PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "Comments on the MESSENGER SPICE Archive" PUBLICATION_DATE = 2017-05-12 END_OBJECT = TEXT END COMMENTS ON THE MESSENGER SPICE DATA ARCHIVE ============================================ This document contains comments and errata concerning the MESSENGER SPICE Data Archive. 1. Text Kernel File Format -------------------------- All SPICE text kernel files (LSK, PCK, SCLK, IK, FK) provided on these volumes have lines terminated by only (UNIX convention.) This is dictated by NAIF's archiving approach to include a consistent set of UNIX binary (IEEE architecture) and text ( only for end of line marker) kernels on the archive volumes. However, the format of the text kernels is specified in their associated labels as ASCII (INTERCHANGE_FORMAT = ASCII.) This is a violation of the PDS standard stating that lines in ASCII files must be delimited by the combination of . This line termination treatment is standard practice for SPICE volumes in the PDS. 2. Use of SPACECRAFT_NAME in the Labels --------------------------------------- PDS labels for SPICE kernels provided in this data set contain the deprecated keyword SPACECRAFT_NAME instead of the keyword INSTRUMENT_HOST_NAME. This is standard practice for SPICE volumes in the PDS and is dictated by NAIF's archiving approach to make SPICE archives for more recent missions consistent with SPICE archives for older missions, for which use of SPACECRAFT_NAME was legitimate. The deprecated keyword SPACECRAFT_NAME is set to either "MESSENGER" or "MERCURY SURFACE, SPACE ENVIRONMENT, GEOCHEMISTRY AND RANGING". "MESSENGER" is the preferred name and will be used for future kernels. 3. Values of INSTRUMENT_NAME in the Labels ------------------------------------------ PDS labels for SPICE kernels provided in this data do not set the keyword INSTRUMENT_NAME to "SPICE KERNELS", that is the name of the instrument described by the instrument catalog file SPICE_INST.CAT provided in the data set. Instead this keyword is set to either "N/A" or the name(s) of the instrument(s) or structure(s), the geometric parameters of which a particular kernel file provides. While this error does prevent the individual data products from being associated with the "SPICE KERNELS" instrument, it does not affect usability of the SPICE data provided in this data set in any way because the SPICE toolkit does not use any information from the PDS label to access the data. The other side of this error is that the data set does not include instrument catalog files for the following instruments named in the INSTRUMENT_NAME keyword in the PDS labels: "ENERGETIC PARTICLE AND PLASMA SPECTROMETER" (EPPS) "GAMMA RAY AND NEUTRON SPECTROMETER" (GRNS) "MAGNETOMETER" (MAG) "MERCURY ATMOSPHERIC AND SURFACE COMPOSITION SPECTROMETER" (MASCS) "MERCURY DUAL IMAGING SYSTEM NARROW ANGLE CAMERA" (MDIS NAC) "MERCURY DUAL IMAGING SYSTEM WIDE ANGLE CAMERA" (MDIS WAC) "MERCURY LASER ALTIMETER"(MLA) "RADIO SCIENCE SUBSYSTEM"(RS) "XRAY SPECTROMETER"(XRS) 4. Missing FILE_RECORDS Keyword in the Binary Kernel Labels ----------------------------------------------------------- All labels for binary SPICE kernels provided in this data set are missing the FILE_RECORDS keyword, which is required because these labels have the RECORD_TYPE keyword set to FIXED_LENGTH. While this error violates the PDS standards, it does not affect usability of the SPICE data provided in this data set in any way because the SPICE toolkit does not use any information from the PDS labels to access the data. 5. CK File Time Correction Factors ---------------------------------- In previous releases, the times associated with each attitude record in the kernel files were incorrect and needed to be adjusted. In this release these discrepancies have been accounted for, and no correction factor need be applied. The following note, included in previous errata, should be disregarded: 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 will have this correction already made. 6. Incorrect SCLK and Mission Phase Values in the Comment Area of CK Files -------------------------------------------------------- The values of the SPACECRAFT_CLOCK_START_COUNT, SPACECRAFT_CLOCK_STOP_COUNT, and/or MISSION_PHASE_NAME keywords in the copy of the PDS label embedded at the top of the comment area of CK files are incorrect for some CK files. The values of these keywords provided in the detached PDS labels are correct. 