The following description applies to the Ulysses Magnetometer and Ephemeris data files for the 1992 Jupiter Encounter, submitted in June 1996 by Joyce Wolf for the Ulysses Magnetometer Team at JPL and Imperial College (A. Balogh, Principal Investigator). Files and Data Coverage The data set covers the period Jan 25 through Feb 18, 1992 (days 25 to 48 inclusive). Files VHMxx_xx.TAB and FGMxx_xx.TAB contain one minute averages of the magnetic field components and magnitude measured by either the VHM (Vector Helium Magnetometer) or FGM (Fluxgate Magnetometer), where xx_xx = Days of Year covered (25 = Jan 25). The three days of closest approach (38-40) are FGM; the others are VHM. The file DATA/EPHEM/TRJxx_xx.TAB contains positions and attitude of Ulysses. Time resolution is the same as the final SEDR: 1 minute for Days 32-47, 3 hours for Days 25-31, 1 hour for Day 48. File Formats Each line in the VHM/FGM files contains time in the format yyyy-mm-ddThh:mm:ss.sssZ (0000 hrs on Jan 25, 1992 would be 1992-01-25T00:00:00.000Z), BR, BTHETA, BPHI, BMAGNITUDE in the format (1x,a24, 4f10.3). The time tag is the midpoint of the one minute averaging interval. BMAGNITUDE is the average of the field magnitude, not the magnitude of the average field vector. Field units are nT. BR, BTHETA and BPHI are one-minute averages of the field components in R-THETA-PHI coordinates (see below). Each line of the TRJ file contains time in the format yyyy-mm-ddThh:mm:ss.sssZ (0000 hrs on Jan 25, 1992 would be 1992-01-25T00:00:00.000Z), R, RLATJG, RLONJG, RLATEC, RLONEC, AXISLAT, AXISLON, XSU, YSU, ZSU in the format (1x,a24, 1x,f10.5, 6(1x,f8.3), 3(1x, 1pe15.8) ). R is the distance from Jupiter to Ulysses measured in RJ (1 RJ = 71398 km). The next 6 parameters are angles measured in deg. RLATJG and RLONJG are the latitude and west longitude of Ulysses in the Jovigraphic System III (1965.0). RLATEC and RLONEC are the latitude and longitude of the Jupiter-to-Ulysses unit vector in ECL50 (Earth Mean Ecliptic and Equinox of 1950.0). AXISLAT and AXISLON are the latitude and longitude of the Ulysses spin axis in ECL50. XSU, YSU, and ZSU are the Cartesian components of the Sun-to-Ulysses vector in ECL50. Coordinate System The field components are given in the R-THETA-PHI system, which is that conventionally used for comparison with models. The R axis is from Jupiter to Ulysses; the THETA axis is perpendicular to R and lies in the plane containing R and Jupiter's rotation axis and is positive southward; PHI completes the orthogonal right-handed system. The TRJ file contain all the parameters necessary to transform the field components into System III, ECL50, or inertial spacecraft coordinates. See Computation of Coordinate Transformations, below. Data Processing VHM files were produced by first averaging high resolution (1s or 2s) field data in inertial spacecraft coordinates. Then the averages were transformed into R-THETA-PHI coordinates, using parameters from the Final SEDR (Supplementary Experiment Data Records). FGM files were produced in a similar manner by R.J. Forsyth at Imperial College. All files were then reformatted at the PDS/PPI Node to provide time tags consistent with those used on the rest of the ULYSSES JUPITER ENCOUNTER CD-ROM, and merged into multiple day files. TRJ files are simply convenient extractions of parameters from the Final SEDR. Which were reformatted and merged at PDS/PPI Node in same manner as were the VHM/FGM files. Accuracy Since the VHM sensor has greater resolution (4 pT in the +/- 8 nT range), it was decided that the best quality dataset would consist of VHM data for the majority of the encounter period and FGM for days 38-40 when the VHM was in saturation. We feel that