Data Set Overview : This data set includes the complete set of SPICE data for one NEAR mission phase 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 possibly 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(YYDDD) STOP TIME(YYDDD) ----------- ------------------- ------------------- NGCRU4_0001 1998358 2000010    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 GEOMETRY/SPK directory.  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 GEOMETRY/PCK directory.  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 GEOMETRY/IK directory.  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 GEOMETRY/CK directory.  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 GEOMETRY/LSK directory.  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 GEOMETRY/SCLK directory.   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 Overview : This volume contains SPICE kernel files created during mission operations only. No post processing has been done on these data.  SPK Files : Two kinds of SPK files are provided in this archive: SPK files for the spacecraft orbit and SPK files for EROS, Earth and Sun.  Spacecraft Orbit SPK Files -------------------------- SPK files are for the spacecraft are created by the NEAR JPL Navigation team. The kernels in this archive are specifically created for science users and distributed through the Science Data Center. These kernels are merged from a series of operations SPK kernels. The merged kernels remove all of the predicted data from the operations kernel, except the final predicted segment in the kernel. For science use they must be loaded sequentially by the spice kernel load routines, so that the oldest are loaded first. This will ensure that reconstructed values are used whenever possible.  Solar System Body SPK Files --------------------------- The solar system body SPK files were provided by the JPL Navigation team by way of the NAIF group. The accuracies for the bodies in each file can be obtained by inspecting the comment portion of each file using the COMMNT utility from the SPICE toolkit, which is available from NAIF. The asteroid SPK files were provided directly from the JPL Navigation team. The comment portion of the Mathilde and Eros SPK files provide detailed information regarding their usage and accuracy.   CK Files : C-kernel files provide orientation of the spacecraft. With the exception of NIS, the NEAR instruments have fixed orientation. MSI, NIS, XGRS and NLR all nominally are oriented along the spacecraft positive X-axis. The Solar panels and high gain antenna are nominally oriented in the positive z-axis. The small difference of instrument orientation from the X-axis are given in the instrument kernel (IK) files. The data Ck files are taken directly from the attitude telemetry produced by the spacecraft Flight Computer (FC). The FC data is reformatted at full resolution into the Ck files. No interpolation is done on these data.   EK Files : Events kernel files are often used to digitally represent an experimenter's notebook( ENB EK's) or to list a summary of all commands sent to a spacecraft, as is the case with Sequence EK's. In the case of NEAR, E-kernels are used in a very different way: to efficiently represent the shape of EROS. This representation is often referred to as a 'shape' or 'plate' model. There are two plate models of EROS in this delivery, one at a lower resolution, having only 1566 plates and another at a higher resolution, having 7516 plates. These plate E-kernels are specifically designed for use with the SPICE plate library, developed specifically for NEAR. This library is used to perform geometric calculations related to fields of view, observing geometry, etc. for shape models defined as a plate E-Kernel. The plate library can be obtained by contacting NAIF.   PCK Files : PCK files provide size, shape and orientation data for 'target' bodies such as Mathilde and EROS. A description of these data items and reference to their source is provided inside the text PCK files, which is a simple text file that can be viewed using any word processor, text editor or text display utility. The binary PCK files contain a comment area for each file. SPICE Toolkit utilities like SPACIT and COMMNT can be used to extract the comments from these files.   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.   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). The SPICE SCLK file is produced by the NEAR Mission Operations Center.  The time correlation accuracy provided in SCLK files is informally reported by the MOPS team to be better 20 milliseconds during orbital phases. This accuracy has been corroborated by independent estimates to within 500ms.  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.