7. Missing records added to SCLK -------------------------------------------------------- Two records (29-JAN-2008 and 29-JUL-2013) had been missing from the SCLK due to an operations error and were manually added in release 11 (2014-03-07) and subsequent releases. 8. Change to the MDIS pivot (gimbal) CK -------------------------------------------------------- Beginning with Release 11 (07-MAR-2013), the MDIS pivot (gimbal) CK (i.e., data/ck/msgr_mdis_gm*.bc) was modified to include a new intermediate frame, MSGR_MDIS_ART_CAL. This is a transformation from the existing MSGR_MDIS_ART to the MSGR_MDIS_BASE frames and is based on a model of temporal drift of the alignment of the pivot system extrapolated past the end of mission. It is used by the MDIS instrument team for detailed calibration. Since this new MSGR_MDIS_ART_CAL frame is extrapolated past the end of the mission, it has a time much later time stamp than the others. This means that the STOP_TIME of the kernel as indicated in its PDS label is also much later (eg., STOP_TIME = 2015-12-31T23:59:59.851). The STOP_TIME values in all earlier versions of this kernel reflect the time of the last MSGR_MDIS_ART data point and approximately correspond to the data cutoff date for the associated PDS delivery. All subsequent versions of this kernel are expected to contain this new frame with its end of year 2015 or later time association. Users should be aware of the new meaning of the STOP_TIME in the PDS labels associated with this and future versions of the MDIS pivot ck. 9. Note on the resetting of the on-board MET counter -------------------------------------------------------- The MESSENGER on-board MET counter was originally designed to support a mission of 5.3 years with some margin. The mission was later redefined to last almost eight years and the original design of the MET counter was retained. That counter contains a 28-bit integer seconds component which would overflow after counting 3106 days, about 8.5 years. The launch was on August 3, 2004, so the MET counter was expected to overflow in February 2013. In order to have the MET counter "rollover" occur at a convenient time, it was commanded in January 2013 to reset to 1000, during the first 2-year Extended Mission. At approximately 08-JAN-2013-20:31:07.375090 TDT, the MESSENGER spacecraft was commanded to reset the MET counter to 1000. Prior to that commanded time, the MESSENGER Operations SCLK Kernel was manually modified to accommodate the rollover. Unfortunately, the actual on-board rollover did not occur at exactly the time expected, and the SCLK kernel mapping between MET and TDT was therefore inaccurate following the rollover. An automated entry was then made to the SCLK kernel for a time about three hours later, at 08-JAN-2013-23:19:54.375180 TDT, which compensated for the inaccuracy so that all following mappings between MET and TDT meet mission accuracy requirements. 10. Incorrect PRODUCER_ID Values -------------------------------------------------------- The PRODUCER_ID fields in the detached and attached labels are incorrect for several of the kernels. The value of the PRODUCER_ID field in the following kernels is "JHUAPL", but should be "NAIF/JPL": lsk/naif0010.tls pck/pck00010.tls The value of the PRODUCER_ID field in the following kernels is "JHUAPL", but should be {"NAIF/JPL","JHUAPL"}, since both institutions were involved in creating them: pck/pck00008_msgr.tpc pck/pck00009_msgr.tpc pck/pck00010_msgr.tpc pck/pck00010_msgr.tpc pck/pck00010_msgr_v10.tpc spk/msgr_de405_de423s.bsp 11. New document describing the relativistic nature of time correlations -------------------------------------------------------- A new document, document/seg_14_005.pdf, had been added to the archive. This document describes the relativistic nature of time correlations as they affect the SCLK. Document seg_14_005.pdf supersedes and replaces the existing document, sea_2007_010.pdf. 12. SPK Discontinuity -------------------------------------------------------- The spacecraft SPK data/spk/msgr_040803_141008_150328_od395sc_0.bsp delivered in release 13 has a small orbital discontinuity at 2014-09-03T05:15:29 UTC. The orbital period jumps by 0.04 seconds or 3 orders of magnitude greater than expected in 1 second. The distance to Mercury does not vary differently, but there are other orbital parameters that make sudden small jumps at this time. This small discontinuity is the result of merging two short-term predict SPKs. This discontinuity is not present in the more accurate final reconstructed trajectory contained in the SPK delivered for this release (data/spk/msgr_040803_150430_150430_od431sc_0.bsp). 