PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "MGS-M-SPICE-6-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "MGS MARS SPICE KERNELS V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" START_TIME = 1996-11-06T08:00:00 STOP_TIME = "UNK" DATA_SET_RELEASE_DATE = 2000-01-04 PRODUCER_FULL_NAME = "BORIS V. SEMENOV" DATA_OBJECT_TYPE = "SPICE KERNEL" DETAILED_CATALOG_FLAG = "Y" DATA_SET_DESC = " Data Set Overview ================= This data set includes the complete set of SPICE data for the Mars Global Surveyor in the form of SPICE kernels, which can be accessed using SPICE software available to read these files. The SPICE data contains geometric and other ancillary information needed to recover the full value of science instrument data. In particular SPICE kernels provide spacecraft and planetary ephemerides, instrument mounting alignments, spacecraft orientation and spacecraft sequences of events. Data needed for relevant time conversions is also included. This data set is spread across multiple volumes, each containing the complete set of SPICE kernels for two or more mission phases, a single mission phase or a portion of a mission phase. The volume coverages are summarized in the table: VOLUME ID START TIME STOP TIME --------- ------------------- ------------------- MGSP_0001 1996-11-06T08:00:00 1998-05-28T00:00:00 MGSP_0002 1998-05-28T00:00:00 1999-03-09T00:00:00 Data Types (SPICE kernel types) =============================== SPK kernels contain ephemerides for spacecraft, planets, satellites, comets and asteroids as well as for moving or fixed spacecraft and instrument structures. They provide position and velocity, given in a Cartesian reference frame. SPK files are located under the DATA/SPK directory on the volumes comprising this data set. PCK kernels contain certain physical, dynamical and cartographic constants for target bodies, such as size and shape specifications, and orientation of the spin axis and prime meridian. PCK files are located under the DATA/PCK directory on the volumes comprising this data set. IK kernels (Instrument description kernels) give descriptive and operational data peculiar to a particular scientific instrument, such as internal timing relative to the spacecraft clock and field-of-view model parameters. IK files are located under the DATA/IK directory on the volumes comprising this data set. CK kernels describe pointing, containing a transformation traditionally called the C-matrix which is used to determine time-tagged pointing (orientation) angles for a spacecraft structure upon which science instruments are mounted. CK files are located under the DATA/CK directory on the volumes comprising this data set. EK (Events) kernels are derived from the integrated sequence of events used to produce actual spacecraft commands. EK files are located under the DATA/EK directory on the volumes comprising this data set. LSK (Leapseconds) kernels contain the leapseconds and the values of other constants required to perform a transformation between Universal Time Coordinated (UTC) and Ephemeris time (ET). LSK files are located under the DATA/LSK directory on the volumes comprising this data set. SCLK (Spacecraft Clock) kernels contain on-board clock calibration data required to perform a mapping between Ephemeris time (ET) and spacecraft on-board time (SCLK.) SCLK files are located under the DATA/SCLK directory on the volumes comprising this data set. FK (Frame Definitions) kernels contain information required to define reference frames, sources of frame orientation data and inter-connections between these frames and other frames supported within the SPICE system. This includes mounting alignment information for each instrument. FK files are located under the DATA/FK directory on the volumes comprising this data set. Kernel File Details =================== Details specific to individual files are found in the *INFO.TXT files in the corresponding data directory. The most detailed description of the data in each file is provided in metadata included inside the file -- in the description area of text kernels or in the comment area of binary kernels. Software ======== The SPICE Toolkit contains software modules needed to read SPICE kernel files. SPICELIB software is highly documented via internal headers. Additional documentation is available in separate ASCII text files called Required Reading files. For example, the S- and P- Kernel (SPK) Required Reading File, named SPK.REQ, describes use of the SPK kernel file readers and contains sample programs. The latest SPICE Toolkit for a variety of computer platforms such as PC, Mac, SUN, HP, SGI, VAX, DEC Alpha, NeXT, etc. is available at the NAIF Node of PDS electronically (via anonymous FTP and WWW servers). Each version of the Toolkit is also archived at the NASA National Space Science Data Center. " CONFIDENCE_LEVEL_NOTE = " This volume contains SPICE kernel files created during mission operations and after mission data reconstruction and analysis. Some general information about this collection follows here, but the prospective user is also referred to extensive descriptions about each file that are stored inside each kernel file. These metadata provide detailed information regarding the information source from which the data were derived, the type of processing applied to the source data, applicability of the data, etc. Metadata are located in the ``comment area'' for binary kernel types (SPK, CK, ESQ), accessible using either the COMMNT or SPACIT utility program found in the NAIF Toolkit. Metadata are located after ``\begintext'' markers within the text kernel types (PCK, IK, FK, LSK, SCLK, MK), accessible by using any available text file display tool such as a word processor, text editor, or the unix ``more'' or ``cat'' commands. In some cases data accuracy information does not exist, or may be estimated after mission completion. Where there are questions about data accuracy or ``confidence'' not addressed herein the reader is invited to examine subsequent SPICE archive volumes associated with this dataset collection (if such exist), or to contact the NAIF node of the Planetary Data System for possible further information. SPK Files ========= Three kinds of SPK files are provided in this archive: SPK files for the spacecraft orbit, SPK files for