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MPSR Alignments - 1 UCB, Oct 26, 2006
THEMIS PROBE MISSION PRE-SHIP REVIEW
AlignmentsPaul Turin
LME
University of California - Berkeley
MPSR Alignments - 2 UCB, Oct 26, 2006
Alignment Overview
• Three alignments tasks:– Post-environmental testing alignment verifications for MSSS
and thrusters, comparing to SAI measurements– Alignment measurements of magnetometer booms and
generation of transformation matrices for locating mag mounts to the probe geometric axes
– Check probe alignment on Miller table for spin balance
• Measurements were performed by Bob Connors of LBNL using LBNL FARO Gold CMM arm (0.003” accuracy)
• All measurements and comparisons are complete
MPSR Alignments - 3 UCB, Oct 26, 2006
SAI Supplied Alignment Data
Contains:
Probe Coordinate System(C1)
Probe Ground Alignment Coordinate System(C4)
AXB Axis
MSSS Fiducial Tree
Thruster axes
All UCB measurements recorded in same file
.sat file output from FARO arm:
MPSR Alignments - 4 UCB, Oct 26, 2006
Alignment Verification for MSSS, Thrusters
• Used FARO arm used to pick up probe C4 coordinate system tooling balls
• Measured thrusters and MSSS using SAI fixtures
• Calculated angles between Probe axes and thrusters
• Compared MSSS SAI and SSL
• Goals:– MSSS 1° – Thrusters 0.5°
MPSR Alignments - 5 UCB, Oct 26, 2006
Sun Sensor Alignment Check
UCB fiducial triad normal vectors compared to SAI. The same within the accuracy of the FARO arm (0.06°) and much better than the goal of 1°:
MPSR Alignments - 6 UCB, Oct 26, 2006
Thruster Alignment Check
•Both SAI and SSL measurements exceed requirement of .5° (yellow). Exceedances deemed acceptable by SAI (SAI-TM-3030 & -3054)
•Exceedances accepted based on fuel consumption analysis that shows still less than all thrusters off by .5°
•SSL FARO measurements not very reliable due to req’d contact force and flexibility of thruster
•Holding 2-part tool in place elastically flexes thruster
•Force of Faro contact caused deflection
MPSR Alignments - 7 UCB, Oct 26, 2006
Alignment Measurements for Magnetometers
No MRD alignment requirement, desire is:• Aligned within a few deg, knowledge within 1°
Measurements:• Determine end-to-end magnetometer mount angular offsets
from geometric axes, and total uncertainty
SAI Probe C4 Coordinate
System
+ Final C4 to Fiducial
Alignment Measurements
+ UCB Mag to Fiducial
Alignment Offsets
Total Alignment Offsets
+ Final Alignment uncertainty
SAI Probe C4 coordinate
System uncertainty
+ UCB Mag Mount to Fiducial
uncertainty
Total Uncertainty
MPSR Alignments - 8 UCB, Oct 26, 2006
Magnetometer Theoretical Angles
MPSR Alignments - 9 UCB, Oct 26, 2006
C4 to Mag Boom Fiducial Measurements
Fiducial on stowed boom is measured from probe
C4 coordinate system
This data used to build solid models of actual fiducial w/r/t C4
MPSR Alignments - 10 UCB, Oct 26, 2006
Mag-to-Boom Alignment Data
Mag Mount to Fiducial Alignment Offsets:
This data used to build solid models of actual mag positions w/r/t fiducial:
MPSR Alignments - 11 UCB, Oct 26, 2006
Solid Models Generated from Measurement Data
Mag-to-Boom Alignment Model
Mag-to-Boom Theoretical Model Probe-to-Mag boom Fiducial Model
MPSR Alignments - 12 UCB, Oct 26, 2006
Models Combined to Create End-to End Model
MPSR Alignments - 13 UCB, Oct 26, 2006
Angles and Worst-Case offsets
MPSR Alignments - 14 UCB, Oct 26, 2006
Mag Mount CS Unit Vectors in PCS
MPSR Alignments - 15 UCB, Oct 26, 2006
Mag Mount CS Unit Vectors in PCS cont.
MPSR Alignments - 16 UCB, Oct 26, 2006
Transformation matrices
Actual mag mount CS unit vector direction cosines in PCS become transformation matrix for getting from sensor mount into probe coordinates. Combined with G2S and M2U transformations gives end-to-end solution.
MPSR Alignments - 17 UCB, Oct 26, 2006
FGM Boom Total Measurement Uncertainty
Mag Boom Measurement
Errors
Probe Measurement
Errors
Probe Geometric Axis to Magnetic Axes Uncertainty
MPSR Alignments - 18 UCB, Oct 26, 2006
Effect of worst-case mag boom misalignments on spin balance and CG
•Because all of the mag to probe measurements are angular, the actual mag offsets (and hence their effects of spin bal) are unknown.
•Effect was checked by assuming location of angular error is at the shoulder, which leads to worst-case translation. Resulting tilt and CG shift was calculated and shown to be negligible.
MPSR Alignments - 19 UCB, Oct 26, 2006
Spin Balance Alignment
• Probe position was checked on Miller table to verify that the probe geometric axis was coincident with the table spin axis.
• Uncertainty in measurement is 0.013° and .005”.
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