ACTDP Development Program
To develop the needed cryocooler technology for 6K missions of interest, NASA initiated the Advanced Cryocooler Technology Development Program (ACTDP) under the leadership of the Jet Propulsion Laboratory and in collaboration with the NASA Goddard Space Flight Center (78). As shown in the above figure, the ACTDP effort was structured as a two-phase process containing an initial study phase followed by a second hardware development and test phase. The effort started with the generation of detailed requirements and specifications in summer 2001, leading to a community-wide request for proposals in November 2001, and the award of four parallel Phase I contracts by April 2002. The four study-phase contractors included:
Study Phase Activities
In the Study Phase, each contractor developed a detailed preliminary design with supporting laboratory test data sufficient to confidently enter into the hardware development and demonstration phase. The study phase culminated with a Preliminary Design Review (PDR) in September 2002 and delivery of a final study report that was evaluated by NASA and served as the primary basis for down-selection to the Demonstration Phase. The concepts developed by the four contractors are described in the accompanying 6K ACTDP Cooler Concepts link and represented the starting point for the their development efforts; the concepts could thus be expected to evolve and to be refined over time.
Mission Focus. Three focus missions were used to guide the ACTDP cooler development (78). These included a Next Generation Space Telescope (NGST) concept, which later became the James Webb Space Telescope--JWST), a Terrestrial Planet Finder (TPF) mission concept, and a Constellation-X mission concept. Both the NGST and TPF concepts included the use of infrared detectors operating between 6-8 K, typically arsenic-doped silicon arrays, with IR telescopes from 3 to 6 meters in diameter. The Constellation-X concept, on the other hand, proposed the use of X-ray microcalorimeters operating at 50 mK and would require ~6K cooling to precool its multistage 50 mK magnetic refrigerator.
Consensus top-level cooler requirements for the NGST, TPF and Con-X mission concepts were identified and served to focus the ACTDP cryocooler designs. Key requirements included:
Demo Phase Activities
NASA chose to persue three of the Study Phase concepts into an initial risk reduction portion of the Demonstration Phase with the objective of first completing the detailed design and development testing of the highest risk portions of the three concepts. the goal was to carry at least two of the concepts through the complete detailed design, fabrication, performance and environmental testing, and delivery of an Engineering Model (EM) cryocooler system by the end of FY2005 (92). The requested EM mechanical cryocoolers were to be fully flight-like in form, fit, and function, and allow assessment of their ability to meet all key thermal, structural, and reliability/lifetime performance requirements. They had to also be capable of providing the required cooling system performance over the full range of interface temperatures, and be suitable for multi-year life-testing. Consistent with prototype hardware, the EM mechanical cryocooler would not have formal flight drawings, or flight-approved materials, electronic parts, or fasteners, except where they were critical to performance.
Brassboard Electronics. In order to drive and operate the EM mechanical cooler, the demonstration phase of the ACTDP effort also inttially included the development and delivery of Brassboard cooler drive electronics that were flight-like in function (e.g. power and control functionality), but not flight-like in form. In particular, the brassboard electronics were expected to be rack mounted for operation in a lab environment and need not address flight structural, thermal, or space radiation issues. Their fundamental job was to be capable of operating the EM mechanical cryocooler over its full range of capabilities to allow assessment of the cryocooler's overall design with respect to key efficiency, control, and refrigeration performance requirements. Any digital functionality of the brassboard electronics was expected to be simulated with PC-based hardware and software.
Engineering Model Electronics Option
As a contract option, the contractors were also initially asked to propose delivering an Engineering Model (EM) form of the cryocooler electronics. The EM electronics would fully demonstrate the form, fit, and function of flight model electronics to allow assessment of the ability of the circuit and mechanical design to meet key electrical, thermal, structural, and EMI performance requirements over the expected flight operating temperature range. The EM electronics circuit and packaging design would have to be based on flightworthy radiation hard, high reliability parts and processes that are compatible with the specified flight operating temperature, radiation, and SEE environments. However, the fabricated EM electronics unit would not need to have formal flight drawings, or flight-approved radiation hard, high reliability materials, electronic parts, or fasteners, except where they were critical to performance. The EM electronic unit would be suitable for powering the EM Mechanical cryocooler system during multi-year life-testing.
Follow-on Flight Hardware Transition
In April 2005, midway throught the ACTDP development program, the James Webb Space Telescope Project reached a decision to use an ACTDP cryocooler to replace the originally selected solid-hydrogen dewar in its 6K Mid Infrared Instrument (MIRI) (92). As a result, a solicitation for a 6 K/18 K cryocooler was placed in fall 2005 and resulted in the selection of the TRW (now Northrop Grumman Aerospace Systems -- NGAS) ACTDP cooler concept for use in JWST's MIRI instrument. With this successful transfer of the ACTDP technology to flight status, the ACTDP project fulfilled its fundamental objective and ended. Continuing development of the 6K MIRI cooler was then passed over to the JWST project (99,100,106,111,112).
Dr. Ronald Ross
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Latest update: July 30, 2013