PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2015-07-07 First PRL delivery" RECORD_TYPE = "STREAM" OBJECT = DATA_SET DATA_SET_ID = "RO-C-RPCLAP-2-PRL-EDITED-V1.0" OBJECT = DATA_SET_MISSION MISSION_NAME = "INTERNATIONAL ROSETTA MISSION" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = ERIKSSONETAL2007 END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "ROSETTA-ORBITER 67P RPCLAP 2 PRL EDITED V1.0" DETAILED_CATALOG_FLAG = "N" DATA_OBJECT_TYPE = TABLE START_TIME = 2014-01-21T00:00:00.000 STOP_TIME = 2014-11-20T00:00:00.000 DATA_SET_RELEASE_DATE = 2015-07-07 PRODUCER_FULL_NAME = "ERIK P G JOHANSSON" ABSTRACT_DESC = "This dataset contains EDITED raw data from the Rosetta RPC-LAP instrument, acquired during the prelanding phase (PRL) at comet 67P/Churyomov-Gerasimenko 1." DATA_SET_DESC = " Data Set Overview ================= Contents: A. Operations overview B. Dataset status C. Scientific use A. Operations overview ---------------------- LAP operations are described in the operations report, IRFU-ROS-OPR-PRL in the DOCUMENT/FLIGHT_REPORTS directory of this archive. B. Dataset status ----------------- This dataset contains scientifically useful data from the Rosetta RPC-LAP instrument. The data contained are primary instrument data, in instrument units (TM) and NOT calibrated to physical units (volts and amperes) and with instrumental offsets NOT removed. See the caveats in Section C below for data use. A strong caveat with the present dataset is the timing. The instrument timing as such should be good, but a few days prior to dataset delivery it was found that our conversion between spacecraft clock time SCT and UT differs by as much as 2.3 seconds. This means that when the present dataset is used, any user requiring absolute timing accuracy better than a few seconds, or wishing to compare to other Rosetta instruments at such time resolution, must use the SCT rather than the given UT values. This issue will be removed in a future delivery, and the present archive is to be seen as an interim version. C. Scientific use ----------------- The data can be used for scientific analysis, but this requires some familiarity with this type of data. At a later stage, a DERIVED data archive will be delivered, providing directly useful scientific quantities (e.g. plasma density, wave spectra, electron temperature). Caveats: a. For probe-to-spacecraft potential (Vps) time series: this is a commonly used proxy for the plasma density in tenuous plasmas. However, because the perturbations from the solar panels, the wake formed behind the s/c and solar panels in the solar wind, and the photoelectron cloud around the spacecraft are all sensitive to the probe location, Vps can be used as a density proxy only during intervals of constant pointing. See the paper by Edberg et al ('Simultaneous measurements of the Martian plasma environment by Rosetta and Mars Express', Planet. Space Sci., 57, 1085-1096, 2008. doi:10.1016/j.pss.2008.10.016) for an example of how Vps may be used as a plasma density proxy. Perturbations from wake and photoemission have been studied by Sjogren (report available at http://www.space.irfu.se/exjobb/2009_alex_sjogren/). b. For the same reasons, the probe bias sweeps are also sensitive to the spacecraft pointing. However, for all sweeps obtained prior to the comet phase, except some acquired in Earth's plasmasphere, the ion contribution to the data is so low that the photoemission saturation current can be obtained at all angles for which the probe is sunlit. Note however that the probe may be partially shadowed by its supporting rod (the stub), and that surface inhomogeneities may cause the photoemission to vary also with the pointing. c. For all sweeps obtained before coming close to the nucleus in September, and for some parts also later on, the dominating contributions to the probe current are probe photoemission (at negative bias voltage) and collection of photoelectrons emitted by the spacecraft and solar panels (at positive bias voltage). Hence, probe sweep data can be interpreted in terms of local plasma parameters only in the Earth's plasmasphere. The main reasons for occasionally running such sweeps in other environments, e.g. the solar wind and the Earth's magnetosphere, are to gather data for investigation of spacecraft-plasma-probe interactions and to monitor probe photoemission. d. It