Spacecrafts of the future could feature streamlined electronics systems thanks to a five-year, US$12 million project.

By adapting existing silicongermanium (SiGe) technology, scientists have developed a transistor that can withstand the extreme conditions of deep space, without altering its original composition. The work exploits the natural benefits of the SiGe alloy, such as lighter weight and higher durability, to develop new circuit design models.

Professor John Cressler, of the School of Electrical and Computer Engineering at the Georgia Insititute of Technology, claims that as SiGe can withstand the adverse conditions of space, much of the protective wiring and radiation shielding currently required could be dispensed with and electrical units could be located anywhere on the vehicle, providing an ‘environmentally invariant electronics platform’.

Silicon-germanium combines both materials in an epitaxial layer at nanoscale dimensions. To demonstrate its capabilities, the team chose IBM’s 0.5μm SiGe technology as a test sample. Cressler led a research consortium of over 50 people, drawn from five universities, three companies and NASA, who funded the work, to explore the possibilities of SiGe and develop a prototype Remote Electronics Unit (REU) device. It is a 16–channel general purpose sensor interface.

After exposing the SiGe REU to cold temperature (-180˚C) testing, and a radiation beam (at temperature), the researchers were able to prove it can function in extreme space environments, where radiation from galactic cosmic rays and solar wind, as well as the extreme temperatures (from -230˚C to 120˚C), normally pose problems.

Up to now, spacecrafts have been designed with a central electrical hub or ‘warm electronics box’ that is thermally sealed and covered with bulky radiation shielding, with wires running around the structure to the various sensors and external equipment. ‘The overheads are enormous and are a large driver for the way missions are built today,’ notes Cressler.

Prototype from the past

The REU was based on a component of the now-cancelled Lockheed Martin X-33 Spaceplane in the 1990s, made by BAE systems. Richard Berger, Systems Architect at BAE worked on adapting it, and said that the unit was a ‘very specific demonstration of how to integrate [SiGe] circuits and is a point solution that can be applied to a number of missions. Berger suggests it could be used in communications with a base on the moon or another planet, citing it’s capacity for digital and analogue signals.

Cressler adds that in an effort to drive the field of space electronics forward, the team did not try to protect any of the intellectual property rights. ‘We wanted it to be available to everyone. [If you want] innovation and technology to become widespread, putting up barriers is not the best way to do that.’ Berger agrees that ‘corporate protectionism [can] probably limit the rate advancements can occur,’ but conceded that it was the nature of business.

IBM Fellow David Harame, who was involved in the work, comments that ‘what he [Cressler] has really demonstrated is the whole set of circuit families that enable you to use SiGe in those kinds of [extreme] environments’.

The final phase has resulted in a suite of modelling tools, system designs and guidelines, a reusable library of SiGe circuits, and proven device models being supplied to NASA.

Although US President Barack Obama may have cancelled NASA’s plan to return to the moon, Cressler seems sure that the space programme will continue, and whatever part of the galaxy it heads to, SiGe parts could play a key role in getting there.