1. EMAS Stirling Cooler Operations June 29, 2011 Mike Watson

2. 2 E-MAS CryoTel GT Stirling Cooler Characteristics: Does not have over/under (80C/-40C) temperature protection in this controller model Next generation controller (available October of 2011) should have this feature Cooling capacity diminishes by.06W/C when above 35C Model installed on EMAS has been upgraded with a dual frequency absorber to minimize vibration. This absorber can be tuned once it is installed on system with guidance from SunPower. 120,000 hours MTBF For heat load during operation: While cooling at full capacity, the device will dump 240W plus the heat lifted from the system. Therefore, a maximum of 285W (at 240K) will need to be dumped At steady state, the device will dump 240W X (% of full load capacity at that temperature) + heat lifted from system. For example, if we controlled to lift 10W at 90K, the heat dumped would be 240*(10/19)+10 = 136W.

3. 3 E-MAS CryoTel GT Stirling Cooler Operational modes Vacuum chamber during TVAC testing Cryocooler fins replaced with bolt-on LN2 heat exchanger Cooling manually throttled at external dewar as necessary Benchtop during lab testing/operation Either use LN2 HX or fins No analysis conducted for this method. Flight Ram air injected through cryocooler fins Low altitude Sea level conditions Mach.35 High altitude Mach.7 Temperature and pressure from ER2 flight data from MidLats and Tropics Copper collar clamps: same for all setups LN2 in / out: VCR Fittings Ram air / Chilled air Cover removed

4. 4 E-MAS CryoTel GT Stirling Cooler Low altitude flight Altitude = Sea level Temp = 38C (100F) Pressure = 1 atm Mach.35 Using maximum heat load 285W (only generated during portions of cooldown) Using turbulent flow correlations for Nusselt / heat transfer coefficient calculations Results Average collar temperature approaching cryocoller high temperature limit Operational impacts: May need to throttle back on cooling set point May need to wait until plane achieves a certain altitude before restarting cryocooler

5. 5 E-MAS CryoTel GT Stirling Cooler High altitude flight Altitude = 65000 ft Temp = -60C Pressure = 60mbar (.06 atm) Mach.7 Using maximum heat load of 285W (only generated during portions of cooldown) Heat transfer coefficient difficult to estimate Limited data on air properties (specifically thermal conductivity) Fin geometry and input air conditions indicate that flow will be turbulent throughout heat exchanger Using laminar flow correlations for simplicity and conservativeness NOTE: thermal conductivity of air begins to drop rapidly above an altitude of 80K feet (or 10-50 Torr). This will significantly reduce the ability to cool the cryocooler. Results Gradient mostly through copper clamps May see ~1-2W of reduced cooling capacity this operating temperature Possible that might reach lower temperature limits during lower steady state heat loads and higher conductivities than calculated. This risk is avoided by lowering the setpoint and driving the heatload up.