WASHINGTON — NASA has not yet said when a competition for the next small-scale robotic mission to another planet might begin, but the Goddard Space Flight Center in Greenbelt, Md., declared its intent to win Sept. 9 with a call for key subsystems to be used on a mission to Venus, an asteroid or a comet.

In its Sept. 9 Partnership Opportunity Document, Goddard said it is “seeking partners for spacecraft, navigation, mission operations center, and related spacecraft subsystems” that could be folded into a proposal for NASA’s next Discovery-class planetary science mission, competition for which the center expects to begin around November or December of 2014. Responses are due Oct. 4.

Goddard, which is not yet seeking concepts for either science instruments or mission concepts, estimates there will be $475 million worth of funding for the next Discovery mission, which it expects will launch in either 2021 or 2022. The center said it might, before October, expand its list of allowable destinations to places besides Venus or small bodies.

The most recent Discovery mission, the twin Gravity Recovery and Interior Laboratory probes, launched in 2011. The next Discovery mission, a Mars lander called InSight selected in August 2012, is to launch in 2017.

Goddard’s Sept. 9 notice offers one of the clearest pictures available today of internal NASA thinking about the next Discovery competition, for which no official start date has been announced. 

“It would be premature for me to tell you when a New Frontiers or Discovery call would come out,” Jim Green, director of NASA’s Planetary Science Division, told the Astrobiology and Planetary Science Committee of the National Research Council’s Space Studies Board Sept. 4. “I need a little more time to do that.”

Discovery and New Frontiers are competitively selected mission lines that, excluding the price of a launch, are capped at inflation-adjusted levels of roughly $425 million and $700 million, respectively. 

Among the unknowns NASA will have to resolve before it knows when it will have money for another Discovery mission is the final cost of the Mars 2020 rover. That craft will be based on the Curiosity rover that marked one year on the martian surface Aug. 5. NASA’s preliminary estimates show Mars 2020 costing about $1.5 billion — nearly $1 billion less than it eventually took to launch Curiosity in 2011, which was two years later than scheduled. 

“While we have a notional cost cap for that, we still have a lot to do before we have everything in place to know the total cost of [Mars] 2020,” Green said. 

Also a factor is the final cost of the InSight mission, the 12th in the Discovery line. InSight is due to reach Key Decision Point C, a milestone at which mission managers set a firmer life-cycle cost, in November, Green said Sept. 4.

Although popular in Congress, including with influential members of appropriations panels that write the first drafts of NASA’s budget each year, the Planetary Science Division has lately found itself at the bottom of the Science Mission Directorate’s totem pole. 

The division was tapped in 2012 to cover budget overruns for the James Webb Space Telescope, a flagship astrophysics mission projected to cost the agency $8.8 billion to build, launch and operate for five years following its 2018 launch aboard Europe’s Ariane 5 rocket. NASA’s Planetary Science Division has also had to make do with less funding so that the NASA Earth Science Division, popular with a White House that has made climate change research a priority, could have more funding.

Nevertheless, Planetary Science caught a small break in 2013 after a protracted debate between the White House and Congress, netting nearly $1.3 billion, or about 7 percent more than the administration requested in NASA’s final operating plan for the year.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...