PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2019-10-04 NOTE = "SP-Kernel Information" END_OBJECT = TEXT END General information about SPICE SP-kernels ========================================== The purpose of the SP-kernel (SPK), which stands for S(pacecraft) and P(lanet) Kernel, is to allow ephemerides for any collection of solar system bodies, spacecraft or any other objects in 3D space to be combined under a common file format, and accessed by a common set of subroutines. SP Kernels provide the state of a target relative to its center of motion, where ``state'' implies Cartesian position and velocity at a requested epoch. The SPK format is supported by a collection of subroutines that are part of the SPICELIB library, the major component of the SPICE Toolkit. These subroutines can be integrated into a user's application programs. Information about obtaining the SPICE Toolkit is located in the ``software'' subdirectory of the main directory of this dataset. To use SP-kernels, a Leapseconds Kernel (LSK) is required. Also, to use SP-Kernels containing states defined relative to non-inertial or project-defined frames, a Frames Kernel (FK) and/or Planetary Constants Kernel (PcK) are required. Refer to the SPK Required Reading (spk.req) document provided with the Toolkit or available from the NAIF Node of the PDS, to get more information on how to access SP-kernel data. SELENE Main Orbiter SP-kernels Provided in This Data Set ========================================================= This directory contains the SPICE SP-Kernel files for the SELENE mission (known as Kaguya). All files are in IEEE big endian binary format. The following files are present in this directory: SEL_M_071020_081226_SGMI_05.BSP reconstructed spacecraft ephemeris SPK files, created by the RISE team. This file is IEEE big endian binary format. SEL_M_071020_090610_SGMH_02.BSP reconstructed spacecraft ephemeris SPK files, created by the RISE team. This file is IEEE big endian binary format. SEL_MAIN_GRGM900C_L660_DIRALT_20081030-20090610.bsp reconstructed spacecraft ephemeris SPK files, created by Goossens Sander. This file is IEEE little endian binary format. de421.bsp DE421 planetary ephemeris SPK file containing ephemeris data for the Solar System planet barycenters, Sun, Mercury, Venus, Earth, Moon, and Lunar. If more than one SPK covering the same period of time is present in either of the SELENE spacecraft SPK sets, the SPK with the latest version supersedes all SPKs with earlier versions. Kernel File Details =================== The most detailed description of the data in each SPK file is provided in metadata included inside the comment area of the file. This information can be viewed using utility programs COMMNT and SPACIT included into the NAIF Toolkit. SEL_M_071020_081226_SGMI_05.BSP ------------------------------- This SPICE kernel contains the orbit for the Main satellite of the Kaguya (SELENE) project, as processed and determined at the National Astronomical Observatory of Japan, RISE Project. The start and end times of the orbit are (in UTC) Start: 2007-10-20T00:00:00.00 End : 2008-12-26T04:30:00.00 The gravity model used in the processing was SGM100i, which is the current latest gravity field model based on SELENE and historical tracking data (see Goossens et al., J. Geod., 85, 205-228, 2011, doi:10.1007/s00190-010-0430-2). This model is based on the processing of the SGM100h model (see Matsumoto et al., J. Geophys. Res., E06007, 2010, doi:10.1029/2009JE003499), with the difference that SGM100i also includes all S-band same-beam VLBI tracking between the sub-satellites. The orbit of the Main satellite was determined using available 2-way (range and Doppler) tracking, 4-way tracking between the sub-satellite Rstar and the Main satellite, and VLBI tracking between the sub-satellites Rstar and Vstar. In addition, laser altimeter crossovers were also used in the orbit determination for the months January and March 2008 (see Goossens et al., J. Geod., 85, 487-504, 2011, doi:10.1007/s00190-011-0446-2). Overlap analysis showed that including the crossovers reduces the orbit differences. It was also found that for some arcs in