ROSINA operation during SC thermal characterisation Report for the period 16.-18. Feb. 2009 Table of Content 1. COPS 2. DFMS 3. Open tasks / CPPCR 4. Conclusions 1. COPS The nude gauge of COPS was switched on to the highest sensitivity. No sensor problems were encountered with COPS during the whole period. The pressure measured by COPS was a strong function of the SAA. As soon as the SAA z-angle reaches 178Deg the pressure rises by two orders of magnitude. It drops then after some time to a level which is still 10 times larger than when the SAA z-angle is smaller than 178Deg.This points to outgassing from the -x-panel of the SC. Fig. 2: COPS nude gauge pressure vs z-angle. Slew1 is from 70 to 175 degrees, slew 2 from 175 to 192 and sleback from 192 to 70. 2. DFMS DFMS was switched on on Feb 16, 1240h. It went through different modes over the next two days: asteroid mode, low and high resolution mass spectra over the full mass range. Except for one sensor error due to a housekeeping hickup it performed flawlessly. The temperature was always above -20DegC for the detector due to the constant heating by the detector heater as well as the non-op SC heater. DFMS saw the same pressure increase as did COPS although it does not react as fast as COPS to sudden pressure peaks (see fig. 3). Mass spectra revealed that it is due to water only. No traces of hydrazin were seen once the z-angle went beyond 180Deg although they were clearly present as long as the angle was less than 180Deg (see fig. 4). Fig. 3: DFMS measurements during SC slew from 175Deg to 192Deg at 1400h UTC There is a clear increase of the Oxygen during this time. Measurements before and after the slew show that the oxygen comes mainly from water, not from CO or CO2. Fig. 4: DFMS mass spectrum: CH3NH is a hydrazin fragment. NO may be a product of thruster firing. 3. Open tasks / CPPCR R_RN005: Background is highly dependent on the solar aspect angle. One source of the high outgassing could be the Philae lander. This has to be investigated. Therefore, the next time the lander is operated, we would like to measure the ambient pressure with COPS. When the lander heats up, it may release gas. We would also like to switch at least COPS into monitoring mode whenever the SC does a flip or a slew rehearsal. For the Lutetia flyby the flip should occur as long as possible before the CA. If this time is restricted due to the operation of VIRTIS, it has to be explored if the -x panel could be exposed for several days to the sun prior to the start of the Lutetia operations. The best option would certainly be if all panels of the S/C could be exposed to sunlight periodically. R_RN006: DFMS detector temperature: During this period the RDP heater worked continuously with no SW hickup. In addition the non-op heater was switched on. With the new thermal modelling done by our partners at Lockheed the temperature of the detector at switch-on and during operation was correctly predicted. Without the non-op heaters the temperature would also have stayed within limits. The model shows that there should be no problem for the detector even at large distances from the sun as long as the two heaters can be operated. Nevertheless, tests with a spare detector in the lab at -50DegC will be performed in the very near future. The temperature limit will be updated with the next SW patch. 4. Conclusions Outgassing of the S/C is a problem and has to be taken into account for all operations at Lutetia and near the comet.