The scheduled viewing efficiency for the mission averaged 64% during the last year, allowing the observing program to transition from Cycle 2 to Cycle 3 in November. The average efficiency was approximately 5% lower than expected due to ten interruptions of the observing schedule caused by high levels of solar activity. The science and mission operations teams are to be commended for the many rapid re-plans and highly efficient returns to the science time-line after these events. We eagerly anticipate the passing of solar maximum.
Observers were active in both the Target Of Opportunity (TOO) and Director's Discretionary Time (DDT) programs. Nine TOO targets with 40 observations and 17 DDT targets with 33 observations were accepted. Of these targets, 7 were fast response requests and required a mission schedule interruption and re-plan.
The Education and Public Outreach group have focussed on communicating the wealth of new science results to the press and public. Numerous Chandra press releases were made during the last year, together with many additional image releases made through the CXC website. In addition, the group developed new education material for web access, released an updated CD-Rom, and held three workshops for educators.
The spacecraft and Science Instruments have continued to operate smoothly with no major anomalies. Two significant flight software patches were uplinked, one to allow the return to autonomous control of the gratings and the other to widen the momentum unloading threshold. The grating patch provided a workaround to the HETG A- and B-side limit switch anomaly that occurred early in the mission, and has been operating as expected since June 2001. The momentum unloading threshold was increased to reduce the number of firings of the momentum unloading propulsion system and bring the firing rate below the pre-launch qualification level. The approach has been very successful, with the rate now below the required level and the trend in the right sense.
Three safing actions occurred during the last year: one normal sun-mode transition and two bright star holds. In all cases the causes were understood and steps were taken to avoid future similar transitions. The recovery back to the science time-line was completed efficiently in all cases. Also of operational note was the nominal performance of the Observatory though two eclipse seasons and through the 2001 Leonids meteor storm (see article this issue).
The Science Processing team have continued to improve the average throughput of data from observation to release to the Observer from two weeks to one week. Also over the last year we have seen usage of the Chandra Archive increase. The archive holdings now total over 1 TB with 4.4 million files, and retrievals now total almost 2 TB.
Releases of CIAO were made in April (R2.1) and October (R2.2), and the web-interface archive browser (ChaSeR) was released in December together with the tools required to propose for cycle 4.
We look forward to continued smooth operations and exciting science results in 2002-2003.
-Roger Brissenden