PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "B. TRANTHAM, 2012-10-22" RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = RO INSTRUMENT_ID = "RPCIES" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = " ROSETTA PLASMA CONSORTIUM - ION AND ELECTRON SENSOR" INSTRUMENT_TYPE = "PLASMA INSTRUMENT" INSTRUMENT_DESC = " Instrument Overview =================== The Ion and Electron Sensor (IES) is one of the 5 instrument members of Rosetta Plasma Consortium (RPC). The objective of the instrument is to measure the flux of ions and electrons as a function of energy and direction in the solar wind, and in the environment during the flybys of Earth, Mars, the two asteroids, and comet 67p/Churyumov-Gerasimenko. Scientific Objectives ===================== The scientific objectives of the instrument are to measure and understand the dynamics, structure, and evolution of the plasma properties in these environments. Of particular interest is the interaction of the solar wind with the comet, especially the formation of pickup ion structures and their relation to the local magnetic field. Calibration =========== The IES instrument was calibrated on the ground in the ion calibration facility at the Southwest Research Institute, San Antonio, TX, USA. In addition cross-calibrations are performed in flight with the RPC-LAP and RPC-ICA instruments. Operational Considerations ========================== RPC-IES should be operated continuosly as long as power and telemetry rate permit. When possible, all other RPC instruments should be operated while RPC-IES is in operation in order to allow joint analysis of the resulting data. RPC-IES high voltages should be turned off 5 min before until 5 min after thruster firings to prevent arcing. RPC-IES Instrument Description ========= The Rosetta Ion and Electron Sensor (RPC-IES) is comprised of a double toroidal top-hat electrostatic analyzer (ESA), one analyzer for electrons, the other for ions, arranged back-to-back. The common entrance aperture has a 360 degree field of view in the symmetry (denoted here by azimuth) plane. Electrostatic angular deflection optics give a scanned field of view of +/- 45 degrees normal to the sensor symmetry axis (denoted here by the elevation angle). The instrument objective is to obtain ion and electron distribution functions over the energy range from 4.32 eV/e to 17.67 keV/e, with a basic time resolution of 128 s. This geometry allows IES to analyze both electrons and positive ions with a single entrance aperture, simultaneously. The IES top hat analyzers have toroidal geometry with a smaller radius of curvature in the deflection plane than in the orthogonal plane. This toroidal feature results in a flat deflection plate geometry at the poles of the analyzers and has the advantage that the focal point is located outside the analyzers rather than within them, as is the case with spherical top hat analyzers. The IES field of view (FOV) thus encompasses a total solid angle of 2.8 Pi steradians. Ions and electrons approaching the IES first encounter a toroidal-shaped grounded grid encircling the instrument. Once inside the grid the electric field produced by bipolar electrodes deflects ions and electrons with a range of energies and incident directions into a field-free entrance aperture containing serrated walls to minimize scattering of ultraviolet light and stray charged particles into the instrument. The particles then enter the top hat region and the electric field produced by the flat electrostatic analyzer segments of the ion and electron analyzers. Particles with an energy accepted by the ESA and within a narrow 4% energy pass band will pass through the analyzers and be focused onto either the electron or ion microchannel plates (MCPs), which produce charge pulses on 16 discrete anodes for each, which define the azimuth acceptance angles. For electrons the anodes are of equal width so the azimuth resolution is 22.5 degrees. (It was discovered after launch that electron channel 11 was noisy so it was decided not to download the data from that channel. Hence only fill data appear for that channel.) For ions the 16 anodes are divided unequally in size, with 9 of them (each 5 degrees wide) oriented in the direction expected to view the solar wind most of the time (anodes 3 to 11). The remaining 7 anodes are each 45 degrees wide. For both electrons and ions the nominal resolution in the elevation