Project Manager's Report

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Project Manager's Report

Chandra completed its sixth year of successful scientific operations on 23 July 2005, with the spacecraft and science instruments continuing to perform in an outstanding manner. The 6-year milestone was celebrated with the 6 Years of Science with Chandra symposium held in Cambridge in November. The quality and depth of the results presented at the symposium spoke to the impact that Chandra is having on our field. Of particular note was the number of papers that involved multiwavelength data from Chandra, Spitzer and Hubble - NASA’s three Great Observatories. As we head into the 7th year of observations, it is not surprising that over-subscription rates remain very high for the Chandra user research programs, including the General Observer, archive research, and Directors Discretionary Time programs, and the Chandra Fellows program, which is now in its 8th cycle. As the mission progresses, it is clear just how important a role Chandra plays as NASA’s prime X-ray astronomy asset.

The staff of the CXC worked hard during the last year to maintain the high standards met throughout the mission so far. Of particular note were the increasing temperatures measured in all spacecraft subsystems as the passive thermal insulation degrades due to continued exposure to radiation. The rising temperature has resulted in increasingly more complex mission planning constraints and has started to have a measurable impact on the average observing efficiency for the mission - down to 61% compared to 65% in 2004. As a result of the new thermal constraints, an increasing number of observations are now being split into multiple segments and scheduled with other observations or segments that help ensure a favorable overall thermal profile. The Flight Operations Team and the Science Operations Team are monitoring the thermal situation carefully and working to minimize the impact on the science return for the mission.

The observing program transitioned from Cycle 6 to Cycle 7 observations in December, although we expect a number of remaining Cycle 6 observations to be interleaved with Cycle 7 observations through the first quarter of the year. There were 7 schedule interruptions in the last year due to high levels of solar activity, resulting in an overall loss of about 3% of the scheduled observing time. The mission planning team responded efficiently to all the solar re-plans and minimized the science lost. Planners also responded quickly to the 13 Target Of Opportunity (TOO) observations that required schedule interruptions. Its exciting to see so many TOOs being requested following SWIFT’s launch in November 2004.
The spacecraft continued to operate well overall with no safe modes or major anomalies. Operational highlights included completing the earth eclipse seasons of summer 2005 and winter 2006 with nominal power and thermal performance, and passing through a lunar eclipse without incident on November 1.

The Flight Operations Team was also busy developing a number of flight software patches designed to increase the safety and science efficiency of Chandra. A patch was created to provide the capability to transition to Normal Sun Mode following execution of the Science Instrument safing actions (SCS 107) in response to a high radiation event. The capability ensures a favorable thermal attitude in cases when stopping the command load would violate a propulsion line thermal constraint. A second patch increased the value of the Electron Proton Helium INstrument (EPHIN) E1300 channel threshold by a factor of two. The new value will reduce the number of false triggers of the science instrument safing sequence (SCS 107) during periods of puffed-up radiation belts, and when EPHIN is at high temperature. The change will also help with mission planning by relaxing a thermal constraint. A third patch modified SCS 107 to move the Science Instrument Module (SIM) only once when SCS 107 is executed, rather than twice. The previous implementation consisted of two moves, the first to an intermediate position to allow the HRC camera door to be closed, and a second to its final HRC-S position. Because the HRC door is no longer closed during SCS 107 runs, the extra movement could be eliminated, reducing the likelihood of excessive SIM motor heating.

The science instruments also continued to operate well overall, with only a small number of minor anomalies that had little impact on the science return. ACIS experienced a recurrence of a latch-up of the threshold crossing plane circuit that affected one observation in July. The t-plane was cleared at the start of the following observation by commands that reset the ACIS Front End Processors. The reset commands are routinely included in the loads in anticipation of an occasional occurrence of this anomaly, the last having been in November 2001. ACIS also experienced an unexpected power-down of its Digital Electronics Assembly side-A. This event was thought to be due to a single event upset.
HRC experienced nominal operations with the exception of a brief episode of anomalous secondary telemetry in December. The anomalous data were seen in the engineering portion of the telemetry stream and had no impact on operations. No corruption of the X-ray event data was observed.

A number of important changes to the Chandra Operations Control Center ground system took place last year, including the transition in July to a direct network link to JPL (previously all mission data and communications had been routed through the GSFC closed I/ONet), and the migration to a new version of the ground system hosted on the Linux operating system. The ground team worked hard to perform the required testing to ensure a seamless transition from the old IRIX operating system and Silicon Graphics hardware. The team also prepared carefully for the 2005 leap-second and all systems handled the extra second on December 31 without difficulty.

The Science Data Processing team continued their excellent record for throughput of data, with the average time from observation to delivery of data reduced to less than 2 days. The Chandra archive holdings grew by 0.3 TB to 2.6 TB (compressed) during the year and now consists of 9.6 million files. A new mirror site for the archive was established at IUCAA in Pune, India.

The Data System team released software updates in support of the Cycle 7 proposal submission deadline and Peer Review, and for the Cycle 8 Call for Proposals in December. Work has also continued on preparations for the third full re-processing of the Chandra archive.

The Education and Public Outreach team was very active with 24 press releases, a NASA Media Telecon and 10 additional image releases. The interest in the Chandra web site and educational products remained at near record levels last year.
We look forward to continued smooth operations and exciting science results.

Roger Brissenden