X-Ray Calorimeter ~ Concept Presentation ~

1. X-Ray Calorimeter ~ Concept Presentation ~ Cryogenic System Mike DiPirro Peter Shirron Paul Whitehouse Feb 17, 2011

2. Introduction • The cryogenic system provides the thermal environment necessary to operate the focal plane and 1st and 2nd Stage SQUIDS at 50 mK while allowing x-rays in and providing a stable mechanical and low magnetic field environment for at least a 3 year lifetime • This is accomplished using a multistage mechanical cryocooler, a 3 stage ADR, and a multistage, shielded dewar • No cryogens are used except to increase the cooldown rate for ground testing

3. Cryocooler vs. Stored Cryogens • US cryocoolers have reached a level of maturity where they have long life, high reliability and a TRL for this particular use of at least 5 • NGAS cryocooler on MIRI has minimum 5 year lifetime, TRL 6 • Ball cryocooler based on TIRS, Air Force 10K cooler and development under ACTDP • Lockheed uses multistage pulse tube developed under ACTDP and demonstrated to 3 K • Creare/Raytheon also has flight cooler heritage • Japanese cryocooler systems are just beginning to reach this level of reliability so mechanical redundancy for those cryocoolers may be warranted • No orbiting mission has had a cryocooler fail before its life expectancy • The NICMOS cryocooler is still working (since 2004) and the Suzakucryocooler is still working since 2005 for example • Stored cryogen systems have lower reliability (WIRE, NICMOS Solid N2, Suzaku), are roughly equal in cost (the COBE liquid helium dewar would have been >$30K in today’s dollars for a lifetime of < 1 year), and require special handling and launch pad considerations

4. Cryostat Block Diagram Aperture cover KEY filters Detector 50 mK stage main shell Calorimeter/ADR insert Vent valve Focal Plane Assembly (FPA) at 50mK 50 mK filters conductive bond Microcalorimeter SQUID readout amplifiers Antico detector thermal link heat switch 3-stage Adiabatic Demagnetization Refrigerator (ADR) superconducting cable ADR Stage 1 4K SQUIDs & termination resistors ADR Stage 2 Calorimeter/ADR Insert 0.6K Detector Control ADR Stage 3 1.3 K ADR Control 4.5 K Custom cryostat encloses the FPA and ADR, as well as the readout amplifiers JT stage 18 K 75 K 260-300 K cold head Loop Heat Pipe to radiator Commercial Cryocooler Cryocooler Compressors

5. Architecture • Cryocooler to achieve 40 mW of cooling from room temperature to 4.5 K with intermediate stages of cooling • Cryocooler is derived from a composite of 4 possible cryocoolers from US vendors • Cryocooler is sized to draw 450 W maximum power (no extra contingency needed) • Power system, radiators and electronics are sized for this maximum power allowing maximum flexibility in future trade-offs • Detectors and 3-Stage ADR are housed in a cryostat with a room temperature outer shell, a 4.5 K housing for the ADR and detector package and 2 intermediate cooled shields to intercept parasitic heat at about 70 and 18 K • Uses S-glass composite struts for support • Allows ground test without extra cooling (except for cool down boost by liquid helium) • Cryocooler even without explicit temperature control will achieve ~ 30 mK stability at 4.5 K (Astro-H testing) • Entire cryogenic system maintains recommended factor of two margin in cooling power (AIAA Spacecraft Thermal Handbook vol. II)

6. Heat Load Summary

7. Cryocooler Considerations • EDU is assumed. Allow at least one year to demonstrate performance at this level • Cryocooler is at TRL 5 currently • This may require a Phase A for this program to bring technology to TRL 6 (1+ yr and <$5M) • ETU (essentially a flight spare) will unnecessarily lengthen development (pre-CDR) so is not recommended • Use existing technology as much as possible • Saves time and money on cryocooler and other component development since performance characteristics will be apparent from the start • The mechanical part of US cryocoolers is very reliable – there is no need for redundancy here • Recommend electronics redundancy to improve reliability to >98% • Once a cryocooler is selected it is expected to perform better than the enveloping performance characteristics used for this study (mass, input power, cooling power, etc. • Expect cryocooler (including 2 flight electronics boxes, 1 flight set of coolers, and 1 EDU set of coolers and electronics to cost ~ $35M (not including purchasing overhead) • ~$12M ROM from Ball for single set of flight units (no redundancy) • ~$35M for MIRI cryocooler from NGAS (redundancy and full flight spare + TRL 6 development) • ~$25M for XMS cryocooler starting from TRL 6 is reasonable

8. Dewar Considerations • Dewar without a cryogen system is inherently much more robust and reliable • No cryogen leaks • Fewer welds and joints • Parasitic heat loads are more easily tolerable • Still require company with expertise in manufacturing cryogenic systems • High performance MLI blankets • Care in welding and in leak tight joints • IRAC/Spitzer development lesson learned • Strut suspension • Readily available material (S-Glass) • Robust and easy to manufacture compared to straps • Relatively low mass of cold components lowers parasitic heat load • Cold mass is dominated by ADR • Strut conduction is roughly proportional to cold mass • Choice of cryocooler may require increasing number of shields to 3 from 2 with some increase in volume and warm mass • If the overall height of the instrument became an issue, the cryocoolers can be mounted on the side of the dewar instead of on time, but more mass must be accounted for the longer thermal straps

9. Conclusions • Mechanical cryocoolers provide a high-reliability method of achieving 4.5 K for a 3 year mission • Sizing all systems for maximum cooling performance provides most flexibility for future trade-offs (JWST/MIRI experience) • Dewar allows high fidelity ground testing • 300 K outer shell assumed • This may not provide as good performance as passively cooled outer shell, but ground testing will be very flight-like in thermal performance (test-as-you-fly) • Cooling system is flight-like (no GSE cryocoolers needed) and only use cryogens to speed initial cool down • Low mass for dewar enabled by choosing cryocooler over cryogens • Some refinements of design do not “break” the thermal system • Stiffer struts or larger diameters may be necessary for practicality • Cooling system margins are robust