Data Set Overview: : This archive contains data from the Dynamic Science Experiment conducted during the Stardust spacecraft encounter with comet Wild 2 on January 2, 2004. The data in this archive are organized into two tables in standard PDS format. The first of these tables provides high rate attitude control system (ACS) data spanning 40 minutes around closest approach while the second table provides attitude control thruster firing information (aka ``small forces'') spanning 3 hours around closest approach. This data provides a significant measure of the spacecraft's performance and the attitude control system's reaction to particle impacts.   Parameters : The primary parameters contained in the attitude data table are quaternions providing spacecraft orientation relative to the EME 2000 inertial reference frame (also known as the J2000 frame), spacecraft angular rates given in the spacecraft-fixed reference frame, and attitude and angular rate errors. The primary parameters contained in the small forces data table are thruster firing period begin and end times, accumulated delta-V values and numbers and duration of firings for each of the thrusters.   Processing : The source data for both tables were generated on-board the spacecraft and were sent down within packets in the spacecraft telemetry stream.  On the ground the attitude parameters were extracted into a text file containing data in tabular format using standard JPL Advanced Multimission Operations System (AMMOS) tools for channelized telemetry access. This text file was then slightly modified -- commas delimiting columns were inserted, UTC time tags were re-formatted to be in ISO format, and string column values were quoted -- to fully comply with PDS requirements.  The small forces parameters were similarly extracted from telemetry and then saved in a Small Forces File (SFF) using the MAKSFF process developed and run by NAIF. For inclusion into this archive the SFF file, which was a variable length line ASCII text file containing a table with a fixed number of columns, was augmented with two more columns (begin and end time as UTC) and re-formatted similarly to the attitude data to comply with PDS requirements.   Data : Both data files in this archive are plain ASCII text files, each containing a single PDS-style table with fixed-width, comma-delimited columns. Each file contains a few-line text header preceding the data. In the attitude data file the header lines list telemetry channel IDs, names, channel data types, and formats. The small forces data file header lines provide the original SFF file header. Each of the two data files is accompanied by a detached PDS label, described in detail in the ONLABELS.TXT document included in the archive. The format of the table columns is defined by an external table format file, pointed to by the label.  Attitude Data ------------- The channelized attitude telemetry produced by the ACS was collected at different rates during encounter. The data before and after closest approach was recorded at 2-second intervals. For the closest approach, which occurred at 2 January 2004 19:21:32 UTC, from 19:09:29 through 19:36:28 UTC most of attitude data was recorded at 0.1-second intervals. One exception is the body rate error data, which was still recorded at 2-second intervals and, therefore, appears to be ``stuck'' at one value while all other parameters are changing.  The ACS_MODE channel included in the attitude data file describes whether the ACS was controlling attitude according to the ground-commanded reference attitude (ENCOUNTER ABSOLUTE pointing mode, or ENC_ABS), or to the flight software-updated trajectory (ENCOUNTER RELATIVE pointing mode, or ENC_REL). Before and after the roll slews, the ACS_MODE was ENC_ABS. When the roll was commanded, the mode changed to ENC_REL. After closest approach, the return roll was commanded and the mode changed to ENC_ABS. For about 30 seconds after these command mode changes, the rate and attitude data reflects the slews. At all other times it reflects the attitude close to the fixed attitude that the controller was trying to maintain.  Body rates provided in the attitude file are filtered Inertial Measurement Unit (IMU) data, and attitude errors are computed from the estimated spacecraft quaternion compared to the reference quaternion. Since the controller was maintaining a fixed attitude (except during the slews) the body rate is the same magnitude but with opposite sign of the rate error. The measurement noise of about 0.00002 rad/sec is clearly seen in the rate data during the whole period covered by the file.  Small Forces Data ----------------- The flight software included an idealized thruster model, and was configured to produce data summarizing a 1-second interval of thruster activity and the resulting change in spacecraft velocity. Although the control system ran at 10Hz, the 1-second small forces data collection interval was chosen as a compromise between providing every pulse detail with the risk of overwriting the data, and not providing enough resolution for analysis.  The small forces data included the time the packet was recorded, the number of commanded thruster pulses for each thruster, the total on-time for each thruster in milliseconds, and the computed delta-V in the inertial EME-2000 reference frame. This data was collected only when necessary; that is, if no thruster commands occurred over an interval, no small forces data were generated. The average spacecraft attitude quaternion for the interval was also included in the packet.  