0055NSSDCA::ANON_DIR:[COHO.P10MAG.MINUTE]P10HVM_15M.SFD00040083Note: this document is an extract from the SFDU metadata text for the 15-minute0081averaged IMF data in NSSDC data set 72-012A-01I. The mission, experiment, and0080data processing details also apply to the 1-minute data, except that the new0081one-minute data in 72-012A-01J have been supplied to NSSDC in RTN coordinates0080with SCET-UT times.                                                         00040024								JFC  7/12/9500040083===============================================================================0044CCSD3ZF0000100000001CCSD3VS00002MRK**00100040026/* VOLDESC.SFD file */00040038Technical_Contact:      Joyce Wolf0045                        Mail Stop 169-5060053                        Jet Propulsion Laboratory0048                        4800 Oak Grove Drive0046                        Pasadena, CA 9110900040065                        Electronic Mail (SPAN):  JPLSP::JWOLF0048                        Phone:  818-354-7361000400040044CCSD$$MARKERMRK**001CCSD3SS00002MRK**00200040062Data_Set_Name:          Pioneer 10 HVM Cruise Data Archive00040065Data_Source:            Pioneer 10 Helium Vector Magnetometer00040047Scientific_Contact:     Dr. Edward J. Smith0053                        Jet Propulsion Laboratory0045                        Mail Stop 169-5060048                        4800 Oak Grove Drive0046                        Pasadena, CA 9110900040059                        Electronic Mail:  JPLSP::ESMITH0051                        Telephone: 818-354-224800040079Spacecraft_Characteristics:  Launched on March 3, 1972, Pioneer 10 made its0081closest approach to Jupiter on Dec. 2, 1973.  Since then, it has been heading0076out of the Solar System, downstream with respect to the direction of the0058interstellar wind.  In 1990 it was 50 AU from the sun.00040081The spacecraft's spin axis is directed toward the Earth.  On board are twelve0081instruments for measuring fields and particles.  The spacecraft is powered by^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^0044radioisotope thermal generators (RTG's).000400040076Investigation_Objectives:   The primary investigation objectives for the0082Pioneer 10 Helium Vector Magnetometer cruise data were to determine the large-0082scale structure and dynamics of the interplanetary magnetic field in the outer0081solar system and to study how they are influenced by changing solar activity.00040026Instrument_Attributes:00040071A.  Instrument_Description: The Helium Vector Magnetometer produces0082measurements of the 3 orthogonal components of the ambient magnetic field in a00800-3 Hz passband.  The instrument switches automatically among 8 ranges, plus0079or minus 4, 14, 42, 144, 640, 4000, 22000, and 140000 nT.  The measurements0082are digitized to 8 bits and a sign bit, giving a sensitivity of 1/256 of full-0076scale in each range.  For more information, refer to Smith, E. J., B. V.0080Connor, and G. T. Foster, Jr., "Measuring the magnetic fields of Jupiter and0079the outer solar system," IEEE Trans. Magn., vol. MAG-11, pp. 962-980, 1975.00040077B.  Instrument_Performance:   The instrument performed normally until its0030failure in December, 1975.000400040079C.  Measured_Parameters:   3 orthogonal components of magnetic field; third0050component is parallel to spacecraft spin axis.000400040081D.  Instrument_Accuracy:   Two factors determine the accuracy with which each0079component of the field is determined.  One is the scale factor relating the0081change in field to the corres-ponding change in output voltage.  The straight0079line representing this scale factor intercepts the B axis (V = 0) at a non-0057zero value (the instrument "offset" or "zero level").00040077The HVM is operated in a feedback mode so that the scale factor is highly0080linear and very stable.  An in-flight calibration (IFC) is incorporated into0080the instrument such that, on receipt of a command, carefully calibrated step0080field changes are applied to the sensor to produce an end-to-end calibration^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^0081of all three axes.  During the lifetime of Pioneer 10 and 11, we performed an0081in-flight calibration approximately every two weeks.  No change in instrument0077response as large as one bit has ever been observed on either instrument.0077Thus, the scale factors are considered known to within 0.25 percent, and,0043accordingly, the errors are negligible.00040082Accurate estimates of the offsets must be determined in flight.  Since Pioneer007610 is a spinning spacecraft with two magnetometer axes lying in the spin0081plane, two of the offsets can be continuously monitored by averaging the data0081on a given axis over a large number of revolutions.  By analyzing the results0078over many long intervals, it is estimated that these two offsets are being0034determined to within 0.005 nT.00040080The offset on the sensor axis parallel to the spin axis is more difficult to0082determine.  We use the method developed by Davis and Smith (also independently0079developed by Hedgecock), as improved upon by Belcher. The basis of this so-0073called variance method is to choose the BZ offset so as to reduce the0081variations in B-magnitude to a minimum in the least squares sense. Experience0076indicates that the method yields a relative accuracy of about 5 percent.00040078Data_Set_Quality:       There are no significant known errors in the data.00040082Data_Processing_Overview:  Data reduction was done on an IBM 7044 and a Univac00091108.00040076Raw data points consisted of Ground Received Time, triaxial magnetometer0077measurements in counts (0 to 511), and magnetometer range (0 to 7).  Each0082measurement was converted into nanotesla using range-dependent scaling factors0080and offsets.  Spin-plane offsets were calculated daily by averaging spinning0082data, and are estimated to have errors of less than .005 nT.  The other offset0081(parallel to the spin axis) was estimated over periods of several weeks using0080either the Leverett Davis method of minimizing the variance of the square of^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^0073the magnitude, or John Belcher's variation of that method; errors are0034estimated at less than .02 nT.00040072The magnetic field vectors were then despun into spacecraft inertial0076coordinates and rotated through the roll angle CKAH (Clock Angle of Sun,0075provided by Ames in File 3 on our EDR tapes).  These field vectors were0075transformed from PE to SH (or SJ during Jupiter Encounter) before being0079written onto the RDR tapes.  (In the PE system, Z is along the Pioneer spin0072axis, nominally toward Earth, and X lies in the plane containing the0078directions from Pioneer to the Earth and Sun and is orthogonal to the spin0077axis, Z.  In SH, also known as Radial-Tangential-Normal, X is the Sun-to-0077Pioneer direction and Y is parallel to the Sun's equatorial plane.  For a0081complete definition of these systems, see the description of COORDSYS in file0016FORMAT.SFD.)00040081From the RDR tapes, Ground Received Time 1-minute, 1-hour, and 1-day averages0080of the field components, crossproducts of components, squares of components,0073direction cosines of components, field magnitude, and square of field0062magnitude were calculated and submitted on tapes to NSSDC.00040082For this cruise data archive, each 15-minute (or 1 hour) Spacecraft Event Time0076parameter average has been constructed from those GRT 1-minute parameter0078averages whose midpoints (converted to SCET) lie within the SCET averaging0078interval.  The number of seconds in each minute for which data existed was0031used as a weighting factor.00040078Lit_References:         Smith, E. J., B. V. Connor, and G. T. Foster, Jr.,0083                        "Measuring the magnetic fields of Jupiter and the outer0074                        solar system," IEEE Trans. Magn., vol. MAG-11,0046                        pp. 962-980, 1975.00040076                        Other references may be found in these articles.000400040024CCSD$$MARKERMRK**0020004^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^