PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "G.Neumann, 2001-07-13" RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "NEAR-A-NLR-5-CDR-EROS/ORBIT-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "NEAR NLR LEVEL 2 DATA PRODUCTS V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = TABLE START_TIME = 2000-03-05T00:00:04 STOP_TIME = 2001-02-12T19:42:43 DATA_SET_RELEASE_DATE = 2001-07-16 PRODUCER_FULL_NAME = "DAVID E. SMITH" DETAILED_CATALOG_FLAG = "N" DATA_SET_DESC = " Data Set Overview ================= The NEAR Laser Rangefinder (NLR) Level 2 Data Products include the along-track profiles of NLR data in SI units, together with spacecraft position, orientation, and timing data. The radius of 433 Eros with respect to its center of mass is the primary profile parameter. Surface slope and topographic relief are not as easily defined on an irregular object as on the Earth. We provide the geopotential arising from the mass of the asteroid and its rotation, based on the NLR shape model NLR125AR.IMG, a rotation rate of 3.3166E-04 rad s^(-1), and an assumed homogeneous density of 2670 kg m^(-3). Geophysical studies may use the potential as a proxy for topographic height, scaled by a regional average gravitational acceleration [CHENGETAL2001]. Ranges from level 1 NLR data are the source of the level 2 data product. Precision orbits were generated at NASA-GSFC, and supplemented where appropriate by JPL navigation team orbits, ancillary timing and attitude information supplied by the NEAR SDC and instrument data derived from in-flight analysis. These data were merged to create the calibrated profile data. Each level 2 data product is a text format table corresponding to a daily level 1 EDR file, and is described by a detached label. The file naming convention is LyydddNv.TAB, where L=laser, and yyddd contains the two-digit year and the three-digit day of observation. The letter v stands for processing version. Version 'D' is based on the most recent JPL navigation team orbits, version 'G' and 'J' on GSFC's precision orbit series 393, where version 'J' is supplemented by JPL orbits at times of spacecraft maneuvers. There is only one version of the data for each specific orbit on the volume. The orbital mission phase employed only normal format packets. In these packets, the spacecraft mission elapsed time (MET) is recorded at the time of the first major frame in the packet. A normal rate packet contains up to 56 observations, so that the last observation may occur up to 55 seconds after the nominal packet time in the case of 1 Hz data. The SPACECRAFT_CLOCK_STOP_COUNT and STOP_TIME values reflect the time recorded in the last packet for a given UTC day. Thus the last observation may occur later than the nominal STOP_TIME. Parameters ========== Profiles are tables of longitude, latitude, and radius at the laser bounce point, together with time stamps, the spacecraft position, and instrument threshold setting. Processing ========== Ranges are converted from counts to meters of one-way range from NLR to 433 Eros as described in the calibration document NLRCALIB.TXT. Precision orbit data for the NEAR-Shoemaker spacecraft is provided by the NASA-GSFC analysis team and the JPL navigation team, and is archived in the form of SPICE format spacecraft ephemeris (SPK) files. The MET time associated with each shot, with minor frame given in decimal seconds, is converted to Ephemeris Time in seconds past J2000 (ET) using the project's time conversion (SCLK) file. The spacecraft position at the ET shot time is interpolated from the SPK file. The spacecraft orientation SPICE file (CK) is resampled at 1-second intervals of whole seconds. Its quaternions are convolved with a 9-point, centered, finite-impulse-response filter to reduce high-rate gyro noise before conversion to matrix form. The filtered spacecraft orientation matrix transforms vectors from the J2000 inertial reference frame to the instrument deck (NEAR_SC_BUS_PRIME) frame. Observations are directed toward the positive X'-axis in this frame. A fixed boresight offset with respect to this frame is assumed. The Euler angles of the boresight are provided as a SPICE instrument kernel (IK) file, from which a transformation matrix from NEAR to NLR frame is derived. The J2000-to-NLR frame matrix is calculated from the smoothed CK by matrix composition. The one-way time-of-flight from the laser range is added to the laser fire time to obtain the bounce point time, and the calibrated one-way range vector is projected from the spacecraft state at this time along the boresight to obtain the surface bounce point position