PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2017-05-12 NOTE = "MESSENGER C-Kernel Information" END_OBJECT = TEXT END General Information About SPICE C-kernels ========================================= In the SPICE system, pointing data for an instrument platform, or for a specific instrument, are stored C-kernels. The pointing of a platform or an instrument is often expressed in terms of a transformation matrix from some standard inertial reference frame to a instrument-fixed frame. In the past, the instrument was often a camera, and the transformation was thus dubbed the ``C-matrix''; hence the choice of C as the name for the pointing kernel. The data contained in C-kernel files can be accessed and manipulated by a collection of FORTRAN 77 subroutines which are part of the SPICELIB library or C functions which are part of the CSPICE library. These subroutines/functions can be integrated into user application programs. The SPICE system toolkit for a number of computer platforms or information regarding how it can be obtained is located in the ``/software'' subdirectory of the main directory of this data set. To use C-kernels, a Spacecraft Clock Kernel (SCLK) is required. Also, for C-Kernels containing orientation of a project-defined frames, a Frame Definitions File is required. Refer to the ``ck.req'' document provided with the toolkit or available from the NAIF Node of PDS if SPICE toolkit is not included with this data set to get more information on how to access C-kernel data. MESSENGER C-kernels Contained In This Data Set ============================================== The following MESSENGER C-kernels are provided in this data set (only name portion of the file name is shown; the extension of all file names is ``.bc''): -- MESSENGER Spacecraft Orientation CK Files: msgr_ or msgr__v Spacecraft orientation C-kernels covering a particular month of the mission produced. YY is the year, MM is the (numeric) month. Later deliveries use the second naming convention which includes a version number ranging from 01 to 99. These files also contain orientation of the +X to -X solar panels. msgr_mdis_sc_v Spacecraft orientation CK files produced for use with MDIS. These files only include attitude data bracketing MDIS observations during the period of time between the start date and end date given in the file name. They are an aggregate of several sources of attitude history: (1) MDIS captured attitude history. Due to the fact that the spacecraft is not required to record attitude data at 1-Hz, the instrument itself can capture attitude data at this desired rate. These data are 16-bit integral valued quaternions, as opposed to the normal 32-bit floating point quaternions and angular rates in the standard spacecraft housekeeping telemetry. Angular rates included during these times are fabricated by the usual MSOPCK algorithm. (2) Standard 1-Hz spacecraft attitude telemetry. At times during operations in cruise and orbit, the high rate (1-Hz) housekeeping data is available and can be subset to bracket MDIS exposures and included in these files. (3) MDIS image header quaternions. During the first flyby of Mercury the housekeeping telemetry was set to a low sampling rate, and the MDIS captured attitude was disabled. The only source of reliable attitude data covering these images were the image headers themselves. This data is only included when the other sources are unavailable. In these limited cases, the angular rate is set to the zero vector. If necessary the version number may be incremented to indicate the contents of a previously delivered file have been updated. These kernels are inherently full of gaps, as they are designed only to cover individual MDIS exposures. msgr_mdis_sc050727_100302_sub_v1.bc Spacecraft orientation CK file produced for use with MDIS. These files only include attitude data bracketing MDIS observations during the period of time between the start date 2005-JUL-27 and end date 2010-MAR-02 given in the file name. This file contains orientation and derived angular rates for MDIS attitude history telemetry. The orientation and angular rate of the inertial, 'J2000', frame is given with respect to the "MSGR_SPACECRAFT" frame. This file is a carefully constructed subset of the MDIS attitude history telemetry C-kernel designed to be loaded after the standard spacecraft housekeeping telemetry C-kernels. It provides higher time resolution (1 Hz) coverage during MDIS exposures that is otherwise not present in the standard spacecraft C-kernels. The majority of the data in this file is collected from the MDIS attitude history telemetry packets, but around the time of the first Mercury flyby this telemetry stream was disabled. Unfortunately the spacecraft housekeeping was also not being captured at 1-Hz. The only reasonable data available then were the quaternions from the MDIS image headers. These data were converted into a C-kernel by a custom program, CKHDR. Content captured in this kernel between 2008-JAN-09 11:01:13 (TDB) and 2008-JAN-15 15:55 (TDB) is derived directly from image headers. All other data are from the MDIS spacecraft attitude telemetry. -- MDIS Pivot Platform (Gimbal) Orientation CK Files: msgr_mdis_gm_v The MDIS gimbal orientation C-kernels produced by the instrument team covering the period between the start date and the end date supplied in the filename. Resolver readings captured in the MDIS image headers are run through a flight calibrated model used to produce the data contained in these kernels. See the comments for details. The version number may be incremented if the contents of an already delivered file are updated due to an improvement in the model or some other reason. As with the MDIS spacecraft orientation C-kernels, these files are inherently full of gaps as they are designed only to cover individual MDIS exposures. -- USGS MDIS Smithed CK Files: msgr_mdis_sc20_usgs_v The MDIS C-smithed CKs were created from an original CK provided by the US Geological Survey (USGS) and reorganized by NAIF into four separate kernel files so that the number of segments in a kernel would not exceed SPICE library limitations. These CKs contain orientation and angular rates for the MESSENGER spacecraft frame 'MSGR_SPACECRAFT' relative to the inertial frame 'J2000', derived in 2015 by USGS as part of the MESSENGER MDIS image bundle adjustment done by the USGS' ISIS3 jigsaw application. Each of these kernels covers a different time period. In the filenames, is the year and the version number. These kernels were generated for the purpose of storing C-Smithed pointing updates generated through