Document title: VOLDESC.SFD for NDADS DE NACS_ASCII datatype Project: DE NDADS Datatype: NACS_ASCII Super-EID: DOCUMENT There may be other documents also identified by this super-EID. NDADS filename: NACS_VOLDESC_DE.SFD TRF entry B46557.txt in NSSDC's controlled digital document library. Feb. 1998. Document text follows: ---------------------- VOLDESC UPDATE *********** APRIL 1995 ************ dieter bilitza This is the PI-provided SFDU VOLDESC file for the first of the seven tapes. The time periods covered by the different tapes are as follows: LOG_VOL_TIME_COVERAGE: 1981-08-08 TO 1981-11-15 LOG_VOL_TIME_COVERAGE: 1981-11-16 TO 1982-01-19 LOG_VOL_TIME_COVERAGE: 1982-01-20 TO 1982-04-29 LOG_VOL_TIME_COVERAGE: 1982-04-30 TO 1982-07-18 LOG_VOL_TIME_COVERAGE: 1982-07-19 TO 1982-10-16 LOG_VOL_TIME_COVERAGE: 1982-10-17 TO 1982-12-31 LOG_VOL_TIME_COVERAGE: 1983-01-01 TO 1983-02-15 VOLDESC UPDATE *********** APRIL 1995 ************ dieter bilitza CCSDXZLM0001SMARK001CCSDXVNM0002SMRK0001 LOG_VOL_IDENT: USANASANSSDDEB3_0001 LOG_VOL_CLOSING_DATE: 1990-05-16 LOG_VOL_FILE_STRUCTURE: STANDARD LABEL WITH VAX FILES-11 TAPE_DENSITY=6250 BPI TAPE_TRACKS=9 TAPE_LENGTH=2400 INCHES COMPUTER_MFGR: DIGITAL EQUIPMENT CORPORATION OPERATING_SYSTEM: MICROVMS 4.7 COMPUTER_SYSTEM: MICRO VAX II TECHNICAL_CONTACT: DR. A. E. HEDIN CODE 614 NASA/GSFC GREENBELT, MD 20771 PHONE: 301-286-8393 SPAN: PACF::HEDIN PREV_LOG_VOL_IDENT: NONE CCSDXVNM0002EMRK0001CCSDXKNM0002SMRK0003 DATA_SET_NAME: MAF AMBIENT DENSITES DATA_SOURCES: DYNAMICS EXPLORER B, NEUTRAL ATMOSPHERE COMPOSITION SPECTROMETER (NACS) INVESTIGATOR_CONTACT: MR. G. C. CARIGNAN SPACE PHYSICS RESEARCH LABORATORY UNIVERSITY OF MICHIGAN ANN ARBOR, MI 48109 PHONE: 313-764-9462 SPAN: SPRLB::CARIGNAN 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 mag- netosphere, 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 tem- perature spectrometer, Fabry-Perot interferometer, 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, all- owing 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 original- ly targeted at 30%. The lifetime of the spacecraft was shorter than anti- cipated because of the less than nominal performance of the launch vehicle. The launch was on Aug. 3, 1981 and the DE-2 satellite reentered the atmosphere on Feb. 19, 1983, with the last contact the day before. TIME_SPAN_OF_THE_DATA: 8-AUG-81 TO 15-JAN-83 INVESTIGATION_OBJECTIVES: The NACS objective was to provide high resolution measurements of the abundances of neutral species with particular emphasis on variability driven by interactions in the atmosphere-ionosphere-magnetosphere system. INSTRUMENT_ATTRIBUTES: A. DESCRIPTION_OF_INSTRUMENT: The Neutral Atmosphere Composition Spectrometer (NACS) was a quadrupole mass spectrometer employing an electron beam ion source operating in the closed mode and a discrete dynode multiplier detector operating in the counting mode. The gas inlet orifice to the gold plated antechamber was pointed along the orbit path during normal spacecraft despun operations. The mass selection and instrument voltage levels, etc. could be changed on command allowing a large variety of modes. (See Carignan et al., The neutral mass spectrometer on Dynamics Explorer, Space Science Instrumentation, 5, 429-411, 1981.) B. OPERATION_MODE: The nominal mode of operation sampled 8 different masses (4, 14, 16, 30, 32, and 40) every 1/8 second. Occasionally the sweep mode was employed (sampling 256 mass positions between 0 and 51 amu) in order to check instrument performance. C. MEASURED_PARAMETERS: Output counts from the detector were converted to particle density in the ion source antechamber based on prelaunch calibration factors. Source densities were corrected by subtraction of background or minimum densities determined from spinning orbits and converted to ambient densities based on simple gas kinetic equations for a moving vehicle. Atomic oxygen was assumed to completely recombine in the ion source. Atomic nitrogen was assumed to combine with atomic oxygen in the ion source. Densities were obtained for helium (from mass 4), atomic oxygen (from mass 32 or 16), molecular nitrogen (from mass 28 or 14), argon (from mass 40), and atomic nitrogen (from mass 30). D. PERFORMANCE_OF_THE_INSTRUMENT: