WASHINGTON — NASA announced June 27 it will send a spacecraft to Titan, the largest moon of Saturn, to fly across its surface to study how life there, and on the early Earth, could have developed.

The agency said it selected Dragonfly as the next mission in its New Frontiers line of medium-class planetary science missions. Dragonfly was one of two finalists, along with the Comet Astrobiology Exploration SAmple Return (CAESAR) mission, the agency picked in December 2017 for study.

Dragonfly is scheduled for launch in 2026, arriving at Titan in 2034. The spacecraft will touch down in dune fields in the moon’s equatorial regions. From there Dragonfly, effectively a drone the size of a Mars rover and equipped with eight rotors, will fly from location to location across the surface of the moon.

Scientists plan to have Dragonfly makes its way to a crater called Selk about 80 kilometers in diameter. “We think that, at Selk Crater, the three ingredients you need for life were mixed together,” said Curt Niebur, lead program scientist for New Frontiers at NASA, during a NASA webcast announcing the mission. Those ingredients are water, organic compounds and energy. “We want to get Dragonfly to that crater so we have a chance to directly investigate what happened when you mix those three things together.”

Studying Selk Crater and other locations on Titan should help scientists understand what conditions were like on the early Earth when life formed, he added. “We can’t go back in time on Earth and learn the lessons about the chemistry that eventually led to life, but we can go to Titan and we can pursue those questions.”

Dragonfly is designed to fly about 175 kilometers across Titan over two and a half years. The spacecraft will use a radioisotope thermoelectric generator (RTG) to generate electrical power, storing it in a battery for use during flight and other mission activities.

“Flying on Titan is actually easier than flying on Earth,” said Elizabeth “Zibi” Turtle, the principal investigator for Dragonfly at Johns Hopkins University Applied Physics Lab. Titan’s atmosphere, she said, is four times denser at the surface than on Earth, and the moon’s gravity is one-seventh that of Earth. “It’s the best way to travel, and the best way to go long distances.”

Dragonfly will make extensive use of drone technology developed terrestrially, she said. “This is actually technology that is very mature on Earth,” she said in a later media teleconference. “Really what we’re doing with Dragonfly is innovation, not invention. We’re applying technologies that already exist to another planet.”

Convincing NASA of that, however, was not easy. Thomas Zurbuchen, NASA associate administrator for science, said that when the agency received the original Dragonfly proposal, if identified about 10 significant risks in its design. “The science was so compelling that, when we looked at all the risks that were there, and there quite a number of them, we basically said we want to give them a chance.”

The Phase A study completed by the Dragonfly team eliminated those risks. One concern identified by reviewers was that a “vacuum cleaner” system used to collect materials for analysis by instruments inside the spacecraft could get clogged or contaminated by hydrocarbon materials commonplace on Titan. Niebur said the mission made “some big design changes” to lower the risk of clogging.

Another area was demonstrating that Dragonfly could fly as expected on Titan, including its ability to fly autonomously. “We can literally test as we fly” here on Earth, Turtle said. “We can really demonstrate its capability by flying here on Earth before we fly on Titan.”

One change from the original proposal is a one-year slip in the mission’s launch date, from 2025 to 2026. That change will give the Dragonfly team more development time, although doesn’t delay the mission’s arrival at Titan since the original trajectory had a longer cruise period.

“The team could benefit greatly by some additional time to work through some of the challenges,” Lori Glaze, director of NASA’s planetary science division, said. “From our perspective, this gives this mission the greatest chance of success.”

NASA hasn’t selected a launch vehicle for Dragonfly, and launch costs, along with post-launch operations, aren’t included in the $850 million cost cap for this New Frontiers competition. Dragonfly will use flybys of Venus and Earth after launch to reach Titan.

Dragonfly was, anecdotally, the favorite among many planetary scientists over CAESAR. That mission would have flown to comet 67P/Churyumov-Gerasimenko, the same comet studied by the European Space Agency’s Rosetta mission, and collected samples of the comet’s nucleus for return to Earth.

Zurbuchen said that he selected Dragonfly for three reasons, one of them being its science. “The science is compelling,” he said. “We have questions about this world out there, Titan, that frankly only now we know how to ask.” A second factor was the work it did to mitigate risks, and the third was the strong leadership of the mission.

Zurbuchen praised CAESAR and its team, led by Steve Squyres, best known for being principal investigator for the Mars Exploration Rovers and chairing the latest planetary science decadal survey. “He has been a very aspirational leader for many of us,” Zurbuchen said of Squyres. “For many of us, he set the standard of what it means to build an integrated team.”

CAESAR, or a mission like it, could propose for later competitions, although Glaze said the next New Frontiers competition won’t be until about 2022. “Some of the best ideas take multiple shots on goal before they become reality,” Zurbuchen said.