Document title: DE RIMS mission analysis files voldesc Project: DE NDADS Datatype: RIMS Super-EID: DOCUMENT There may be other documents also identified by this super-EID. NDADS filename: DOCUMENT_RIMS_VOLDESC.SFD TRF entry: b46610.txt in NSSDC's controlled digital document library, Feb. 1998. Document text follows: ---------------------- DATA_SET_NAME: RIMS MISSION ANALYSIS FILES (MAF) DATA_SOURCES: DYNAMICS EXPLORER A, RETARDING ION MASS SPECTROMETER INVESTIGATOR_CONTACT: Dr. C.R. CHAPPELL NASA/MSFC DA01 MSFC/ALABAMA 35812 PHONE: (205)544-3030 SOURCE_CHARACTERISTICS: A. DESCRIPTION_OF_SPACECRAFT: On August 3, 1981, a Delta rocket launched from Vandenberg Air Force Base successfully placed the two Dynamics Explorer (DE) spacecraft into coplanar polar orbits. The purpose of the mission was to acquire data to study the processes coupling the magnetosphere, ionosphere, and upper atmosphere. The two spacecraft were manufactured by the Government System Division of RCA, and the instruments were provided by various principal investigators. A complete description of the mission, spacecraft, instruments, and ground data systems appears in an issue of Space Science Instruments (Volume 5, pp. 345-573, 1981) edited by R.A. Hoffman. The high-altitude satellite, DE-1, carried an auroral imager and detectors designed primarily for field and particle measurements. The low-altitude satellite carried more aeronomic-type instruments. The orbits of the two satellites remained very nearly coplanar during their joint lifetimes providing the unique opportunity to acquire data at two altitudes along common magnetic flux tubes. DE-2, operating at ionospheric altitudes, reentered the atmosphere in February, 1983. DE-1 is still operational as of December, 1990. B. ORBIT_INFORMATION; The high altitude spacecraft carrying the RIMS experiment operates in an orbit of 24,875 km apogee and 675 km perigee. The orbit plane drifts westward at a rate of 1 hour MLT every 15.4 days; the orbit line of apsides drifts 0.328 degrees magnetic latitude each day. The period of the orbit is 7.5 hours. Note that while the DE-1 orbit will provide coverage for most all local times and latitudes out to the apogee at 4.65 Re, the 3 to 1 ratio between the drift of the line of apsides and the westward drift of the orbital plane will result in uneven coverage in local time for a given altitude. In particular, in the 12-18 magnetic local time sector, the higher altitudes in the auroral latitude region will not be fully sampled. C. PERFORMANCE: Both spacecraft were power limited and considerable effort was expended in selecting portions of orbits for maximum science return. DE-1 had a duty cycle of nearly 90% during the early portion of the mission, but in general varied between 16-55%. DE-2 had a duty cycle between 16 and 36%. Times of magnetic conjunction between the spacecraft, or between one spacecraft and a collaborating ground observatory were given high priority. Also data acquisition during passages through geophysical regions like the dayside cusp and plasmapause were emphasized. TIME_SPAN_OF_THE_DATA: 1982-10-08T04:52 TO 1983-06-13T02:31 INVESTIGATION_OBJECTIVES: The Retarding Ion Mass Spectrometer (RIMS) is an instrument designed to measure the details of the thermal plasma distribution. It combines the ion temperature determining capability of the retarding potential analyzer (RPA) with the composition determining capabilities of the mass spectrometer. The RIMS has multiple sensor heads to sample all directions relative to the spacecraft velocity. The instrument has furnished fundamental information in the following specific areas: A) the density of H+, He+, O+, N+, He++, and O++ in the ionosphere, plasmasphere, plasma trough and polar cap. This includes the density distribution along B in the vicinity of the satellite apogee. B) The temperature of H+, He+, O+, N+, He++, and O++ ions in the ionosphere, plasmasphere, plasma trough and polar cap (energy range 0 to 50 eV). C) The bulk flow velocities of H+, He+, O+, N+, He++, and O++ in the plasmasphere, plasma trough, and polar cap. D) The changing character of the cold plasma density, temperature, and bulk flow in regions of interactions with hot plasma such as at the boundary between the plasmasphere and the ring current. E) The detailed composition of ionospheric plasma in the 1 to 40 amu range. INSTRUMENT_ATTRIBUTES: A: DESCRIPTION_OF_INSTRUMENT: The Retarding Ion Mass Spectrometer (RIMS) experiment onboard the DE-1 satellite was designed to perform energy and mass analysis on low energy ions (<50 eV) with mass ranging from 1 to 40 amu. The instrument is fully described by Chappell, et al. (The Retarding Ion Mass Spectrometer on Dynamics Explorer-A, Space Sci. Instrum., 4, p477, 1981). The RIMS has significantly improved capabilities over previous retarding potential analyzer instrument by providing ion mass separation so that