SSEWG, 10-11 May 2010

Report on Missions in Operations Gerhard Schwehm; Head, Solar System Science Operations Division

General

All missions continued nominally with only very minor problems experienced and a very high level of science data return. The highlights in the reporting period were the very close fly bys of Mars Express at Phobos and the successful aerodrag experiments performed with the Venus Express spacraft. Activities are well underway to prepare for the Mission Extension Operations Reviews, MEORs, which will be held on 30 June for Cluster, Mars Express, Venus Express and PROBA 2. SOHO and Hinode, which are not operated by the Agency, will be discussed in a dedicated meeting earlier in June. The approach is essentially the same as for the previous cycle in 2008: all missions whose currently approved operations end on or before 31 December 2014 are being considered for possible inclusion in this cycle and will be reviewed. The activities of the Mission Manager and Project Scientists in close collaboration with the Science Working Teams of the missions under considerations have been focussing on the technical and operational aspects that will be the prime topics of the MEORs. Subsequently the extension cases –focussing on the science that could be achieved in any further extension– will have to be prepared. These will be submitted to the advisory structure for evaluation during the autumn.

Summary Mission Reports

For SOHO, the Solar and Heliospheric Observatory, the spacecraft status continues to be nominal, with the High Gain Antenna (HGA) Z-axis in a fixed position. A nominal station keeping and momentum management manoeuvre followed by a 180 degree roll were performed on 3 February 2010. 0.0134 kg of fuel was used. The remaining hydrazine is 115.5 kg. The solar array degradation after 172 months of flight is 20.51%, which corresponds to 1.43% per year. SOHO was presented to NASA’s Senior Review on 21 April. The result of the review will be published in the summer.

JSOC and ESOC operated the four Cluster spacecraft and instruments as planned in the master science plan. The solar arrays on all 4 spacecraft, after showing decreased performance in the second half of last year seem to have recovered and even improved slightly (by ~ 3W) in performance. This means that the switching of the High Power Amplifier on S/C 1 to low power mode can be delayed to later this year and we may not need to switch for S/C 2 in 2010. This switching is required when the available power onboard drops below 190 W; to enable instruments and platform to continue operations, data must be sent back at a lower bit rate. I.e. that we will be able to maintain an extremely high science return from the mission. Since the perigee has been decreasing significantly (25000 km altitude in 2001 and 10000 km now) the spacecraft are transmitting too much power to ground (above the limits set by International Telecommunication Union regulation) when close to perigee. It was therefore agreed that below 6000 km the Cluster transponder will be off. This is equivalent to around 50 minutes per orbit, however, these loss times have been slowly reducing. The ion instrument on Cluster 3 that was turned off by instrument monitoring in November last year was declared as no longer operational by the CIS Principal Investigator. To offset this loss, as is done on Cluster 2 with the ‘spare’ telemetry from CIS, the C3 CIS telemetry has been reallocated to the PEACE instrument. Key plasma parameters (density, plasma flow) are still measured by other instruments on this spacecraft. The Cluster Active Archive (CAA) has now close to 1000 registered users. The CAA has adopted a new GUI, General User Interface, that has several new features that will help the users to find the right datasets more easily and faster than before, such as the dataset availability is now dynamically checked for the selected interval, and only the datasets that are available for the given interval may be selected. Furthermore, instead of dataset names, the user will now find dataset titles that are more descriptive for the datasets and the most popular datasets are added to a short- list that can be viewed from the drop down menu. Details can be found at http://caa.estec.esa.int/caa/news.xml#News32.

It is expected that our Chinese colleagues will eventually announce the end of the operational mission for Double Star TC2 as contact hasn't be regained. The archiving phase of the Double Star science data is underway and already some improvements in the data quality by re-analysing and re-calibrating the data sets could be achieved.

Mars Express and its payload performed nominally during the reporting period The close Phobos flybys of Mars Express were the highlight during the reporting meeting. Over a series of close flybys that started early March the payload could gather a large volume of unique data. Especially the closest approach of around 67 km for a radio science pass provided a clean and uninterrupted science measurement of the Phobos gravity field. The evaluation of the data will require some time and we hope that the results will become available in summer. While excellent science data were collected during the Phobos fly-by campaign, a number of observations unfortunately failed due to small timing errors in the payload operations sequences provided by the instrument teams. With two maneuvers, performed on the 21st and 22nd of March, Mars Express was successfully put into its final orbit, a so-called 88:25 resonance.

