CCSD3ZS00001markerzzCCSD3VS00002markeraa LOG_VOL_IDENT: USANASANSSDSMDD_0001 LOG_VOL_INITIATION_DATE: 1995-08-28 LOG_VOL_CLOSING_DATE: 1995-08-28 LOG_VOL_FILE_STRUCTURE: FILES-11 STRUCTURE LEVEL 2 COMPUTER_MFGR: DIGITAL EQUIPMENT CORPORATION OPERATING_SYSTEM: VMS, VERSION 6.1 COMPUTER_SYSTEM: VAX 4000/500 TECHNICAL_CONTACT: Robert A. Power and/or Dr. William R. Coley William B. Hanson Center for Space Sciences University of Texas at Dallas, M.S. Fo2.2 P. O. Box 830688 Richardson, Texas 75083-0688 214-883-2851 SPAN Address - UTSPAN::UTADNX::UTDSSA::POWER Internet Address - power@utd500.utdallas.edu PREV_LOG_VOLS: NONE CCSD$$MARKERmarkeraaCCSD3SS00002markerab DATA_SET_NAME: RETARDING POTENTIAL ANALYZER FILES (RPA) DATA_SOURCES: SAN MARCO, RETARDING POTENTIAL ANALYZER (RPA) AND ION DRIFT METER (IDM) SCIENTIFIC_CONTACTS: Dr. R. A. Heelis William B. Hanson Center for Space Sciences University of Texas at Dallas, M.S. Fo2.2 P. O. Box 830688 Richardson, Texas 75083-0688 214-883-2851 SPAN Address - UTSPAN::UTADNX::UTDSSA::HEELIS Internet Address - heelis@utdallas.edu SOURCE_CHARACTERISTICS: A. DESCRIPTION_OF_SPACECRAFT The San Marco D spacecraft was approximately spherical in shape and housed a science instrument payload consisting of a solar uv spectrometer, a neutral mass spectrometer and wind instrument, an ion drift meter, a retarding potential analyzer, a vector electric field instrument, and a drag balance experiment. B. ORBIT_INFORMATION The San Marco spacecraft was launched on March 25, 1988 into a 2.9 degree inclination orbit with apogee 614 km and perigee 260 km. The spacecraft was spin stabilized, with a rotation rate of 6 rpm and the spin axis oriented perpendicular to the orbit plane. C. PERFORMANCE The San Marco Spacecraft performed well throughout its relatively short lifetime. Data was obtained through the period 88111 to 88339 with a duty cycle of about 50 to 75 minutes per day. INVESTIGATION_OBJECTIVES: The San Marco science objectives were directed principally into further understanding of the large scale electrodynamic properties of the equatorial ionosphere and the conditions prevailing at the times of occurrence of F-region plasma instabilities. The combination of measurements of neutral atmosphere dynamics, from which the electric fields are produced, and the charged particle dynamics, are the required elements of such an investigation. INSTRUMENT_ATTRIBUTES: A. DESCRIPTION OF INSTRUMENT The Retarding Potential Analyzer (RPA) consists of two sensors. One, a planar sensor views along the spacecraft velocity vector once per spin and with appropriate timing, an energy analysis of the ram plasma is obtained at that time. Subsequent analysis of this data provides information of the ion temperature and ram energy (see Hanson and Heelis, Space Sci. Instrum., 1, 201, 1981). A second sensor is a conducting band that surrounds the spacecraft in the spin plane. Some fraction of this band is always exposed to the ram plasma and after spin modulation has been removed from the signal a continuous derivation of the total ion concentration can be determined from this signal. The Ion Drift Meter (IDM) consists of a planar sensor that view along the ram direction once per spin. The arrival angle of the plasma with respect to the sensor is determined from the asymmetry in the current collected on segmented collectors inside the sensor (see Hanson and Heelis, Space Sci. Instrum., 1, 201, 1981). The collectors can be configured to measure either vertical (in the spin/orbit plane) or horizontal (perpendicular to the spin/orbit plane) arrival angles. Comparison of the change in the vertical arrival angle with that expected from the spacecraft spin yields the vertical ion drift velocity and the horizontal arrival angle measured near ram provides the horizontal ion drift velocity. B. OPERATIONAL _MODES: Nominal operation of the RPA and IDM provide a measure of the ion temperature, velocity and composition once per spin or approximately every 10 seconds. The RPA operation provides a normal ion current versus retarding potential (RPA) output and an electronically