Europa is more than just one of Jupiter’s many moons—it’s also one of the most promising places in the Solar System to search for extraterrestrial life. Beneath 10 kilometers of ice, there is a liquid water ocean that can support life. But with surface temperatures of -180 Celsius and extreme radiation levels, it’s also one of the most inhospitable places in the Solar System. Exploration of Europa may be possible in the coming years thanks to new research applications for silicon-germanium transistor technology at Georgia Tech.
Regents Professor John D. Kressler in the School of Electrical and Computer Engineering (ECE) and his students have been working with silicon-germanium heterojunction bipolar transistors (SiGe HBT) for decades and have found that they have unique advantages in extreme environments like Europe.
“Because of the way they’re made, these devices actually survive these extreme conditions without making changes to the underlying technology itself,” said Kressler, who is the project’s investigator. “You can build it for what you want it to do on Earth, and then you can use it in space.”
The researchers are in the first year of a three-year grant in NASA’s Ocean Life Discovery Technology Concepts (COLDTech) program to design the electronics infrastructure for upcoming missions to Europa’s surface. NASA plans to launch the Europa Clipper in 2024, an orbiting spacecraft that will map Europa’s oceans and then eventually send a Europa Lander lander to drill into the ice and survey the ocean. But it all starts with electronics that can function in Europe’s extreme environment.
Cressler and his students, along with researchers from NASA’s Jet Propulsion Lab (JPL) and the University of Tennessee (UT), demonstrated the SiGe HBT’s capabilities for this hostile environment in a paper presented at IEEE Conference on Nuclear and Cosmic Radiation Effectsin July.
The challenge of Europe
Like Earth, Jupiter also has a liquid metal core that generates a magnetic field, producing radiation belts of high-energy protons and electrons from the incoming solar wind. Unfortunately, as a moon of Jupiter, Europa sits right in these radiation belts. Indeed, any technology designed for Europa’s surface would not only need to be able to survive the cold temperatures, but also the worst radiation encountered in the solar system.
Fortunately, SiGe HBTs are ideal for this hostile environment. The SiGe HBT introduces a nanoscale Si-Ge alloy inside a typical bipolar transistor to nano-engineer its properties, effectively producing a much faster transistor while maintaining the economies of scale and low cost of traditional silicon transistors. SiGe HBTs have the unique ability to maintain performance under extreme radiation exposure and their properties naturally improve at lower temperatures. Such a unique combination makes them ideal candidates for exploring Europe.
“It’s not just doing the basic science and proving that SiGe works,” Kressler said. “It’s actually developing electronics for NASA to use on Europa. We know that SiGe can withstand high levels of radiation. And we know it remains functional at low temperatures. What we didn’t know was whether it could do both at the same time, which is necessary for missions to Europa’s surface.”
Testing the transistors
To answer this question, the GT researchers used JPL’s Dynamitron, a machine that fires high-flux electrons at very low temperatures, to test SiGe in a Europa-type environment. They exposed the SiGe HBT to one million electron volts at a radiation dose of five million rads of radiation (200-400 rads are lethal to humans), at 300, 200 and 115 Kelvin (-160 Celsius).
“What had never been done was to use electronics like we did in this experiment,” Kressler said. “So we’ve been working literally for the first year to get the results that are in this paper, which is essentially definitive proof that what we’ve been saying is actually true — that SiGe survives the conditions on Europa’s surface.”
Over the next two years, GT and UT researchers will develop actual SiGe circuits that can be used in Europe, such as radios and microcontrollers. More importantly, these devices can be used seamlessly in almost any space environment, including the Moon and Mars.
“If Europa is the worst environment in the solar system and you can make them work on Europa, then they will work everywhere,” Kressler said. “This research brings together past research that my team here at Georgia Tech has been doing for a long time and shows really interesting and new applications of these technologies. We are proud to use our research to break new innovative ground and thereby enable new applications.”
Materials provided by Georgia Institute of Technology. The original was written by Tess Malone. Note: Content may be edited for style and length.