Document title: Volume description SFD for NDADS DE-2 RPA_DUCT_ASCII datatype Project: DE NDADS Datatype: RPA_DUCT_ASCII Super-EID: DOCUMENT There may be other documents also identified by this super-EID. NDADS filename: DUCT_VOLDESC_DE.SFD TRF entry B46566.txt in NSSDC's controlled digital document library. Feb. 1998. Document text follows: ---------------------- CCSDXZLM0001SMARK001CCSDXVNM0002SMARK002 LOG_VOL_IDENT: USANASANSSDDEB7_0002A LOG_VOL_INITIATION_DATE: 1992-09-21 LOG_VOL_CLOSING_DATE: 1992-09-21 LOG_VOL_CAPACITY: 2.2GB LOG_VOL_FILE_STRUCTURE: VAX FILES-11 STRUCTURE LEVEL 2 Written with BACKUP utility as a save set. TAPE_LENGTH: 106 METERS VOLUME_DRIVE_MFGR_AND_MODEL: AVIV, model ACT850 COMPUTER_MFGR: DIGITAL EQUIPMENT CORPORATION OPERATING_SYSTEM: VMS, VERSION 5.5 COMPUTER_SYSTEM: VAX 4000/500 TECHNICAL_CONTACT: Robert A. Power and/or Dr. William R. Coley TRANSFER_SOFTWARE: VMS BACKUP utility TECHNICAL_CONTACT: Robert A. Power and/or Dr. William R. Coley Center for Space Sciences University of Texas at Dallas, M.S. Fo2.2 P. O. Box 830688 Richardson, Texas 75083-0688 214-690-2851 SPAN Address - UTSPAN::UTADNX::UTDSSA::POWER PREV_LOG_VOLS: USANASANSSDDEB7_0001A CCSDXVNM0002EMARK002CCSDXKNM0002SMARK003 DATA_SET_NAME: RETARDING POTENTIAL ANALYZER FILES (RPA) DATA_SOURCES: DYNAMICS EXPLORER 2, RETARDING POTENTIAL ANALYZER (RPA) AND ION DRIFT METER (IDM) SCIENTIFIC_CONTACTS: Dr. William B. Hanson and/or Dr. R. A. Heelis Center for Space Sciences University of Texas at Dallas, M.S. Fo2.2 P. O. Box 830688 Richardson, Texas 75083-0688 214-690-2851 SPAN Address - UTSPAN::UTADNX::UTDSSA::HEELIS SOURCE_CHARACTERISTICS: A. DESCRIPTION_OF_SPACECRAFT: The Dynamics Explorer 2 spacecraft was one of two satellites launched for the Dynamics Explorer program. The two spacecraft were launched together into coplanar polar orbits for the purpose of studying coupling between the magnetosphere, ionosphere, and the atmosphere. The DE-2 spacecraft was placed in a low elliptical orbit whereas the DE-1 orbit was highly elliptical. Instruments aboard the DE-2 spacecraft were: magnetometer, vector electric field instrument, neutral atmosphere composition spectrometer, wind and temperature spectrometer, Fabry-Perot intereferometer, ion drift meter, retarding potential analyzer, low altitude plasma instrument, and Langmuir probe. B. ORBIT_INFORMATION: Because the Delta launch vehicle did not complete a full burn the DE-2 satellite was placed in a lower than anticipated polar orbit, initially 1012 by 309 km. The orbital period was 98 min. The DE-1 and DE-2 satellites were launched by the same vehicle so that their orbits would be coplanar, allowing occasional two-point measurements along magnetic field lines. The DE-2 spacecraft spun once per orbit and the spin axis was perpendicular to the orbital plane so that one axis of the satellite always was aligned with the center of the earth. C. PERFORMANCE: The DE-2 spacecraft performed well through its lifetime. Power limitations forced the duty cycle to be limited to an average which was originally targeted at 30%. The lifetime of the spacecraft was shorter than anticipated because of the less than nominal performance of the launch vehicle. The launch was on August 3, 1981 and the DE-2 satellite reentered the atmosphere on February 19, 1983, with the last contact the day before. INVESTIGATION_OBJECTIVES: Among the science objectives for the DE program was the study of the electrodynamics of the ionosphere and its application to ionosphere- magnetosphere interactions. The RPA/IDM objectives were to provide a measure of the vector ion drift velocity in the ionosphere and the ion temperature, concentration and composition. This data is used in studies of the ionospheric electric field and ionosphere-thermosphere interactions. INSTRUMENT_ATTRIBUTES: A. DESCRIPTION_OF_INSTRUMENT The Retarding Potential Analyzer (RPA) consists of two planar sensors that view approximately along the spacecraft velocity vector. One sensor provides a measure of the total ion flux entering the sensor aperture from which structure in this parameter can be measured with extreme sensitivity. The other sensor has internal grids that can be stepped through positive voltage waveforms to modulate the incoming ion flux that reaches the collector. The resulting ion-flux versus retarding potential measurements are used to derive the ion temperature, the ion drift velocity along the sensor look direction ,and the ion composition. ( See Hanson et al., Space Sci. Instrum. 