PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2005-01-28 NOTE = "This file describes the Pioneer 11 Saturn HVM data sets provided by Joyce Wolf (of the HVM instrument team). The document was originally named 'SATURN.DOC'." END_OBJECT = TEXT END This file contains information concerning the Pioneer 11 Saturn data sets made available to UCLA for archiving purposes in April, 1994. For questions or problems, contact Joyce Wolf at JPL, 818-354-7361 (email jwolf@jplsp.jpl.nasa.gov). Contents: [1] Format of HVM (Helium Vector Magnetometer) Data Files [2] Format of Trajectory File [3] Saturn Encounter Data Processing [4] HVM Range Changes [5] Time Resolution (Sample Rate) [6] Transforming to Other Coordinate Systems ****************************************************************************** [1] Format of HVM Data Files High resolution data for 1979, Days 242 through 251, was placed in VAX binary flatfiles, one per day. Each record is 24 bytes long and contains 5 parameters: TIME, BXPE, BYPE, BZPE, BT. The first parameter is 8 bytes long, of type REAL*8; the other four are each 4 bytes long, of type REAL*4. TIME is the Ground Received Time of each field vector measurement. It is measured in seconds since 00:00, Jan 1, 1966. To convert to Spacecraft Event Time, you need to subtract the one-way light time from Earth to Pioneer 11. BXPE, BYPE, and BZPE are the components of the measured magnetic field in PE coordinates. Units are nanoteslas. The PE system has its Z axis along Pioneer's spin axis, which nominally points toward the Earth; its X axis is the unit vector in the direction of the vector cross product E x Z, where E is the north perpendicular to the Ecliptic; and Y = Z x X. BT is the magnitude of the magnetic field. Units are nanoteslas. Since these are high resolution data, with no averaging, BT is just the square root of the sum of the squares of the components. Some spikes and other bad points were edited and the values replaced by a flag of 1.E34. ****************************************************************************** [2] Format of Trajectory File The trajectory file, SATRAJ11.DAT, is a copy of a tape submitted to NSSDC. Each record contains the following parameters: SCTIME -- Spacecraft ephemeris time, in decimal days from day 244. GRTIME -- Ground received universal time, in decimal days from day 244. CC -- One way light time in seconds WLTAE -- AE system latitude of the P11-to-Earth vector WLNAE -- AE system longitude of the P11-to-Earth vector SLTAE -- AE system latitude of the P11-to-Sun vector SLNAE -- AE system longitude of the P11-to-Sun vector RLTAE -- AE system latitude of R, the Saturn-to-P11 vector RLNAE -- AE system longitude of R, the Saturn-to-P11 vector RLTKG -- KG system latitude of R RLNKG -- KG system longitude of R SDRAA -- The Sun-Saturn-P11 angle RR -- The magnitude of R, in Saturn radii. The format used was (2D20.10, 11F15.6). All angles are in degrees. The value used for Saturn's radius was 60000 km. The value used for the speed of light was 299792.458 km/sec. AE denotes the heliocentric system with the Earth's Ecliptic as the plane of reference and the +X axis in the direction of the Vernal Equinox (first point in Aries). KG denotes the Saturn-fixed coordinate system. The source for the values in SATRAJ11 was the post-encounter SEDR trajectory tape distributed by the Pioneer Project at Ames. The latitudes and longitudes were computed from the parameters on the tape as follows: WLTAE = -ATAN2D(ZPGSFF,SQRT(XPGSFF**2+YPGSFF**2) WLNAE = 180 + ATAN2D(YPGSFF,XPGSFF) where XPGSFF,YPGSFF,ZPGSFF are the components of the Earth-to-P11 vector, referred to the Ecliptic of 1950.0. SLTAE = -CELLTP, the celestial latitude of P11. SLNAE = CELLNP-180, where CELLNP is the celestial longitude of P11. RLTAE = ATAN2D(ZP1SFF, SQRT(XP1SFF**2+YP1SFF**2) RLNAE = ATAN2D(YP1SFF,XP1SFF) where XP1SFF,YP1SFF,ZP1SFF are the components of the Saturn-to-P11 vector, referred to the Ecliptic of 1950.0. RLTKG = B1LATP, Saturn-fixed latitude of P11. RLNKG = B1LONP, Saturn-fixed longitude of P11. ****************************************************************************** [3] Saturn Encounter Data Processing Reduction of the Saturn encounter HVM data was performed on a SEL/32 computer in the same way that the cruise data were processed; that is, raw vector measurements were decalibrated, despun into inertial spacecraft coordinates, rotated into the Pioneer Ecliptic system, and written in SEL binary format to an RDR tape. (RDR = Reduced Data Record.) However, in 1984 L. R. Doose (Pioneer 11 Photopolarimeter Imaging Team) provided Leverett Davis with more accurate determinations of the spacecraft roll orientation during the Saturn encounter. The new roll angles were supposed to have errors of less than 0.1 deg. Days 244 and 245 were reprocessed with these values, and a new RDR tape for days 242-251 was created. A minute average tape was calculated from this RDR tape and submitted to NSSDC in 1987 to replace the minute average tape