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For Release: Aug. 26, 1999
Chandra X-ray Observatory: Engineering Marvel of the Large, Small and Sophisticated
You could read a newspaper from half a mile away or see the letters of a stop sign from 12 miles. Thats the kind of strength and accuracy packed into the worlds most powerful X-ray telescope NASAs Chandra X-ray Observatory.
Chandra, a member of NASAs family of Great Observatories, is a remarkable technological achievement, a claim supported by todays release of the telescopes spectacular first celestial images.
The journey from Chandras program inception to initial image has been a challenging one. Along the way, the program, managed by the Marshall Space Flight Center in Huntsville, Ala., has focused on precision engineering and attention to detail. For some, it has been a career-long pursuit.
"Its literally a dream come true," said Arthur G. Stephenson, director of the Marshall Center. "There are people here at Marshall, and elsewhere, who had a vision and have devoted more than 20 years of their lives to the Chandra program. With these spectacular images, they have seen their dreams become reality."
Launched by the Space Shuttle just one month ago today, the observatory travels one-third of the way to the Moon during its orbit around the Earth every 64 hours. At its highest point, Chandras highly elliptical, or egg-shaped, orbit is 200 times higher than that of its visible-light-gathering sister, the Hubble Space Telescope.
With its combination of large mirror area, accurate alignment and efficient X-ray detectors, Chandra has 10 times greater resolution and is 50 to 100 times more sensitive than any previous X-ray telescope.
Chandras mirrors are the smoothest ever created. If the surface of the state of Colorado were as relatively smooth, Pikes Peak would be less than 1 inch tall.
"The Chandra team not only produced and polished the mirrors, but we had to create the systems to put them together, align all the components to within miniscule tolerances, assemble them into a spacecraft that could survive the rigors of launch and space, then test them and validate their performance," said Jean Olivier, deputy manager of the Chandra program. "Our NASA and contractor team was seamless," added Olivier of the Marshall Center.
In many instances, the Chandra team had to come up with new processes for things that had never been done before. They developed, built and validated a measurement system that was used to make sure the cylindrical mirrors were ground correctly and polished to the right shape. The eight mirrors are the largest of their kind -- the biggest 4 feet in diameter and 3 feet long. The mirror group weighs more than 1 ton.
The team created and executed a system to carefully assemble the mirrors into a total package that could survive the rigors of a rocket ride, weightlessness and the temperature extremes of space. The spacecraft is made of graphite epoxy to meet stringent weight requirements.
And yet, Chandra is the largest and heaviest payload ever deployed from the Space Shuttle. Fully fueled, Chandra weighed 12,930 pounds. With the Inertial Upper Stage set of boosters added to the craft, the assembly totaled 50,162 pounds and measured 45.3 feet long by 64 feet wide with its solar arrays deployed.
On the other end of the size spectrum, micro-technology was used in manufacturing processes to make components for Chandras imaging systems. Spectrographic transmission gratings, used to precisely determine the energies of incoming X-rays, had never been built before. The gratings include tiny gold bars that are closer together than a wavelength of visible light. It would take hundreds of the bars to equal the thickness of a sheet of paper. Plastic membranes, thin as a soap bubble, support the bars.
"While all of these incredibly small and large items were being designed and built we also had to make sure that they all came together to form the very best overall system," Olivier said. "The spacecraft had to be precise and reliable. Also, the ground control system and its operating staff had to be able to efficiently and safely operate Chandra for five years or more.
"We tested, tested and re-tested the spacecraft and ground system together to make sure they were compatible. On the optics system testing we made sure that we had at least two ways to cross-check all results. In some instances we had even more checks."
Calibrating and validating the telescopes scientific operation proved to be another challenge. Unlike optical astronomy, where there are established, well-known targets in the universe that can be used for calibration purposes, there arent any for X-ray images.
A new world-class X-ray Calibration Facility was built at the Marshall Center to precisely calibrate Chandras X-ray optics. The facility also provided opportunities for additional cross-checks of the total optical system and for an independent check of Chandras optical performance.
From X-rays entering the optics to the quality of the images produced by the science instruments, the testing verified the exceptional accuracy of Chandras optics.
Chandra is so finely tuned it can detect objects separated by one-half arc second. That is like identifying two dimes side-by-side from 2 miles away.
Now, the first images from Chandra validate the extraordinary engineering work performed by the team.
"There are a lot of words to describe that effort dedicated people with technical excellence and integrity, thorough testing and teamwork," Olivier said. "And, it feels wonderful to know our hard work to make something great is paying off.
"Were all very proud."
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