Chandra has managed to stay a step or three ahead of our expectations, starting from the first engineering test (the day after the covers were opened) when we found an unexpected X-ray jet in the quasar PKS 0637-752 selected as a point source to check the system focus, moving to the First Light image of Cas A a week later which revealed the long-sought, but previously unseen (likely) neutron star remnant from the supernova explosion, and continuing onwards since those heady first days. The Telescope System built by Hughes Danbury Optical Systems, Eastman Kodak, Optical Coating Laboratories Inc. and their teammates is superb, actually exceeding some of its specifications. The ACIS image of SN1987A shown at the January 2000 AAS meeting illustrates Chandra's ability to see structure on scales even smaller than 1 . The images are incredibly rich, and the grating spectra clearly demonstrate why high resolution spectroscopy is so important for advancing our understanding of the physics of the X-ray sources.
As outlined in Martin Weisskopf's Project Science Report and Roger Brissenden's CXC Manager's Report, there have been challenges along the way - particularly with the increased charge transfer inefficiency (cti) and its impact on the spectral resolution of the Front Illuminated ACIS CCDs. The Chandra team met the immediate challenge of ascertaining the cause of the cti problem and preventing further damage. Then many, many person-years of additional effort have been invested in understanding the details of the problem, testing possible ways of ameliorating the effects (and implementing a few which have significantly improved the performance), calibrating the actual on-orbit properties of the chips, monitoring them and adjusting observing strategies to minimize further damage, and developing additional software needed to analyze the calibration and science data. There are also a few HRC and Aspect effects which have been noted over the first several months which are being handled through software enhancements either already available or on the way.
At times, I have compared our experiences over the past 8 months with becoming parents for the first time or learning to drive. When we started powering on the various Chandra subsytems and instruments, many of us practically lived in the Operations Control Center (but kept out of the way of the Controllers and the Flight Team who had ``real" work to do). When we first started pointing at celestial targets, we were amazed at how superbly the TRW Pointing Control and Aspect Determination system and the Ball Aspect Camera performed. I would check the spacecraft status by phone or by computer from home before turning in for the night (except when the Red Sox were on the West Coast - then things were a bit more scrambled). I would check again at 6 or 7AM upon waking, and I would just smile broadly or give a solo ``high-five" when the Shift Reports indicated that the satellite had knocked off the next target or two and was proceeding AS PLANNED.
We also have learned what is required to schedule the observations - in the beginning we often had the uplink loads for the satellite ready to go just minutes (or an hour or two) before they were needed. Now we are able to review and approve a week's worth of observations several days before the uplink (except of course when Targets of Opportunity or other contingencies come up - the former regularly, the latter infrequently). We modified our plans to shut down during the Radiation Zone passages (around perigee) to include a ``pad" of about 10 ks on each side to allow for the imprecise knowledge of the boundaries which depend on solar activity along with the need to protect the ACIS from further exposure to low energy protons. In a sense, our team had a Driver's License (achieved through lots of training and help from MSFC, TRW, CSC and Lockheed-Martin along with the rest of the OCC folks before launch). Equipped with that ``slip of paper", we have been learning how to operate Chandra. Through hard work, skill, and the requisite bit of good luck, we have had only a minor bumper scrape or two, and Chandra is in excellent shape and in good hands.
NASA has released the NRA for Cycle 2 proposals which are due June 1, 2000. I suspect that the Peer Review panels will be seriously tested to select the best from what I anticipate will be many outstanding proposals. I truly look forward to implementing the winning proposals and seeing the science results from Chandra.
- Harvey Tananbaum, CXC Director