5, 503, 1981) The Ion Drift Meter (IDM) consists of two sensors that view approximately along the spacecraft velocity vector. Each sensor has a square entrance aperture to a gridded region in front of a collector with four quadrant sectors. By comparison of the ion currents to each sector it is possible to measure the angle of arrival of the ions in two mutually perpendicular directions perpendicular to the look direction of the sensor. From this angular information, knowledge of the ion velocity along the sensor look direction from the RPA and knowledge of the spacecraft attitude, it is possible to derive the ambient ion drift along the two mutually perpendicular directions. ( See Heelis et al., Space Sci. Instrum., 5, 511, 1981) B. OPERATIONAL_MODES: The nominal modes of operation for the RPA provides a measure of the total ion flux 64 times per second and a measure of the ion flux versus retarding potential every second. The retarding voltage wave form may contain a high frequency "wiggle" from which a derivative signal can be obtained. The steps comprising the retarding voltage waveform could be changed to obtain data more efficiently. The IDM provides absolute measures of the ion arrival angle 4 times per second and measurements of the angle relative to an absolute value, established every 8 seconds, at the rate of 32 samples per second. C. MEASURED_PARAMETERS: The RPA provides a measure of the total ion concentration by incorporating the spacecraft velocity into the measured ion flux. The ion flux versus retarding potential data provide the input to a non-linear least squares fitting procedure that derives the ion temperature. The ion drift velocity along the sensor look direction is also derivable from this procedure if either the spacecraft potential is known or, as is usually the case, if two widely spaced masses comprise the ion composition. D. PERFORMANCE_OF_THE_INSTRUMENT: The RPA data provide high resolution measurements of the ion concentration for the entire duration of the DE-2 lifetime. Due to a failure in the instrument memory system, measurements of the ion flux versus retarding potential are unavailable from 81317 06:26:40 UT to 82057 13:16:00 UT. The component of ion drift along the look direction of the sensor, the ion temperature and the ion composition are not available during this period. The IDM provided data on the ion arrival angle for the entire duration of the DE-2 lifetime. Interpretation of this data in terms of ion drifts requires the assumption of zero ram drift during the period of RPA failure. This is usually not a serious limitation (see DATA_SET_QUALITY). E. RESOLUTION: Two different types of geophysical data files have been produced for inclusion on this volume. The first is the RPA geophysical data file which is produced from a combination of RPA and IDM data. The resolution is determined by the basic RPA retarding voltage sweep time and the efficiency of the least-squares analysis. RPA geophysical data files provide ALL geophysical parameters measured by the RPA and IDM at a resolution of usually 2 seconds and sometimes 4 seconds. The second type of file is the DUCT geophysical data file which provides measurements of the total ion concentration every 64 times per second. These files are designated DUCT. PARAMETERS: RPA data files contain time tagged orbit data and geophysical data for each analyzed sweep. DUCT data files contain geophysical data in 8 second blocks corresponding to the standard segment of data on the DE spacecraft. Each 8 second block of DUCT data, generally containing 512 ion concentration measurements, is accompanied by some basic orbit position information. DATA_SET_QUALITY: RPA data files have been nominally screened for obvious errors in least- squares analysis. Some errors are, however, quite