Radiation resistance is baked into the Perseverance Mars rover. Here’s why that’s important.
Think about the number of times your computer on Earth has crashed. Now imagine how challenging that would be during a rover mission on Mars.
From time to time, the Curiosity rover has gone into “safe mode” to deal with glitches and software problems since it landed on Mars in August 2012. But each time, the mission has recovered to continue its epic climb up a Martian mountain in search of habitable environments.
All those “lessons learned” from safe mode incidents are now embedded into the new Perseverance rover, the more powerful cousin of Curiosity that started rolling on Mars on March 5.
Recovering from glitches takes technical skill, especially on Mars’ dusty, radiation-soaked surface. In many cases, radiation and circuits mix poorly. But that can’t be allowed to happen on Mars, where circuits on Perseverance control everything from the cameras to the laser, to the complex system that will cache potentially habitable rock samples for a future sample-return mission.
So what’s the solution? Xilinx — the company providing integrated circuits for several of Perseverance’s instruments — has had its technology on Mars since NASA’s Opportunity and Spirit rovers in 2004. Xilinx can’t give away all of its “secret sauce” that keeps the circuits safe — it’s proprietary — but a lot of it comes down to appropriate shielding and backup.
“We build the hardness in,” Minal Sawant, Xilinx’s director of the aerospace and defense vertical market, said of the company’s approach to keeping the circuits resistant to radiation. Sawant noted that several classified satellites have also used Xilinx circuits for long-standing missions in the harsh environment of radiation belts near Earth, so Xilinx has experienced radiation first-hand in Earth orbit and on Mars, and knows how to deal with it.
On Perseverance, the circuits are “triple-module redundant,” which means that Xilinx manufactures three copies of each circuit powering an instrument or a camera on the rover. “If one [circuit] gets hit, the other two still function. That’s how you ensure it’s hardened,” Sawant said.
The job gets harder with each successive generation of rover because the circuitry gets denser. That’s because each rover is tasked with gathering and transmitting more information to Earth than previous missions. “As we innovate more and more, there’s more density added,” Sawant explained.
There also are more possible points of failure with each generation of rover. For example, Spirit and Opportunity each carried only nine cameras; Perseverance has 23. The instruments and tasks have grown ever-more complex, too. Remarkably, however, Xilinx’s circuitry has stood the test of time.
Spirit and Opportunity were supposed to last 90 Earth days on Mars, but each lasted several years. Curiosity — which also carries Xilinx products — had a two-year prime mission after landing in 2012, but is still going strong after nearly seven Earth years on the Red Planet. Given that track record, Sawant is hopeful Perseverance will also survive for a long time.
An image of NASA’s Curiosity rover on Mars composed of 57 separate photographs the rover took on May 12, 2019. (Image credit: NASA/JPL-Caltech/MSSS)
One way to make the integrated circuits more responsive is to design them to be easily adjustable. We all know the value of applying software updates to our computer, and doing the same for a rover on Mars is tremendously helpful. On Curiosity, for example, a software update in 2016 allowed the rover to be more autonomous in picking targets to laser. Xilinx aims to offer similar flexibility for its integrated circuits.
“We make these chips that are very configurable,” Sawant said. “A designer or a user can put a specific algorithm or design in it, and do the function. It’s not a fixed function, but more of a programmable function … an ability to change as needed.”
Xilinx’s systems have already survived a powerful test with Perseverance. The circuits were used in the “vision compute” element of Perseverance’s landing system that enabled it to pick the right spot to land on Mars. Specifically, Xilinx products handled visual tasks like image filtering, detecting and matching. Another crucial part of the landing involved Perseverance’s range and velocity measurements, using a radar terminal descent sensor powered by Xilinx technology.
Sawant pointed out that even though those landing systems don’t need to survive for years on the surface, they have to go through several months of travel, experiencing the shaking of launch, the extreme cold and hot environments of space, and space radiation.
Xilinx’s integrated circuits are used in four instruments on Perseverance, all designed to withstand years of Mars radiation. These instruments are the Planetary Instrument for X-ray Lithochemistry, or PIXL, which identifies chemical elements; a UHF transceiver to relay telecommunications; Mastcam-Z, which takes panoramic pictures of the surface; and Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals, or SHERLOC, which performs fine-scale detection of minerals, organic molecules and potential signs of life.
Xilinx circuitry is also working well on the NASA OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) mission to asteroid Bennu, which has been in space since 2016 and won’t return with samples to Earth until 2023. Xilinx aims to launch its technology on the NASA Europa Clipper mission to orbit the icy Jupiter moon, too, which may require six years of cruise time in space after its planned 2024 launch.
Xilinx is one of several companies powering systems and instruments on the Perseverance rover. Another is Vaisala, working with the Finnish Meteorological Institute (FMI). The collaboration provided sensors for the Spanish-led Mars Environmental Dynamics Analyzer on board the rover — a Red Planet weather station that examines temperature, wind speed and direction, relative humidity and dust particles, and more. This group is also aware how challenging Mars can be.
“The rover’s equipment needs to operate in the harsh Martian environment, with very low pressure conditions and cold temperatures, and it must be able to resist possible global dust storms,” Maria Genzer, FMI’s head of planetary research and space technology group, said in a statement in February. “In addition to the environmental aspects … the distance between Mars and Earth makes the mission challenging. There is no one to fix the instrumentation if something goes wrong.”
As for Xilinx, the newest generation of its integrated circuits — released in May 2020 — will not only be resistant to radiation in multiple orbits around Earth or missions across the solar system, but will also include a machine-learning ecosystem. Machine learning (a facet of artificial intelligence) enables computers to learn from a dataset and to apply that information to make decisions.
With an Earth-orbiting satellite, for example, one application could be discarding optical images that include clouds, and only sending down images with clear conditions, Sawant said. More broadly, machine learning has already been used on Mars for applications such as identifying new craters.
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