x-ray light into the wavelengths of its constituent elements, and a microcalorimeter that would measure the temperature and spectral properties of the x-ray-producing object.

But Congress kept delaying the start date—until 1987, then 1988, then 1989. "It kept getting pushed ahead, year by year, and we were getting very frustrated," says Garmire."Finally, in 1991 we were given the go-ahead"—and, more important, the funding.

Yet Garmire's team faced difficulties with the project even before the funding arrived. "It was a big challenge because we still hadn't gotten the CCDs to work as well as we had proposed they would," says Garmire. The chips being developed at Texas Instruments, under Garmire's supervision, just weren't good enough. "The company made a lot of them, but none were reliable enough: the charge transfer in the CCD was too low to get good operation. So we were nervous that we were going to have trouble having them made in time. We went through a lot of agony until 1989, when we finally switched to Lincoln Labs." Lincoln succeeded in making usable CCDs, but at a price: about $10 million.

"Then, in 1992, 15 years after AXAF was first proposed, we could see the ax beginning to fall," recalls Garmire. A study performed by the National Academy of Sciences reported that AXAF would exceed its original budget by more than $5 billion. "This got a lot of people worried, because around the same time Congress had cut the SSC," the Superconducting Super Collider, which was to have been the world's largest and most powerful particle accelerator until Congress decided that it was too expensive to support.

Something had to be done so that AXAF would not follow in the SSC's footsteps. For the next few months, Garmire and the other scientists tried to decide how AXAF could be made cheaper without jeopardizing its imaging capability. One solution, they determined, was to place the telescope in a high Earth orbit - in this case, halfway to the moon. Originally, AXAF had been intended to function like the Hubble Space Telescope— #151;in a low orbit where it could be serviced by the Space Shuttle. In a high Earth orbit, servicing would be impossible, but the price tag would be much cheaper, Garmire says, because, "You pay only at the beginning when it's launched. Then the only costs are to operate it, and that's not very high. Hubble needs $250 million each year for servicing alone; AXAF is expected to cost only about $10 million a year total.

"But if something goes wrong," he adds, "you're stuck," since the Shuttle can't reach it. "And that makes us very nervous. Everybody has to really do things right the first time, because you don't have a second chance."

Because of the higher orbit, the spacecraft's weight also had to be reduced—by about ten tons, or the weight of an empty tractor trailer. "The biggest reductions were in the spacecraft itself," Garmire reports. "The primary metal was switched from aluminum to carbon-fiber epoxy structures, which are more expensive, but tremendously lighter." But the science experiments, too, had to be redesigned to reduce weight. Instead of using aluminum, which is relatively heavy, Garmire's team turned to light-weight beryllium for their base, reducing the instrument's weight from 350 pounds to 250. "Thankfully, we didn't have to reduce the number of CCDs," he says.

Unfortunately, this scrimping and saving wasn't enough, and in the end two science instruments had to be eliminated. To Garmire's relief, his CCD Imaging Spectrometer wasn't one of them. "The Bragg Crystal spectrometer was cut because it was questionable if it could be developed in time, even with the delays, and the microcalorimeter was dropped because it couldn't be made within its cost and weight limitations," explains Garmire. "The cutbacks were a loss, but they did help to reduce the weight"—and cost—of the total facility.

In 1998 the two remaining science instruments, Garmire's and the high resolution camera, were carefully installed onto the foot of the spacecraft. AXAF was complete except for the final testing, which commenced in May 1998 at TRW, the prime contractor. "By June 17, AXAF had been in a thermal vacuum chamber"—where all the air is pumped out to simulate the vacuum of space—"for 35 days," says Garmire. "On the last two days we were planning to open its door to see if any stray light entered when we shined lights on it to simulate the sun." When placed into orbit, he explains, the telescope's door will be positioned away from the sun; ideally no sunlight should ever enter the spacecraft. The light-gathering chips are sensitive to visible light and must remain in the dark to avoid interference with their data-collecting ability.

But on June 18, when the operator at TRW gave the command to open the metal door, nothing happened—absolutely nothing. The door was stuck shut. "This was a really big disaster," Garmire recalls. The malfunction broke the actuator, a piece of equipment that opens and closes the door. "We spent four months testing all the possible reasons why the door failed, and as of today I still can't say for absolute certain why it happened." However, he adds, we've done every test and changed the design a little bit to mitigate any possible problems. We've tested the new door extesively and each time it's worked, so we're very confident that we can open it in orbit. "Any big observatory like this requires a tremendous amount of teamwork and coordination," says Garmire, "especially when things don't go the way you planned. NASA's Marshall Space Flight Center, the overall project management, has played an essential role in coordinating all the different activities between TRW, the science experiments, and getting money from NASA. They really made things happen."

In December, NASA announced that the Advanced X-ray Astrophysics Facility would be renamed the Chandra X-Ray Observatory, in honor of the late Indian-American Nobel laureate Subrahmanyan Chandrasekhar. Chandra was finally launched July 22, 1999, 22 years after the project was first proposed. Garmire was there, at NASA's Kennedy Space Center in Florida, to see it go up.

Gordon Garmire, Ph.D., is Evan Pugh Professor of Astronomy and Astrophysics in the Eberly College of Science, 503 Davey Lab, University Park, PA 16802; 814-865-1117; garmire@astro.psu.edu. His research is funded by NASA through a contract with Marshall Space Flight Center in Alabama. Collaborators include the Massachusetts Institute of Technology's Center for Space Research, MIT's Lincoln Labs, The California Institute of Technology, the Jet Propulsion Laboratory, and Carnegie Mellon University.