direction is 5 degrees. This resolution would provide 18 measurement bins over the 90 degrees full elevation FOV. However, in order to simplify the instrument electronics, the FOV has been divided into 16 (=24) bins. This results in a small gap in coverage between bins. The selected energy will correspond to a particular 5 degree elevation entrance angle, depending on the ratio of voltages on the angle deflectors and the ESAs. Note that the use of the terms 'azimuth' and 'elevation' angle for IES differs from the conventional terminology of 'polar' and 'azimuth'. Viewing Maps (from the RPC-IES IK data) ====================================== IES/Electron Sector Layout The IES/Electron Sector's 360.0 x 90.0 degrees aperture is split into 256 sectors -- 16 in-plane (azimuthal) by 16 cross-plane (polar). In the in-plane direction the sectors are numbered from 0 to 15, in the cross-plane direction the sectors are also numbered 0 to 15. All 16 in-plane sectors are 22.5 degrees wide with their center view directions 22.5 degrees apart. In the cross-plane direction all sectors have the same size of 5 degrees with their center view directions 6 degrees apart. In-plane the 'view direction' of each sector is looking inwards, from the sector position through the center of the aperture. This diagram illustrates in-plane (azimuthal) IES/Electron sector layout: ^ +Yies | A# indicate the azimuthal V12 | V11 sector # position in V13 ....|.... V10 the sensor assembly. .' A4 | A3 `. V14.' A5 | A2`. V9 V# indicate the # sector . A6 | A1. view direction. V15. | . V8 .A7 | A0. For example, for . o--------------> +Xies Sector 2 the view .A8 / +Zies A15. direction is the vector V0 . / . V7 emanating from the .A9 / A14. aperture center through V1 .A10 / A13. V6 the point designated `. / A11 A12 .' by V2. V2 `......... ' V5 / V3 V4 V Azimuthal sector '3' view direction This diagram illustrates cross-plane (polar) IES/Electron Sensor sector layout: +Yies Polar Sector '3' ^ ^ view dir. P# indicate the polar V8 | V7 / sector # position in .----|----. V3 the sensor assembly. V15 ,-' P8|P7 `/. V0 .' | P3 `. `.P15 | / P0.' V# indicate the # sector `. | / .' view direction. `. | / .' `. | / .' For example, for polar `. |/.' Sector 3 the view <-------------`o'+Xies direction is the vector +Zies .' `. emanating from the .' `. aperture center through .' `. the point designated .' `. by V3. .'P15 P0`. `. .' V15 `-. P8 P7 ,-' V0 `---------' V8 V7 IES/Ion Sector Layout The IES/Ion Sector's 360.0 x 90.0 degrees aperture is split into 256 sectors -- 16 in-plane (azimuthal) by 16 cross-plane (polar). In the in-plane direction the sectors are numbered from 0 to 15, in the cross-plane direction the sectors are numbered 0 to 15. Not all 16 in-plane sectors have the same size: seven of them -- sectors 0-2 and 12-15 -- are 45 degrees wide while the other nine -- sectors 3-11 -- are 5 degrees wide. In the cross-plane direction all sectors have the same size of 5 degrees with their center view directions 6 degrees apart. In-plane the 'view direction' of each sector is looking inwards, from the sector position through the center of the aperture. This diagram illustrates in-plane (azimuthal) IES/Ion sector layout: +Yies ^ | A# indicate the azimuthal | sector # position in V15 ....|.... V0 the sensor assembly. .' A7 A11 `. .' A3 | A12 `. V# indicate the # sector V14. | . V1 view direction. . A2 | A13 . . | . +Xies For example, for . o--------------> Sector 12 the view . / +Zies . direction is the vector . A1 / A14 . emanating from the V13. / . V2 aperture center through . / . the point designated `.A0 A15.' by V12. V12 ......... ' V3 / V11 V7 V Azimuthal sector '12' view direction This diagram illustrates cross-plane (polar) IES/Ion Sensor sector layout: +Yies Polar Sector '3' ^ ^ view dir. P# indicate the polar V8 | V7 / sector # position in .