NASA Glenn researchers develop electronics for longer Venus surface missions
GLENN RESEARCH CENTER, Ohio — Venus is our closest planetary neighbor. However, its mean surface temperature is at a horrendous 863 °F (462 °C) with a crushing atmospheric pressure 90 times that of Earth; consequently, the operating lifespan of any spacecraft visiting its surface has been very short. The work of a group of scientists at NASA’s Glenn Research Center in Cleveland, Ohio, may change all that.
To date, the record-holder for survival on the surface of Venus is the Soviet spacecraft Venera 13. The probe landed on Venus in 1982 and transmitted data from the surface for 127 minutes before the spacecraft’s electronics fried in the harsh environment. The huge investment necessary for putting a spacecraft on another planet is hard to justify for such a brief window of possible data transmission.
The group recently completed an important technology demonstration that could vastly increase our capability for a much longer duration mission on the surface of Venus.
Silicon carbide circuits
For years, the team at NASA Glenn has been pursuing the experimental development of extremely durable silicon carbide (SiC) semiconductor integrated circuits. It has been known for decades that SiC is a very chemically inert, robust material. It has electrical properties that allow it to maintain its ability as a semiconductor at very high temperatures.
“The majority of the battle in our research over the last decade has not been inside the SiC itself,” NASA Glenn electrical engineer Phil Neudeck told Spaceflight Insider. “It’s been in the interconnects. It’s been in the packaging and the integration of all those things. That’s where the real durability battle has been.”
Making an integrated circuit involves connecting semiconductor transistors. The NASA Glenn engineers could not use silicon connectors because silicon connectors are not capable of operating at extremely high temperatures.
“The real challenge was […] to make the whole circuit of reasonable complexity to actually do useful things and last for a long time in this harsh of an environment,” Neudeck said.
This circuit development presented unique challenges for survivability in the extremes on the surface of Venus. An example is that there is a particular kind of transistor common to most computer electronics called a MOSFET – metal oxide semiconductor field-effect transistor. It is a very high-functioning transistor, and if the NASA Glenn researchers could get a silicon carbide MOSFET to work reliably at the very high temperatures of the Venus environment, they would use such a transistor.
However, that particular transistor is inherently not as reliable at high temperatures as another transistor called a JFET – junction gate field-effect transistor. The NASA Glenn engineers have been able to successfully build JFET transistors with all SiC junctions, making them highly robust and durable.
The researchers knew the circuits were stable in Earth atmosphere ovens for thousands of hours. But how would they really survive in the Venus environment, where temperatures are hot enough to melt lead, and the pressure is equal to that at 1 km deep in the ocean.
That question was answered by one of NASA’s many acronyms – GEER.
Glenn Extreme Environment Rig
GEER is the Glenn Extreme Environment Rig. It is a high-tech pressure vessel capable of simulating the temperature, pressure, and atmospheric gas mix of Venus, or any other extreme environment, for an extended period. Last spring, the engineers put the newly developed SiC circuits into GEER, where they withstood the simulated Venus environment extremes for 521 hours – nearly 22 days – more than 100 times longer than any electronics survived on previous Venus missions.
It is likely that the circuits could have survived much longer. They were still fully functioning at the completion of the test, which was shut down only because the GEER unit was scheduled for testing on another device.
Venus lander designs
The durability demonstrated by the circuits in this test present exciting possibilities for future Venus lander designs. The small fleet of seven Soviet Venera and Vega spacecraft that landed on Venus in the ’70s and ’80s housed their electronics in specially sealed chambers that were insulated and cooled to about 14 °F (–10 °C) before they descended into the planet’s extreme atmosphere. Such housing and cooling equipment adds significantly to the weight of a spacecraft and drives up costs while preventing other scientific instruments from being included.
The durability of the SiC electronics developed at NASA Glenn will eliminate the need for that cooling equipment. With the decreased weight as a result of the more durable electronics, future NASA Venus landers will be able to carry a greater number of scientific instruments, expanding the scientific value of the mission per its investment.
“Our next steps are to start to design and build a range of circuits and bring those circuits together in order to move towards, potentially, a Venus surface weather station,” NASA Glenn senior electrical engineer Gary Hunter told Spaceflight Insider. “It would measure a series of properties on the surface and periodically send that data on the surface over an extended period of time, 60 days for example, to an orbiter or other communication devices above the surface. So we need to develop and integrate other types of circuits, to be able to operate such a thing as a Venus weather station.”
The Venus weather station is one of a number of Venus surface missions that are at various stages of development or consideration at NASA and other space agencies. The NASA Glenn researchers’ goal is to get the electronics ready for any and all of them that might be chosen to make the journey to the horrific environment on the surface of Venus.
“This demonstration showed a capability that wasn’t necessarily counted upon before,” Hunter said. “I think now our job is to build upon that, show further complexity, show further integration, so as to enable new kinds of science missions.”
Michael Cole is a life-long space flight enthusiast and author of some 36 educational books on space flight and astronomy for Enslow Publishers. He lives in Findlay, Ohio, not far from Neil Armstrong’s birthplace of Wapakoneta. His interest in space, and his background in journalism and public relations suit him for his focus on research and development activities at NASA Glenn Research Center, and its Plum Brook Station testing facility, both in northeastern Ohio. Cole reached out to SpaceFlight Insider and asked to join SFI as the first member of the organization’s “Team Glenn.”