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Q&A: Chandra Mission

Q:
What was Dr. Steven Kissel role in the operation of Chandra?

A:
Dr. Kissel explains his work in the following quote.

"My role in Chandra operation, specifically design and fabrication actually began with the Astro-D (ASCA) satellite which was the first use of X-ray CCDs in space. Participation in this US/Japan mission was intended to provide experience with X-ray CCDs in order to prove their suitability as detectors for the Chandra (then called AXAF) observatory. The great success of ASCA was encouraging and lessons learned in that program guided design and test strategies used in AXAF. An example of this was the realization that a "room temperature readout" capability would be crucial to verifying detector performance during assembly and pre-launch activity. One of my tasks was to make sure this capability was achieved.

One of the Chandra science instruments, the ACIS (Advanced CCD Imaging Spectrometer) uses and array of 10 Lincoln Laboratory fabricated CCDs. We received several hundred such devices each of which required testing and evaluation. My role was to fabricate testing facilities, X-ray calibration beam lines and cooling systems for example, and to undertake the initial testing or "screening". This evaluation determined the correct operating parameters, voltages and clocking waveforms, that would yield maximum performance from the subsequent detector assembly. During this period much practical experience about CCD operation was learned and incorporated into the higher assembly. An example of this is the little known but quite essential "jitter dac" trick which is used at the start of every science observation to tame a start up dark current instability.

The role which has had the longest lasting impact is that of the "institutional memory of CCD operation" which basically means that I get to try all the unusual operational techniques before they get applied to the actual spacecraft. This activity continues even to this date where questions about radiation damage, high temperature bakeout and CTI suppression can only be addressed by laboratory experiments on "sibling" CCDs.

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