TFAWS 2006 SIM PlanetQuest: Milli-Kelvin Analysis of the … · 2006. 7. 27. · Space Interferometry Mission A NASA Origins Mission SIM TFAWS 2006 F. Kelly August 7, 2006 -3 SIM

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A NASAOriginsMission

SIM

F. Kelly August 7, 2006 -1TFAWS 2006

TFAWS 2006SIM PlanetQuest: Milli-Kelvin Analysis of the Collector

Subsystem Thermal ModelFrank Kelly8/7/2006

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Presentation Agenda

• The SIM PlanetQuest Mission• Spacecraft Subsystems

– Collector Bay Hardware

• Temperature Requirements• Thermal Control Approach• Milli-Kelvin Modeling Approach Flow Chart

– Spacecraft FEM– OOPCC Optical Assembly FEM– Spacecraft Slew Scenario during Normal Operation– Results for OOPCC Optical Assembly– Thermal-Structural Temperature mapping

• Conclusion

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SIM PlanetQuest• Part of the NASA Astronomical Search for Origins

program (ASO)• Orbiting Michelson Interferometer

– 10m baseline– Locate small planets (4 times Earth radius) around the nearest

250 stars– Earth trailing orbit

• Launching between 2011 and 2015– 5 year primary mission life– 10 year goal

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SIM Instrument Subsystem Concept

Outboard Collector Bay

Combiner

Inboard Collector Bay

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Collector Bay Assembly Concept

CMP Bench

M1-Optic

OOPCC Fiducial

COL Bay Truss

COL Bay Structure

TCC Fiducial

TCCTM

SID Mirror

SID Outer Gimbal

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Temperature Requirements

• Instrument optics and optical support structure have small allowable flight temperature (AFT) ranges and tight stability requirements– AFT ranges are between 10 and 30°C– Stability requirements between 10 and 150 mK/hr

MIN MAXSiderostat Optic 10 30 25Siderostat Strut 10 30 150COB Composite Bench 10 25 100COB M1 Optic 15 25 40COB M2 Optic 15 25 40COB M3 Optic 15 25 40Collector Bay Stucture 5 35 500Collector Bay Truss 10 30 500DCC Optic 10 30 10TCC Optic 10 25 10OOPCC Glass 10 25 10

AFT Range (°C) Stabilty Requirement (mK/hr)Hardware

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Thermal Control Concept and Implementation• Collector bay is cold biased

– Ensures heater control authority– Minimizes stability impact on critical optics– Collector aperture always faces space with no view of the Sun

• Optics must be held at on-ground alignment temperatures (approx. 20°C)– Optics are heated with thermal enclosures

• Optic and optical support structure heaters controlled with PID• PID set-points can be changed during mission to correct for ground

to orbit temperature differences• PID heaters provide tight temperature control

• Less critical hardware heated with steady state thermal switch and/or insulated with MLI

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Milli-Kelvin Modeling Process Flow Chart

Coarse Thermal Model of SIM

Spacecraft (IDEAS)

Detailed Thermal Model of Optical

Assembly (IDEAS)

Detailed Structural Model of Optical

Assembly

Coarse Thermal Model with the detailed Optical

Assembly Thermal Model substituted (IDEAS)

Temperature Results Mapped to Detailed Structural Model

using (TMG)

Compared Against Thermal

Requirements

Structural Results for Detailed Optical Model

Compared Against Structural

Requirements

Covered in Presentation

Temperature Results for Detailed Optical Model

(TMG)

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Instrument Thermal Model

• 34,700 elements• Incorporates both collector bays

and the combiner subsystem• Proportional control used to

simulate PID control

Siderostat

Compressor Optical Bench

Collector Bay Structure

Outboard

Collector Bay

Combiner

Inboard

Collector Bay

OOPCC

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Substitution of the Coarse OOPCC Mesh with the Detailed Mesh

Coarse Mesh of Optical Assembly

Detailed Mesh of Optical Assembly

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OOPCC FEM in Course Mesh

Transplanted OOPCC Assembly

Spacecraft Model

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Analysis – Mission Slew Scenario

15°

• Siderostat optic can rotate 15° on the sky

• Each 15° tile is observed for one hour• Observatory then rotates a maximum

of 15° to the next tile

Anti-Sun Tile

SIM Observatory

Tile on Edge of Sun Exclusion Area

Collector Bay Aperture

Sun

120°Observation

Tile

Collector

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OOPCC Predicted Temperature Results

OOPCC Gradient (ΔT), Raw and with Linear Drift Removed - 120° Orange Peel Slew (1.1°/min)