subtle and caution should be exercised in interpretation of temporal discontinuities in the ion temperature or ion drift velocity along the spacecraft look direction. As much data as possible has been retained in the data files and the rms error is available for each entry. The accompanying IDM data for each entry has not been interpolated for the time tag given as the mid-point of the RPA sweep. Thus time shifts of 1/8 second may exist between the specified and actual time for the cross track drifts. IDM data is of high quality since only absolute ion drift velocities have been retained in the data files. This higher resolution data has not been corrected for the presence of ion drifts along the sensor look direction. If such a drift Vr exists then the value in the file should be corrected by the factor (Vs +Vr)/Vs, where Vs is the spacecraft velocity along the sensor look direction. This correction factor can be as high as 20%. DUCT data is of high quality since there is little interpretive work required in its conversion from ion current. The spacecraft velocity along the look direction of the sensor is used to convert ion flux to ion concentration. Apparent variations in ion concentration of order 10% may result from variations of order 1 km/sec in the ambient ion drift velocity along the look direction of the sensor. Such changes should be apparent in the RPA data files. DATA_PROCESSING OVERVIEW: A. DATA_PROCESSING CYCLE: Raw telemetry segments were reduced to RPA mission analysis files (MAF's) utilizing production processing on the project computer. The cpu commitment to RPA analysis could not be retained during the periods when the TM was initially available. Thus a situation in which TM file promotion was required for RPA analysis evolved. This quickly resulted in a backlog of unprocessed TM which still exists. Though data files for most data segments exists some files do not exist at all and others require complete reprocessing due to inadequate least-squares analysis. B. HISTORY All data was originally reduced on project computers at GSFC. More recently an attempt to transfer telemetry files to local computers at the investigators site has been undertaken. Some data files originate from reduction of telemetry on local computers. This data is usually of higher quality and higher temporal resolution owing to the resources that can be applied to it. It is not identified in any way as originating from this source. DATA_USAGE: Usage of the geophysical data is not formally restricted. Users are urged to be cautious in interpretation of structure and discontinuities in the RPA data. In many cases such structure is real, but it may also be caused by the production of false minimums in the least-squares analysis. Review of data by the scientific contacts above is required to ensure it is used correctly. DATA_ORGANIZATION: Geophysical data files exist for each DE2 telemetry segment. These data files may be identified by orbit number or by approximate UT start time. TYPE_OF_FILE_RELATIONSHIPS: Generally there will be a DUCT file corresponding to each RPA file. CCSDXKNM0002EMARK003CCSDXKNM0002SMARK005 LOG_VOL_TIME_COVERAGE: 1982-02-21 TO 1982-09-06 TYPE_OF_FILE_TIME_COVERAGE: RPA 1982-02-21T09:04:14 1982-09-06T17:18:20 DUCT 1982-02-21T09:02:06 1982-09-06T17:19:16 NAMING_CONVENTION: RPA and DUCT files are named according to the U.T. starting date and time of the data in the file. Example: RPA821141206.DAT indicates that this is an RPA file for the year (19)82, day 114, hour 12, minute 06. FILE_TIME_COVERAGE: The length of a file can vary from less than 1 minute to approximately 1 complete orbit of the DE-2 satellite (approximately 100 minutes). PREV_LOG_VOL_TIME_COVERAGE: USANASANSSDDEB7_0001A 1981-08-03 TO 1982-02-21 CCSDXKNM0002EMARK005CCSDXRNM0003SMARK006 NESTING=L REF=RPAFORMAT.SFD CCSDXRNM0003EMARK006CCSDXRLM0003SMARK007 ADI=NSSD0012 CLASS=I NESTING=N SCOPE=EACH REF=[DYNEXP.RPA]RPA*.dat;* CCSDXRLM0003EMARK007CCSDXRNM0003SMARK008 NESTING=L REF=DUCTFORMAT.SFD CCSDXRNM0003EMARK008CCSDXRLM0003SMARK009 ADI=NSSD0013 CLASS=I NESTING=N SCOPE=EACH REF=[DYNEXP.DUCT]DUCT*.dat;* CCSDXRLM0003EMARK009CCSDXZLM0001EMARK001