is also necessary to only compare data acquired at the same bias. This is why data are presented as (current, voltage) pairs. e. The bias values in the files, current and voltage alike, is not measured but constructed from the instrument command log and known modes. Bias settings changes therefore show up in the data files when a bias command is issued, while it can be seen in the data that it really takes effect 2-3 seconds later. This caveat does not apply to probe bias sweeps. f. After hibernation, LAP probe 2 (P2) showed strong signs of contamination. Clear signs of this include that current to P2 is always lower than to P1 at similar bias voltage, low photoemission on P2 causing a lot of saturated data in the initial operations in May and June when the applied bias current was too high for the limited photoemission to support, a very long time constant on P2 voltage when a new bias current is set, and sweeps in both direction (available from macro 204) showing clear hysteresis effects. Data from P2, be it fixed bias or sweeps, should therefore be treated with greatest care ane be avoided by any but the most experienced users. The PI discourages any use of P2 current data except for diagnostics. g. The macros used for Langmuir mode operations in most of the period covered by this archive were mainly 505, 506 and 604. The first two of these are normal mode macros with a limited bias sweep voltage range (+-18 and +-12 V, respectively) in order to conserve telemetry, while the macro 604 sweeps end at +20 V. This was suitable for getting the current-voltage characteristic in the solar wind, but when the cometary plasma turned out to be both dense and hot in September, and the s/c potential thus mostly negative, often below -10 V, it was often insufficient for well catching the full probe characteristic, including the electron attraction part. The burst mode macros 204 and 807 cover a wider bias range, as does the normal mode macro 515 uploaded to the instrument on October 30 which somewhat alleviates the problem by covering the bias range from -5 V to +31 V, but routine coverage of the full +-31 V bias range of the instrument did not start until better macros were uploaded after the end of the period covered in this archive. The value of +10 V for the bias value in fixed bias voltage operations is not ideal for the same reason, and the variations of s/c potential in response to density fluctuations in the plasma can sometimes be so strong that there even is anticorrelation of probe current with plasma density. h. There is obvious interference from the MIP instrument when using its LDL mode (macros 801 and 807 in this dataset). This affects mainly the data sampled at kHz frequencies at fixed bias and in sweeps. For the fix bias snapshots at 18.75 kHz sampling frequency, this mostly affects the first samples in a record, but can in longer records sometimes be seen also further into the record. In sweeps in macro 807, MIP interference can be detected as spikes where one or twp samples deviate from their neighbours. Some MIP interference may occur also outside of LDL operations, as may of course interference from other sources. i. Until the end of operations at the comet, the first priority of the LAP team will have to be the science operations of the instrument, to make sure there will be useful data to archive. The archived data set is complete, and there is no possibility to scan every part of it for every possible problem, so there may be numerous data quality issues in addition to this list. While the data clearly have a great science potential, analysis has to be done with great care. Anybody using the present dataset is strongly encouraged to contact a LAP CoI for cooperation. Parameters ========== Primary data: 1. Probe-to-spacecraft potential time series, measured at controlled bias current. Available at two time resolutions: - Sampled at 57.8 Hz, further downsampled to typically 0.9 Hz when not in burst mode, quasi-continuous data with short gaps every 32 s. - Sampled at 18.75 kHz, in brief snapshots repeated with a cycle which is a multiple of 32 s (typically between 32 and 160 s) 2. Probe current measured at controlled bias voltage. Available in three varieties: - Probe bias voltage sweeps. Bias voltage stepped, probe current measured, duration a few seconds, repeated with a cycle which is a multiple