separate RPA and spin curves are obtained for each programmed species. These enhanced instrument capabilities combined with the DE-1 orbit produced a unique opportunity to investigate the variable dynamics and composition of the low-energy ion population in the near-earth space environment. The DE-1 RIMS consists of four instrument assemblies interconnected to form one experiment. Three of the assemblies are sensor heads and one is the central electronics. The three heads are labeled according to the mounting axis on the DE-1 spacecraft: Radial, +Z, and -Z. The radial sensor views perpendicular to the spacecraft spin axis, while the sensors on the ends of the spacecraft view parallel and anti-parallel to the spin axis for complete phase space coverage. The central electronics assembly (CEA) provides the spacecraft interface, all data processing, command decoding, and complete timing control of the entire RIMS experiment. Each sensor head consists of a RPA followed by a magnetic mass analyzer with two separate exit slits corresponding to two mass ranges in the ratio 1:4. The total mass range covered is 1 to 40 amu. Surrounding and attached to the entrance of the sensor head is a 20-cm circular aperture plane. The plane is connected to a relay which can, on command, connect to to either spacecraft chassis ground or to the aperture potential power supply output. The aperture potential power supply can be set by spacecraft minor mode A command to 0, -2, -4, or -8 volts to partially compensate for a non-zero spacecraft potential. The retarding grid of the RPA is connected to the retarding potential power supply through a shielded conductor. The retarding potential may be set to any one of 1024 linearly spaced steps from 0 to +51.125 V with a resolution of 0.05 volts. The RPA collector plate is connected through a co-axial cable to a 5-decade logarithmic amplifier. The reference voltage for the front end of the log amp is the output of the aperture potential power supply. The output of the log amp is converted, by command from the CEA, to a 10-bit digital word using an analog/digital (A/D) converter. The digital word is held in a holding register until the CEA is ready to read and process the data. Those ions passing into the Ion Mass Spectrometer (IMS) are sorted according to their charge to mass ratio. The proper combination of ion accelerating voltage, magnetic field strength, and ion beam radius in the magnetic field determine the mass of the ion focussed on each collector slit. Varying the ion accelerating voltage varies the ion mass detected. Ions of mass 1 to 8 amu and 4 to 32 amu can be focussed on the low and high mass slits, respectively. Ions exiting the collector slides are counted by the CEM detectors. The ion mass range is also programmable by a minor mode command. Any 32 of 4096 voltage steps may be selected. All 32 steps may be the same, in which case the mass analyzer will be locked onto a given set of mass peaks having the ratio 1:4. The two- channel IMS uses channel electron multipliers (CEMs) as detectors. The two CEMs in each sensor head are powered by a single multiplier high- voltage power supply which can be set, by spacecraft minor mode A command, to any one of four voltages, -1200, -2100, -2400, and -2800 V. The IMS accelerating voltage comes from a sweep high voltage power supply that can be addressed to any one of 4096 linearly space steps between 0 and -2250 V. B: OPERATION_MODE: The RIMS instrument, being programmable by spacecraft major and minor mode commands, operated in a variety of survey modes during the experiment lifetime. The operating sequence is controlled by an internal memory in the CEA which is programmed by ground command. The RIMS commonly performed two basic operational functions during the mission: 1) The RPA voltage is swept over a selected range for a given mass and, 2) The RPA voltage is set to zero and a sweep is made over a selected mass range. There are several variations of these modes, several specialized modes, and several combinations of sweeps, aperture biasing, and cycling patterns. Users of the RIMS mission analysis file data set must be aware of the instrument mode setting for the segment of data being analyzed. The documentation data set, RIMSMODE.TXT, accompanying the primary data set of MAF files, lists the RIMS minor mode B commands employed during the mission keyed to the data's universal time. Information on the meaning of the mode mnemonics is given below. The mode commands furnished by the spacecraft to the RIMS instrument: Major Mode Relay Commands: Radial Aperture Plane Grounded Radial Aperture Plane Programmed Z Aperture Plane Grounded Z Aperture Plane Programmed Major Mode Logic Commands: Radial High Voltage Enable +Z High Voltage Enable -Z High Voltage Enable Fixed Scan Enable Memory Dump Major Mode Hardware Commands: Memory Load Memory Dump RPA Mode Cyclic Mode IMS Mode