ISIS processing techniques (control nets, jitter analysis, etc...). These CK kernels are intended to mimick CKs provided by individual mission (NAV teams) in regards to reference frames, but not necessarily format (i.e., CK types). Because of their specialized purpose, these kernels are not listed in the metakernels provided with this archive volume. See the comments in each of these kernels for further details on their contents, how they were created, and their intended use. msgr_mdis_sc20_wacg_usgs_v.bc The USGS performed a control on a new set of MESSENGER MDIS images for the purposes of improving the spatial registration of MDIS color products. These new smithed CK kernels (reorganized by NAIF into five separate kernel files from a single original so as not to exceed SPICE library limitations), are comprised of all the Wide Angle Camera WAC-G filters identified in the 3-, 5- and 8-color mosaics. The results of the image control has updated the pointing attitude for each image. Spacecraft position was not solved for, so the mission reconstructed SPK, msgr_040803_150430_150430_od431sc_2.bsp, was used to establish the absolute position of the MESSENGER spacecraft when each image was acquired. These CK kernels should be considered independent of the previous CK kernels released that were part of the process that created the digital elevation model (DEM). The main differences in the new kernels and processing steps are: 1) An additional 2,190 WAC-G images were added to the existing 100,432 images in the DEM network 2) All control measures in the network were registered to the subpixel 3) The 100,432 images were initialized with the controlled CK data 4) All images used the DEM in image matching and bundle adjustment process. This approach biased the results toward the DEM solution (by design). It is expected that the pointing attitude for images in both sets of kernels (namely, WAC-G images) will be slightly different. When processing color images, this new kernel is recommended over the previously released smithed kernel set described above. 5) Note that only the WAC-G filter was included in the control so there is no update to the pointing attitude of the other WAC filters. Image matching techniques can be applied to the other WAC filters in each color set (much like was done to the 3-, 5- and 8-color products). Notes on Using MDIS Data: MDIS Non-ISIS Users: First load the mission metakernel (mk) for the year of interest archived in extras/mk/ followed by the standard MDIS attitude history kernel, msgr_mdis_sc040812_150430v1.bc. MDIS ISIS Users: First load the planetary ephemeris kernel $ISIS3DATA/messenger/kernels/tspk/de423s.bsp. (This is required by the ISIS system but will be overridden by the MESSENGER SPK as it contains the necessary spacecraft and body ephemeris.) Then load the mission metakernel (mk) for the year of interest archived in extras/mk/ followed by the standard MDIS attitude history kernel, msgr_mdis_sc040812_150430v1.bc. Using the USGS C-Smithed CKs with the Monochrome MDIS Products: First load the mission mk for the year. Load the msgr_mdis_sc201*_usgs_v1.bc for the year. Using the USGS c-Smithed CKs with the Color WAC-G MDIS Products: First load the mission mk for the year. Load the msgr_mdis_sc20_wacg_usgs_v1.bc for the year. Users of the USGS MDIS CKs are advised to use the mission ephemeris SPK with these kernels and not the GSFC reconstructed SPKs (data/spk/msgr___recon_gsfc_0.bsp) as these SPKs, although more accurate, would break the control used for these CKs (because the mission ephemeris SPK was used as truth). Note the ISIS MESSENGER kernel structure is being modified to follow these guidelines and will be provided in a future ISIS release. Retired Files ============= As the mission progressed and understanding of the various spacecraft systems and data sources evolved, several previously produced C-kernel products are now retired. Their replacements are outlined in detail above. The usage of the following files is discouraged: mdis_gm_nl040819_090201v1.bc mdis_hdr_sc_080109_080115v1.bc msgr_mdis_gm_*.bc (note the '_' after "_gm" in the filename) msgr_mdis_sc_*.bc (note the '_' after "_sc" in the filename) The latest and recommended CKs are listed in the latest versions of the metakernels (extras/mk/*.tm). Spacecraft C-kernel Updates =========================== Some of the CKs are new versions of already delivered kernels. The newer ones are identified by the version numbers in their file names. The newer versions fix errors or improve accuracy. The latest versions always supersede all previous versions unless they fall under other precedence rules specifically noted in this description. The version 2 spacecraft CKs provided in the release 3 fix timing errors in the CKs with the same coverage provided in the release 1. The magnitude of the error was 1 second for CKs covering up to 2005-OCT-24 16:34:03 and 2 seconds for CKs covering from 2005-OCT-24 16:34:03 to 2007-JUL-01 00:01:42. Versions of the CK files delivered in release 1 have the file naming convention msgr_.bc. Later versions of these kernels and all new kernels follow the convention: msgr__v.bc. Versions of these monthly CKs range from 01..99. Previously archived versions of monthly CK files without a version number are designated as version 01. Subsequent versions will begin with version 02. All spacecraft CKs generated prior to October 2014 (before release 14) were regenerated for the final release. This was to make certain that any adjustments made to the attitude data since the earlier versions were delivered are included in the PDS archive. Kernel File Details =================== The most detailed description of the data in a binary CK 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. Only for the CKs provided in the release 1, due to the way in which the MESSENGER telemetry is time stamped, the times associated with each attitude in the kernel files must have a correction factor subtracted from them. On 24 OCT 2005, (day of year 297) the MESSENGER flight software was upgraded from version 4.8 to version 4.9, and this correction factor changed. Before 24 OCT 2005 at 16:34:03 subtract 1 second. After 24 OCT 2005 at 16:34:03 subtract 2 seconds. Subsequent releases of the CK files have this correction already made. Contact Information =================== Regarding MESSENGER project specific information provided in this data set: Mike Reid (240)-228-4537 Mike.Reid@jhuapl.edu address: The Johns Hopkins Applied Physics Laboratory 11100 Johns Hopkins Road Laurel, MD 20723 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