A set of thruster calibration activities undertaken by the navigation and spacecraft teams over the course of the mission showed that the timing of the deltaV values computed by the spacecraft was very accurate while the deltaV magnitude was within +/- 30 percent of the values estimated from ground tracking data.  Using Attitude and Small Forces Data Together --------------------------------------------- Individual thruster firing records from the small forces file may be correlated to the attitude data by looking for a fast change in the spacecraft rate immediately following the firing and slower change in the spacecraft orientation for the period from this truster firing to the next one. Firing of a particular thruster or a set of thrusters usually results in change in a particular rate component. Therefore identifying the thruster(s) that fired in addition to the time of firing is essential. Also, the frequency at which the thrusters were firing at different times during the encounter along with the information about which of the thrusters were firing may indicate how much ``effort'' the ACS was spending to compensate for the effect of the surrounding dust environment while trying to maintain the commanded attitude.   Ancillary Data : Since neither of the two data files provided in this data set was supplemented with additional geometry data prior to archiving, the following SPICE kernels archived in the Stardust SPICE data set, SDU-C-SPICE-6-V1.0, may be used for computing any derived geometry parameters that might be needed to analyze the data:  Kernel Type File Name ------------ ------------------------ LSK naif0007.tls SCLK sdu_sclkscet_00105.tsc FK sdu_v17.tf SPKs sdu_l_2003_w2.bsp sdu_w2_opnav.bsp ------------ ------------------------  The spacecraft orientation data -- both quaternions and angular rates -- provided in the attitude and small forces data files were used in making, and are available in, the following SPICE CK files provided in the Stardust SPICE data set, SDU-C-SPICE-6-V1.0:  Kernel Type File Name ------------ ------------------------ CKs sdu_sc_rec_2003_w2_v2.bc sdu_sc_rec_w2_opnav.bc ------------ ------------------------   Coordinate System : The two reference frames, with respect to which the data included in this archive are provided, are:  - Earth Mean Equator and Equinox vector of 2000 JAN 01 12:00 (EME J2000), and  - Stardust spacecraft reference frame shown in this diagram:  || Dust Collector Main || Array Solar Array Shield || Shield .-. o HGA || .-. +Z ^| | ._____|_____. o | |:|:o:\:/:o: `-' || |-------------------. . Solar || | |/| Array || | .-----. CIDA | | <-------o| | | ' | | Return +X +Y | | . __/ | | Capsule | | `. `. |\| | |--- `. `.---- -----' o--------- | | `. `. \_______/ `-' `.'`. .'   The orientation quaternions stored in both tables provide orientation of the Stardust spacecraft reference frame relative to the EME J2000 reference frame. These quaternions are of the popular engineering style: Q : {r1*sin(phi/2), r2*sin(phi/2), r3*sin(phi/2), cos(phi/2)}, where R : (r1, r2, r3) is a unit vector specifying the rotation axis defined in the base frame. (This is not the formation style used within the SPICE system.) A rotation matrix formed from such a quaternion, when left multiplied by some vector given in the base frame, will rotate that vector into the target frame: rt : RM*rb. For help in understanding quaternion syntax and use refer to the discussion on quaternions provided in the PDS Standards Reference, also available from the NAIF node document database as ``A Brief Discussion of Quaternions as Used in Space Remote Sensing.''  The delta V components provided in the small forces data file are given with respect to the EME J2000 reference frame.  The angular rates and attitude and rate errors provided in the attitude data file are given with respect to the Stardust spacecraft reference frame.   Software : The data in this data set are in standard PDS format and, therefore, can be displayed by a number of PDS-provided tools or loaded into commercial programs that support comma-delimited formats. For this reason no special processing software is included in this data set.   Contact Information : For any questions regarding the data in this archive, contact:  Dr. John D. Anderson, Stardust Radio Science and Dynamic Science Experiment Lead

Confidence Level Overview : Overall flawless Stardust spacecraft ACS performance during the Wild 2 encounter, internal consistency of the data, and independent confirmation of correctness of the attitude and and small forces data by processing of the tracking and images over the course of the mission give a high level of confidence in accuracy of this data.   Review : This data was reviewed by the Dynamic Science Experiment team members as part of the post-encounter data analysis activities.   Data Coverage and Quality : This set includes all high rate ACS data produced by the spacecraft during the closest approach period of the Wild 2 encounter. No known gaps exist in the coverage provided by the data products.  Only complete packets, the integrity of which was verified by the standard JPL AMMOS telemetry tools using embedded checksums, were used to generate the data products provided in this data set. Consistency of the data was verified by cross-checking between the attitude and small forces data products and between the actual data products and the nominal encounter attitude profile.   Limitations : None.