ROSINA Steins Flyby Report for the period 2.-6. Sep. 2008 Table of Content 1. COPS 2. DFMS 3. Anomaly reports 4. Open tasks / CPPCR 5. Conclusions 1. COPS COPS was switched on to the highest sensitivity with both gauges. No sensor problems were encountered with COPS during the whole period. The total pressure measured by COPS was close to the detection limit of 1e-11 mbar outside of thruster activities and up till the S/C flip shortly before closest approach (see fig. 1). The peaks during the Wheel Off-Loading's are expected. The peaks during the S/C flip were not expected. They are most probably due to the sun illumination of the -x panel of the S/C which normally is not exposed to sunlight and which may have accumulated frozen gases. The peak has a very sharp rise and a slow decay. The slow decay is compatible with thermal effects. The correlation with the Sun aspect angle has not yet been performed. The ram gauge is much less sensitive than the nude gauge, therefore very little effects are seen. However, there is a small increase in the ram gauge pressure during closest approach. The COPS pressure is normally transmitted in the housekeeping, one value every minute. One hour before to one hour after CA COPS transmitted science data with a pressure value every 2 s. Part of these data can be seen in fig. 2. Because COPS has an integrator of 10s performing a running average, the data are delayed and smeared. However, there is clearly a peak at closest approach. 2. DFMS DFMS was switched on Sept. 2, 0600h in an outgassing mode. In this mode the ion source is heated to 300 DegC. On Sept. 4, 1800h DFMS performed a calibration mode and afterwards started to measure in the asteroid mode. This mode consists of repeated measurements of mass 15.5 amu/e in low resolution mode. In this mode mass 15 and mass 16 both fall onto the detector and can be measured simultaneously. On Sept. 5, 0600h DFMS was switched to stby due to an expected TCM (which didn't take place). By the end of this stby mode the LEDA detector reached a temperature of -30°C and DFMS was switched off by the DPU. All subsequent commands from the timeline targeted at DFMS failed because DFMS was off, which led to a numer of DSP error events. ESOC switched on manually the non-op heaters at 10:48. An attempt to switch on DFMS again failed at 13:07. A second attempt was successful at 15:05. After that DFMS stayed on and resumed measurements with the next command of the timeline at 15:45 h. The non-op heaters were left on. DFMS was switched to stby again on 0500 h, Sept. 6 for another TCM and resumed measurements again 1 h later. On Sept 6, 1800h it was switched off together with COPS. The sensor error due to the cold temperature of the LEDA is documented in ROS-SC-166. This error is due to several facts: - The RDP heater was not working properly due to an instability in the ROSINA SW. It was more or less randomly switched on/off. (see fig. 3) - DFMS is colder than predicted by thermal models. - Once the LEDA detector gets too cold DFMS is switched off by the DPU. This does not automatically switch on the non-op heaters. The detector is then neither heated by the power of DFMS nor by the non-op heaters which makes matter worse. In order to correct this problem several actions have to be taken: 1. Correct SW to ensure a continuous operation of the RDP heater at temperatures below +20DegC. 2. Correct SW so that DFMS is not switched off completely if the detector is too cold but be kept in stby to keep the power on. 3. Correct the thermal modelling in order to be able to predict the temperatures correctly. 4. Find a way to switch on the non-op heaters automatically if DFMS is switched off by the DPU and not by the OBCP procedure. 5. Find a way to keep the non-op heaters on automatically during operations if the temperatures are low. 6. Qualify the detector to lower temperatures (-40DegC). 3., 4. and 6. have already started. Discussions with the detector manufacturers have shown that it should not be a problem to go to lower temperatures. This will be discussed further and eventually tested on the model in Bern. 1. and 2. need a SW update during PC10. 5. has to be discussed between the experimenter and ESOC. Nevertheless DFMS produced excellent scientific data (see fig. 4 & 5). The scientific analysis has been started. The oxygen peak measured by DFMS was much more pronounced during the closest approach than during normal background measurements. However, the S/C flip also produced a high oxygen peak and it remains to be seen what amount of oxygen can be attributed to the S/C water and what to the Steins exosphere. This needs modelling with the Rosetta S/C model. An interesting feature has been seen during the S/C flip: the COPS pressure rises much more rapidly than the DFMS oxygen signal. This means that the first gas sublimating from the S/C is probably not water but a molecule which does not contain oxygen. This is also compatible with the fact that COPS measured a much higher pressure peak during the flip than during CA whereas for the oxygen of DFMS both peaks have similar amplitudes. 3. Anomaly reports One anomaly report was raised: ID: ROS_SC-166 RN DFMS switch OFF during Steins flyby 4. Open tasks / CPPCR R_RN005: Background is highly dependent on the solar aspect angle. This has to be investigated. The best option would certainly be if all panels of the S/C could be exposed to sunlight periodically. R_RN006: DFMS detector temperature: more modelling needed, may also need tests at different solar aspect angles during PC10, a SW update and a procedure concerning parallel operation of the non-op heaters and operation of DFMS. 5. Conclusions COPS performed very stable and yielded good scientific data. DFMS has a temperature problem which is partly due to a SW problem. This has to be solved together with a new qualification of the detector and an investigation of how the non-op heaters can be used during operation. Apart from this problem DFMS delivered excellent data. Outgassing of the S/C is a problem and has to be taken into account for all operations near the comet.