submitted in 1983. The files on this RDR tape were converted to VAX binary flatfiles for the UCLA archive. Some spikes and other bad data were flagged. ****************************************************************************** [4] HVM Range Changes The HVM instrument has 8 ranges. Seven of those were employed during the Saturn encounter. Investigators using the high resolution data should be aware of the digitization levels at the different ranges; at the higher ranges, signals of amplitude less than one count are probably artifacts of the data reduction processing. Times in the following table are the Ground Received times of the start of the minute in which the range change occurred. GRT New Range Approximate Scale (nT per count) 242,00:00 0 0.015 243,18:14 1 0.051 244,03:05 2 0.17 10:52 3 0.58 13:33 4 2.5 15:35 5 15 17:06 6 88 19:21 5 15 20:25 4 2.5 23:06 3 0.58 245,03:08 2 0.17 08:14 1 0.051 246,03:41 0 0.015 (On days 246 and 247 the instrument switched between Range 0 and Range 1 a number of times.) ****************************************************************************** [5] Time Resolution (Sample Rate) The time resolution of the HVM data depended upon the P11 telemetry bit rate and telemetry format, both of which changed a number of times during the course of each day. The most common time resolution is 3/4 sec, but 3/8 sec is also frequently used. Times given in the following table are the Ground Received times of the start of the minute in which the change occurred. GRT New Time Resolution (sec) 242,00:00 0.375 00:35 0.75 08:55 0.375 19:56 0.75 243,01:54 0.375 03:24 0.1875 03:25 0.375 03:53 0.75 04:02 0.375 05:13 0.75 10:03 0.375 14:32 0.75 17:48 0.375 22:23 0.75 244,17:55 0.375 19:32 0.75 20:43 0.375 23:12 0.75 245,18:05 0.375 20:38 0.75 247,00:43 1.5 10:11 0.75 10:25 1.5 18:08 0.375 20:13 0.75 23:41 1.5 248,18:56 3.0 249,00:17 6.0 08:09 3.0 23:26 6.0 250,06:03 12.0 17:04 6.0 251,00:25 12.0 ****************************************************************************** [6] Transforming into Other Coordinate Systems Two Saturn-centered systems that were used in analysis were the RK system and KG system, defined below. In order to transform the magnetic field vectors from the PE system into these systems, we went from PE to AE (the celestial system referred to the Earth's Ecliptic and Equinox), and then from AE to RK to KG. The angles WLTAE,WLNAE, RLTAE, RLNAE, RLTKG, and RLNKG are available in the file SATRAJ11. See section [2]. PE (PIONEER ECLIPTIC) COORDINATE SYSTEM: This system is Pioneer-centered. It is defined by the vectors P and E: P is the direction of the Pioneer spin axis, which nominally points from Pioneer to Earth; E is the northward perpendicular to the ecliptic, which is just (0,0,1) in AE coordinates. The Z axis is along P; in AE coordinates, it is given by the unit vector U3 = (COS(WLTAE)*COS(WLNAE), COS(WLTAE)*SIN(WLNAE), SIN(WLTAE)). The X axis is the normalized cross product E x U3 / |E x U3|; it is parallel to the ecliptic plane, and is given in the AE system by U1 = (-SIN(WLNAE), COS(WLNAE), 0). The Y axis completes the right-hand orthogonal system, and is given by the cross product U2 = U3 x U1. The transformation matrix from PE to AE is composed of the three column vectors U1, U2, and U3. RK (PIONEER SATURN) COORDINATE SYSTEM: This is a Saturn-centered coordinate system, defined by the vectors R and K. R is the direction from the center of Saturn to Pioneer; K is the direction of the rotation axis of Saturn (value used was .0912749927, .4615744529, .8823932798). The X axis is given in AE by the unit vector U1 = R = (COS(RLTAE)*COS(RLNAE), COS(RLTAE)*SIN(RLNAE), SIN(RLTAE)). The Y axis is parallel to Saturn's equatorial plane, and is given by the normalized cross-product U2 = (K x U1) / |K x U1|. The Z axis completes the right-hand orthogonal system and is given by U3 = U1 x U2. The transformation matrix from AE to RK coordinates is composed of the row vectors U1, U2, and U3. KG (KRONOGRAPHIC) COORDINATE SYSTEM: This is a Saturn-fixed coordinate system, rotating with the planet, defined by the vectors K and G. K is the direction of Saturn's rotation axis, as above in Section 4.7, and G lies in Saturn's equatorial plane and in the direction of the prime meridian. The Z axis is along K, the X axis is along G, and the Y axis completes the orthogonal right hand system. One may compute the unit vectors of the RK system in KG coordinates as follows: U1 is the direction from the center of Saturn to Pioneer, given by (COS(RLTKG)*COS(RLNKG), COS(RLTKG)*SIN(RLNKG), SIN(RLTKG)). U2 is the normalized cross-product (K x U1) / |K x U1|, where in KG coordinates K is just (0,0,1). U3 completes the right-hand orthogonal system and is given by U1 x U2. The transformation matrix from RK to KG coordinates is composed of the column vectors U1, U2, and U3. (To transform to KG from other coordinate systems, first transform to AE, then to RK.) ****************************************************************************** (End)