in inertial coordinates with respect to the asteroid center of mass. The inertial position is then rotated to the asteroid body-fixed coordinate system using satellite/planet position and orientation files (PCK) supplied by the project. The asteroid-located radius vector is given in both radial coordinates and as a Cartesian position vector. The angle subtended by the bounce point to NEAR spacecraft position vector and the radius vector is calculated. This angle is loosely termed the EMISSION_ANGLE, assuming a spherical body. Normally an emission angle greater than 90 degrees would indicate a missed shot, but due to the irregular shape of 433 Eros, emission angles >120 degrees were obtained. The angle subtended by the NEAR to Eros center vector and the NEAR to bounce point vector (OFF_NADIR angle) is also provided. Lastly, the potential due to gravity and rotation at the shot location is calculated [CHENGETAL2001] assuming a uniform density of 2670 kg m^-3 and the NLR125AR.IMG shape model. The potential is evaluated via a surface integral over a 2 by 2 degree grid, refined to 1/4 by 1/4 degree in the vicinity of the shot. Data Format =========== The Level 2 data product comprises the along-track time series of the NLR instrument's science data in physical units, produced using precision orbits, ancillary timing and attitude information supplied by the NEAR SDC, and instrument data derived from in-flight analysis. Each Level 2 data product is a text format table corresponding to a daily level 1 EDR file, and is described by a detached label. The file naming convention is LyydddNv.TAB, where L=laser, and yyddd contains the two-digit year and the three-digit day of observation. The letter v stands for processing version. The current Level 2 versions denote the source of spacecraft ephemerides: D - reconstructed orbits provided by the JPL Navigation Team, during the initial asteroid encounter and the final descent phase. G - reconstructed orbits provided by the GSFC NLR investigation. J - GSFC orbits supplemented by JPL orbits around times of Orbit Change Maneuvers and Momentum Correction Maneuvers. There will be only one version of the data for each specific orbit. These files are stored in the LEVEL2/TOPO directory. A JPEG image representing each of these level 2 data files on the volume can be found in the browse/ directory. There is also a single Level 2 observation log file. This table contains the start times and basic parameters for the start of collection of each observation set by the NEAR NLR. The log file is stored in the LEVEL2/LOG directory. Ancillary Data ============== None. Coordinate System ================= NLR data files use an EROS centered body-fixed coordinate system with positive east longitude. The transformation from inertial (J2000) coordinates to body-fixed is represented by the project-supplied SPICE format attitude and orientation files used to generate level 2 data products. Software ======== None. Media/Format ============ The archival data set was written on CD-WO by the NEAR/NLR Project. The CD-WO volumes conform to ISO 9660 Level 2 standards." CONFIDENCE_LEVEL_NOTE = " Overview ======== Data in this archive have been reduced as part of mission data analysis activities of the NEAR/NLR Science Team. Review ====== This archival data set was reviewed by the NEAR/NLR Science Team prior to final submission to the Planetary Data System (PDS). Prior to creation of the final version of the archival data set, key elements of the archive were distributed for preliminary review. These included electronic versions of example PDS labels, example data files, CATALOG files, and other relevant documentation. These materials were distributed to PDS personnel, the experiment investigator, and others, as appropriate. Data Coverage and Quality ========================= The data coverage was determined by the orientation of the instrument X' axis during science data acquisition by several instruments. NLR did not control pointing for the bulk of the time, so the coverage is largely unplanned. Nevertheless, sufficient density of coverage was obtained in all of the orbit phases to resolve topography of features greater than 50 m in extent. Limitations =========== The limitations in this data set follow from the quality of the execution, which is described above under Data Coverage and Quality." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = EROS END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = NEAR INSTRUMENT_ID = NLR END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CHENGETAL2001" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END