Data Set Information
DATA_SET_NAME HAYABUSA LIDAR V1.0
DATA_SET_ID HAY-A-LIDAR-3-HAYLIDAR-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : The HAYABUSA spacecraft included a LIght Detection and Ranging (LIDAR) altimeter. The primary objective of LIDAR was to establish the range between the HAYABUSA spacecraft and the asteroid Itokawa for navigation purposes during the surveying and collection phases of the mission. It provided excellent estimates of the location of the spacecraft relative to the asteroid. The secondary scientific objective of the LIDAR included determining the mass of the asteroid, and measuring its global surface elevation and roughness. The Calibrated Data Record (CDR) contains LIDAR science and telemetry data that has been converted to engineering and physical units. The Experiment Data Record (EDR) is the source for the science data, while the House Keeping Experiment Data Record (HKEDR) and telemetry provides the data needed to determine the position of the HAYABUSA spacecraft relative to the asteroid. Resulting orbit, geometric, and calibration data have been incorporated, to determine the location of the LIDAR boresight on the surface of the asteroid provided in the CDR. With an appropriate shape model and density estimates for Itokawa, these can be used to obtain topographic profiles of the surface [e.g., CHENGETAL2002] of Itokawa. Further information about the Hayabusa LIDAR data set may be found in [BHARNOUIN-JHAETAL2008]. Data : All the HAYABUSA LIDAR data records are ascii tables. Each EDR contains three columns of data. The first column is the the Mission Elapsed Time in units of spacecraft ticks when the LIDAR range was measured. One spacecraft tick equals 1/32 of a one second. The second column is equal to this same time but translated into units of Universal Coordinated Time UTC. The third column equals the range measured by the LIDAR at the time indicated. The LIDAR collected data at 1 Hz (1 return per second) for the entire duration of the encounter with Itokawa (~3 months). The EDR is composed of three files: EDR20050911_20050929.TAB which corresponds to data acquired during the GATE Position Phase when the HAYABUSA spacecraft was at ~20km distance from the surface of the asteroid; EDR20050930_20051028.TAB which corresponds to data acquired during the HOME Position Phase when the HAYABUSA spacecraft was at 3-7km distance from the surface of the asteroid; EDR20051029_20051125.TAB which corresponds to the TOUCH DOWN phase when the HAYABUSA spacecraft attempted to sample the surface of Itokawa. The housekeeping (HKEDR) file has not been included in the archive because the mission has not yet given permission for it to be archived in PDS. When permission is given to archive it, it will be added. The first three columns of this HKEDR are identical to those in the EDR file. The next two columns provide the illuminated centroid of Itokawa within the reference frame of the wide angle camera, ONC-W1. This camera is part of the AMICA instrument package and more information is given in the description for that instrument. In brief, it is a 512 by 512 pixel imager with a field of view of 60 degrees. The software aboard the HAYABUSA spacecraft imager found the centroid of the largest illuminated object in the field of view of this ONC-W1, with DN values greater than a threshold of 5DN. This happened at 2 min intervals, and was accompanied by a LIDAR range and time listed in the first three columns of the HKEDR file already discussed. The first of the two pixel values gives the x or sample location of the centroid. The second one gives the y or line location of the centroid. The one HKEDR file includes data for the entire mission. A pixel value for x and y of zero implies the asteroid filled the entire field of view of the ONC-W1. The CDR data files are of two kinds. The first is an unfiltered (UF) version of the data after the processing described in the next section was undertaken. The second is composed of the same set but was filtered (F) to remove any estimated surface point which was located more that 10m from the predicted intersection of the vector defining the pointing of the LIDAR boresight and the shape model of the asteroid. The filenames include F and UF respectively. The CDR files include information on both the HAYABUSA LIDAR and the boresight of the Near Infra-Red Spectrometer aboard HAYABUSA. The NIRS data is provided as a courtesy to others HAYABUSA related efforts because it is exactly aligned with the LIDAR. Both filtered and unfiltered CDR files provide: the spacecraft mission elapsed time (MET); the time in UTC; the X,Y and Z LIDAR estimates of the spacecraft location after processing; the estimated X,Y,Z position of the LIDAR