Document title: Documentation for the NDADS PIONEER P10_HVM_IP_15M_ASCII datatype Project: PIONEER NDADS Datatype: P10_HVM_IP_15M_ASCII Super-EID: DOCUMENT There may be other documents also identified by this super-EID. NDADS filename: VOLDESC_HVM_IP_P10_15M.TX TRF entry: b46624.txt in NSSDC's controlled digital document library, Feb. 1998. Document text follows: ---------------------- CCSD3ZF0000100000001CCSD3VS00002MRK**001 /* SFDU document filename: FORMAT_HVM_IP_P10_15M.TXT NDADS Project/Datatype/EID = PIONEER/P10_HVM_IP_15M_ASCII/VOLDESC_SFD */ /* Note: file names referenced in this SFDU document have been changed for consistency with NDADS conventions and the renaming of the original data set files on tape from NSSDC data set 72-012A-01I */ Original_Vol_Ident: USA_NASA_NSSD_P10A_0001 Original_Vol_Creation_Date: 1992-06-30 Original_Medium_Description: Half-inch magnetic tape, 9 track, 6250 bpi Technical_Contact: Joyce E. Wolf Mail Stop 169-506 Jet Propulsion Laboratory 4800 Oak Grove Drive Pasadena, CA 91109 Electronic Mail (SPAN): JPLSP::JWOLF Phone: 818-354-7361 Prev_Vols: None CCSD$$MARKERMRK**001CCSD3SS00002MRK**002 Data_Set_Name: Pioneer 10 HVM Cruise Data Archive Data_Source: Pioneer 10 Helium Vector Magnetometer Scientific_Contact: Dr. Edward J. Smith Jet Propulsion Laboratory Mail Stop 169-506 4800 Oak Grove Drive Pasadena, CA 91109 Electronic Mail: JPLSP::ESMITH Telephone: 818-354-2248 Spacecraft_Characteristics: Launched on March 3, 1972, Pioneer 10 made its closest approach to Jupiter on Dec. 2, 1973. Since then, it has been heading out of the Solar System, downstream with respect to the direction of the interstellar wind. In 1990 it was 50 AU from the sun. The spacecraft's spin axis is directed toward the Earth. On board are twelve instruments for measuring fields and particles. The spacecraft is powered by radioisotope thermal generators (RTG's). Investigation_Objectives: The primary investigation objectives for the Pioneer 10 Helium Vector Magnetometer cruise data were to determine the large- scale structure and dynamics of the interplanetary magnetic field in the outer solar system and to study how they are influenced by changing solar activity. Instrument_Attributes: A. Instrument_Description: The Helium Vector Magnetometer produces measurements of the 3 orthogonal components of the ambient magnetic field in a 0-3 Hz passband. The instrument switches automatically among 8 ranges, plus or minus 4, 14, 42, 144, 640, 4000, 22000, and 140000 nT. The measurements are digitized to 8 bits and a sign bit, giving a sensitivity of 1/256 of full- scale in each range. For more information, refer to Smith, E. J., B. V. Connor, and G. T. Foster, Jr., "Measuring the magnetic fields of Jupiter and the outer solar system," IEEE Trans. Magn., vol. MAG-11, pp. 962-980, 1975. B. Instrument_Performance: The instrument performed normally until its failure in December, 1975. C. Measured_Parameters: 3 orthogonal components of magnetic field; third component is parallel to spacecraft spin axis. D. Instrument_Accuracy: Two factors determine the accuracy with which each component of the field is determined. One is the scale factor relating the change in field to the corres-ponding change in output voltage. The straight line representing this scale factor intercepts the B axis (V = 0) at a non- zero value (the instrument "offset" or "zero level"). The HVM is operated in a feedback mode so that the scale factor is highly linear and very stable. An in-flight calibration (IFC) is incorporated into the instrument such that, on receipt of a command, carefully calibrated step field changes are applied to the sensor to produce an end-to-end calibration of all three axes. During the lifetime of Pioneer 10 and 11, we performed an in-flight calibration approximately every two weeks. No change in instrument response as large as one bit has ever been observed on either instrument. Thus, the scale factors are considered known to within 0.25 percent, and, accordingly, the errors are negligible. Accurate estimates of the offsets must be determined in flight. Since Pioneer 10 is a spinning spacecraft with two magnetometer axes lying in the spin plane, two of the offsets can be continuously monitored by averaging the data on a given axis over a large number of revolutions. By analyzing the results over many long intervals, it is estimated that these two offsets are being determined to within 0.005 nT. The offset on the sensor axis parallel to the spin axis is more difficult to determine. We use the method developed by Davis and Smith (also independently developed by Hedgecock), as improved upon by Belcher. The basis of this so- called variance method is to choose the BZ offset