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From Dayton to Mars

Allan Crasto

UDRI researchers helped NASA plan Perseverance mission

By Pamela Gregg, Communication Administrator, 937-229-3268

As the Perseverance rover descended to the surface of Mars just before 4 p.m. Feb. 18, University of Dayton Research Institute scientist Chad Barklay closely watched NASA’s live feed of its Joint Propulsion Lab control room, listening for touchdown confirmation.

Exactly four years prior, Barklay and UDRI colleague and engineer Allan Tolson were also closely watching as they essentially cooked a generator similar to the one that will power the Mars 2020 rover, heating it up to temperatures never before experienced by the unit or its sister units on earth and Mars. By assessing the effects of high heat on the prototype unit, the laboratory test was designed to predict whether the Multi-Mission Radioisotope Generator (MMRTG) attached to Perseverance would continue to perform normally should it encounter unanticipated extreme temperatures during the rover’s mission.

The successful test helped NASA prepare for the Mars 2020 mission, which launched in July and successfully delivered Perseverance by sky crane to the red planet surface seven months later.

Since opening UDRI’s MMRTG Laboratory in late 2013, Barklay—group leader for advanced high-temperature materials in UDRI’s power and energy division—and his team have designed and performed qualification and evaluation tests on generators in support of NASA’s Curiosity and Perseverance rover and future deep-space missions. Their research, sponsored by the Department of Energy, provides critical information on the performance of the power units over time and under the punishing temperatures and other harsh operating conditions of space.

“The MMRTG is essentially the lifeblood of the rover,” said Barklay, who helped develop the layout and assembly procedures for the MMRTG that continues to power Curiosity at Mars’ Gale Crater. “Heat generated by naturally decaying isotopes within the generator’s core keep the rover warm during the extreme cold of Martian nights, and is also converted to electricity to power the rover’s mechanical, computer and communication systems. The information we provide on MMRTG performance helps mission planners understand how much power they’ll have and how long they’ll have it for the science they want to do.”

In addition to helping NASA plan for the routine, UDRI researchers also help the agency prepare for the unexpected, Barklay said.

“There are a number of factors that can affect generator performance, including heat. Four years ago, there were still several potential elements of the pending Perseverance mission that each could have caused the MMRTG to run hotter than the its predecessor unit on Curiosity, including landing site, which hadn’t been selected yet; the Martian climate at time of landing; the age of the generator at launch; and some minor design differences in the rover that could affect heat transference from its generator. So we were asked to design and conduct what was basically a worst-case-scenario experiment that would assume the hottest temperatures for each of those factors, and then some.”

To prepare for that 2017 test, Barklay and Tolson wrapped a generator in an insulating material, then heated the unit to 428 F—approximately 100 degrees hotter than the maximum temperature Curiosity’s generator experiences. They held the unit at that temperature for 24 hours, neither sleeping nor leaving the generator unattended, prepared to quickly shut down the experiment if they observed any behavior that threatened the system.

“The outcome was highly successful; better than we could have hoped,” Barklay said.

For several years after opening, the MMRTG lab was equipped with the first two multi-mission generators built by NASA. These earthbound generators, designed for qualification and testing, are identical to their sister units on the Curiosity and Perseverance rovers with one significant exception—they are powered by electricity rather than by the plutonium at the core of generators attached to the rovers on—and on the way to—Mars.

In the last two years, one of the prototype generators was shipped to Johns Hopkins Applied Physics Lab for research and testing related to the Dragonfly rotocopter mission to Saturn’s moon, Titan, currently scheduled for launch in 2026. The second generator traveled first to the Idaho National Lab and NASA’s Joint Propulsion Lab before ultimately landing at Kennedy Space Center last year for final testing prior to the launch of Mars 2020.

Barklay anticipates the test generators returning to Dayton at some point in the future. In the meantime, his team built a thermal simulator that mimics the NASA generators in appearance and behavior. “We made some modifications to the thermal simulator that will allow us to adapt to advancing generator technology if needed,” Barklay said. “For now, we’ll continue to support the missions of Curiosity, Perseverance and future deep space exploration, and we’re hoping to do some work in support of Dragonfly.”

The simulator was also used for a research study into the possibility of using MMRTGs to power lunar experiments, should the U.S. go back to the moon, Barklay said. He will publish and present a paper on the study at the IEEE Aerospace Conference in early March.

Barklay, who formerly worked at Mound Laboratories in Miamisburg—which he calls the birthplace of radioisotope generator technology—said he will never tire of watching launches and landings, in spite of the number he has already seen.

“Nothing can really prepare you for the emotions you experience when watching,” he said. “It’s amazing to feel part of something so much bigger than yourself, and it’s a profound experience to realize that you and your colleagues contributed to the success of the mission.”

Feb. 19, 2021


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