WASHINGTON — As NASA selects its next major planetary science mission, the agency is also funding studies of very small missions that seek to capitalize on advances in smallsat technology.

NASA issued a media advisory June 26 stating it would announce the selection of “a major new science mission to explore our solar system” at 4 p.m. Eastern June 27. The advisory didn’t give additional details about the mission, but one of the participants in a media teleconference is the lead program scientist for the agency’s New Frontiers program of medium-class planetary science missions.

NASA chose two finalists for the next New Frontiers mission in December 2017 for further study. One, Comet Astrobiology Exploration SAmple Return, or CAESAR, would visit the comet 67P/Churyumov-Gerasimenko — the same comet studied by the European Space Agency’s Rosetta mission — and return samples of its nucleus to Earth. The other, Dragonfly, would land on Saturn’s largest moon, Titan, and then travel from point to point across its surface.

The agency had been finalizing reviews of the two proposed missions, although the planetary science community didn’t expect a selection this month. “We are close to being able to make an announcement and a decision about New Frontiers,” said Lori Glaze, director of NASA’s planetary science division, during a June 24 presentation at a meeting of the agency’s Small Bodies Assessment Group (SBAG) in College Park, Maryland. “This will be coming some time in July.”

New Frontiers is NASA’s largest program of competitively selected planetary science missions. Proposals for this latest round of the program had to fit within a cost cap for development of $850 million, although total mission costs, when launch and operations are included, will likely exceed $1 billion.

The impending New Frontiers selection comes a week after NASA selected mission proposals at the other end of the cost spectrum. On June 19, NASA chose three proposed small planetary missions for further study as part of its Small Innovative Missions for Planetary Exploration, or SIMPLEx, program.

The three concepts, selected from 12 proposals submitted last year, will receive funding over the next year for initial development through preliminary design review. The missions are required to weigh no more than 180 kilograms, allowing them to launch as secondary payloads, and cost between $15 million and $55 million.

One of the finalists, Escape and Plasma Acceleration and Dynamics Explorers (EscaPADE), would be developed by the University of California Berkeley. It features two small satellites that would go to Mars to study how the planet’s atmosphere loses mass and interacts with the solar wind. Janus, by the University of Colorado and Lockheed Martin, would use a pair of smallsats, weighing about 40 kilograms each, to fly by binary asteroids. Lunar Trailblazer, by Caltech and the Jet Propulsion Laboratory, is a lunar orbiter to map water ice deposits using advanced infrared instruments.

“We were delighted with the compelling proposals that we saw and that they’re really trying to be relevant in a variety of different areas,” Glaze said at the SBAG meeting. Janus, for example, could also support NASA’s work in planetary defense, while Lunar Trailblazer could play a role in NASA’s human lunar exploration plans.

That means such missions could be funded outside of the planetary science program at NASA, enabling multiple selections if they pass their initial reviews. “We have the potential to select more than one ultimately,” she said. “There is a potential for different funding sources for each of them.”

Other space agencies are also investing in small planetary science missions. ESA announced June 19 the selection of Comet Interceptor as its first “F-Class” or “fast” mission in its Cosmic Vision science program. Such missions must weigh less than 1,000 kilograms, with a cost of no more than 150 million euros ($170 million.)

Comet Interceptor will launch in 2028 as a secondary payload on ESA’s Ariel exoplanet science mission. It will travel with Ariel to the Earth-Sun L-2 Lagrange point, 1.5 million kilometers from Earth, and wait there until a suitable comet is found within range of the spacecraft. It will then use onboard propulsion to travel towards it, splitting into three modules to take measurements of the comet and its gas, dust and plasma environments.

Placing the mission in storage at L-2 will allow it to respond rapidly to a newly discovered comet, something not possible if the mission was developed only after the comet’s discovery. “With Comet Interceptor, we’ll be able to respond quickly to study one of the most important and ancient objects from our solar system and maybe beyond,’ said Geraint Jones of University College London, one of the scientists that led the proposal for the mission.