Precision Oven Thermal Design

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Precision Oven Thermal Design
HMI00385

• Carl Yanari
• HMI Thermal Control
• carl.yanari_at_lmco.com
• 650-424-2942

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Precision Oven Thermal Agenda

• Driving Requirements
• Thermal Design Approach
• Design Trades
• Thermal Model Status
• Future Work

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Driving Requirements

• Oven Temperature
• Operating range 28 to 35C
• Actively controlled to a target temperature of
  300.1C
• Temperature dependency of science data drives
  oven temperature requirement
• Oven Temperature Stability
• Temperature transients limited to 0.01C/Hr
• Science sensitive to rapid temperature transients
  in Michelsons

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Thermal Design Approach

• Based on improvements to heritage MDI thermal
  control design
• Proportional heater control
• Vary heater power to maintain temperature rather
  than on-off, duty cycle control to minimize
  thermal transients
• Conductive thermal isolation from optical bench
• Use fiberglass (or other low conductivity
  material) supports
• Radiative thermal isolation from environment
• Use Multi-Layer Insulation (MLI) blanket or
  Aluminum tape
• Michelson thermal isolation
• Low conductance standoffs
• Thermal cover/shield
• Dampens thermal transients

Thermal shield around Michelson
Michelson on low conductance standoffs
MLI or Al Tape on outside
Controller pre-amp boards mounted on oven wall
Oven Wall 0.1 in thick for radiation
shielding and temperature uniformity
Low conductance support legs
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Thermal Design Trades

• MLI Blanket vs. Al Tape
• MLI provides more radiative thermal isolation
  than aluminum tape
• Degree of MLI benefit dependent on conductive
  thermal isolation provided by support legs and on
  stability of the Optics Package
• Level of heat leaks through legs, harnesses, and
  grounding strap can cause thermal coupling to be
  conduction dominated whereby a blanket would
  provide little benefit
• Contamination concerns with MLI within the optics
  package
• Particulate generation and outgassing
• MLI used on heritage, contamination sensitive
  Spacecraft
• Clearance issues for MLI
• Currently insufficient clearance to accommodate a
  blanket
• Aluminum tape was used on MDI
• Titanium vs. Fiberglass legs
• Titanium thermal conductivity 16X that of
  fiberglass
• Requires titanium legs to be smaller diameter or
  thinner tube wall thickness than fiberglass legs
  of the same length to achieve the same degree of
  isolation
• Fiberglass used on MDI
• Evaluation in progress

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Precision Oven Thermal Model

• Initial MDI oven detailed thermal model developed
  to investigate MDI Michelson temperature
  transient effects observed during flight
• 1800 nodes, 4500 conduction hook-ups, and 31600
  radiation hook-ups
• Investigation on-going
• Standalone HMI precision oven thermal model being
  developed
• Boundary conditions from HMI thermal model
• Includes Michelson detail developed for MDI model
  to determine transient effects

Detailed Michelson
Michelson thermal shield
Support legs to be added
Heater Controller preamp board to be added
Motor housing to be modified to reflect true shape
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Future Work

• Understand observed MDI Michelson transient after
  motor activation
• HMI oven thermal design includes transient
  temperature mitigation
• Continue to develop detailed precision oven
  thermal model
• Required to determine transient effects on
  Michelsons
• Required for determining optimum temperature
  sensor location
• Thermal model validated during engineering test
  unit thermal vacuum test
• Reduced model will be developed for integration
  into the HMI thermal model
• Complete trade studies
• MLI trade will be finalized once support leg
  design is determined
• Design heater locations and heater control
  subsystem
• Size heater for cold case plus added margin
• Use MDI heritage thermal control algorithm
• Use MDI heritage temperature sensor averaging
  design for control
• Locate temperature sensors
• Location of sensors critical for heater operation