The NACS instrument returned usable data from shortly after launch until the spacecraft reentered the atmosphere (Feb. 19, 1983). This was occasionally interrupted by very brief periods in which the spacecraft was placed in a spinning mode. Data during these periods are used for background determination and special processing. The detector multiplier gain increased steadily after launch until reduced by command on 30 March 1982. Output counts were corrected for a small dependence on the multiplier gain. Prelaunch calibration was marred by laboratory equipment problems which resulted in larger than anticipated uncertainty in absolute values. E. RESOLUTION: Each MAF record contains ambient densities averaged over one second. For each second, there will normally be 8 samples of a given mass. PARAMETERS: The MAF files contain: The time of the midpoint of the data and ambient densities for atomic oxygen(O), molecular nitrogen(N2), helium(He), atomic nitrogen(N), and argon(AR). Relative errors are contained in the lowest eight bits of each density word. DATA_SET_QUALITY: Data quality below 500 km is generally quite good. Quality deteriorates at higher altitudes as oxygen and molecular nitrogen approach their background values (which could only be determined from infrequent spinning orbits) and the count rate for Ar becomes low. The difference between minimum (background) and maximum count rate for atomic nitrogen (estimated from mass 30) was so small that results are generally poor without special processing not included in this data set. Data were lost between 12 March 1982 and 31 March 1982 when the counter overflowed. Relative errors are packed into the ambient density word but do not include a 25% absolute calibration error. DATA_PROCESSING_OVERVIEW: A. DATA_PROCESSING_CYCLE: The raw telemetry data are routinely converted into source density files in mission analysis file format (MAF) and then to ambient density files in MAF format. Source density files were not generally saved. There is usually one final MAF file per pass (tape recorder on time). B. HISTORY: MAF files were produced routinely as telemetry became available. Telemetry was rescanned for missing passes at later times. Duplicate passes or parts of passes should have been eliminated and separate segments joined. The extreme segmentation or length of some telemetry passes resulted in the inability of the Sigma 9 to bring all the data on line within the alloted processing time and results in some passes still being incomplete. Files were initially produced with a calibration constant which was later changed, based on re-examination of laboratory data and equipment. All files have been updated to final values. DATA_USAGE: Data are used to obtain the ambient densities for atomic oxygen(O), molecular nitrogen(N2), helium(He), atomic nitrogen(N), and argon(AR). Data quality below 500 km is generally quite good. Quality deteriorates at higher altitudes as oxygen and molecular nitrogen approach their background values (which could only be determined from infrequent spinning orbits) and the count rate for Ar becomes low. The difference between minimum (background) and maximum count rate for atomic nitrogen (estimated from mass 30) was so small that results are generally poor without special processing not included in this data set. Data were lost between 12 March 1982 and 31 March 1982 when the counter overflowed. DATA_ORGANIZATION: SEE CONTENTS IN NSSD0007 CCSDXKNM0002EMRK0003CCSDXKNM0002SMRK0005 LOG_VOL_TIME_COVERAGE: 1981-08-08 TO 1981-11-15 NAMING_CONVENTION: File names are of the form Nydddsssc, where: the letter N is at the beginning of all files, y is the last digit of the year 1981 to 1983; ddd is the daycount (Jan 1 = 1); sss is the high order hundreds of seconds of the first data point (time=sss*100 sec); and c is 0 or other arbitrarily assigned integer. FILE_TIME_COVERAGE: Filenames and start and stop times and dates are listed in the NACS_START_STOP_TIMES_DE.DOC inventory file. PREV_LOG_VOL_COVERAGE: NONE CCSDXKNM0002EMRK0005CCSDXRNM0003SMRK0006 NESTING= L REF= FORMAT.SFD CCSDXRNM0003EMRK0006CCSDXRLM0003SMRK0007 ADI= NSSD0007 CLASS= I NESTING= N SCOPE= EACH REF=N*.* CCSDXRLM0003EMRK0007CCSDXZLM0001EMARK001