derived derivative output (RDA), each of which can be used to derive the ion temperature. The total ion concentration is available from the band collector at approximately 8 measurements/second with a 64 measurements/second burst for the 1 second period when the RPA is pointing approximately in the ram direction but data at this frequency requires careful removal of spin modulation effects and is not included in the data files provided here. C. MEASURED_PARAMETERS: The RPA provides a measure of the total ion concentration by incorporating the spacecraft velocity into the measured ion flux at zero retarding potential. The ion current versus retarding potential provides an input to a non-linear least-squares fitting procedure that derives the ion temperature and the ram energy of the ions. Upon removal of the ram energy due the spacecraft motion, the remaining signal may be assigned to the spacecraft potential if the ambient ion drift is assumed to be zero as is the case here. If two ion species with widely spaced masses are available in sufficient concentration, than an independent derivation of the ion drift and the vehicle potential is possible. D. PERFORMANCE_OF_THE_INSTRUMENT: The RPA and IDM performed well throughout the lifetime of the mission. Measurements were made in the altitude region 172 km to 594 km where O+ is the dominant ion at all times. The assumption of zero ram drift (compared to the spacecraft velocity) does not seriously effect the derivation of ion drift from the IDM. E. RESOLUTION: The RPA and IDM must view approximately along the ram direction in order to make reliable measurements. Thus the geophysical parameters of ion drift and temperature are available once per spin or approximately every 10 seconds. PARAMETERS: RPA and IDM parameters are incorporated into a single file together with key orbit position data all of which are tagged by universal date and time. DATA_SET_QUALITY: The RPA IDM data files have been initially screened for quality. Any obvious errors, due to lack of appropriate vehicle orientation information or to failure of the least-squares analysis routine, have been removed. Nevertheless, certain additional cautions should be exercised when examining this data. Ion temperatures below 500 K have been removed from the data set but caution should be exercised if brief excursions (one or two points) to temperatures below 1000 K are encountered. Drift velocities typically lie within + 200 m/s but a continuous time series of large almost constant velocity should be viewed with suspicion due to inadequate specification of the vehicle attitude. DATA_PROCESSING_OVERVIEW: A. DATA_PROCESSING CYCLE: All available data has been processed through a series of continuously refined algorithms. The data set quality is now the best that can be achieved without single point evaluation. B. HISTORY: Telemetry data and orbit data were transferred from NASA/GSFC to UTD for analysis. Specialized procedures for computing spacecraft spin rate have been employed that may not be the same as those used elsewhere in the San Marco program. DATA_USAGE: Usage of the data in these files is not formally restricted. Users are urged to contact the science or technical representatives before embarking on detailed analysis to avoid any unintended misuse of the data. DATA_ORGANIZATION: All geophysical data resides in a single file. Individual data records are spaced at approximately 10 second intervals (once per spin) when the satellite was turned on. CCSD$$MARKERmarkerabCCSD3KS00002markerac LOG_VOL_TIME_COVERAGE: 1988-04-20 TO 1988-12-04 TYPE_OF_FILE_TIME_COVERAGE: 1988-04-20T07:35:48 TO 1988-12-04T09:06:38 NAMING_CONVENTION: The single file containing all the RPA and IDM data is named SANMARCO_RPA.DAT FILE_TIME_COVERAGE: The data file contains the complete available San Marco RPA and IDM data set. PREV_LOG_VOL_TIME_COVERAGE: NONE CCSD$$MARKERmarkeracCCSD3RS00002markerad REFERENCETYPE=CCSDS2 LABEL=ATTACHED; REFERENCE="SANMARCO_RPA_FORMAT.SFD" LABEL=NSSD3IF0022600000001; REFERENCE="SANMARCO_RPA.DAT" CCSD$$MARKERmarkeradCCSD$$MARKERmarkerzz