The trade-offs that must be considered when selecting a cryocooler for infrared detector cooling are complex. When split-
Stirling cryocoolers are used, the designer can select the expander separately from the compressor. However, there will be performance implications. Larger systems provide benefits in terms of performance margin and operating lifetime, but may not meet size and mass goals. Larger cryocoolers tend to generate more heat, albeit over a larger surface area, and generate higher vibration forces. The expander coldfinger must be stiff enough to achieve image plane motion requirements. The transfer tube should be as short and with as few bends as possible, while the path available for the transfer tube may be affected by the geometry of the expander and compressor. Several characteristics of tactical cryocoolers are considered in this paper in such a way that trends can be identified and design choices can be clarified. A step-by-step approach is recommended that will lead to a design solution in the most direct manner. This is accomplished by starting with "show-stopper" choices, then progressing to choices where concessions can be more easily made. The implications of the interfaces to the cryocooler will also be briefly discussed. Cryocooler developments at RVS that will expand the available design space are described. This enabling technology provides more options in terms of cryocooler size and performance, and continues the trend toward longer operating lifetime and higher reliability.
Raytheon has manufactured closed-cycle cryocoolers for both tactical military and space applications for over thirty years. Tactical and space cryocooler technologies have historically been treated as distinct both at Raytheon and throughout the industry. Differing technical requirements, operating lifetimes, and order quantities have driven these types of coolers to dramatically different design approaches and cost levels. For example, a typical space cryocooler system today costs approximately $2M as compared to roughly $10,000 for a tactical cryocooler. However, stimuli from both the tactical and space cooler user communities are driving the markets together. Tactical cryocooler requirements are starting to push towards operating lifetime requirements more characteristic of the space coolers (e.g., 20,000+ hours). Space cryocooler users, in particular Missile Defense Agency, are pushing for substantial cost reduction. In response, Raytheon is developing a low cost space cryocooler with an intended dual-use capability to also serve the tactical marketplace. This cooler leverages proven flexure-suspension technology to achieve long life, and a low cost concentric pulse tube cold head design has been developed that can be packaged into the existing Standard Advanced Dewar Assembly, Type One (SADA-I). The cooler meets or exceeds the SADA-I operational requirements (capacity, efficiency, etc.) as well. For the space-version of the cooler, the electronics cost has been reduced by an estimated 80% versus current designs, largely by approaching the vibration cancellation requirement from a dramatically different perspective. Fabrication of the brassboard expander is nearly complete, and the prototype design is well underway. The design approach, development progress, and proposed applications are presented.
Raytheon has consolidated the products and expertise of the former Hughes Mahwah (Magnavox) and Torrance cryocooler operations to the Raytheon Infrared Operations (RIO) located in Goleta, CA (formerly SBRC). Co-location of the cryocooler operations with the detector/dewar operations yields infrared systems with reduced cost. This paper describes the current capabilities of the linear and rotary cryocooler products as well as developments underway and planned. Development goals include cost reduction, high performance while operating in extreme environmental conditions (> 90°C skin temperatures), and long life (> 20,000 hrs). Technologies developed by a Raytheon sister division for space cryocoolers are now being applied to tactical cryocoolers at RIO. Data, specifications, and a technology roadmap for the product-line cryocoolers encompassing cooling capacities including 0.2-, 0.35-, 0.75-, 1.0- and 1.75-watt ranges will be shown.