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”.