and Near Infra-Red Spectrometer (NIRS; Co-aligned with the LIDAR) footprint; the predicted X,Y,Z position of the LIDAR footprint at the intersection of the LIDAR boresight vector with the asteroid shape model; incidence, emission and phase angle of the center of the LIDAR/NIRS field of view (FOV); size of the LIDAR FOV; size of the NIRS (FOV); longitude and latitude of the LIDAR/NIRS (FOV); predicted longitude and latitude of the LIDAR/NIRS (FOV) at the intersection of the LIDAR boresight vector with the asteroid shape model; mean incidence, emission and phase angle of the FOV of NIRS which lies on the asteroid; mean longitude and latitude of the NIRS FOV which lies on the asteroid; predicted minimum and maximum longitude and latitude of the NIRS FOV from the intersection of the NIRS boresight vector with the asteroid shape model; number of points 3x3 grid within the NIRS FOV that falls on asteroid used to estimate the previous mean, minimum and maximum longitude and latitude values. Processing : The CDR incorporates the best orbital solutions and LIDAR boresight locations derived by the HAYABUSA LIDAR team. As a first step, a new algorithm was developed to better locate the Hayabusa spacecraft relative to the asteroid. The most important data initially used was the housekeeping (HKEDR) data of the x-y pixel of the illuminated centroid obtained by the ONC-W1 (WAC) camera of AMICA. Additional data included the project supplied information on the pointing of the WAC (SPICE C-kernels), as well as a good shape model of Itokawa (generated by B. Gaskell and part of the HAYABUSA PDS delivery). Our algorithm assumes that the spacecraft attitude (i.e., its pointing) provided by the SPICE C-kernels as determined by the on board star cameras remained correct throughout the mission. The algorithm consists of first using a preliminary spacecraft location, the spacecraft attitude data and the shape model to create simulated images of Itokawa as seen by the WAC at the time the actual HKEDR was acquired. A predicted x-y pixel location for the illuminated centroid was computed from these simulated images simultaneously with a predicted range to where the LIDAR was pointing at the surface of the Itokawa. These predicted HK-data were then compared to the actual HKEDR in order to correct the spacecraft position. This comparison was repeated iteratively until the predicted and actual x-y pixel locations were within 0.1 pixel, and the predicted and measured ranges were within 0.5 to 3 m of each other, depending on the range of the spacecraft relative to the surface of the asteroid. The algorithm used to reproduce the HK data provides at 2 min intervals excellent estimates of the spacecraft position relative to Itokawa for most of the time that Hayabusa observed Itokawa. The data acquired by the LIDAR, however, was taken at 1 s intervals. Therefore, good estimates of the spacecraft position were still required for those periods between when HK data was acquired. After some trial and error, good estimates were obtained by initially using linear interpolation to first guess the locations of the spacecraft between those estimates provided by the HK data. We then fit all the positions using least squares to a second order polynomial or parabolic function between spacecraft maneuvers. Such a function should have a form that compares favorably with solutions to the semi-orbital equation of motion for the Hayabusa spacecraft that include the solar pressure acting on the spacecraft, because major maneuvers occurred fairly frequently (between a few hour to a few day intervals). Analysis of the resulting data indicate significant improvements on how well the new trajectory estimate for Hayabusa relative to what was initially provided by the project in the form of SPICE SP-Kernels. In this delivery, we provide two CDR files for each time range. The first includes boresight locations that have not been further filtered after the above processing was undertaken. The second set is filtered to remove bad data: any estimated surface point which was located more that 10m from the predicted intersection of the vector defining the pointing of the LIDAR boresight and the shape model of the asteroid were removed. This difference of 10m was chosen because most small scale variations in surface topography on Itokawa are less than this amount. After all these efforts, ~87% of the LIDAR points were found useful. This is equal to ~1.3 million LIDAR shots. Ancillary Data : As part of analysis, we found that the AMICA SPICE image kernel needed further modification. A new version (amica_v202.ti) was prepared by Olivier Barnouin-Jha. In order to generate the CDR dataset, we used several project provided SPICE kernels including