Precision Oven Thermal Design

1. HMI00385 Precision Oven Thermal Design Carl Yanari HMI Thermal Control carl.yanari@lmco.com 650-424-2942

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

3. Driving Requirements • Oven Temperature • 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 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

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