1. Precision Oven Thermal Design
HMI00385
Precision Oven Thermal Design
Carl Yanari
HMI Thermal Control

2. Precision Oven Thermal – Agenda
Driving Requirements
Thermal Design Approach
Design Trades
Thermal Model Status
Future Work

3. Driving Requirements Oven Temperature Oven Temperature Stability
Operating range 28 to 35°C
Actively controlled to a target temperature of 30±0.1°C
Temperature dependency of science data drives oven temperature requirement
Oven Temperature Stability
Temperature transients limited to 0.01°C/Hr
Science sensitive to rapid temperature transients in Michelsons

4. 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

5. 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

6. 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 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
Michelson thermal shield
Detailed Michelson
Support legs to
be added
Heater Controller preamp
board to be added
Motor housing to be modified to reflect true shape

7. 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