Data Set Overview : This data set includes a substantial collection of navigation and other ancillary data for the Viking Orbiter spacecraft (VO1 and VO2) in the form of SPICE kernels, which can be accessed using SPICE software. 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, spacecraft sequences of events, and data needed for relevant time conversions. This data set is contained on a single virtual volume, VOSP_1000, including data from most mission phases and covering from 1976-06-01 through the end of the mission, 1980-09-01. 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 of 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 of 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 of 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 of 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 of 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 of 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 of 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 of this data set. Kernel File Details : A brief overview of the different types of Viking Orbiter kernels included in this data set is provided in the CONFIDENCE_LEVEL_NOTE section of this file while 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, etc. is available at the NAIF Node of PDS electronically (via anonymous FTP and WWW servers). Refer to information in ``software/softinfo.txt'' for details regarding obtaining this software. Each version of the Toolkit is also archived at the NASA National Space Science Data Center. Loading Kernel Files into a SPICE-based Application : The easiest way to make data from a collection of SPICE kernels available to a SPICE-based application is to list these kernels in a meta-kernel and load it into the program using the high level SPICE data loader routine FURNSH. This data set provides such meta-kernel(s) under the ``extras/mk'' directory. For more information about the MGS meta-kernel(s), see the file ``extras/mk/mkinfo.txt''. Credits : NAIF thanks the following people for contributing their data to this data set: - K. Edwards, D. Cook, E. Eliason, R. Batson, S. Wu; USGS Astrogeology Brunch - E. Guinness and S. Slavney; Washington University - M. Caplinger; Malin Space Science Systems - M. Davies and T. Colvin; The Rand Corporation - T. Duxbury and A. Konopliv; JPL

This data set contains all Viking Orbiters (VO1 and VO2) navigation and ancillary data that the NAIF group could collect and analyze during a year long restoration that took place in 1995-1996. Additional kernels based on the initial versions from 1995-1996 were created by NAIF between 2000 and 2008 and were added to the data set in 2008. The main goal of this restoration effort was to collect all available VO data of this kind in one place and to make them available to future users in consistent formats as SPICE kernel files. During this process data wasn't just copied from files in other formats to SPICE files; rather analysis of the data quality and consistency was done. When the same kinds of data were obtained from different sources they were compared and the results of these comparisons were reflected in data files and related documents. Also, some brand new data (spacecraft orbit data) were obtained. In particular the following results of this work can bring improvements to future VO imaging data interpretation: - newly reconstructed VO trajectory for the primary, extended and continuation mission phases which provided more accurate VO trajectory in comparison with orbits determined during the Viking era, - results of VO image time tags quality and reliability analysis and of an attempt to correct some of these tags based on this analysis; - an extensive set of VO orientation data including both the original data produced by the Viking Project and the orientation corrections done by some science groups as the result of cartographic analysis. Some general information about this data set 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, LSK, SCLK), accessible by using any available text file display tool such as a word processor, text editor, or the unix ``more'' or ``cat'' commands. SPK Files : Two kinds of SPK files are provided in this archive: SPK files for the spacecraft orbit and an SPK file for Phobos, Deimos, Mars, Earth and the Sun. Spacecraft Orbit SPK Files -------------------------- Two sets of VO trajectory data are available in SPICE SPK format -- trajectory data from the ``original'' SEDR (Supplemental Experiment Data Record) generated by the Viking Project and VO spacecraft trajectories reconstructed by A. Konopliv, JPL in 1995. Data from the first set were actively used during the last 20 years by different groups working on Viking Orbiter images registration -- USGS Astrogeology (R. Batson, S. Wu), Rand Corporation (M. Davies,T. Colvin), Malin Space Science Systems (M. Caplinger) and others. The information from this set was also stored in multiple derived products at USGS, Flagstaff and the PDS Geosciences node at Washington University, St. Louis. The second set, Konopliv's, became available only a short time ago as the result of orbit restoration using Viking Project era tracking data and the latest Mars gravity model. Unfortunately no tracking data for the VO1 survey mission were available at the time of restoration efforts. Therefore, Konopliv's data covers all mission phases (till the end of 1978) excepting the survey phase for both V01 and VO2. Konopliv's trajectory solutions, generated years after the end of the mission using a substantially better Mars gravity field model, are definitely more accurate for some intervals during the mission. Unfortunately, this is not true for the whole mission because for some periods data about propulsive maneuvers was not used and/or trajectory was extrapolated over large periods of time without tracking data, resulting in a great reduction in accuracy. For a more detailed comparison of the two solutions refer to the ``vo_spks.txt'' document provided in this data set. Solar System Body SPK File -------------------------- The file ``mar033.bsp'' contains the latest (as of the publishing date of this data set) ephemeris data for Mars, 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). NAIF did not attempt to reconstruct and/or capture the planet and satellite ephemeris data used during and after the VO mission because the latest ephemeris data provided in this data set is definitely more accurate and, therefore, supersedes earlier ephemeris solutions. Additional information about SPK files provided in this data set is available in the file ``data/spk/spkinfo.txt''. CK Files : All CK files provided in this data set contain orientation of the VO1 or VO2 instrument scan platform with respect to the B1950 inertial frame. This orientation was calculated from the following source data sets representing VO camera orientation: -- combination of the image orientation data from the original