PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2017-05-12 NOTE = "SP-Kernel Information; updated MReid:JHU/APL,10Jun11; updated MReid:JHU/APL,02Dec11; updated MReid:JHU/APL,04Apr12; updated MReid:JHU/APL,05Dec12; updated MReid:JHU/APL,09Jun14; updated MReid:JHU/APL,27Oct15; updated MReid:JHU/APL,21Feb17." END_OBJECT = TEXT END General Information About SPICE SP-Kernels ========================================== The purpose of the SP-kernel -- 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. The SPK files can be accessed and manipulated using the SPICE Toolkit APIs, calls to which can be integrated into user application programs. The information regarding how to obtain the SPICE system toolkit for a number of languages and computer platforms is located in the ``/software'' subdirectory of the main directory of this data set. To use SP-kernels, a Leapseconds (LSK) is required. Also, to use SP-Kernels containing positions given relative to the non-inertial and project-defined frames, a Frame Definitions (FK) and Planetary Constants (PCK) files are required. Refer to the ``spk.req'' document provided with the toolkit to get more information on how to access SP-kernel data. MESSENGER SP-kernels Provided In This Data Set ============================================== The following MESSENGER SP-kernels are provided in this data set (only name portion of the file name is shown on the right; the extension of all file names is ``.bsp''). Three file naming conventions are used. The first one given below was used through release 5. In release 6, the orbit determination number and "sc" were appended to the base file name. In release 7 and forward the base file name ends with a single-digit version number. -- MESSENGER Mission Spacecraft Trajectory SPK files: msgr_YYMMDD_YYMMDD_YYMMDD Official full-mission merged reference trajectory SPKs containing the spacecraft ephemeris created by merging a series of reconstructions and short-term predictions onto the modeled whole-tour SPK. msgr____odsc.bsp The first date in the file name is the file coverage start date, the second -- the end date for the best ephemeris before end-of-mission final reconstructed ephemeris, third -- the file coverage end date. The is the orbit determination number and "sc" indicates that it is a spacecraft ephemeris. Normally the file with the latest "end of reconstructed portion date" supersedes all other files of this kind. The best ephemeris date is determined from the date given in the kernal comment as the "End date for best ephemeris before end-of-mission final reconstructed ephemeris" by rounding to the end of the day given. (In effect, adding one day.) msgr____odsc_.bsp Spacecraft SPKs released from 2012 onward have a version number appended to their filenames. is a digit from 0 to 9 indicating the version of this SPK. Otherwise, the file naming convention is identical to the previous one. This was added to accommodate updates to an SPK that may be made within the same orbit determination solution. msgr_040803_150430_150430_od431sc_2.bsp Final reconstructed spacecraft SPK created after the end of orbital operations. Also contains the planetary ephemeris. A planetary SPK should not be loaded with this kernel. msgr_antenna_v.bsp SPK that contains the fixed locations of the antennas on-board the MESSENGER spacecraft. -- MESSENGER GSFC Reconstructed Spacecraft Trajectory SPK files: msgr___recon_gsfc_.bsp MESSENGER GSFC Spacecraft Orbital Operations SPK files are named based on their coverage periods, where _ represent the year, month, and day of month of the beginning of the coverage to the end of the coverage. is the version number. msgr_110318_110714_recon_gsfc_1.bsp msgr_110716_120430_recon_gsfc_1.bsp msgr_120501_130430_recon_gsfc_1.bsp msgr_130501_140430_recon_gsfc_1.bsp msgr_140501_150429_recon_gsfc_1.bsp The Mercury Laser Altimeter (MLA) instrument and Radio Science teams at Goddard Space Flight Center (GSFC) produced five additional spacecraft SPKs covering the orbital phases of the MESSENGER mission. These SPKs are based on MLA instrument and Radio Science data and provide a greater precision than the official mission SPK based on reconstructed ephemeris (msgr_040803_150430_150430_od431sc_2.bsp) and can be used in place of it in most cases. There are some gaps in this ephemeris around maneuvers, so a user might want to load the mission SPK first followed by the appropriate GSFC one. The MLA and Radio Science Teams reprocessed all of the MESSENGER tracking data in order to provide updated reconstructed orbits for the MESSENGER mission. The new processing utilizes radio science gravity model and MLA altimetric data. The SPKs were derived from a complete reprocessing of the MESSENGER Deep Space Network (DSN) tracking data simultaneously with the altimeter data from the MLA. The analysis used the NASA GSFC Orbit Determination and Geodetic Parameter Estimation Software (GEODYN), version 1612. The spk msgr_140501_150429_recon_gsfc_1.bsp covers the final year of the mission which includes the low-altitude campaign performed in the final months. See the commentary embedded within the kernels themselves for full descriptions. 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. Retired Files ============= As the mission progressed additional ephemeris became available, several previously included SPK-kernel products are now retired. Their replacements are outlined in detail above. The usage of the following files is discouraged: -- Planetary SPK files: de405 DE405 planetary ephemeris SPK file containing ephemeris data for the Solar System planet barycenters, Sun, Mercury, Venus, Earth, Moon, and Mars. This version of ephemerides is a standard NAIF product that was officially used by the project during mission operations. This kernel was replaced by msgr_de405_de423s.bsp for MESSENGER processing through to the end of orbital operations. msgr_de405_de423s.bsp msgr_de405_de423s combined planetary ephemeris SPK containing data from both de405 and de423s. This kernel contains the results of merging portions of DE405 with DE423, to produce a single SPK file that should be valid for the bulk of the entire MESSENGER mission. The only exception to this is there are segments of planetary ephemerides associated primarily with planetary flybys included in the spacecraft ephemeris. This kernel replaces the NAIF de405 and de423s kernels for MESSENGER processing. It is itself superseded by the final reconstructed spacecraft SPK, msgr_040803_150430_150430_od431sc_2.bsp, which also includes the relevant planetary ephemeris. Contact Information =================== Regarding MESSENGER project-specific information provided in this data set: Mike Reid The Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Road Laurel, MD 20723 USA (240) 228-4537 Mike.Reid@jhuapl.edu For general information about SPICE system: Charles H. Acton, Jr, (818) 354-3869, Charles.Acton@jpl.nasa.gov, or Boris Semenov (818) 354-8136 Boris.Semenov@jpl.nasa.gov address: Navigation and Ancillary Information Facility (NAIF) Jet Propulsion Laboratory MS 301-121 4800 Oak Grove Drive Pasadena CA 91109 USA