PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2008-02-28 NOTE = "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 as C-kernels (CK). The pointing of a platform or an instrument is often expressed in terms of a transformation matrix from some standard base 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 subroutines that are part of the SPICELIB library, the major component of the NAIF Toolkit. These subroutines can be integrated into user application programs. Information about obtaining the SPICE Toolkit is located in the "software" subdirectory of the main directory of this dataset. To use C-kernels, a Spacecraft Clock Kernel (SCLK) is required. Also, for C-Kernels containing orientation of project-defined frames, a Frame Kernel file is required. Refer to the CK Required Reading (ck.req) document provided with the Toolkit or available from the NAIF Node of the PDS, to get more information on how to access C-kernel data. New Horizons C-kernels Contained on This Volume ============================================== This directory contains the SPICE C-kernel files for the New Horizons mission. All files are in IEEE big endian binary format and suitable for use on UNIX workstations and MACs. The following CK files are provided in this directory merged_nhpc_2006_v011.bc New Horizons spacecraft orientation CK file based on attitude telemetry covering the year 2006 merged_nhpc_2007_v005.bc New Horizons spacecraft orientation CK file based on attitude telemetry covering the year 2007 New Horizons CK File Naming Scheme ================================= The New Horizons CK provided on this volume are named according to the following scheme: merged_nhpc_YYYY_vXXX where: merged indicates the file is a "merge" of multiple CK files produced internally by the NH mission nhpc indicates the spacecraft and YYYY is the year covered by the kernel XXX is the file version number The file with the highest version number supersedes all files with the same name but earlier version numbers. Kernel File Details =================== Attitude informatrion in the New Horizons spacacraft flows between the various subsystems in the following way, ending up in S/C telemetry packets (ApID 006) and then in the C Kernels after ground processing: Star tracker (10Hz) IMU (Inertial) data (100Hz) \ / | \ / | \ / | \ / | Attitude estimator (1Hz) | \ | \ | \ | \ | \ | Attitude controller (25Hz) | | (Attitude, | Rate, and | Time info) | S/C Packets (1Hz) | | (Attitude and Time) | C Kernel Two flags are contained in the S/C Packets: 1) Quality 0 = No Attitude Data Available 1 = Star Tracker Only Data, No IMU Data Available 2 = IMU Data Available, No Star Tracker Data Available 3 = Both Star Tracker and IMU Data Available 2) Knowledge FALSE = G&C does not have Attitude Info TRUE = G&C has Attitude Info The values of these flags are NOT carried into the C Kernels. However, the kernels will only be generated using data with quality = 1, 2, or 3. In most cases (all times except during anomalies), quality will = 3. Nominal accuracy of the attitude data is 471 microradians per axis at 3 sigma. If no star tracker data is available (quality = 2), however, accuracy can be off by another 181 microradians during encounter mode or 1090 microradians in non-encounter mode. All of these numbers are worst case, and accuracy in general should be even better than 471 microradians. 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 the utility programs COMMNT and SPACIT included in the NAIF Toolkit. The Toolkit is available from the NAIF website. Contact Information =================== Regarding New Horizons project specific information provided in this data set: Joe Peterson or Andrew Steffl address: Southwest Research Institute 1050 Walnut St., Suite 300 Boulder, CO 80302 USA (303) 546-9630