so as to reduce the variations in B-magnitude to a minimum in the least squares sense. Experience indicates that the method yields a relative accuracy of about 5 percent. Data_Set_Parameters: Averages of field components (BX, BY, BZ); averages of squares and crossproducts of components (BX2, BY2, BZ2 and BXBY, BXBZ, BYBZ); averages of field direction cosines (BXCOS, BYCOS, BZCOS); average of field magnitude (BMAG) and average of square of field magnitude (BMAG2). Heliocentric positions of the spacecraft and Earth, referred to the ecliptic and equinox of date. are also included. Data_Set_Quality: There are no significant known errors in the data. Data_Processing_Overview: Data reduction was done on an IBM 7044 and a Univac 1108. Raw data points consisted of Ground Received Time, triaxial magnetometer measurements in counts (0 to 511), and magnetometer range (0 to 7). Each measurement was converted into nanotesla using range-dependent scaling factors and offsets. Spin-plane offsets were calculated daily by averaging spinning data, and are estimated to have errors of less than .005 nT. The other offset (parallel to the spin axis) was estimated over periods of several weeks using either the Leverett Davis method of minimizing the variance of the square of the magnitude, or John Belcher's variation of that method; errors are estimated at less than .02 nT. The magnetic field vectors were then despun into spacecraft inertial coordinates and rotated through the roll angle CKAH (Clock Angle of Sun, provided by Ames in File 3 on our EDR tapes). These field vectors were transformed from PE to SH (or SJ during Jupiter Encounter) before being written onto the RDR tapes. (In the PE system, Z is along the Pioneer spin axis, nominally toward Earth, and X lies in the plane containing the directions from Pioneer to the Earth and Sun and is orthogonal to the spin axis, Z. In SH, also known as Radial-Tangential-Normal, X is the Sun-to- Pioneer direction and Y is parallel to the Sun's equatorial plane. For a complete definition of these systems, see the description of COORDSYS in file FORMAT_HVM_IP_P10_15M.TXT.) From the RDR tapes, Ground Received Time 1-minute, 1-hour, and 1-day averages of the field components, crossproducts of components, squares of components, direction cosines of components, field magnitude, and square of field magnitude were calculated and submitted on tapes to NSSDC. For this cruise data archive, each 15-minute (or 1 hour) Spacecraft Event Time parameter average has been constructed from those GRT 1-minute parameter averages whose midpoints (converted to SCET) lie within the SCET averaging interval. The number of seconds in each minute for which data existed was used as a weighting factor. Lit_References: Smith, E. J., B. V. Connor, and G. T. Foster, Jr., "Measuring the magnetic fields of Jupiter and the outer solar system," IEEE Trans. Magn., vol. MAG-11, pp. 962-980, 1975. Other references may be found in these articles. CCSD$$MARKERMRK**002CCSD3KS00002MRK**003 Vol_Time_Coverage: 1972-03-03 through 1975-11-17. File_Naming_Convention: Pioneer 10 HVM average files on NDADS are named according to the time of the data in the file as follows: yyddd_yyddd_HVM_IP_P10_15M.ASC where yyddd_yyddd (dates in year & day of year) gives the start and stop dates for the 15-minute Pioneer 10 interplanetary data set from HVM in ascii format. The start and end dates are set at, or within, consecutive six month intervals (e.g., Jan. 1 - June 30, July 1 - Dec. 31). File_Time_Coverage: Datatype/EID = P10_HVM_IP_15M_ASCII/yyddd_yyddd NDADS File Name Date Coverage (yy-mm-dd) 72063_72182_HVM_IP_P10_15M.ASC 1972-03-03 through 1972-06-30. 72183_72366_HVM_IP_P10_15M.ASC 1972-07-01 through 1972-12-31. 73001_73181_HVM_IP_P10_15M.ASC 1973-01-01 through 1973-06-30. 73182_73365_HVM_IP_P10_15M.ASC 1973-07-01 through 1973-12-31. 74001_74181_HVM_IP_P10_15M.ASC 1974-01-01 through 1974-06-30. 74182_74365_HVM_IP_P10_15M.ASC 1974-07-01 through 1974-12-31. 75001_75181_HVM_IP_P10_15M.ASC 1975-01-01 through 1975-06-30. 75182_75321_HVM_IP_P10_15M.ASC 1975-07-01 through 1975-11-17. /* Please note that data file 73182_73365_HVM_IP_P10_15M.ASC contains data from the Jupiter Encounter: 1973-11-25 through 1973-12-15. These 21 days are in the SJ coordinate system, not the SH system used for interplanetary data. See the format file FORMAT_HVM_IP_P10_15M.TXT for coordinate system definitions. */ CCSD$$MARKERMRK**003CCSD3RF0000300000001 REFERENCETYPE=$VMS; LABEL=ATTACHED; REFERENCE=FORMAT_HVM_IP_P10_15M.TXT; /* Project/Datatype/EID = PIONEER/P10_HVM_IP_15M_ASCII/FORMAT_SFD */ LABEL=NSSD3IF0012100000001; REFERENCE= *_HVM_IP_P10_15M.ASC /* Project/Datatype/EID = PIONEER/P10_HVM_IP_15M_ASCII/yyddd_yyddd */