**NSSDCA ID:** PSFP-00294

**Availability:** Archived at NSSDC, accessible from elsewhere

This description was generated automatically using input from the Planetary Data System. Overview ======== This data set contains the attitude data for the rotor of the Galileo spacecraft. The data provided are derived from the Attitude and Articulation Control System (AACS) data downlink as provided by the Galileo project to the magnetometer team. This data set covers portions of the Jupiter Approach (JA) and all orbit operation mission phases (J0-J35). The data are discontinuous. The sampling frequency varies with mission phase. The coverage period is from 1995-11-28T01:34 to 2001-09-21 (exact time of last sample is currently unknown). Data Sampling ============= The data set is derived from 3 downlink sources, depending on the mission phase. During the recorded intervals, attitude data are played back with the other recorded fields and particles data. During these periods data are available every minor frame (~2/3 second). Attitude data in these periods are all sampled at the same time, no interpolation is required. When real-time Science (RTS) data are being acquired, attitude data are acquired simultaneously once every 5 major frames (~5 minutes). When neither RTS or recorded data are being acquired, AACS data are only returned in the engineering stream, not as a true data stream. The data during these intervals are subcommutated. Right Ascension (RA), Declination (DEC), and Rotor Twist values are not synchronously sampled. In order to make the data from these intervals useful, the RA and DEC data have been linearly interpolated to the time of the twist samples. Samples from these intervals are available about once every two hours. Only the MAG and DDS instruments acquire data during these mission phases. This sampling frequency is adequate given the long averages acquired by these instruments during these mission phases. Data Processing =============== When data are simultaneously available from all three AACS channels, no processing is applied other than to convert data numbers into radians. When data are not simultaneously sampled, the RA and DEC values are linearly interpolated between samples to the time of the TWIST samples. Beginning in Phase 2A, the rotor spin angle was no longer included in the downlink. This value is calculated on the ground by using the values of RA, DEC, and TWIST and the difference between Earth's equatorial and ecliptic poles. The EME-50 to System III (1965) rotation matrix is computed by using the SPICE SPK kernel S980326B.XSP (final prime mission reconstruction). These values can be reproduced by using the following pseudo-code fragment: INTEGER I, LU CHARACTER*24 SCLK DOUBLE PRECISION ET, E502J2K (3,3), J2K2S3(3,3), E502S3(3,3) C C Load Kernels C CALL CLPOOL() CALL LDPOOL ('P_CONST.KER') CALL LDPOOL ('LEAP_SEC.KER') CALL LDPOOL ('P_CONST.KER') CALL SPKLEF ('GLL_JUP.SPK', LU) C C Begin loop through data, reading a sclk and computing a matrix C READ (10, 999) SCLK CALL SCS2E (-77, SCLK, ET) CALL IRFTRN ('FK4', 'J2000', E502J2K) CALL BODMAT (599, ET, J2K2S3) C C Reverse sign of row three to make system left handed C DO 10, I = 1, 3 10 J2K2S3(3,I) = -J2K2S3(3,I) CALL MXM(E502J2K, J2K2S3, E502S3) C End loop, E502S3 contains the EME50 -> System III rotation matrix Data ==== All data are archived in a single ASCII table. Column Type Description <units> -______________________________________________________________ time char Spacecraft event time (UTC), PDS time format. sclk char Spacecraft clock counter. RA real Rotor right ascension, EME-50. <radians> DEC real Rotor declination, EME-50. <radians> TWIST real Rotor EME-50 spin phase angle. <radians> SPIN real Rotor ECL-50 spin phase angle. <radians> A11 real EME50->SYS3 matrix row 1, column 1 value. A12 real EME50->SYS3 matrix row 1, column 2 value. A13 real EME50->SYS3 matrix row 1, column 3 value. A21 real EME50->SYS3 matrix row 2, column 1 value. A22 real EME50->SYS3 matrix row 2, column 2 value. A23 real EME50->SYS3 matrix row 2, column 3 value. A31 real EME50->SYS3 matrix row 3, column 1 value. A32 real EME50->SYS3 matrix row 3, column 2 value. A33 real EME50->SYS3 matrix row 3, column 3 value. Ancillary Data ============== There are several SPICE kernels used in the production of this data set. All of the SPICE kernels used to produce this data set are contained on the MWG archive volume DVD in the EXTRAS/SPICE/KERNELS directory. The kernels (PDS PRODUCT_ID) used to create this were: S980326B.TSP - Prime Mission Reconstruction (JA - E12) S000131A.TSP - GEM reconstruction (E12-E26) S020128A.TSP - GMM (I27-I33) reconstruction, A34/J35 predict. MK00062B.TSC - Galileo spacecraft clock kernel. NAIF0007.TLS - Leapseconds kernel. PCK00006.TPC - Planetary constants kernel. Coordinates =========== The basic rotor coordinate system has its Z-axis aligned with the spin axis (positive in the opposite direction as the HGA) and its +Y-axis pointing outward from the spacecraft body along the magnetometer boom. X completes the right handed set. This coordinate system spins with the rotor at a period of approximately 19 seconds. Earth Mean Equator and dynamical equinox of Besselian year 1950 (EME-50) is an inertial coordinate system used by the Galileo project for navigation purposes. This system also commonly known as Fundamental Catalog (4) or 'FK4' by the SPICE software. At the reference epoch, this system has its +Z axis parallel to the Earth's north pole and its +X axis points to the first point of Aries. System III (1965) is the standard planetographic (left handed) coordinate system as defined by the IAU for Jupiter [DESSLER1983]. The Central Meridian Longitude is taken at 00 UTC on January 1, 1965. The rotation period for Jupiter is defined to be 9h 55m 29.71s (870.536 deg/day).

- GO-J-POS-6-REDR-ROTOR-ATTITUDE-V1.0

- Planetary Science: Fields and Particles

Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II

Name | Role | Original Affiliation | |
---|---|---|---|

Mr. Steven P. Joy | Data Provider | University of California, Los Angeles | sjoy@igpp.ucla.edu |

Mr. Steven P. Joy | General Contact | University of California, Los Angeles | sjoy@igpp.ucla.edu |

Mr. Bill Harris | General Contact | University of California, Los Angeles | bharris@igpp.ucla.edu |