WASHINGTON — With a new presidential mandate to settle on a heavy-lift rocket design no later than 2015, NASA plans to complete by June 21 a study examining the feasibility of a common main engine for rockets that would launch civil, commercial and national security payloads, according to officials with the space agency.

“We’ve got Air Force participation right now,” Cris Guidi, deputy director for NASA’s Constellation Systems Division, said of the study, which began May 11 and would “engage the broader community.” She said that while affordability would set the tone for the entire heavy-lifter development program, the acquisition approach is focused on finding the “sweet spot to enable a national engine for everybody’s use.”

Guidi was speaking May 25 at a workshop in Galveston, Texas, during which NASA formally rolled out initial plans for new human and robotic space exploration technology efforts, fleshing out proposals criticized by lawmakers and others for lacking detail when the agency unveiled them in February. The two-day workshop — streamed live on the Web  — was aimed at giving industry and academia an opportunity to ask questions and pitch ideas for NASA’s new direction, including plans to back private-sector development of a crew transportation system in low Earth orbit while studying heavy-lift launch options and seeding “game-changing” technologies that could advance the agency’s new exploration agenda.

Guidi said NASA received 43 responses to a May 4 request for information on the nascent heavy-lifter program. Separately, the agency hopes to ultimately award several study contracts under a May 19 broad area announcement intended to resume work on a heavy-lift launch study “performed last year by some NASA civil servants.” NASA recently shelved a study of Ares 5 heavy-lift launch plans after U.S. President Barack Obama proposed canceling Ares 5 and the rest of the Moon-bound Constellation program in its 2011 budget request to Congress.

The in-depth review, which would entail a more comprehensive review of heavy-lift technologies than the feasibility study initiated in May, would involve input from industry and academia for a period of about six months, Guidi said.

“We want to perform an in-depth study to figure out the most affordable approach to this,” she said, adding that while the study would focus on development of a liquid hydrocarbon engine, it would also consider the affordability and reliability of solid-rocket engines. The Ares 5 design features variants of the giant solid rocket motors used on the soon-to-be-retired space shuttle.

“Any procurement that we release from NASA is open to anybody; we’re not limiting anybody from participating in this effort,” she said. In earlier remarks, however, she said a secondary goal of the new heavy-lift effort is to “build up a robust liquid propulsion industry base.”

Phil McAlister, who is overseeing NASA’s effort to develop human-rating requirements for commercial crew vehicles, explained the agency’s rationale for backing a market for commercial space transportation.

“Routine space access for humans is the goal of our commercial human spaceflight plan,” McAlister said during the conference, adding that NASA intends to fund a variety of commercial crew concepts put forth by large aerospace companies and by small, entrepreneurial firms. The aim is to “get the best of both,” he said.

McAlister said NASA expects to fund multiple commercial providers launching four astronauts to the station twice a year beginning in 2015 or 2016. He said a key element of the commercial crew acquisition strategy involves “fixed government investment,” with payments made to companies as their hardware and other development efforts achieve set milestones. He said “traditional cost-plus-type relationships are not being considered for the development phase going forward.”

NASA released a draft of its proposed human-rating requirements for commercial crew vehicles May 21, and expects industry input on the document by June 11.

The agency will rely on commercial providers to “make their systems safe,” McAlister said. “NASA will, though, have in-depth insight into those vehicle designs, predominantly through co-locating NASA personnel on site with the contractor so we can see the real-time test data as it’s coming through.”

The degree of oversight, he said, will depend largely on vehicle design, as “some have more risky features than others.” For example, commercial providers that incorporate flight-proven technologies into their vehicles could require less scrutiny and less-rigorous testing than those featuring novel designs or unproven technologies.

“We’re going to have a lot of tests” regardless, McAlister said.

NASA will not specify launch or landing sites for commercial crew providers, so long as they meet agency requirements for safe, cost-effective and reliable transportation, he said. Private companies would be responsible for all facilities and infrastructure, though they could request government-furnished equipment.

Commercial providers would be required to certify their own mission readiness, he said.

“Launch director authority is to reside with the commercial provider,” McAlister said, adding that if a safety issue crops up, NASA “would be able to pull our astronauts from that mission. If the providers want to go forward with the mission, that’s up to them.”