0.064

0.066

0.068

0.070

0.072

0.074

0.076

0 5 10 15 20

Duration (hr)

ΔT (C

)

-0.0002

-0.0001

0.0000

0.0001

0.0002

0.0003

0.0004

Post

-Pro

cess

ed Δ

T (C

)

Delta-T

Delta-T (Linear Drift RemovedDuring Hour Long Observation)

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OOPCC Predicted Stability Results

OOPCC Change in Gradient Over Time (dT/dt) Using Temperatures with Linear Drift Removed - 120 Orange Peel Slew (1.1/min) - Only

Obseravational Periods Shown

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

0 5 10 15 20

Duration (hr)

dΔT/

dt (m

K/h

r) d-Delta-T/dt

Current WA Requirement

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Predicted Temperature Mapping

Thermal FEM Structural FEM

• After thermal anlysis is complete the temperature results are mapped to a more detailed mesh for structural analysis.

• Temperature mapping for time t0 shown below*.

* Temperatures Relative to 20°C

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Conclusion

• Milli-Kelvin Analysis can be preformed when using the proper modeling process– Creation of both a coarse system level model and detailed

optical assembly model needed– Coarse system level model used as a boundary condition for

the detailed optical model

• Current SIM thermal design meets temperature stability requirements on the OOPCC optic

• SIM absolute temperature requirements are met through the robustness of the thermal design (i.e. PID control)

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Back-Up Slides Predicted Temperature Post-Processing

Post-Processed SID Axial Temperature Gradient

-12

-10

-8

-6

-4

-2

0

0 10 20 30 40 50 60 70Time (min)

Tem

pera

ture

Gra

dien

t (Δ

mK

)

SID Axial Temperature Gradient

3.83

3.84

3.85

3.86

3.87

3.88

3.89

3.90

3.91

3.92

0 10 20 30 40 50 60 70Time (min)

Tem

pera

ture

Gra

dien

t (Δ

K)

Raw DataLinear Drift over Observation Period

Post-Processed Stability

-80

-60

-40

-20

0

20

40

0 10 20 30 40 50 60 70Time (min)

dT/d

t (m

K/h

r)

Science Observation PeriodS/C Slew



• OPD is the optical path length difference between the starlight beam and the metrology beam.

– The linear drift in the raw OPD data caused by changing temperature is taken out through post-processing.

– The design requirements are written against the post-processed OPD value.

• Temperature Post-Processing Example– Step 1: Linear drift of temperature results computed

during the hour long observation period (WA)– Step 2: Linear drift of temperature results removed– Step 3: The stability is computed by taking the derivative

of the post-processed temperature results. Stability is compared against requirements.

Stability Requirement

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Collector Predicted Stability Results

• All collector optics meet thermal stability requirements• Narrow angle requirements (stability over 90s) easily met

due to long time constants and PID control

ComponentNarrow-Angle (mK/90 sec)

Wide-Angle (mK/hr)

Narrow-Angle (mK/90 sec)

Average* Wide-Angle (mK/hr)

Narrow-Angle (mK/90 sec)

Wide-Angle (mK/hr)

Siderostat Mirror 2 25 0.20 15 1.8 10M1 Mirror (1) 0.05 5 1.9 35M1 Mirror (2) 0.02 5 2.0 35M1 Mirror (3) 0.03 5 2.0 35M2 Mirror (1) 0.01 3 2.0 37M2 Mirror (2) 0.01 3 2.0 37M2 Mirror (3) 0.01 3 2.0 37M3 Mirror (1) 0.00 2 2.0 38M3 Mirror (2) 0.01 2 2.0 38M3 Mirror (3) 0.01 2 2.0 38TCC 2 10 0.04 5 2.0 5OOPCC 2 10 0.08 5 1.9 5CMP (1) 0.03 64 3.0 36CMP (2) 0.03 86 3.0 14CMP (3) 0.03 96 3.0 4COL Bay Structure 50 500 0.08 231 49.9 269* Times involving extreme changes in spacecraft attitude where temperature stability is poor are neglected

40

40

40

2

1003

2

2

Stability Requirements Model Predictions Margin(Temporal Gradients) (Temporal Gradients) (Temporal Gradients)

Documents

TFAWS 2006 SIM PlanetQuest: Milli-Kelvin Analysis of the … · 2006. 7. 27. · Space Interferometry Mission A NASA Origins Mission SIM TFAWS 2006 F. Kelly August 7, 2006 -3 SIM