Phobos, Deimos, Mars, Earth and Sun, and SPK files for the solar array and high gain antenna structures and the locations of the MAG/ER instrument components on the solar arrays. Spacecraft Orbit SPK Files -------------------------- Most of the included SPK files provide the orbit of the MGS spacecraft. Most missions have a single source for this kind of data, but for MGS there are three sources: the Mars Surveyor Operations Project (MSOP) Navigation Team (NAV), the Mars Orbiter Laser Altimeter (MOLA) Team based at the Goddard Space Flight Center (GSFC), and the Inner Planet Navigation and Gravity Group (IPNG) based at JPL. The MOLA and IPNG groups have produced multiple solutions for some of the mission phases, presumably yielding ever more accurate results as the gravity model used and other data handling improvements come into play. It is possible that any or all of these three groups will produce yet more--and presumably further improved--solutions in the future; these should eventually be available from NAIF. There has been considerable discussion solutions from which of these three teams is the ``best.'' Each solution set has multiple aspects that are different from the others, making comparisons quite difficult, and in any case there is no single set of criteria that would define ``best'' for all users. Though some solutions, by agreement with the Mars Surveyor Operations Project Science Manager, were designated the ``official'' orbit products for the mission phases included in this archive (see notes in the SPKINFO.TXT files), it is known that all three solution sets have been used by different science teams in reducing data for formal Planetary Data System archives. For all three solution sets, each archival SPK file covering a particular mission phase was made by merging together numerous shorter duration individual files. The component files used to make a merged product can be discerned by reading the descriptive information (metadata) found in the comment area of each file, and by producing a detailed SPK file summary using the SPACIT utility program provided in the NAIF Toolkit. Since NAIF is not the producer of any of these orbit solutions, NAIF staff have limited ability to detail and contrast them. What information NAIF does currently have available is included in the ``comment area'' of each file. It is possible that more or better metadata for these or later solutions will be available in an archive update later on. It is also possible that NAIF will produce some sort of comparison of these solutions, or will offer tools for helping the customer do so. Some factors that could affect choice of spacecraft SPK file are noted below. 1) Completeness of coverage: are there gaps in the orbit data, or missing mission phases? 2) Discontinuities: are position and velocity data continuous across individual orbit data fits comprising the merged product? More particularly, how large are these discontinuities? 3) What kinds of data were used in producing the orbit solutions? (In all cases, doppler and range data were used. For the MOLA/GSFC solutions, laser range points were also used.) 4) What models were used (particularly what Mars gravity model) and how might this affect the orbit solution? Solar System Body SPK Files --------------------------- The file (mar033) contains ephemeris data for Phobos, Deimos, Earth and the sun. Formal one-sigma accuracy information for Phobos and Deimos are reported as follows: Body Downtrack Crosstrack Radial Uncertainty Uncertainty Uncertainty ------ ----------- ----------- ----------- Phobos 15 km 7 km 3 km Deimos 30 km 16 km 3 km Accuracies for Mars-Sun and Mars-Earth directions (positions obtained from SPK files) are at the level of 0.001 arc-sec (1 sigma). Spacecraft Solar Array, High Gain Antenna and MAG/ER SPK Files -------------------------------------------------------------- Included in the SPK archive are two files containing location information (fixed offsets) for spacecraft structures--the high gain antenna and the Magnetometer instrument components mounted on solar arrays. See the metadata for each of these files--found in the comment area--for detailed descriptions of how the files were produced. CK Files ======== C-kernel files provide orientation of a structure: the spacecraft bus, the solar arrays or the high gain antenna. There is only one CK file provided for each structure for a given mission phase. All three kinds of CK files are produced from engineering telemetry downlinked from the spacecraft. As is often the case with spacecraft engineering telemetry-based measurements, considerable uncertainty exists as to the accuracy of such measurements, and, data quality (accuracy and completeness) can vary significantly. Solar Array CK Files -------------------- CK files providing orientation of the solar arrays relative to the spacecraft bus are provided to support interpretation of data collected by the MAG/ER instruments mounted on these arrays. The situation is complicated somewhat due to the non-complete deployment of one of the two arrays. There is no currently known mechanism for estimating the accuracy of the solar array CK files; however it is assumed that they nevertheless satisfy the requirements of the MAG/ER experiment. High Gain Antenna CK Files -------------------------- CK files providing orientation of the high gain antenna (HGA) relative to the spacecraft bus are provided to support the Radio Science experiment. They may also be used to help with calibration or data processing for the MAG/ER experiment. There is no currently known mechanism for estimating the accuracy of the HGA CK files. (It may be possible that the Radio Science experiment will later yield some assessment of this accuracy.) Spacecraft Bus CK Files ----------------------- CK files providing the orientation of the spacecraft bus (``the spacecraft'') are provided to support interpretation of data obtained by all science experiments. The stated requirement on spacecraft orientation knowledge is better than three mrad per axis, 3-sigma. It has been informally reported that the achieved orientation knowledge is significantly better than this, but at the time of this archive production there are no known reports substantiating this or providing further details. Processing of the Mars Orbiter