of 32 s. - Sampled at 57.8 Hz, further downsampled to typically 0.9 Hz when not in burst mode, quasi-continuous data with short gaps every 32 s. - Sampled at 18.75 kHz, in brief snapshots repeated with cycle which is a multiple of 32 s (typically between 32 and 160 s). - In addition, there are a few calibration sweeps taken with the probe disconnected to evaluate instrument offsets. These are used in the preparation of the CALIBRATED data but have no scientific value on their own. Data from these are included in the EDITED data. 3. Housekeeping data. These are only included with the EDITED archive and consist mainly of instrument digital status. They have no direct scientific value on their own and no user or this archive should have any interest in them. Processing ========== Processing of the CALIBRATED data involves the following steps: 1. Time tagging. 2. Determination of instrument offsets from instrument calibration runs (operational macro 104). This is done by a stand-alone application. The resulting offsets are stored in the CALIB directory as (bias, offset) pairs in TM units. 3. Compensation of probe current measurements for instrument offsets, using the most recently determined of the offset calibration files of step 2 above. 4. For each measured value (volts or amperes), the corresponding bias value (amperes or volts, respectively) is added to the data. All data are thus presented as (current, voltage) pairs, where the bias is not measured but reconstructed from the instrument command history (see Caveat f above). 5. Generation of table files and corresponding PDS label files. Data ==== All data are presented as ASCII tables with stand-alone PDS labels. The content of the data is described in each label. There is one file for every acquisition period (32 s in duration) and data type, meaning there is a large number of files. The files names indicate the data content, as described in Section 3.1.4 of the EAICD. In brief, the convention is as follows: File name: RPCLAPYYMMDD_AAAa_bcdefghxx.EXT YYMMDD = year, month and day, all with two digits. AAA = Alphanumeric counter reseting at zero every new day. a = Type, T=20 bit ADC, S=16 bit ADC, H = Houskeeping b = Format, R=Edited Raw C=Calibrated D=Derived c = Instrument mode E = E-Field (Current bias and voltage measurments) D = Density (Voltage bias and current measurments d = Bias mode, S=Sweeping B=Constant Bias e = Sensor: 1 = Probe 1, 2 = Probe 2, or 3 = Derived from 1 and 2 f = Analog filters, 8 = 8 Khz 4 = 4 Khz g = Telemetry rate, M = Minimum N = Normal B = Burst h = For science data this character is always an S. x = For contingency, not present if not needed. Example: EXT is either LBL or TAB. Note that the alphanumeric counter is independently generated for EDITED and CALIBRATED archives, so EDITED and CALIBRATED data from the same time do not necessarily reside in files with similar (except for the b = R or C above) names. Ancillary Data ============== For any scientific analysis, needed ancillary information would be spacecraft position and attitude. This can be found in the daily geometry files provided with the data. For this archive version, no geometry files are included for technical reasons. This will be remedied in later versions of this dataset. The user is suggested to use the SPICE software with appropriate kernels. Coordinate System ================= Please see EAICD for description of coordinate systems in the geometry files. Other data are independent of coordinates. Software ======== N/A Media/Format ============ Electronic transfer " CONFIDENCE_LEVEL_NOTE = "This archive contains instrument output in telemetry units, verified by the PI team." ARCHIVE_STATUS = "PRE PEER REVIEW" CITATION_DESC = "Eriksson, A.I., Gill R., and Johansson, E.P.G., Rosetta RPC-LAP archive of edited data from the pre-landing phase, RO-C-RPCLAP-2-PRL-EDITED-V1.0, ESA Planetary Science Archive and NASA Planetary Data System, 2015." DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_SET_TERSE_DESC = "This dataset contains EDITED data from Rosetta RPC-LAP, acquired during the prelanding phase at comet 67P/Churyomov-Gerasimenko 1." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = "67P/CHURYUMOV-GERASIMENKO 1 (1969 R1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = RO INSTRUMENT_ID = RPCLAP END_OBJECT = DATA_SET_HOST END_OBJECT = DATA_SET END