The minor mode commands are separated into two categories. Minor Mode A Commands: A 32-bit serial word that is received and stored in a command register. The trailing edge of the command envelope sets a control bit indicating a new command is ready to be loaded into the instrument control register at the next 1 pps pulse. Minor Mode B Commands: 1 32-bit serial word that is received and stored in a command register. This command is used exclusively for loading the 32-word instrument memory. The sequence of 32 words sets up the IMS and RPA steps that will be executed during the instrument cycle. The following is a summary of the RIMS nominal operating modes: IMSON,RPAON,APPON "Turn-on" and initiation command. STOPIT "Turn-off" command. HIXXZ A family of modes in which the instrument is measuring only one mass pair and concentrating on either high mass or angular resolution. The two unspecified locations in the mnemonic denoted by X will specify the heavier of the pair while the location denoted by Z refers to an RPA program. XVXXZ A family of survey modes in which the instrument splits its observing pattern between the H+/He+ mass pair and one other mass pair. The definition of the unspecified location is the same as in the previous case. The total cycle time is 16 sec. SXYYZ The alternate memory is used to observed the H+/He+ pair and the normal memory to observe another mass pair. The XX denotes the heavier of the mass pair under normal memory control. Each mass pair is sampled for 8 seconds. Total cycle time is 16 seconds. TXYYZ A survey mode which is similar to the previous survey model with the exception of the sequencing pattern. In this case, the H+/He+ setting is maintained for 8 sec with an RPA cycle each 0.25 sec. In the subsequent 8-sec half of the cycle time, the instrument toggles between the alternate mass pairs each 0.25 sec. The total cycle time is 16 sec. MXXYY A mass sweep mode starting at mass XX and ending at mass YY. The specified mass numbers of those of the heavy mass channel. The lower mass channel with be operating and measuring mass species of 1/4 of the specified high mass values. Note: The sweep may not be continuous within the specified range if prior instrument experience has indicated that certain mass numbers are unpopulated. The cycle time is 0.5 sec. CXXYY A mass sweep mode with interspersed RPA analysis of the H+/He+ pair. The cycle time is 16 sec. SHXXY A special mode for high latitude studies. The three ions O+, H+, and He+ are measured with RPA scans for each. The cycle time is 1/2 second. SSZZZ Special science modes designed after launch. Contact RIMS science team. PLPHN Plasma mode used to investigate spacecraft/plasma interactions. Geophysical data may be available, but will require special interpretation. N is the program number. INSTR Instrument check out, test, and calibration modes. Note that the instrument may be operating with an additional potential applied to the entrance aperture. The following commands identify the applied bias voltage: NAMMAP2X -2 volts NAMMAP4X -4 volts NAMMAP8X -8 volts PH20AAAA -2 volts PH20ADTD -2 volts PH40AAAA -4 volts PH40ADTD -4 volts PH80AAAA -8 volts PH80ADAA -8 volts PH80ADTD -8 volts PL80ADAA -8 volts HI04A02X -2 volts HI04A03X -4 volts HI04A04X -8 volts SH16M02X -8 volts SSNV801X -8 volts SSN8V01X -8 volts T816Q03X -2 volts T816Q04X -4 volts T816205X -8 volts SS04P01 -8 volts STUDIES OF THE RIMS DATA SET SHOULD BE CONDUCTED ONLY WITH A THOROUGH UNDERSTANDING OF THE RIMS OPERATIONAL MODES AND THE INSTRUMENT RESPONSE TO THESE MODES. The convention of naming modes as given above were generally but not rigorously followed. i.e., there may be times in which a mass scan mode MXXYY alternated with measurement of H+/He+. C. MEASURED_PARAMETERS: The output of each detector is connected to a pulse amplifier whose output is sent to a level detector. The discrimination level is set to a high or low value by spacecraft minor mode A command. Pulses from the discriminator are coupled to an 18-stage binary counter. Four bits of the counter are located in each head, and the other 14 bits of each accumulator are located in the CEA. The CEA contains the circuitry for compressing each accumulator output into a 10-bit base 2-floating point number (6-bit mantissa and 4-bit exponent) for output into the telemetry buffer. Note that the RIMS instrument is assigned 26 8-bit telemetry words. One 8-bit word is reserved for status information, five groups of 5 8-bit telemetry words each are used for measurements -- where each group is considered a telemetry channel by the processor. With this convention, each telemetry channel can contain 4 each 10-bit instrument words. Each RIMS sensor head has three data outputs, the RPA and high and low mass IMS channels, and therefore output 9 measurements each 1/4 frame for a total of 36 10-bit instrument words per telemetry minor frame. Since the 40 