NASA has received dozens of new proposals for robotic missions for launch in 2021 to explore different parts of the solar system. Scientists have submitted concepts for sending probes to the moon, asteroids, comets and other planets for a chance to win $450 million in federal funding for their mission.

Scientists had to complete their proposals by February 18 for consideration for the next mission in NASA's Discovery program, a series of low-cost science focused probes whose goal is to explore different parts of our solar system.

Jim Green, director of NASA's planetary science division, said Feb. 19 that the agency plans to select at least two finalists from the proposals in May to receive $3 million federal grants for detailed concept studies. NASA should pick a single winner by September 2016, he told a meeting of the Outer Planets Assessment Group.

"We'll rapidly get down to making some announcements as soon as we can get through the evaluation," Green says.

The mission must be ready for launch in 2021 and it can not cost more than $450 million dollars, not including the launcher although some of the cost can come from international partners without counting against the $450 million cost cap.

The mission with be the 13th in the history of the Discover program, which began in the early 1990s and launched its first probe in 1996. Some of the Discover program's missions to date include the Mars Pathfinder rover, the NEAR Shoemaker that first orbited an asteroid, NASA's MESSENGER spacecraft now orbiting Mercury, and even the Dawn mission that is currently approaching the dwarf planet Ceres. The 12th Discovery mission, the InSight Mars lander, is set for launch in March of next year with a mission of touching down on the red planet and measuring its seismic activity.

The government has sweetened the deal on this mission by offering to supply a deep space optical communications system to test new high-speed data links with Earth and an extra $30 million above the original cap of $450 million if scientists use the laser telecom unit. This unit has been tested between the moon and Earth but has yet to prove itself at great distances.

This latest solicitation came four years after the last opportunity for low-cost missions in 2010, which resulted in the InSight Mars lander set for launch next year. Green says that NASA has funding in the White House's proposed budget to speed up the pace of Discovery missions, with another call for proposals as soon as late 2017.

"Our plan is to bring Discovery calls in closer," Green says. "Right now, the president's budget supports about every 36 months. It's not the 24 months that we'd like, but this is far healthier than it had been projected in the past."