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An Interview with
Dr. Harvey Tananbaum, Director Chandra X-ray Center

August 29, 1995
Harvey Tananbaum

The Advanced X-ray Astrophysics Facility (AXAF) is scheduled for launch aboard the Space Shuttle in August, 1998. A crucial component of the AXAF X-ray observatory is the four pairs of nested cylindrical mirrors. They must be shaped, ground and polished to tolerances of a few parts in ten million making them the smoothest mirrors ever built.

Q: Could you give us an update of the progress this year on the mirrors for the AXAF X-ray telescope?

We have had a very positive year. We finished working on all the glass (for the mirrors). The grinding, the shaping, the polishing, the smoothing--all of the work at Hughes Danbury (Hughes Danbury Optical Systems) was completed before the first of the year, a few months ahead of schedule. We exceeded the contract requirements and goals by a significant factor.

Q: Does this mean that the scientific capability of the telescope will be better than expected?

A lot, lot better. The images will be very sharp across the entire energy range of X-rays to be observed by AXAF and the data will be easier to analyze.

Q: To what do you attribute this accomplishment?

We are reaping the rewards of the efforts funded by NASA over the last two decades for work on X-ray optics. Many of the scientists involved in that work, such as telescope scientist Leon Van Speybroeck, have been intimately involved at every step of the way on this project. And the performance of the scientists, engineers and managers at Hughes Danbury was outstanding. The improvement in know-how to make the mirrors from one set of mirrors to the next was fantastic. The first mirror took 6 or 7 polishing runs to finish. The last ones took 2 or 3. It is a shame that we don't have a follow-up mission so we can keep the team together.

Q: What is the next step?

As the mirrors have been completed, they have been shipped to Optical Coatings Laboratory, Inc. in California to be coated with iridium to improve their efficiency for collecting and focussing X-rays. This is also a very challenging and critical procedure. The coating must preserve the smoothness of the mirrors, and they must remain absolutely clean afterwards.

Q: How is the coating going?

The third mirror (out of eight overall) is scheduled for coating the first week in September and from all indications, the work is going very well, meeting or slightly exceeding all of the specifications.

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