bit telemetry channel can contain only 4 10-bit instrument words, only 20 of the 36 instrument words may be loaded into the telemetry channels each telemetry frame (4 instrument words x 5 telemetry channels). The telemetry channel assignments are as follows: Channel Words Data output A 1 Housekeeping and status B 5 Radial IMS low-mass channel accumulation C 5 Radial IMS high-mass channel accumulation D 5 Alternates each 1/4 frame between +Z IMS low & high-mass channel accumulation E 5 Alternates each 1/4 frame between -Z IMS low & high-mass channel accumulation F 5 Alternates each 1/4 frame between radial, +Z, and -Z RPA (electrometer) accumulation D. PERFORMANCE_OF_THE_INSTRUMENT: The RIMS instrument continues to return usable data as of December, 1990. The radial head RPA failed on 81/329 19:50:18. It worked again between 82/045 23:30 and 82-046 06:15 before failing again. Sometime before 82/046 the -Z head aperture bias mechanism failed. At launch the -Z head was found to be biased -2 volts with respect to the other two heads. The anomaly disappeared on day 73 or 74 of 1982. The Z heads show spin variation primarily at low altitudes in cold, dense plasmas at high spacecraft velocities. For a more detailed and complete account of RIMS performance characteristics, see Olsen, et al., DE-1 RIMS Operational Characteristics. NASA TM-86527, 1985. E. RESOLUTION: The instrument cycle is 32 data samples from each data source. The RIMS completes one instrument cycle each 0.5 sec. Each data sample represents a period of 15.625 msec. This interval consists of an measurement integration interval and a data processing interval. During the measurement interval, the IMS accumulators are active for a period of 12 msec. The 3.625 msec data processing interval is used to process the data accumulated during the integration interval and to establish the mass voltage and retarding voltage for the next integration period. The mission analysis files (MAF) data format record consists of 8 seconds of RIMS data (512 samples per channel, each sample 15.625 msec, in time order. One record is 5624 bytes in size. PARAMETERS: Each MAF file data record consists of 8 seconds of RIMS data (512 samples per channel, each sample 1/64 sec measurement), in time order. One record is 5624 bytes in size. The first 100 locations (16 bit words) of this record contains timing, orbit/attitude, B-field, and instrument mode information. Since the instrument mode takes some logic to decode, subroutines are provided that perform the decoding of the instrument flags, determination of RPA/IMS settings for any sample through the 512, and decommutation of the D and E channels (Z-head data). DATA_SET_QUALITY: Data quality is, in general, excellent. Data is not always recorded at altitudes down to the DE-1 perigee of 675 km. At the lower altitudes, the plasma density can be quite high and the RIMS instrument is generally shut off to protect the particle detecting channeltrons from excessive counting rates. However, on occasion, saturation of the detecting channeltrons may be seen in the radial head data during low altitude-high density passes. Detection of very low energy ions is made difficult by the presence of floating spacecraft potentials. The potential is generally about 1 volt negative at the lowest altitudes, so that the entire population of 0-50 eV positive ions is sampled. However, when the spacecraft potential floats to positive values at higher altitudes, those particles whose ram energy (energy of the ion in reference frame of the spacecraft due to the spacecraft motion) is less than the spacecraft potential, will not be properly sampled. The DE-1/RIMS instrument has attempted to deal with this problem by the addition of a voltage bias plate at the entrance aperture of the instrument. The diameter of the external aperture plane is 10 cm, which may be compared to the spacecraft dimension of 1 meter in height and 1/4 meter in diameter. The instrument retarding voltages are referenced to this aperture plane, so that to the RIMS detector the effect of the bias is similar to a change in spacecraft potential, though sheath effects can complicate the interpretation of the results data. Thermal plasma measurements of DE-1 using the aperture bias mode in the outer plasmasphere and over the polar cap show the existence of very cold plasma, less than an eV, which would otherwise have been hidden from the particle detector by positive spacecraft potentials. See Olsen et al., DE-1 RIMS Operational Characteristics, NASA TM-86527, 1985. DATA_PROCESSING_OVERVIEW: A. DATA_PROCESSING_CYCLE: The RIMS instrument data is provided by GSFC to ES53/MSFC on 1600 BPI magnetic tapes. The RIMS data is routinely extracted and combined with orbit/attitude and magnetic field parameters to produce mission analysis files and microfiche summary plots. There is usually one final MAF file per pass (RIMS instrument