DESCRIPTION |
Instrument Overview
===================
The instrument used in the Dynamic Science Experiment conducted
during the Stardust spacecraft encounter with comet Wild 2 on
January 2, 2004 was the Stardust spacecraft itself, or more
specifically the spacecraft's Attitude Control System (ACS).
During the encounter ACS provided a significant measure of the
spacecraft's performance and the control system's reaction to
particle impacts.
Throughout the encounter the control system maintained a
three-axis stabilized attitude. The controller also included
the capability to command a roll (about the spacecraft X-axis)
just before closest approach. Using an updated comet trajectory
computed in flight software, the controller commanded a slew to
keep the comet in view of the Navigation Camera. As the comet
passed, the controller commanded a return slew.
The spacecraft commanded two groups of thrusters for control.
Four 1.0 lbf (nominal) thrusters were available for the
bang-bang control and slews. Four 0.2 lbf (nominal) thrusters
were used for limit cycling and small error correction. Four of
each were available as spares. The larger thrusters were
designated TCM thrusters; the smaller, RCS thrusters. RCS
thrusters 1-4 and TCM thrusters 1-4 were used during encounter.
RCS 5-8 and TCM 5-8 were not used.
Scientific Objectives
=====================
The ACS provided data on attitude changes which result from
particle impacts. Analysis of this information could be useful
in diagnosing large particle impact events. For more
information see Anderson et al 2003.
Calibration
===========
N/A.
Operational Considerations
==========================
N/A.
Detectors
=========
The detectors used in this experiment included the ACS that
measured source data for and computed spacecraft orientation
and angular rate and ACS thrusters electronics used to record
thruster firing times and durations.
Electronics
===========
N/A.
Location
========
This section contains information about ACS thruster locations
and thrust vector directions, spacecraft center of mass
location, and spacecraft moments of inertia.
Spacecraft mass, kg:
M = 330.979
Spacecraft products and moments of inertia with respect to
(w.r.t.) the spacecraft coordinates translated to spacecraft
center of mass, kg/meter^2:
Ixx = 87.6748
Iyy = 200.2580
Izz = 241.1340
Ixy = 0.2169
Ixz = 4.1547
Iyz = -1.4881
Spacecraft center of mass w.r.t. spacecraft reference frame,
meters:
CM = [ -1.18277, -0.000567, 0.0340397 ]
Effective thrust direction unit vectors w.r.t. spacecraft
reference frame (unit vector):
RCS1 = [ 0, -0.2588, 0.9659 ]
RCS2 = [ 0, -0.2588, 0.9659 ]
RCS3 = [ 0, 0.2588, 0.9659 ]
RCS4 = [ 0, 0.2588, 0.9659 ]
RCS5 = [ 0, -0.2588, 0.9659 ]
RCS6 = [ 0, -0.2588, 0.9659 ]
RCS7 = [ 0, 0.2588, 0.9659 ]
RCS8 = [ 0, 0.2588, 0.9659 ]
TCM1 = [ -0.1736, 0.2549, 0.9513 ]
TCM2 = [ 0.1736, 0.2549, 0.9513 ]
TCM3 = [ 0.1736, -0.2549, 0.9513 ]
TCM4 = [ -0.1736, -0.2549, 0.9513 ]
TCM5 = [ -0.1736, 0.2549, 0.9513 ]
TCM6 = [ 0.1736, 0.2549, 0.9513 ]
TCM7 = [ 0.1736, -0.2549, 0.9513 ]
TCM8 = [ -0.1736, -0.2549, 0.9513 ]
Thruster location w.r.t. spacecraft reference frame, meters:
RCS1 = [ -0.7176, 0.2606, -0.5072 ]
RCS2 = [ -1.662, 0.2606, -0.5072 ]
RCS3 = [ -1.662, -0.2606, -0.5072 ]
RCS4 = [ -0.7176, -0.2606, -0.5072 ]
RCS5 = [ -0.7691, 0.2606, -0.5072 ]
RCS6 = [ -1.611, 0.2606, -0.5072 ]
RCS7 = [ -1.611, -0.2606, -0.5072 ]
RCS8 = [ -0.7691, -0.2606, -0.5072 ]
TCM1 = [ -0.6132, 0.257, -0.5159 ]
TCM2 = [ -1.767, 0.257, -0.5159 ]
TCM3 = [ -1.767, -0.257, -0.5159 ]
TCM4 = [ -0.6132, -0.257, -0.5159 ]
TCM5 = [ -0.6647, 0.257, -0.5159 ]
TCM6 = [ -1.715, 0.257, -0.5159 ]
TCM7 = [ -1.715, -0.257, -0.5159 ]
TCM8 = [ -0.6647, -0.257, -0.5159 ]
This -Z view of the Stardust spacecraft illustrates locations
of the thrusters:
.-.
| |---------------.---------------.--------------.
| | | | |
| | | | |
| | | CIDA | | +Y Solar
| | +Y |.-------. | | Array
| | ^ /.---------.-. | |
| |----------|----\`---------'-' -'--------------'
`-' || T1-T5-----------T6-T2 .-.
|| |O O * * * * O O|/| .' `.
+Z || | R1 R5 R6 R2 | |/ \
<-------x| | | o | Return
+X | | R4 R8 R7 R3 | |\ / Capsule
| |O O * * * * O O|\| `. .'
.-. | T4-T8-----------T7-T3 `-'
| |---------------.-| |---| |-.--------------.
| | | `-----' `-' | |
| | Periscope NAVCAM| | -Y Solar
| | | | | Array
| | | | |
| | | | |
| |---------------'---------------'--------------'
`-'
O -- TCM Thrusters
* -- RSC Thrusters
Operational Modes
=================
The spacecraft was 3-axis stabilized during the whole mission.
During the comet Wild 2 encounter the spacecraft had its +X
axis pointed to the incoming comet dust stream while keeping
the spacecraft-to-comet vector in spacecraft the XZ plane to
allow tracking of the nucleus by the navigation camera.
Subsystems
==========
The Stardust ACS subsystem included thrusters, IMU, star
camera, and controlling electronics and software.
Stardust performed attitude control and propulsive maneuvers
using a redundant helium-fed mono-propellant (hydrazine)
propulsion subsystem. This subsystem was comprised of one
titanium propellant tank and a total of 16 thrusters (two
strings of 8), all mounted on the lower deck of the spacecraft
(opposite the high-gain antenna and solar panels - pointing
toward the -Z axis of the spacecraft to avoid potential
contamination of the aerogel collector located on the +Z size
of the spacecraft). Eight of these were 0.2 lbf thrusters and
were used primarily for attitude control. The other eight were
1.0 lbf thrusters and were used for propulsive maneuvers.
Measured Parameters
===================
The parameters measured during this experiment included
spacecraft orientation and angular rate and times and durations
of ACS thruster firings.
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