----|----. V3 the sensor assembly. V15 ,-' P8|P7 `/. V0 .' | P3 `. `.P15 | / P0.' V# indicate the # sector `. | / .' view direction. `. | / .' `. | / .' For example, for polar `. |/.' Sector 3 the view <-------------`o'+Xies direction is the vector +Zies .' `. emanating from the .' `. aperture center through .' `. the point designated .' `. by V3. .'P15 P0`. `. .' V15 `-. P8 P7 ,-' V0 `---------' V8 V7 Electronics =========== Pulses from the segmented anode are amplified by charge-sensitive preamplifiers (CSPs) and recorded in the 16 x 24 bit ion and electron counters. The data are buffered before being sent to the output serial register for transmission to the RPC Plasma Interface Unit (PIU) as serial telemetry packets. The stepping sequences of the angle and energy deflection voltages of the instrument are fixed in memory. The IES instrument contains a single micro-controller (RTX20X10) which communicates with the RPC-PIU over the IEEE 1355 bus, transmits the collected science data, and monitors the instrument status. The flight software is written in the C and Forth programming languages. The PIU stores and re-transmits to the spacecraft the data stream that the instrument produces. No special data handling is required. Commands and command sequences for IES are formulated by the IES team, sent to Imperial College, where they are translated to the proper format and sent to the project ground system. They are eventually uploaded to the spacecraft and are stored for later execution. In some cases the command may be executed immediately. The sequence provides for selection of one or more operational modes (see below) or in some cases repeated cycling through a series of modes. High Voltages ======= The voltages for the ESAs, deflector (DEF), and MCPs are derived from a single supply of 8514 volts. The ESA and DEF voltages are stepped according to LUTs. The ESA sweeps between 0.407 V and 1667 V in 128 approximately logarithmically spaced steps. The DEF steps between -6667 and +6667 V, alternating negative to positive and positive to negative between the 2 deflector plates. The MCP potentials can be set to a potential between +/- 2500 V and +/-3500 V, the positive level for the electrons and negative for the ions. Except for a short test on May 1-2, 2010, the levels have been at 2500 V based on measurements on the ground before flight. Data Binning ======= Since IES produces more data than can be transmitted within its telemetry allocation, in order to compress the data they are binned in a lossy fashion by use of look up tables (LUTs) stored onboard in the instrument. (See the specific documentation on the details of the different data modes.) For example, the counts from adjacent energy steps can be combined and the sums transmitted to ground, or the counts from a range of energy and/or angle bins or any combination of these, are transmitted, depending on the scientific objective for a particular observation period. Hence the appearance of the data structure will depend on the mode for that particular observation. Flyback ======= Cycling of ESA voltages is completed using 128 steps (0 to 127) which include 4 steps (124 to 127) during 'flyback' (FB), the transition from the highest voltage of 1667 V (step 123) to 0 V (step 127). While the actual transition time does not require all 4 steps, i.e. the 0 V level may be attained in 2 steps or less, science data readings during the first three steps of the flyback should be considered unreliable. When flyback steps are averaged, they are averaged only with other flyback steps. Step 127 may be considered as 0V for background measurements if not averaged. Location ======== The IES instrument is located on the +Z deck of the Rosetta spacecraft in the corner formed by the +X and +Y spacecraft surfaces. The instrument is oriented such that the symmetry axis of the ESAs (i. e. through their poles) is at 45 degrees to the +Z as well as the +X and +Y spacecraft surfaces. Hence the azimuth plane of the FOV (and hence the elevation 0 degrees) is also tilted upward 45 degrees. This arrangement was selected in order to minimize interference to the FOV by any spacecraft or other instrument structures but will still allow viewing the solar wind when the spacecraft is oriented favorably (i.e. when the angle between the spacecraft +Z axis and the sun is between 70 degrees and 100 degrees). Operational Modes ================= When powered on, the IES instrument runs its boot PROM code. The boot PROM, by default, checks all RAM, EEPROM and PROM resources within the IES instrument and reports their status in housekeeping. Whether the PAUSE-PROM or RESUME-PROM mode is entered depends on what was planned for the first operation. PAUSE-PROM prevents the PROM from going automatically into the EEPROM code so that telecommanding or maintenance mode telecommands can be executed. The boot PROM can execute the entire suite of maintenance mode commands but only a limited set of telecommands. In order to program the EEPROM