Date: Jul 15, 2010 Author: Joe Singleton Source: MDA (
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by Joe Singleton/jsingleton@nttc.edu
A team of California-based engineers has developed precise and highly versatile electronic components capable of eliminating disruptive vibrations that can come from the cooling systems used in high-performance sensors in satellites and surveillance equipment.
The company behind the engineering team, Iris Tech-nology Corporation (Irvine, CA), packages radiation-hardened refrigeration electronics into units called Modular Advanced Cryocooler Electronics, or MACE. These control modules can be built to user specifications and can include electronics capable of handling any power requirements for low- and high-end sensors and satellites (generally between 100 and 1,000 Watts of input power).
Vibrations that come from cryocooling systems can rattle sensors and result in blurred images. Iris' simple solution to the vibration problem comes in the form of a modular product that can precisely measure cryocooler-induced vibrations and then cancel them out by introducing counter vibrations. The modular technology comes in the form of two key components: a device that measures a cryocooler's force and temperature, and a device that controls a motor to counter vibrations. This modular approach means that these Iris components can be placed in virtually any sensor-cryocooler configuration, including where multiple sensors or coolers are involved.
The Missile Defense Agency funded Iris through a 2007 SBIR Phase II contract to develop a comprehensive electronics system to control high-capacity cryocoolers used in space-based platforms. Specifically, MDA expressed interest in electronics to work with refrigeration devices for cooling focal planes and infrared sensors.
To date, most of Iris' MACE tests have used a 25-inch × 9-inch × 12-inch testbed Stirling-type cryocooler that weighs about 20 kilograms, and contains both a compressor and an expander module. MACE is mated to the cryocooler and comprises two modules: a telemetry aggregation unit (TAU) and a main control unit (MCU).
The TAU, a 5-inch × 5-inch × 1.5-inch spaceflight-compatible box resides close to the cryocooler. Temperature and other sensor-driven signals are received by the TAU, amplified, and then digitized before being sent to the MCU via a high-bandwidth, all-digital data link. Digital transfer of vibration levels ensures that the MCU gets accurate data to act on. Specifically, the digital approach aids accuracy because it minimizes electromagnetic interference that can occur around equipment or other sources. Conventional analog cryocooler electronics are more susceptible to such interference.
The MCU (measuring 10 inches × 10 inches × 3 inches in a spaceflight configuration but presently packaged as a larger non-flight testbed unit) contains the motor drives for the cryocooler and the controller electronics. At the heart of the controller is a field programmable gate array (FPGA) with a processor in it. Once digital signals are passed by cable from the TAU to the MCU, the MCU's FPGA routes these signals into the processor, where algorithms correct any suspected computational errors or anomalies. The corrected signals then are retransmitted from the processor to the motor drives (also located within the MCU box), via the FPGA. The FPGA transmits to the motor drives these corrected signals, which are mathematically designed to eliminate any noise or vibration that can affect a MACE unit. Noise and vibrations tend to destabilize electro-optical infrared sensors and thus reduce image quality. The programming relayed by the signals also enables the cryocooler to maintain temperatures within 0.10 K over a range of 35 K to 120 K.
Iris can incorporate MACE into a variety of cryogenic packages, depending on the needs of an end user. During most of the company's tests for MDA, a 2500-Watt unit with five motor drives was the cryocooler electronics package of choice. While such a large package may be useful in some large satellites, Iris engineers recognized that most prime systems integrators favor smaller and lighter instrumentation. For this reason, the company now is scaling down its testbed unit to allow for a low-power, two-motor drive system. MDA or other government agencies could integrate this 100-Watt unit for use with smaller sensors and components that need cryogenic cooling, especially in environments requiring radiation hardening. Iris does not manufacture the radiation-hardened components—such as FPGAs, operational amplifiers, and random access memory chips—but purchases them from mainline suppliers and assembles them in MACE units.
Iris' modular approach also allows for quick and efficient production of final products. The company can build an entire MACE electronics suite to specifications within a six month period. Carl Kirkconnell, Iris' chief technology officer, said most cryocooler electronics integrators would take three times as long to produce such an electronics suite.
Although the company has not yet ventured far into the commercial, nongovernmental realm, Kirkconnell said the technology could be modified for use in civilian applications that require extreme refrigeration, such as in commercial satellites and infrared cameras for building-perimeter security monitoring. Iris now is positioning itself as a systems integrator to deliver MACE to users in the aerospace market.