the planetary ephemeris kernel pck00008.tpc, the Itokawa Ephmeris and rotation kernel sb_25143_140.bsp and the HAYABUSA clock kernel hayabusa.tsc (the version of 2005-09-06). These and the other SPICE kernels used to prepare the data files are being archived in the PDS SPICE archives. Coordinate System : A planetocentric coordinate system is employed, which is body-centered, using the center-of-figure as the origin. The actual vector from the center of Itokawa to the surface should be primarily employed for scientific purposes becuase of the important curvature of Itokawa where some locations can possess more than one latitude and longitude. However, latitude and longitude data are also provided, but should be used with caution. The latitude is defined by the angle between the equatorial plane and a vector extending from the origin of the coordinate system to the relevant point on the surface. Latitude is measured from -90 degrees at the south pole to +90 degrees at the north pole. Longitude extends from 0 to 360 degrees, with values increasing eastward (i.e., it is a right-handed coordinate system) from the prime meridian. This coordinate system is preferred for use in navigation and geophysical studies in which, for example, estimates of elevation or gravitational potential are generated mathematically. References ---------- Barnouin-Jha, O., A. Cheng, T. Mukai, S. Abe, H. Naru, R. Nakamura, R.W. Gaskell, J. Saito, and B.E. Clark 2008. Small-scale topography of 25143 Itokawa from the Hayabusa laser altimeter. Icarus 198, 108-124. Cheng, A.F., O. Barnouin-Jha, L. Prockter, M. T. Zuber, G. Neumann, D. E. Smith, J. Garvin, M. Robinson, J. Veverka, and P. Thomas, Small-scale topography of 433 Eros from laser altimetry and imaging. Icarus 155, 51?74, 2002.
DATA_SET_RELEASE_DATE 2008-06-12T00:00:00.000Z
START_TIME 2005-09-11T04:56:26.198Z
STOP_TIME 2005-11-25T10:04:00.844Z
MISSION_NAME HAYABUSA
MISSION_START_DATE 2003-05-09T12:00:00.000Z
MISSION_STOP_DATE 2010-06-13T12:00:00.000Z
TARGET_NAME 25143 ITOKAWA
TARGET_TYPE ASTEROID
INSTRUMENT_HOST_ID HAY
INSTRUMENT_NAME LIGHT DETECTION AND RANGING INSTRUMENT
INSTRUMENT_ID LIDAR
INSTRUMENT_TYPE ALTIMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS SUPERSEDED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The resolution of the data is about 50 cm vertically. Along track spacing is variable. Small errors in the HAYABUSA emphemeris solutions and pointing knowledge yield uncertainties in absolute ground spot location to within 10m, but is often better. Timing Uncertainty : The clock aboard Hayabusa possesses an estimated uncertainty of +/- 12 seconds due to a periodicity in the control and operation of the analog signal processing unit. This effect was somewhat remedied by the analysis used by the LIDAR science team. The relative pointing between the ONC-W2 camera and AMICA were statiscally adjusted so that a simulated image using the Hayabusa shape model would match the location of Itokawa observed by AMICA. Both data sets suffer from the same timing problem and our approach would thus have minimized their effect over the lifetime of the mission. Additional errors due to this timing uncertainty are captured by the 10m uncertainty clearly established to be the accuracy of the LIDAR CDR filtered data. Examples of the excellent match between the topography observed, the estimated location of the boresight using the LIDAR CDR dataset and observations of where this boresight should be in AMICA all indicate that this problem has a minor impact on the quality of the Hayabusa LIDAR data set (see Barnouin-Jha et al. [2008] for additional details.) Data Coverage/Quality : After processing, a total of 87% of the mission's data was found useful. Limitations : The HAYABUSA LIDAR data has met many of its design expectations. It has demonstrated a measurement precision of ~50 centimeters over flat terrain. After processing, more than 87% of the data was found useful for topographic analyses.
CITATION_DESCRIPTION Mukai, T., Abe, S., Barnouin-Jha, O., and Cheng, A., Hayabusa LIDAR V1.0. HAY-A-LIDAR-3-HAYLIDAR-V1.0. NASA Planetary Data System, 2008.
ABSTRACT_TEXT The HAYABUSA spacecraft included a LIght Detection and Ranging (LIDAR) altimeter. The primary objective of LIDAR was to establish the range between the HAYABUSA spacecraft and the asteroid Itokawa for navigation purposes during the surveying and collection phases of the mission. It provided excellent estimates of the location of the spacecraft relative to the asteroid. The Experiment Data Record (EDR) and Calibrated Data Record (CDR) from the Hayabusa LIDAR experiment are included in this data set.
PRODUCER_FULL_NAME CAROL NEESE
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