- News
6 December 2010
Georgia Tech-led project yields SiGe prototype for space electronics
A project led by the Georgia Institute of Technology has developed a novel approach to space electronics that could change how space vehicles and instruments are designed (IEEE Transactions on Device and Materials Reliability, issue 4, December 2010). The new capabilities are based on silicon-germanium (SiGe) technology, which can produce electronics that are highly resistant to both wide temperature variations and space radiation.
The $12m, 63-month project ‘SiGe Integrated Electronics for Extreme Environments’ was funded by the US National Aeronautics and Space Administration (NASA). In addition to Georgia Tech, the 11-member team included researchers from the University of Arkansas, Auburn University, University of Maryland, University of Tennessee and Vanderbilt University, as well as BAE Systems, Boeing Co, IBM Corp, Lynguent Inc and NASA’s Jet Propulsion Laboratory.
“The team’s overall task was to develop an end-to-end solution for NASA — a tested infrastructure that includes everything needed to design and build extreme-environment electronics for space missions,” says principal investigator and project team leader John Cressler, who is Ken Byers Professor in Georgia Tech’s School of Electrical and Computer Engineering.
SiGe’s robustness is crucial to its ability to function in space without bulky radiation shields or large, power-hungry temperature-control devices. Compared to conventional approaches, SiGe electronics can provide major reductions in weight, size, complexity, power and cost, as well as increased reliability and adaptability.
Picture: Cressler displays a functional prototype device (a 16-channel sensor interface, tested in simulated space environments) developed for NASA using SiGe ICs.
“Our team used a mature silicon-germanium technology — IBM’s 0.5 micron SiGe technology — that was not intended to withstand deep-space conditions,” Cressler says. “Without changing the composition of the underlying SiGe transistors, we leveraged SiGe's natural merits to develop new circuit designs — as well as new approaches to packaging the final circuits — to produce an electronic system that could reliably withstand the extreme conditions of space,” he adds.
At the end of the project, the researchers supplied NASA with a suite of modeling tools, circuit designs, packaging technologies and system/subsystem designs, along with guidelines for qualifying those parts for use in space. In addition, the team furnished NASA with a functional prototype — a SiGe remote electronics unit (REU) 16-channel general-purpose sensor interface — fabricated using SiGe microchips and tested successfully in simulated space environments.
The now-completed project has moved the task of understanding and modeling SiGe technology to where NASA engineers can start using it on actual vehicle designs, says Andrew S. Keys, center chief technologist at the Marshall Space Flight Center and NASA program manager. “The SiGe extreme environments team was very successful in doing what it set out to do. They advanced the state-of-the-art in analog SiGe technology for space use — a crucial step in developing a new paradigm leading to lighter-weight and more capable space vehicle designs,” he adds.
At best, most electronics conform to military specifications, meaning that they function across a temperature range of –55ºC to +125ºC, explains Keys. But electronics in deep space are typically exposed to far greater temperature ranges, as well as to damaging radiation. The Moon’s surface cycles between +120ºC during the lunar day to –180ºC at night. The SiGe electronics developed by the extreme environments team has been shown to function reliably throughout that entire range. It is also highly resistant or immune to various types of radiation.
The conventional approach to protecting space electronics, developed in the 1960s, involves bulky metal boxes that shield devices from radiation and temperature extremes, Keys says. Designers must place most electronics in a protected, temperature-controlled central location and then connect them via long and heavy cables to sensors or other external devices.
By eliminating the need for most shielding and special cables, SiGe technology helps reduce the single biggest problem in space launches: weight. Moreover, robust SiGe circuits can be placed wherever designers want, helping to eliminate data errors caused by impedance variations in lengthy wiring schemes. “For instance, the Mars Exploration Rovers, which are no bigger than a golf cart, use several kilometers of cable that lead into a warm box,” Keys says. “If we can move most of those electronics out to where the sensors are on the robot's extremities, that will reduce cabling, weight, complexity and energy use significantly.”
NASA currently rates the new SiGe electronics at a technology readiness level of 6 (i.e. the circuits have been integrated into a subsystem and tested in a relevant environment). Level 7 involves integrating the SiGe circuits into a vehicle for space flight testing. At level 8, a new technology is mature enough to be integrated into a full mission vehicle, and at level 9 the technology is used by missions on a regular basis.
Successful collaboration was an important part of the SiGe team’s effectiveness, Keys says. Professor Alan Mantooth, who led a large University of Arkansas contingent involved in modeling and circuit-design tasks, termed the extreme-electronics project highly useful in the education mission of the participating universities, noting that a total of 82 students from six universities worked on the project over five years.
BAE Systems’ contribution to the project included providing the basic architecture for the remote electronics unit (REU) sensor interface prototype developed by the team. That architecture came from a previous electronics generation: the now cancelled Lockheed Martin X-33 Spaceplane initially designed in the 1990s.
In the original X-33 design, explains BAE Systems’ senior systems architect Richard W. Berger, each sensor interface used an assortment of sizeable analog parts for the front-end signal receiving section, which was supported by a digital microprocessor, memory chips and an optical bus interface (all housed in a protective 5-pound box).
The extreme environments team transformed the bulky X-33 design into a miniaturized sensor interface using SiGe. The resulting SiGe device weighs about 200g and requires no temperature or radiation shielding. Large numbers of these robust, lightweight REU units could be mounted on spacecraft or data-gathering devices close to sensors, reducing size, weight, power and reliability issues.
Berger says that BAE Systems is interested in manufacturing a sensor interface device based on the extreme environment team’s discoveries.
Other space-oriented companies are also pursuing the new SiGe technology, Cressler says. NASA wants the intellectual-property barriers to the technology to be low so that it can be used widely. “The idea is to make this infrastructure available to all interested parties,” he adds. “That way it could be used for any electronics assembly — an instrument, a spacecraft, an orbital platform, lunar-surface applications, Titan missions — wherever it can be helpful. In fact, the process of defining such an NASA mission-insertion road map is currently in progress.”
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