13. MESSENGER Mission PCK -------------------------------------------------------- The MESSENGER mission PCK, data/pck/pck00010_msgr_v23.tpc contains the full contents of the NAIF standard pck00010.tpc, but also includes its own parmeter values for the updated Mercury orientation model and planetary radii. These values are derived from newer measurements taken from MESSENGER data than the IAU-approved values given in the NAIF standard PCK and supersede them. This kernel also includes some additional documentary citations in its commentary. 14. Subset MDIS CK -------------------------------------------------------- A new MDIS spacecraft orientation (i.e., attitude history) CK was created for the final release. This kernel, data/ck/msgr_mdis_sc050727_100302_sub_v1.bc, contains a subset of the data contained in the earlier MDIS spacecraft orientation kernels for which regular spacecraft attitude information is not available at 1 Hz time resolution. It supersedes the other MDIS spacecraft orientation CKs and is intended to be loaded after the regular spacecraft CKs. 15. MDIS C-smithed CKs -------------------------------------------------------- Four specialized MDIS spacecraft orientation CKs based on data provided by the USGS are included in this archive. These CKs contain orientation and angular rates for the MESSENGER spacecraft frame 'MSGR_SPACECRAFT' relative to the inertial frame 'J2000'. These kernels were generated for the purpose of storing C-Smithed pointing updates generated through ISIS processing techniques. Because of their specialized purpose, these kernels are not listed in the metakernels provided with this archive volume. 16. Regeneration of monthly spacecraft CKs -------------------------------------------------------- During the active mission, the MESSENGER ground system would sometimes update some of the daily CKs even weeks after they were initially created. It is therefore possible that some of the previously archived monthly CKs were generated from daily CK data that were later updated. To assure that the PDS archive contains all of the final CK data, the monthly spacecraft CKs, except for those covering November 2014 onward, were regenerated. Those from November 2014 onward were generated after mission operations completed and contain the final data for their coverage periods. 17. Additional MDIS C-smithed CK -------------------------------------------------------- The USGS provided additional MDIS CKs based on a control that they performed on a new set of MESSENGER MDIS images using the WAC-G filter for the purposes of improving the spatial registration of MDIS color products. The new CKs are organized by year: data/ck/msgr_mdis_sc2011_wacg_usgs_v1.bc data/ck/msgr_mdis_sc2012_wacg_usgs_v1.bc data/ck/msgr_mdis_sc2013_wacg_usgs_v1.bc data/ck/msgr_mdis_sc2014_wacg_usgs_v1.bc data/ck/msgr_mdis_sc2015_wacg_usgs_v1.bc See data/ck/ckinfo.txt for details. 18. SPKs Produced with MLA and Radio Science Data -------------------------------------------------------- The MLA and Radio Science teams at GSFC have provided two on-orbit SPKs that they created using data from the MLA instrument and Radio Science investigations. These provide a more accurate ephemeris for the on-orbit phases of the MESSENGER mission. In most cases, these can be used in conjunction with or in place of the mission SPK. The new SPKs are named based on their coverage periods, msgr___recon_gsfc_.bsp, where _ represent the year, month, and day of month of the beginning of the coverage to the end of the coverage. is the version: data/spk/msgr_110318_110714_recon_gsfc_1.bsp data/spk/msgr_110716_120430_recon_gsfc_1.bsp data/spk/msgr_120501_130430_recon_gsfc_1.bsp data/spk/msgr_130501_140430_recon_gsfc_1.bsp data/spk/msgr_140501_150429_recon_gsfc_1.bsp See data/spk/spkinfo.txt for details.