TRL5 vibration-free soprtion-based cooler for the temperature range 15 to 30 K H.J.M. ter Brake 1, H.J. Holland 1, C.H. Vermeer 2, J.F. Burger 3, A. Maas 4, R. Kaal 4, M. Linder 5 (5) (3) (1) (2) (4)

ICEC26-ICMC2016 H.J.M. ter Brake Sorption cooler

Advantages of sorption-based JT coolers: -No vibrations (not measurable) -Long lifetime (no moving parts and physi- sorption is fully reversible) -Low level of Electro Magnetic Interference (only heater current which may be bifilar) -Easier integration (all parts in cold section, no room-temperature compressor) -Flexibility: Same design of compressor can be applied to other T-ranges by changing working gas and/or change low pressure.Disadvantage: -Less mature than mechanical coolers (this project aims atTRL 5 in 2016) ICEC26-ICMC2016 H.J.M. ter Brake

4.5 K cooler system design for operation at L2 (e.g Darwin) ICEC26-ICMC2016 H.J.M. ter Brake bar, 1.9 W in 4.5 K ; 5 mW bar, 4.2 W in 14.5 K ; 35 mW

Helium stage: demonstrator 2005 – 2007 (TRL 4) 4.5 K Helium-stage sorption cooler ICEC26-ICMC2016 H.J.M. ter Brake bar, 1.9 W in 4.5 K ; 5 mW

Helium stage: demo experiments Hydrogen stage: can also be “stand- alone”14.5 K cooler 14.5 K Hydrogen-stage sorption cooler ICEC26-ICMC2016 H.J.M. ter Brake bar, 4.2 W in 14.5 K ; 35 mW

CEC June 2013 H.J.M. ter Brake 9 grams of carbon Hydrogen-stage sorption compressor cells

Hydrogen-stage check valves machined in 316L stainless steel flap: Au layer 10  m flat-on-flat for low pressure (0.1 – 3 bar) knife-edge design for high pressure (3 – 50 bar) ICEC26-ICMC2016 H.J.M. ter Brake

Getter Heat SinkAftercoolerGas gap actuator Pinch off tube ThermocoupleHeater Check valve Hydrogen sorption cooler ICEC26-ICMC2016 H.J.M. ter Brake

Measuring results p low [mbar]T equilibrium [K] ESA requirement: ± 25 mK in 24 h, measured: ± 15 mK (4 mK std) Component and breadboard validation in lab environment: TRL4 (status 2013) ICEC26-ICMC2016 H.J.M. ter Brake

Follow-up ESA project “TRL+ project” (Kick Off: 14 Oct 2013) 1.Establish TRL 5, “relevant environment” >> survive launch mechanical loads! (analysis and shaker tests) 2. Show feasibility at higher temperatures (to 25 K or higher) ICEC26-ICMC2016 H.J.M. ter Brake Tip temperature can be varied by varying low pressure which in turn can be set by the buffer temperature. So, tip temperature is controlled by buffer temperature 107 K 137 K 154 K

TRL+ project: Vibration levels Sinus vibration acceleration levels Minimum random vibration power spectral density Goal required random vibration power spectral density ICEC26-ICMC2016 H.J.M. ter Brake

Chemical getter and connecting tube redesigned to withstand random goal levels. Orientation changed: tube is now better aligned with respect with most important vibrations. Pill and container lighter, now is ca 1 gram. Bracket (connection and fixation of gas line) was made of Al now made of stainless steel. No stress caused by difference in CTE. Spacer spokes: little wider and thicker now which results in a 10% higher conductive heat load through the spacer. T sensor in cell container is removed: may cause leak of hydrogen gas via feedthrough (SPF). In addition unclear what T is measured (carbon or gas) TRL+ project: Compressor-cell redesign ICEC26-ICMC2016 H.J.M. ter Brake

TRL+ project: Check-valve redesign Minor changes: - Tolerances reduced to prevent a too small opening between boss and filter. -Connecting lines laser welded instead of being brazed. (stronger connection and prevents damage during mounting, which in the bread boarding caused gas leakages). - Total mass reduced : compressor cell plus valves now is 368 grams (was 388 grams) ICEC26-ICMC2016 H.J.M. ter Brake

TRL+ project: Compressor and check valves test platform Set up for axial shaker tests Compressor with two knife- edge valves that are tested on pressure drop and leak flow rate prior to assembly Completed compressor platform tested on functional performance prior and after shaking Separate valves will be tested also prior and after shaking ICEC26-ICMC2016 H.J.M. ter Brake

TRL+ project: functional tests ICEC26-ICMC2016 H.J.M. ter Brake

TRL+ project: status and planning Check valves assembled Ready for e-beam welding Next, pressure drop and leak flow test After that add to compressor unit ICEC26-ICMC2016 H.J.M. ter Brake

TRL+ project: status and planning Compressor container filled with carbon, closed (e-beam welded) and gold plated Next, mount in heat sink and e-beam weld Then, combine with check valves and functional tests prior to shaking ICEC26-ICMC2016 H.J.M. ter Brake

TRL+ project: conclusion Check valve pressure drop and leak flow measurements Complete compressor cell assembly Operate existing hydrogen cooler at higher temperatures (15 – 30 K?) Combine compressor cell and check valves and mount on plate Functional test experiments of compressor cell Shaking all three directions in-plane and normal, sinus and goal random Functional test experiments of compressor cell Pressure drop and leak flow measurments of check valves TRL 5 established March April May/June June/July August/September October ICEC26-ICMC2016 H.J.M. ter Brake

Test experiments: results cold tip temperature stabilized by PID controller and heater day 1 day K Helium-stage sorption cooler ICEC26-ICMC2016 H.J.M. ter Brake

Test results (lower pressure, Tcold = 3.15 K)