on/off time). The summary plots are reviewed for processing quality. The MAF files are compressed before being archive to optical disk. B. HISTORY: MAF files have been produced routinely as telemetry became available. Inconsistencies in orbit/attitude data, spin phase sorting, and memory mode identification are routinely corrected, where possible,in the MAF production process. DATA_USAGE: The RIMS MAF files are generally accessed using one of the several data analysis programs included with the MAF data set. Each main program includes all software necessary to decompress, read, decode mode information, and sort MAF data according to user inputs. The products of these programs are arrays of numbers to be plotted by user-supplied software packages. Example plots and their usage may be found in many of the references given below. Software is included to produce the following types of arrays: For simple line plots, use: CSSPEC Detector count rate versus spin phase angle. CESPEC Detector count rate versus energy (RPA step). CTSTIM Detector counts rate versus universal time. For the more elaborate color, or grey-scale spectrograms, use: IMSTGS Detector count rate versus mass step versus universal time. SENTGS Produces two arrays: 1) Detector count rate versus spin phase angle versus time 2) Detector count rate versus energy (RPA step) versus time Thermal ion plasma characteristics can be quite variable in the different magnetospheric locations sampled by the DE-1 spacecraft. As such, the frequent non-Maxwellian character of the plasma prohibits the routine reduction from sensor count rate to bulk parameters and leads to analysis through the use of data displays such as energy-time and spin angle-time spectrograms. In the inner plasmasphere and ionosphere where Maxwellian characteristics are more common, simple algorithm and curve-fitting routines may be employed to derive the bulk parameters of ion density, temperature and bulk-flow. (See Olsen, et. al., DE-1 RIMS Operational Characteristics, NASA TM-86527, 1985 for complete discussion.) At low altitudes, ion composition would be measured using both the RPA and mass spectrometer capabilities. In this region mass spectra versus time, latitude, and local time are helpful. As the spacecraft moves over the pole, pitch angle measurements of different ion species are measured to search for polar wind effects. In this region a spin angle-time spectrogram is utilized for data display. Moving toward apogee, the spacecraft can examine the plasmasphere filling and energization processes. Here, both spin angle-time and energy-time spectrograms are employed. DE-1 then moves through apogee to higher latitudes where the interface between the thermal plasma of the plasmasphere and the hot plasma of the ring current can be studied simultaneously. The effects of the low-energy ions on the hot ring current ions are traced using simultaneous energy-time spectrograms for hot and cold plasma as a function of time, L-shell and local time. For additional information, see DE-1 RIMS Operational Characteristics by R.C. Olsen, et al., 1985, NASA TM-86527, where the reduction process from count rate to physical quantities is discussed in some detail. Studies of the RIMS data set should be conducted only with a thorough awareness of the material presented in that manual, or in collaboration with one of the scientists actively involved with RIMS data analysis. A few references to aid in the use and understanding of the RIMS MAF data set: Chappell, C.R., J.L. Green, J.F.E. Johnson, and J.H. Waite, Jr., Pitch angle variations in magnetospheric thermal plasma -- initial observations from Dynamics Explorer-1, Geo. Res. Let., 9, 933- 936, 1982. Chappell, C.R., T.E. Moore, and J.H. Waite, Jr., The ionosphere as a fully adequate source of plasma for the earth's magnetosphere, J. Geophys. Res., 77, 6104, 1987. Chappell, C.R., The terrestrial plasma source: a new perspective in solar-terrestrial processes from Dynamics Explorer, Rev. Geophys., 26, 229, 1988. Craven, P.D., R.C. Olsen, C.R. Chappell, and L. Kakani, Observations of molecular ions in the earth's magnetosphere, J. Geophys. Res., 90, 7599-7605, 1985. Lockwood, M., J.H. Waite, Jr., T.E. Moore, J.F.E. Johnson, and C.R. Chappell, A new source of suprathermal O+ ions near the dayside polar cap boundary, J. Geophy. Res., 90, 4099-4116, 1985. Olsen, R.C., C.R. Chappell, J.L. Burch, Aperture plane potential control for thermal ion measurements, J. Geophys. Res., 91, 3117-3129, 1986. Olsen, R.C., S.D. Shawhan, D.L. Gallagher, J.L. Green, C.R. Chappell, and R.R. Anderson, Plasma observations at the earth's magnetic equator, J. Geophys. Res., 92, 2385-2407, 1987. Waite, J.H., Jr., T. Nagai, J.F.E. Johnson, C.R. Chappel, J.L. Burch, T.L. Killeen, P.B. Hays, G.R. Carignan, W.K. Peterson and E.G. Shelley, Escape of suprathermal O+ ions in the polar cap. J. Geophys. Res., 90, 1619, 1985.