both VHM and FGM datasets have been individually calibrated to the best level that we can achieve at this time. It is possible that further small improvements could be made in the cross calibration between the two sensors; in the present dataset the differences between VHM and FGM at the beginning of day 38 and at the end of day 40 are less than 0.5 nT. For the position of Ulysses in Jupiter-centered coordinates, 1-sigma uncertainties are less than 1 part in 1 million, or less than 0.5 km at closest approach. The attitude of Ulysses during the Jupiter encounter interval is stated to be accurate within +/- 0.005 degrees. Computation of Coordinate Transformations The paragraphs below give methods for computing transformation matrices using trajectory parameters from the TRJ files. As an alternative, note that the appendix in [Smith 1993] contains the orbital elements of Ulysses with respect to Jupiter and demonstrates how to calculate the position of Ulysses in System III and other coordinate systems without recourse to trajectory data files. The transformation matrix from R-THETA-PHI to System III (1965.0) consists of the column vectors of the R, THETA, and PHI axes expressed in System III. The R-axis in System III is cos(RLATJG) cos(360-RLONJG), cos(RLATJG) sin(360-RLONJG), sin(RLATJG). The PHI axis is the normalized crossproduct J x R, where J is the rotation axis which is just 0,0,1, so the unit vector in the PHI direction is -sin(360-RLONJG), cos(360-RLONJG), 0. The unit vector in the THETA direction is the crossproduct PHI x R = sin(RLATJG) cos(360-RLONJG), sin(RLATJG) sin(360-RLONJG), -cos(RLATJG). The transformation matrix from R-THETA-PHI back to ECL50 consists of the column vectors of the R, THETA, and PHI axes expressed in ECL50. R is cos(RLATEC) cos(RLONEC), cos(RLATEC) sin(RLONEC), sin(RLATEC). PHI is the normalized crossproduct J x R, where J (North Pole of Jupiter) is given in the reference [Smith 1993] as -92.002 RA, 64.504 DEC, Earth Mean Equinox and Equator 1950.0. Rotating by 23.4458 deg (1950.0 obliquity) gives J in ECL50 = (-.015037545, -.035534090, 0.999255323). The THETA axis is PHI x R. Inertial spacecraft coordinates are defined as follows: Z is the Ulysses spin axis, which points approximately towards Earth; X is is perpendicular to Z and lies in the plane containing Z and S, where S is the Ulysses-to-Sun vector. X is positive toward the Sun. Z in ECL50 is cos(AXISLAT) cos(AXISLON), cos(AXISLAT) sin(AXISLON), sin(AXISLAT). S in ECL50 is -XSU, -YSU, -ZSU. The Y axis is the normalized crossproduct Z x S, and the X axis is Y x Z. The transformation matrix from ECL50 back to inertial spacecraft coordinates consists of the column vectors X, Y, and Z. The TRJ files in this submission include all the parameters necessary to calculate the above transformations. In a few cases where the direction of the spin axis was not available in the SEDR, the Ulysses-to-Earth direction was substituted in the TRJ files. It is suggested that interpolations in time be performed on vector components rather than angles in order to avoid difficulties near 0 or 360, and that double precision arithmetic be used in matrix multiplication. References Smith, E.J., and Wenzel, K.-P. Introduction to the Ulysses Encounter with Jupiter, J. Geophys. Res., 98, 21111, 1993. Balogh, A., et al. The magnetic field investigation on the Ulysses mission: Instrumentation and preliminary scientific results, Astron. Astrophys. Suppl. Ser., 92, 221, 1992a. Balogh, A., et al. Magnetic field observations during the Ulysses flyby of Jupiter, Science, 257, 1515-1518, 1992. Technical Contact Joyce Wolf JPL 169-506 4800 Oak Grove Drive Pasadena, CA 91109 Phone 818-354-7361 Email jwolf@jplsp.jpl.nasa.gov