February, 2008, the orbit differences increased slightly when crossovers were included, so this version of the orbit kernel used no crossover data for arcs in February. Crossover statistics per month: Jan 2008: 13571 CROSSOVERS, RMS: 23.61 m Mar 2008: 12544 CROSSOVERS, RMS: 23.47 m Orbits are determined with arc lengths of in general 12 hours (6 hours after July 23, 2008 because of an issue with one of the reaction wheels). The arcs are limited because of angular momentum desaturation events. The arcs are cut around these events, resulting in an orbit that is not connected. SEL_M_071020_090610_SGMH_02.BSP ------------------------------- This SPICE kernel contains the orbit for the Main satellite of Kaguya, as computed at the National Astronomical Observatory of Japan, RISE Project. Start: 2007.10.20 02:30:00.00 UT End: 2009.06.10 19:30:00.00 UT Coordinate system during orbit determination: DE421 Based on the SGM100h gravity model (see Matsumoto et al., J. Geophys. Res., E06007, 2010, doi:10.1029/2009JE003499), for orbits until 2009.02.12, 13:40:00.00 UT. After that, for the low-altitude part, the gravity field was LP150Q. Data used were two-way data only. No 4-way data were used in the orbit determination, but they were used in the determination of the gravity field model (except of course for LP150Q). Per special request, this kernel consists of arcs (continuous time spans used for processing the tracking data in batches) that are connected. That means that there are no gaps between arcs, so this orbit is continuous, time-wise. There are however some gaps during altitude manoeuvres, and they are listed below. On top of that, due to the nature of orbit determination, there are jumps at the arc boundaries. Arc lengths were two days for arcs until 2009.02.12, 13:40:00, and one day after that. Unloading events were taken into account in the processing by estimating constant empirical accelerations in three orthogonal directions during unloading times. Data fit for most arcs is around 0.5 mm/s for Doppler data, but the unloadings do introduce extra effects in the processing, and uncertainties in their magnitude and direction lead to orbital errors. Overlap tests showed radial errors of 3 m at least, with much larger outliers possible (see below). For the low-altitude part, and data after Dec. 26, 2008, the spacecraft was in thrustering mode. This is taken into account here by estimating accelerations in two directions (along and cross track, or in the transverse and normal direction). The accelerations have a once-per-orbital revolution period, and one constant in along-track is also included. This is needed to keep the data residuals at a reasonable level, which works quite well, but again due to uncertainties, the orbit is much less precise during this period. The last arc, 2009.06.10 14:00 - 19:30, is not trustworthy, since we lack information about thrustering to manoeuvre the spacecraft into its final orbit. As a result, our orbit does not crash. ----- Gaps due to altitude manoeuvres ----- The spacecraft was three-axis stabilised and its altitude was maintained by doing periodical correction manoeuvres. According to the Mission Working Group Meeting documents, mission instruments were turned off during these manoeuvres. Since it is difficult to do precise orbit determination without good thrustering information during these events, the processing was stopped, resulting in some gaps in the orbits. The times of the gaps are: 07.12.11 02:30 - 16:50 08.02.04 20:30 - 08.02.05 04:15 08.03.29 16:30 - 08.03.30 00:15 08.05.24 15:00 - 20:43 08.07.16 07:30 - 15:30 08.09.10 05:30 - 13:30 08.11.03 00:30 - 09:00 08.12.26 21:00 - 08.12.27 05:30 09.02.20 20:00 - 23:45 09.03.19 18:00 - 22:00 09.04.16 19:00 - 21:30 SEL_MAIN_GRGM900C_L660_DIRALT_20081030-20090610.bsp --------------------------------------------------- See Goossens et al. (2019) for more details. DOI: 10.1016/j.icarus.2019.113454 Contact Information =================== Yukio Yamamoto Japan Aerospace Exploration Agency Institute of Space and Astronautical Science 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa, 252-5210 JAPAN email: darts-admin@ML.isas.jaxa.jp