Three-Stage Cryocooler Cold Head for Advanced Heterodyne Sensors

Future advanced heterodyne sensors for submillimeter-wave receivers require 50 to 100 mW of cooling at 15 to 20 K for the sensor, and 1 to 2 W cooling at 80 to 120 K for the local oscillator, with size and input power suitable for use in a Small Sat. During Phase I, a detailed cryocooler configuration trade study was completed, and the 3-stage pulse tube configuration driven by the Lockheed Martin (LM) Midi compressor was selected based on efficiency and adaptability. An assessment of innovative regenerator materials and direct metal laser sintering (DMLS) additively-manufactured heat exchanger materials was completed, and the decision was made to include DMLS in the design, while keeping the advanced regenerator material as an option as a future improvement. Cooling powers of 100 mW at 20 K and 2 W at 120 K were selected, with 47 W compressor ac power predicted. A solid model of the 3-stage cold head was then generated in Phase I. CU Aerospace (CUA) will use innovative materials and low cost cold head design and assembly, coupled with LMs industry-leading multi-stage pulse tube expertise, to provide NASA with a compact, affordable cryocooler for submillimeter detectors. Our team proposes to: 1) Refine the 3-stage cold head solid model design initiated in Phase I, optimized to provide simultaneously 100 mW cooling at 20 K and 2 W cooling at 120 K, to improve manufacturability and decrease cost compared with heritage LM multi-stage cold heads. 2) Procure all hardware necessary to assemble the 3-stage cold head, and the gas transfer line to connect it to a LM-owned Midi compressor. 3) Assemble and weld 3-stage cryocooler cold head, perform proof pressure testing and leak testing. 4) Integrate cold head with LM Midi compressor and perform cryocooler performance testing over a range of operating conditions, varying the input power, ambient temperature and 1st, 2nd and 3rd stage temperatures to fully characterize cryocooler performance. Future heterodyne sensors for submillimeter-wave receivers require 50-100 mW of cooling at 15-20 K for the sensor, and 1-2 W cooling at 80-120 K for the local oscillator, with size and input power suitable for Small Sats. Multi-stage pulse tube cryocoolers are ideal since the only moving parts are in the compressor thus additional cold stages require no additional moving parts so reliability remains high. Cooling to 15-20 K likely requires a 3-stage pulse tube cold head for highest efficiency. Having multiple stages of cooling allows secondary components such as optics, spectrometers, etc. to be cooled at a higher temperature, and negates parasitic heat loads, electrical leads, RF coax, etc., which can reduce the required cryocooler power significantly. CU Aerospace will use innovative materials and low cost cold head design and assembly, coupled with Lockheed Martin's industry-leading multi-stage pulse tube expertise, to provide NASA with a compact, affordable cryocooler for submillimeter detectors. The technical objectives of this Phase II SBIR are to deliver an optimized 3-stage pulse tube cryocooler cold head capable of simultaneously providing 100 mW cooling at 20 K and 2 W cooling at 120 K when driven by the LM Midi cryocooler, with 260 K heat rejection temperature. Thus, the following objectives are enumerated below: 1) Refine the 3-stage cold head solid model design initiated in Phase I, optimized to provide simultaneously 100 mW cooling at 20 K and 2 W cooling at 120 K, to improve manufacturability and decrease cost compared with heritage LM multi-stage cold heads. 2) Procure all hardware necessary to assemble the 3-stage cold head, and the gas transfer line to connect it to a LM-owned Midi compressor. 3) Assemble and weld 3-stage cryocooler cold head, perform proof pressure testing and leak testing. 4) Integrate cold head with LM Midi compressor and perform cryocooler performance testing over a range of operating conditions, varying the input power, ambient temperature and 1st, 2nd and 3rd stage temperatures to fully characterize cryocooler performance. 5) Quarterly and Final Reports; Review Meetings with NASA COTR.
Benefits: Three-stage cryocoolers are generally required when cooling to 15-20 K as required by heterodyne sensors. Staged pulse tubes are ideally suited for space applications because adding stages does not add moving parts, such as with Stirling or Brayton coolers, so reliability remains high. NASA heterodyne sensors, as well as other instruments requiring temperatures from 10-30K would benefit from a low-mass, reliable 3-stage pulse tube cryocooler to improve mission capability. Multiple-stage cryocoolers can benefit all cryogenic space applications by cooling secondary components and intercepting parasitic heat loads at higher temperature, reducing power and mass. Applications including remote sensing satellite constellations, weather satellite constellations, earth science instruments, and deep space astrophysics instruments can all benefit from multiple-stage cooling.