WASHINGTON — Competition for the next mission in NASA’s New Frontiers line — a cost-capped class of $1 billion robotic solar-system explorers — will begin in 2016, NASA’s planetary science chief told an advisory panel Feb. 19 at NASA’s Ames Research Center in Mountain View, California.

The long-awaited announcement of opportunity for the fourth New Frontiers competition will appear some time after Oct. 1, the start of the U.S. government’s 2016 fiscal year, NASA Planetary Science Division Director Jim Green told the Outer Planets Assessment Group (OPAG), an advisory panel NASA chartered in 2004 to set science priorities for exploration of the outer solar system.

NASA is also looking ahead to the fifth New Frontiers competition, which would begin by 2020, Green added. If the timing holds, NASA would in theory be able to maintain the five-year launch cadence it established for the program in 2006, when the first New Frontiers missions, the New Horizons Pluto probe, blasted off on its looming encounter with the unexplored dwarf planet.

“Now we’re at the point where we can see the New Frontiers program extending beyond Osiris-Rex,” Green told OPAG.

Osiris-Rex, short for Origins Spectral Interpretation Resource Identification and Security-Regolith Explorer, is slated to launch in September 2016 to collect and return a sample of the asteroid Bennu. Osiris-Rex won the third New Frontiers competition in 2011 (the year the New Frontiers 2 mission, the Juno Jupiter probe, launched) and NASA had been coy ever since about when competition for the fourth in the line would begin — until Green spoke at OPAG.

“I am a decadal zealot!” – Jim Green

New Frontiers missions are managed by a single principle investigator, who is responsible for keeping the mission’s development cost under $1 billion. The cost cap does not include the price of a launch vehicle, which is covered under the NASA Launch Services Program.

Green did not say exactly when NASA will call for submissions for the New Frontiers 4 mission, or how many finalists the agency would cull from the proposals it receives. However, he did remind OPAG that there will be strings attached to the solicitation besides the $1 billion cost cap.

Green said NASA will only fund a candidate that proposes to tackle one of five priority New Frontiers  science objectives identified in 2011 by the National Research Council’s planetary decadal survey, “Visions and Voyages for Planetary Science in the Decade 2013-2022.”

“I am a decadal zealot!” Green declared, presenting a slide that featured the types of missions NASA, per rules set by the latest planetary decadal, will prioritize for the New Frontiers 4 competition. Those missions, which are not limited to the outer planets, are:

  • Comet surface-sample return.
  • Saturn probe.
  • Lunar south pole Aitken Basin sample return.
  • Venus lander.
  • Trojan asteroid tour and rendezvous probe.

For the fifth New Horizons competition, NASA will consider all the missions that do not make the cut in the fourth competition, plus:

  • The Lunar Geophysical Network, a mission that would drop instruments all over the moon’s surface to create a crust-to-core map of the satellite’s interior.
  • An Io probe, which would study Jupiter’s innermost Galilean moon — the most volcanically active body yet observed in the solar system.

Early concept studies for some of these missions — the Lunar Geophysical Network, for example — included the use of a nuclear battery known as a radioisotope power system. These systems, long a part of the space program, convert heat given off by decaying pellets of radioactive plutonium-238 into electricity. The heat that is not converted keeps spacecraft instruments warm, making these power sources sought after for missions where solar panels would be impractical, either because of shade or sheer distance from the sun.

Plutonium-238 is scarce, but possibly not as scarce as it was even last year. Some might even be available in time to power New Frontiers 5, although perhaps not New Frontiers 4, now that NASA has raised the possibility of building a solar-powered Europa probe.

Until recently, outer planets scientists assumed any plutonium not reserved for the Mars 2020 mission would be reserved for the proposed Europa Clipper mission.

But in October, the team behind the approximately $2 billion Clipper concept said the mission could be done with solar panels.

Then, on Feb. 20, Alice Caponiti, director of the Energy Department’s office of space and defense power systems, told OPAG domestic plutonium-238 production is projected to ramp up in time to refine enough fuel for Mars 2020 and still be able to produce three fully fueled nuclear batteries known as multimission radioisotope thermoelectric generators for some other mission by 2024.

That would be too late for New Frontiers 4, which would notionally launch in 2021, but in plenty of time for New Frontiers 5, which now stands to follow in 2026.

So if NASA selects the solar-powered Clipper — a decision that is not certain, and in any case not imminent, given that the agency only approved a Europa mission-start in a 2016 budget request now before Congress — the agency would indeed have some plutonium to go around.

Green himself offered no guidance about nuclear power for New Frontiers 4, telling OPAG only that “we’re going to follow the decadal.”

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.