Rosetta has been performing nominally and the activities have been concentrating on the preparation of the last active payload check-out that started on 22 April and is currently in full swing with no major incidents experienced so far. The preparation of the Lutetia flyby on 10 July has been completed and will be reviewed on 21 May, when a Lutetia flyby Readiness Review has been scheduled at ESOC. A new attempt to re-lubricate reaction wheel B was performed early February. The procedure was run as planned but the wheel behaviour does not seem to have improved. The wheel was used in the control loop and its behaviour was carefully monitored. Following the careful analysis of the problem involving experts from industry we have decided to spare wheel B and go back to the nominal three wheel mode for Rosetta. As the four wheels mode was especially introduced for the demanding asteroid flybys this measure will be introduced after the Lutetia flyby. The spacecraft dynamic behaviour during the flyby of asteroid Lutetia was tested in flight in mid March and confirmed the validity of the selected strategy. These tests were already used for payload check-out activities, including upgrades of the onboard S/W for a number of the instruments. Completing a long series of tests the time-of- flight sensor, RTOF, of the ROSINA instrument is now working nominally and the instrument was declared fully operational by the ROSINA PI. The problems that have stopped the operations of the Narrow Angle Camera of OSIRIS during the fly by at Steins have been studied in detail with experts from D/TEC and were eventually resolved. Preventive measures have been introduced by improving the onboard S/W and the operational procedures. During all tests performed in the past weeks and during the Active Payload Checkout, the shutter, which was causing the problem, has worked without any problem.

Venus Express operations continue nominally. A series of aerodrag measurements was successfully performed in April. These measurements are intended to measure the aerodrag from the Venus atmosphere, by putting the solar arrays in a “pseudo windmill” configuration. As the Venus Express pericenter altitude naturally decreases over time and has to be boosted at times to maintain the orbit, such measurement campaigns will be planned before each future pericenter altitude raising maneuver. A pericenter raising manoeuvre was successfully executed on 17 April 2010, raising the pericenter altitude by 97 km.

Hinode spacecraft operations have been nominal with data downlink through S-band. All three instruments are nominal and are collecting high-quality science data. Overall data capture rate by the KSAT stations from January through March 2010 was 98.8% (1356 successful passes out of a total of 1372 accepted passes). All Hinode data (and usage statistics) are available to the community through the Hinode Science Data Centre Europe at the University of Oslo usually less than 24 hours after they have been taken (http://sdc.uio.no/sdc/)

Chandrayaan-1: The European PI teams have continued the preparations of the datasets to be provided to the ISRO science data archive. In particular the work on the C1XS calibration pipeline that was supported by ESAC is close to completion. In addition support was provided to the SARA teams in India and at IRF, Kiruna, on the validation of their data products. As soon as the final SPICE Kernels will have been delivered by ISRO, all data products will be reprocessed by the C1XS/XSM, SIR-2 and SARA teams to complete the Chandrayaan 1 activities supported by the science programme.

PROBA 2 has entered the nominal operations phase and both the platform and the payload are working nominally. The Commissioning Phase was successfully completed in February and the Commissioning Review held at ESTEC on 25 February. The Board expressed its appreciation for the excellent work by both industry and the Agency teams that let to a successful mission. Two actions were specifically stated, the re-analysis of the thermal behaviour of the platform that shows deviations from the test on ground and the analysis of the downlink interferences that showed up early in the mission. The cause of the transmission problem is understood and has been resolved: The spacecraft transmits through two S-Band antennae at the same time to ensure ground coverage at all passes. On the reception antenna, the two signals interfere depending on the geometry and deteriorate. A prediction tool for the ground stations was provided by industry to optimise the downlink pass planning with the downlink geometry, which solved the problem. With all commissioning activities successfully completed the ground segment responsibility for the mission was handed over from industry to ESA. The two instruments for which ESA supports the ground segment, SWAP and LYRA, worked nominally, except for some detector degradation observed for LYRA. The SWAP operated imager operated nominally during the reporting period with a 2 minute cadence. The LYRA radiometer observed at 1Hz cadence during a special campaign with the double segmented Langmuir probe and is now switched back to 100Hz. Two of the detectors on the nominal LYRA unit show degradation. The fairly strong degradation of the Lyman-Alpha channel stopped. The Herzberg channel degradation still proceeds. The Aluminum channel degraded at the beginning of the mission but has stabilized. The PI and instrument manufacturer are convinced that the degradation is caused by the interference filters and not by the detectors itself. The SWAP and LYRA data are since early much directly accessible by the wide community.

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