PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = " SwRI:BLEnke 2020-04-01 - Updated for Release 0005 delivery - added note about superseded file for 2015. SwRI:BLEnke 2024-03-12 - Updated for Release 0007 delivery - Changed the SwRI mailing address " OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2020-06-30 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_YYYY_vXXX.bc New Horizons spacecraft orientation CK files based on attitude telemetry covering the year YYYY. merged_nhpc_2014_v000.bc was superseded by merged_2014_v001.bc merged_nhpc_2015_v001.bc was superseded by merged_2015_v039.bc merged_nhpc_2019_v018.bc was superseded by merged_2019_v029.bc nh_lorri_wcs_vXXX.bc C-Smithed C-Kernel, using stars in the Fields-Of-View of LORRI approach data. - The latest nh_lorri_wcs* version covers distant observations of the Pluto system taken by the LORRI imager from mid-2014 through two days before the Pluto Flyby encounter (P-2d). Observations of Arrokoth are also covered in 2018 and 2019, and distant KBO observations are covered through the end of 2020. For Pluto, these C-Kernels only apply to LORRI observations on approach, through 2015-07-12. Specifically, it does not include any imaging from the Pluto Flyby Encounter on 2015-07-14. For Arrokoth, v002 and later versions apply to LORRI observations before, during, and after the closest approach on 2019-01-01. The files used to produce this C-Kernel were generated by Simon Porter via astrometric correction of the LORRI boresight. This provided updates to RA, DEC & Twist, allowing for updated spacecraft orientation. This updated C-Kernel provides improved attitude during the exposure of each LORRI 1x1 and 4x4 image. Images that provided a correction of greater than 500 microradians, which is equivalent to ~99 LORRI 1x1 pixels or ~25 LORRI 4x4 pixels, were rejected by the automated processing, although they may be valid. This rejection prevents the possibility of significant erroneous pointing corrections. Caveats: Version 003 (and earlier) zeroes out angular rate information when the file is included in the SOC metakernel. Several FITS header keywords (RATEX, RATEY, RATEZ, RATEXY, RATEYZ, RATEXZ, and RATEMAG) will have values of 0.0. Therefore, these kernels have not been used for official SOC production runs up through and including the SBN-PDS KEM1 K5 datasets, nor are they included in the latest metakernel. New Horizons CK File Naming Scheme ================================== The New Horizons CKs provided on this volume are named according to the following schemes: merged_nhpc_YYYY_vXXX nh_lorri_wcs_vXXX where: merged indicates the file is a "merge" of multiple CK files produced internally by the NH mission nhpc indicates the New Horizons spacecraft (nh), Pluto (p), and Charon (c) YYYY is the year covered by the kernel XXX[XXX] is the file version number nh_lorri_wcs indicates C-Smithed reconstructed pointing based on stars identified in the Field Of View of LORRI images taken during the Pluto Approach sub-phase of the Pluto mission phase of the NH mission. Version numbers are automatically generated, so while it is generally true that the file with the highest version number supersedes all files with the same name but earlier version numbers, in actuality the version number is used by Science Operations Center (SOC) pipelines to avoid file naming conflicts. There are a number of events that could reset a sequence of version numbers; also the SOC allows for multiple pipelines owned by different users or even at different locations, and there is no facility for coordinating these version numbers across separate locations. The only way to assess the relative usefulness of the CKs is to check the meta-kernels provided with this data set and/or to review the dates included in the comments embedded in each CK file. Kernel File Details =================== Attitude information in the New Horizons spacecraft 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. N.B. The initial segments are generated from attitude telemetry on a daily basis. Over time, the SOC pipeline combines daily CKs into monthly CKs, and monthly CKs into yearly CKs. The comment area of the CKs are combined along with the attitude informations, so be warned that there is a large accumulation of repetitive information in the comment area of these yearly CKs. Long interpolation intervals in Type 2 CK segments ================================================== Some pointing instances in type 2 segments cover tens of thousands of seconds (e.g. 2008-10-25, 2008-11-15, 2008-11-20). Type 3 CK segments with calculated velocities used for spinning mode ==================================================================== When modelling the transition from 5RPM spinning attitude mode using Type 2 CK segments to non-spinning 3-axis stabilization mode using Type 3 CK segments, the point at which the CK-writing process switched from Type 2 segments to Type 3 segments was too early i.e. while the spacecraft was still spinning. As a result, the Type 3 attitude telemetry was too sparse to accurately model the spinning spacecraft; in some cases lookups into such Type 3 segments will return modelled angular velocities that are inverted (flipped sign) from the actual behavior. An analogous situation occurs during some transitions from 3-axis mode to spin mode, with the transition from Type 3 to Type 2 segments occurring too late. Contact Information =================== Regarding New Horizons project specific information provided in this data set: Joel Parker or Brian Enke address: Southwest Research Institute 1301 Walnut Street Boulder, CO 80302 USA (303) 546-9630