Laser Altimeter (MOLA) data by the MOLA Team at GSFC lead to a determination that the spacecraft clock time tags assigned to the downlinked spacecraft orientation quaternions that comprise these CK files have a time bias. This assessment was verified by the Lockheed Martin Astronautics (LMA) spacecraft control team, although firm determination of the magnitude has been illusive. The situation is further complicated by knowledge that on-board software that results in this timing bias has been changed during the mission. The magnitude of this bias has been estimated in the range of 1 to nearly 2.5 seconds. Work on improving this estimate is on-going and should be reported in later additions to this SPICE archive collection. The bias correction values used in creating the spacecraft bus CK files in this dataset are detailed in the metadata provided in the comment area of each CK file. Caution on Using CK Files ------------------------- While not a data accuracy issue, the CK user is nevertheless cautioned to understand and properly use the data found and tolerance arguments that are inputs to the CK reader provided in the SPICE Toolkit. Descriptions about how to read CK files are found in the CK reader routine headers (top of the source code files) and in the ``CK Required Reading'' document; these are contained in each SPICE Toolkit package. PCK Files ========= PCK files provide size, shape and orientation data for ``target'' bodies such as Mars, Phobos and Deimos. A description of these data items and reference to their source is provided inside the PCK file, which is a simple text file that can be viewed using any word processor, text editor or text display utility. In most cases the data for the PCK provided in this archive are official IAU/IAG/COSPAR values accepted in 1994. These data is generally rather old and in any case certainly does not reflect any new parameter determinations achieved as a result of science instrument data processing for an active mission. This is particularly true in the case of the MGS mission where the MOLA team is providing new estimates of the figure of Mars. Such new estimates will be provided in a new PCK file later in the mission. FK Files ======== Frames kernel files provide specifications for how one reference frame is defined relative to another frame. In one case--that of fixed offset frames such as used for defining the mounting alignment of each antenna relative to the spacecraft--the FK file contains the actual parameter values. Metadata describing these mounting alignment estimates are provided in the one FK file included in this archive. There are no (known) accuracy estimates for these data at the time of this archive preparation. IK Files ======== Instrument kernel files provide specifications for the mounting alignment and--where applicable--field-of-view size, shape and orientation for the named instrument. Metadata describing these estimates are provided in each IK file included in this archive. Parameter values were determined from pre-launch measurements or from manufacturing blueprints. (An update for the MOLA alignment using in-flight measurements is expected later in the mission.) There are no (known) accuracy estimates for these data at the time of this archive preparation. SCLK Files ========== Spacecraft Clock kernel files provide a tabulation of data needed for converting time measurements between ephemeris time (ET) and spacecraft clock time (SCLK). A SPICE SCLK file is made from a similar file--SCLK/SCET file, or SCLKvSCET file--produced by another mission entity. Each newly made SCLK file fully replaces the previous SCLK file. For MGS the time correlation accuracy provided in SCLK/SCET files is informally reported by the Lockheed Martin spacecraft team to be better than 100 milliseconds during cruise and better than 10 milliseconds during orbital phases. (NAIF has not attempted to obtain or produce an independent corroboration of these LMA estimates.) The SPICE SCLK file has essentially the same accuracy as the SCLK/SCET file. SPICE software does not prohibit an SCLK file from being used for time conversions occurring for ``future times'' (or more accurately, for epochs that occur later than the epoch of the last telemetry data used in producing the last correlation coefficients found in the SCLK file). Such ``predict'' time conversions are likely to be inaccurate (changed somewhat) once the epoch of interest has been passed. LSK Files ========= Leapseconds kernel files provide a tabulation of ``leapseconds'' and some other terms used in converting time measurements between ephemeris time (ET) and Universal Time (UTC). ``Spacecraft Event Time'' (SCET) is the commonly used name for UTC events measured at the spacecraft. Metadata describing how the LSK data are obtained or computed is contained inside the LSK text file. The time conversion provided by SPICE LSK files is accurate to approximately 0.000030 seconds. EK Files ======== Two kinds of Events kernel (EK) files are included in this archive: Experimenter's Notebook EKs and Sequence EKs. Experimenter's Notebook EKs kernels are a digital analog to the traditional paper laboratory notebook. Hence Experimenter's Notebook entries represent truth only as seen by the author of the notes--there is no attempt made to independently validate any aspect of Experimenter's Notebook information. Sequence EKs comprise a summary of all commands sent to the spacecraft as well as some ground system events and instrument state (status) summaries. All Sequence EK entries are time tagged. In this archive includes Sequence EKs created the automated process for providing ``as run'' inputs reflecting what was actually sent to the spacecraft, and what execution times were used, was not yet implemented for the in-orbit mission phases. The cruise ESQ was produced from a cruise phase Predicted Events File (PEF) that was hand edited to reflect ``as run'' status. Consequently the validity of this ESQ is uncertain, but there is some reason to imagine that the handwork was well done. " END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = MARS END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = MGS INSTRUMENT_ID = "N/A" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = UNK END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END