Review applauds XMM-Newton's greatly increased efficiency
22 February 2001
After the recommendations of a first review last July of XMM-Newton science operations, ESA's Director of Science has congratulated all those involved for greatly improving the mission's efficiency, particularly the management of the X-ray observatory's observations.Professor Roger Bonnet was speaking at a 'Delta Review' held 13 February at the XMM-Newton Science Operations Centre at VILSPA. The mission's management presented the latest statistics on the observation programme efficiency, the instrument performance and the data distribution. Also present at the meeting were the XMM-Newton Principal Investigators, the Head of ESA's Astrophysics Department Brian Taylor, and David Southwood, the Agency's next Director of Science.
"Compared to the 35% level only six months ago, the efficiency of our science observations has dramatically increased," Science Operations Manager Jean Clavel told them. "Over ten complete revolutions in January we reached 61%. This is comparable to the Chandra mission. Our most recent figures do show a slight drop to 55%, the consequence of both our Perth and Kourou tracking stations being mobilised for the launch of an Italian satellite. But we now have routine hands-on experience and are very confident that we can reach a 70% efficiency."
This further improvement will stem from the Santiago tracking station which has just been brought online. Covering the apogee gap, it will allow greater scheduling flexibility and longer observations, getting the maximum from each 48-hour orbit.
Spacecraft operations are nominal, there have been no problems during eclipse periods and the satellite has comfortable - solar array generated - power energy margins for the remainder of the mission. The ground segment is now receiving 99% of all the available science data telemetry.
The X-ray imagers and X-ray spectrographs are continuing to perform remarkably well. Error margins (for instance with the X-ray photon count) have fallen from 30% in June last year to 10% at present. Cross-calibration - which allows observations to fully exploit the complementary aspects of all the instruments - has also improved to practically 5%, with an ultimate target of 2%.
The observatory has also already carried out a considerable number of coordinated observations with other spacecraft (Chandra, BeppoSAX, and RXTE) or with ground-based telescopes (VLA, VLBI, Cangaroo).
Astronomers have understandably been impatient to quickly receive their observation data, and the review dwelt at length on the issue of data distribution. "Because software was not completely ready we did not want to ship raw data telemetry without also providing processed data which immediately makes sense for scientists," explains Jean Clavel. "Now we have cleared this hurdle and the Science Survey Consortium is routinely processing all the data. The first 21 sets of Observation Data Files (ODF) and associated 'pipe-line' products were shipped on 15 February. Henceforth we will be producing the required CDs within one month, at the most, of an observation."
A final question to be considered was the balance between open- and guaranteed-time observations. Because of the initial lower than expected efficiency, and a number of left over calibration and performance verification observations, the period during which XMM-Newton would exclusively observe guaranteed time has had to be extended. With some slight modifications to the remainder of the guaranteed/open time subdivision, it is now possible to perform an adequate amount of guaranteed time observations, while still finishing AO-1 almost on schedule.
"I am confident that with the time distribution profile that has now been agreed for the remainder of the mission we will have the right mix of guaranteed and open-time observations," says Project Scientist Fred Jansen. "The important factor being the availability of open-time data to the AO-1 proposers."
"I can say that we are all really pleased to see such an improvement in the mission's efficiency and that we no longer have any problems today" said Roger Bonnet. But he insisted that "fully opening the tap" on data distribution was still a major concern. "We must make sure that the extraordinary effort over the past few months is prolonged by getting the data out quickly. But I am extremely satisfied and I am sure that we are going to ensure the observatory's smooth operations for the next decade."