using the activate patch function in maintenance mode, IES must be running from the boot PROM. This is because the boot PROM code runs using a lower clock frequency which is amenable to the EEPROM write timing. The EEPROM code is run at a faster clock frequency to accommodate all the tasks that must be executed during science data acquisition. Housekeeping is generated every 32 seconds. Maintenance and event messages are possible from this mode. RESUME-PROM is a waiting mode to allow telecommands or maintenance mode commands to be received by IES before automatically going to the EEPROM code. Housekeeping is generated every 32 seconds. Event messages are possible from this mode. LVSCI-EEPROM is the first EEPROM mode entered and allows IES commands to be executed. This is the mode used for low-voltage stimulation operation. Housekeeping is generated every 32 seconds. Science and event messages are possible from this mode. HVSCI-EEPROM is entered if an IES-INSTR-PROG-MODE HVSCI telecommand is received. Here, high-voltage telecommands can be executed to turn on the HV supplies and manipulate their settings. All plasma science data are acquired in this mode. Housekeeping is generated every 32 seconds. Science and event messages are possible from this mode. LVENG-EEPROM is used for executing maintenance commands and memory manipulation telecommands. Note that the EPROM cannot be written in this mode due to the timing constraints mentioned in the PAUSEPROM description. Housekeeping is generated every 32 seconds. Maintenance and event messages are possible from this mode. A science data collection mode is determined by the LUT(s) specified in the definition of the mode and determined by the command sequence sent to the instrument. See the 3 tables in the Appendix to the Rosetta-RPC-IES Planetary Science Archive Interface Control Document, Document No. 10991-IES-EAICD-01 for details of the data collapsing for each science mode. These tables give the definitions currently stored in IES memory and show how the full 128 energy by 16 azimuth by 16 elevation bins are selected and or combined to fit either the normal or burst telemetry cases. Acquisition Timing ================== IES uses cycles of varying durations to acquire ION and ELC data across the energy and angular ranges to allow tailoring of energy/angular resolution and time resolution. A cycle requires 128, 256, 512 or 1024 seconds to complete sweeping across the energy range using 128 steps. At each energy step, the deflection voltages are swept using 16 steps (elevations). Each step requires a rise and settle time of 30ms during which no acquisition takes place followed by integration time or acquisition window. The following table lists the cycle durations, and the associated acquisition times. Cycle Duration (seconds): 128 Duration to complete each energy step which inclues 16 elevation steps (seconds): 1 Acquisition/integration time at each elevation/deflection step (milliseconds): 32.5 Cycle Duration (seconds): 256 Duration to complete each energy step which inclues 16 elevation steps (seconds): 2 Acquisition/integration time at each elevation/deflection step (milliseconds): 95 Cycle Duration (seconds): 512 Duration to complete each energy step which inclues 16 elevation steps (seconds): 4 Acquisition/integration time at each elevation/deflection step (milliseconds): 220 Cycle Duration (seconds): 1024 Duration to complete each energy step which inclues 16 elevation steps (seconds): 8 Acquisition/integration time at each elevation/deflection step (milliseconds): 470 Measured Parameters =================== Energy: Range 4.32 eV to 17.67 KeV Resolution 4% Angle: Range (FOV) 90 deg x 360 deg (2.8 Pi sr) Resolution (electrons) 5 deg (elev) x 22.5 deg (azim) (16 azimuthal x 16 elevation) Resolution (ions) 5 deg (elev) x 45 deg (azim) for 7 sectors 5 deg (elev) x 5 deg (azim) for 9 sectors (16 azimuthal x 16 elevation) Temporal resolution: 3D distribution 128s downlink rates Normal: 5 bps Burst: 250 bps Geometric factor: total (ions) 5 x 10e-4 cm^2 sr eV/eV counts/ion per 45 deg sector 5 x 10e-5 cm^2 sr eV/eV counts/ion per 5 deg sector 7 x 10e-6 cm^2 sr eV/eV counts/ion total (electrons) 5 x 10e-5 cm^2 sr eV/eV counts/electron per sector (electrons) 5 x 10e-6 cm^2 sr eV/eV counts/electron" END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "BURCHETAL2007" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END