A HgCdTe avalanche photodiode (APD) focal plane array assembly with linear mode photon-counting capability has been developed for space lidar applications. An integrated detector cooler assembly (IDCA) has been built using a miniature Stirling cooler. A microlens array has been included to improve the fill factor. The HgCdTe APD has a spectral response from 0.9- to 4.3-μm wavelengths, a photon detection efficiency as high as 70%, and a dark count rate of <250 kHz at 110 K. The mass of the IDCA is 0.8 kg and the total electrical power consumption is about 7 W. The HgCdTe APD arrays have been characterized at NASA Goddard Space Flight Center. A series of environmental tests have been conducted for the IDCAs, including vibration, thermal cycling, and thermal vacuum tests. A description of the device and the test results at NASA are given in this paper.
A linear mode photon counting HgCdTe avalanche photodiode (APD) focal plane array (FPA) detector was developed for space lidar applications. An integrated detector cooler assembly (IDCA) was manufactured using a miniature Stirling cooler. The HgCdTe APD demonstrated a greater than 60% photon detection efficiency from 0.9 to 4.3 μm wavelength and a dark count rate less than 250,000/s. The IDCA cooled the FPA to 110K from ambient room temperature at a total electrical power of 7 W. The IDCA has passed environmental tests, including vibration, thermal cycling and thermal vacuum tests.
In response to continuing requirements for smaller, lighter, and lower power cryocoolers for tactical IR applications, DRS Technologies has developed its smallest linear drive cooler for the micro-Integrated Dewar Cooler Assembly (μIDCA). The entire cooler/Dewar assembly occupies slightly more than 4 cubic inches in a rectangular form that measures about 1-inch by 2-inch by 2-inches. The design goals and constraints are presented and the resulting design is discussed. Operating parameters and testing results are summarized. In addition to the review of the μDCA cryocooler, this paper presents a brief update of long-term reliability and life testing for a variety of DRS’ linear drive cryocoolers. This testing program was initiated in the 1990’s and has demonstrated cooler lifetimes in excess of 50,000 hours.
DRS Technologies has designed and delivered Thermal Weapon Site (TWS) and Driver's Viewer Enhancer (DVE) system using its U3500 (320x240) and U6000 (640x480) 1-mil detector arrays. The detectors are modified to enhance its manufacturability, thermal time constant, package life time, and its reliability under shock and vibration to meet TWS and DVE requirements. The U6000 array operates at 30 Hz frame rate with NETD less than 50 mK normalized to F/1.0 optics. At a saving to the system weight and power, these arrays operate from -40°C to +65°C without the aid of a TE cooler. This is accomplished through a combination of sensor calibration and smart ROIC architecture.
In the mid-1990's, DRS Infrared Technologies began an effort to extend the application of flexure spring technology into cryogenic coolers being supplied for tactical military applications. Previous papers have explored the design challenges and reported performance, life, and environmental testing results. In addition, DRS has now extended the flexure spring design into cryocoolers designed to operate in high ambient temperature ranges previously deemed too severe for linear drive cryocoolers. This paper discusses the design considerations that must be addressed at these high temperatures. Performance and test results for one such cooler, designed for a U.S. Navy threat warning sensor, with cryocooler case temperatures of 120°C, are presented.
Flexure spring suspensions have demonstrated the capability of extending cryocooler lifetimes for space-based and commercial cryocooler applications. In the mid-1990s DRS Infrared Technologies, L.P. began an effort to adapt this technology to cryocoolers for tactical sensor applications. The flexure spring suspension system resulting from that effort has been described in previous papers. The flexure spring designs met the various size, weight, performance, and implementation requirements. This paper presents an update of the environmental and life testing that has been done to qualify these designs for military sensor applications.
Flexure spring suspensions have demonstrated the ability to provide long operating lifetimes for cryocoolers intended for space-based applications. Insertion of this technology into coolers intended for tactical or commercial application has been slow due to cost considerations. This paper describes the development and testing of a flexure spring system for small tactical cryocoolers that provides a doubling of operating life while costing approximately the same as the traditional helical coil spring suspension system. The flexure spring system described in this paper successfully achieves the high radial stiffness characteristic of the flexure spring design in a low-cost package. In addition, the concept has been implemented in cryocoolers weighing less than a pound and smaller than a soft drink can. This design has been qualified for use in U.S. Army applications. Qualification and life test data is presented to demonstrate the robustness of the design in tactical environments. The producibility of the design is evidenced by the on-going production of these coolers for various applications.
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