For NASA’s longer-term goals of going beyond low Earth orbit, key propulsion-related projects are among the more than 1,000 individual technology development studies being undertaken. Top propulsion priorities include programs now under way in cryogenic propulsion storage and transfer, solar electric propulsion, the hypersonic inflatable aerodynamic decelerator, nuclear cryogenic propulsion stages, composite cryotanks and solar sails. “Those are the kind of things we’re looking at first,” Lightfoot says.

Many of the programs are already at a test stage, says Lightfoot, who referenced the recent flight from Wallops Island, Va., of an inflatable heat shield. The unit survived to return intact. “I think we showed you can use a large inflatable re-entry shell,” he says.

Additionally, in June NASA completed a second round of robotic refueling demonstrations at the International Space Station, an asset that continues to provide a focus for propulsion development, both for longer-term, exploration-related research and for the raft of commercial companies striving to support cargo and human missions.