1. MISSION PRE-ENVIRONMENTAL REVIEW MASS PROPERTIES & SPIN BALANCE
THEMIS
MISSION PRE-ENVIRONMENTAL REVIEW
MASS PROPERTIES & SPIN BALANCE
David Pankow
University of California – Berkeley

2. Thm-mint-proc-049 – draft 2 Released to GSFC & ManTech on 5/29
Themis PER: mass properties & spin balance
TEST Specifications
Thm-mint-proc-049 – draft 2 Released to GSFC & ManTech on 5/29
SAI-plan-0731 – Released
ManTech-09PC-W158, Rev. 4 – Released
SAI-TM-2873 – Spin Balance Predicts

3. TEST OBJECTIVES Themis PER: mass properties & spin balance
Probe Static Balance: < 0.180” CG offset in X,Y plane (PB.mec-6)
Probe Dynamic Balance: < 1 P.A. offset w.r.t. Geometric Z (PB.mec-7)
Probes will be balanced with Mag Booms Stowed (like Wind, Polar, & Fast)
MB Simulator masses will reflect the deployed boom CG & POI changes
DCG ~ 0.16” • DP.A. ~ 0.5
MB Simulator - MOI’s and mass must be subtracted from measured data
FM-MB masses and moments must be added using measured masses & coord’s.
Probe Mass Properties (CG & MOI confirmation)
Needed for Spin Stability Confirmation (PB.mec-5) & EFI SPB deployments
Spin Stability (IS/IT) > • Mass Tracking (IS/IT)  1.10 ±2%
Transverse MOI measurement’s of One Probe is adequate

4. TEST SEQUENCE Themis PER: mass properties & spin balance First Probe
Calibrate MPMF (Miller Table) and Measure Themis Fixture TARE’s
First Probe
Z (spin) Axis – Measure mass, X,Y CG, then XZ & YZ POI’s (by spinning)
Compute and mount the needed balance masses
Re-Measure mass, X,Y CG, then XZ & YZ POI’s (by spinning)
Measure ZZ axis MOI
X’, Y’ (lateral) Axes, where X’ is Tank CL’s horizontal, and Y’ is vertical
Measure table plane CG and table rotation axis MOI
Four Follow-on Probes
Same as 1st Probe, except lateral axes are not needed
“WET” PCA spin balance will be performed later at ASTROTECH

5. PROBE COORDINATES & BALANCE POINTS (SAI-PLAN-0731)
Themis PER: mass properties & spin balance
PROBE COORDINATES & BALANCE POINTS (SAI-PLAN-0731) +Y
+X’
+Y’ +X

6. SPIN BALANCE TEST FIXTURES Themis PER: mass properties & spin balance
Probe on MPMF
(2 test attitudes)
Probe Spin Adaptor
Probe Turnover Fixture

7. Themis PER: mass properties & spin balance
BACKUP SLIDES

8. Themis PER: mass properties & spin balance
Anticipated SPIN (or Z) Axis PCA MOI Measurement Results
Flight Probes (5 of 5 will be measured & balanced – CBE values here)
51.8 kgm2 ±1% = MPMF Measured Local Izz (5 probes)
259 kgm2 ±1% = Calculated Parallel Axis Contributions (S5 MR2, DR/R small)
311 kgm2 ±1% = Total Izz Contribution
Probe Fuel
/-0.0 kg = Measured Mass (±0.1 kg each probe)
3.35 kgm2 ±4% = Calculated Local Izz (10 tanks - 98% full)
181 kgm2 ±1% = Calculated Parallel Axis Contributions (S5 MR2, DR/R small)
184 kgm2 ±1% = Total Izz Contribution
Probe Carrier Assembly (< ± 10% needed for Star-48 yo-yo despin)
17.5 kgm2 ±10% = best Pro-E value for PC Local Izz
311 kgm2 ±1% = Probe Contribution (from above)
184 kgm2 ±1% = Fuel Contribution (from above)
513 kgm2 ±1% (RSS) or ±1.4% (worst case) = PCA TOTAL