VO SEDR data set generated by the Viking Project and Viking Image Geometry (GEM) data set produced by K. Edwards of the USGS; -- orientation of the images registered by M. Davies of the Rand Corporation; -- orientation of the images registered by R.M. Batson of the USGS Astrogeology Branch; -- orientation of the images registered by S. Wu of the USGS Astrogeology Branch; -- orientation of the images registered by Malin Space Science Systems company (M. Malin, M. Caplinger) using automatic and manual registration methods; The orientation in the CK files was computed by excluding the transformation from the platform frame to each camera frame (this transformation was defined for each camera by a set of camera mounting alignment angles) and merging the platform orientation data sets calculated from camera A and camera B orientation together. Though the CK files generated using the first of the five source data sets listed above -- SEDR/GEM set -- are the most complete, the CKs containing the orientation that came out of the several image registration processes are probably more accurate. The orientation correction resulting from image registration was applied to orientation on each camera independently and it's quite possible that the constraint of constant relative alignment of the cameras was not taken into account during this process. That could cause inconsistency between orientation points on one orbit submitted by two cameras when the data is merged together. In addition to that the USGS approach for cartography and image registration was to assume that all the error in registering images to a base map was due to camera pointing and these were updated to match the base map in use. If however, the error was due to an orbit error, then it seems that using both an updated camera pointing (c-matrix) and an updated orbit position could re-introduce errors. For this reason, using inconsistent kernels -- CK containing pointing adjusted based on old trajectory and SPK containing new trajectory -- can re-introduce error. Refer to the meta-kernels provided in the ``extras/mk'' directory for the lists of kernels can be used together to achieve consistent geometry results. The CK files from the initial set produced in 1996-1997 and archived in 2000 were Type 1 CK files. These CK files proved to be unusable with the high-level APIs of the Frames Subsystem of SPICE. The set of Type 2 CK files containing the same orientation data and eliminating the usage deficiency of the Type 1 files was added to the data set in 2008. Caution on Using CK Files ------------------------- While not a data accuracy issue, the CK user is nevertheless cautioned to understand and properly use the ``found_flag'' and tolerance arguments that are inputs to the CK reader routine 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. Additional information about CK files provided in this data set is available in the file ``data/ck/ckinfo.txt''. 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. NAIF did not attempt to reconstruct and/or capture the planet and satellite constants used during and after the VO mission because the latest constant values provided in this data set are definitely more accurate and, therefore, supersede earlier values. Additional information about PCK files provided in this data set is available in the file ``data/pck/pckinfo.txt''. FK Files : Frames kernel files provide specifications for how one reference frame is defined relative to another frame. The VO FK files provided in this data set contains a complete set of frame definitions for the spacecraft, its structures such as instrument platform, and all of its science instruments. Meta information provided in the comments included in this file consists of the frame definitions, description of the frame relationships, source of and accuracy of the mounting alignment information, etc. Additional information about FK files provided in this data set is available in the file ``data/fk/fkinfo.txt''. IK Files : Instrument kernel files provide specifications for field-of-view size, shape and orientation for the named instrument. In this data set the IK files also provide instrument mounting alignment data. Metadata describing these parameters are provided in each IK file included in this archive. This data set contains IK files for four VO instruments -- the Visual Imaging Subsystem Cameras A and B (VISA and VISB) of VO1 and VO2. The mounting alignment and FOV data stored in the IK files for these instruments was extracted from the SEDR data. An additional set of mounting alignment information provided by T. Duxbury of JPL was included in the comment section of the files. There were no known accuracy estimates for this data at the time of this archive preparation. Additional information about IK files provided in this data set is available in the file ``data/ik/ikinfo.txt''. 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). NAIF was not able to locate a data product containing this mapping of the VO on-board clocks to ET that was generated during or after the mission. Since supporting SCLK time was still necessary for tagging data in the CK files, two SCLK files representing fictitious on-board clocks counting milliseconds since the beginning of the mission were created. These files are included in this data set to facilitate access to the CK data. During the VO data restoration, NAIF analyzed and attempted to correct some of the VO image time tags. The results of this activity were captured in the EK and SCLK files. However the SCLK time based on this correction was not used to tag data in the CK files. For more information regarding VO image time analysis and restoration refer to the ``vo_time.txt'' and ``vo_trec.txt'' documents provided in this data set. Additional information about SCLK files provided in this data set is available in the file ``data/sclk/sclkinfo.txt''. 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. Additional information about LSK files provided in this data set is available in the file ``data/lsk/lskinfo.txt''. EK Files : Two kinds of Events kernel (EK) files are included in this archive: VO image and ancillary data catalogs and EK files containing results of the image time tags analysis and reconstruction. The VO images catalog files capture the original meta information for VO camera images present in the SEDR and in the VO Image catalog maintained by Washington University, St. Louis. This information is included in this SPICE data set for reference purposes. The VO image time tag and time tag reconstruction EK files contain results of VO image time tag analysis and correction performed by NAIF as a part of the VO restoration. Refer to the ``vo_time.txt'' and ``vo_trec.txt'' documents provided  in this data set for more information about these results. Additional information about EK files provided in this data set is available in the file ``data/ek/ekinfo.txt''.