DATA_SET_DESCRIPTION |
Data set Overview : On March, 2, 2004, the Rosetta spacecraft was launched towards comet 67P/Churyumov Gerasimenko. Since then the ROSNA sensor has been tested and optimized for flight during several commissioning slots. All data so far from DFMS and RTOF concern either the in flight calibration gas or back-ground outgassing from Rosetta. Because of several uploads of new voltage settings the data cannot be compared between the different commissioning slots, neither in intensity nor in mass scale! The data can be used only for engineering purposes. The only data which can be used to evaluate the background pressure of Rosetta are the COPS data. Scientific data from DFMS and RTOF will only be available when Rosetta reaches the first asteroid. The explanation of the generated data of the ROSINA sensors can be found in the OPERATION_LOGBOOK.ASC Parameters : DFMS and RTOF data contain neutral gas data as well as ion data. The data are raw, uncalibrated data. COPS contain pressure data of the background pressure and of some thruster firings from the nude gauge. Calibration : COPS data are calibrated. However, the calibration factor has been determined for Nitrogen gas, and may not be appropriate for the outgas-sing of Rosetta. Because the main outgassing component is unknown the correct factor to be used is also unknown. DFMS and RTOF data are uncalibrated and will remain uncalibrated because they have no scientific value. Indeed, the only data which are calibrated and can be calibrated are the COPS data. However, by comparing relative intensities some scientific conclusions can be drawn even from the uncalibrated data. Note on the DFMS data: The user of our level 2 data has to make the conversion from pixel to mass and from ADC counts to ion current himself. In this way he will be aware that the precision is limited and depends on many parameters and he will use the data accordingly. The procedure required to calibrate the DFMS is described in our User manual, Annex D1 (DOCUMENT directory). ROSINA team are currently developing the necessary algorithms, putting emphasis on the quality control for the algorithm. They are defining quality flags for the data which will then tell the user how well the mass scale and the intensity scale have been defined. They are also working to produce level 3 data with calibrated mass scale and intensity. Once this SW is in place they will produce calibrated data for the Lutetia flyby with a suitable quality flag. It does not make sense and it is scientifically not correct if ROSINA team archive the Lutetia flyby data with 'calibrated' units without being sure that they are correct and without being able to give a uncertainty value. Processing : No processing was applied to the data. Coordinate Systems : No coordinate is specified for the data. Software : No software is provided. Media/Format : The standard distribution format for the data is an electronic volume. Coordinate System : The geometry items SC_SUN_POSITION_VECTOR, SC_TARGET_POSITION_VECTOR and SC_TARGET_VELOCITY_VECTOR provided in the label of the data product are relative to the Earth Mean Equator and Equinox reference frame of J2000. SUB_SPACECRAFT_LATITUDE, SUB_SPACECRAFT_LONGITUDE are given in the Cheops reference frame. The SPACECRAFT_ALTITUDE gives the distance to the spacecraft from the target center of mass. These parameters are computed at time t:START_TIME. Distances are given in km, angles in degrees.
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