WASHINGTON — The technology needed to send astronauts to a near-Earth asteroid is close at hand, NASA officials say, but Congress must fund research and development of robotic precursors and advanced propulsion capabilities if the agency expects to affordably meet U.S. President Barack Obama’s 2025 goal for such missions.

Doug Cooke, NASA associate administrator for exploration, said cutting-edge research in key areas, including in-space fuel storage and advanced propulsion, could make space travel more efficient and reduce the cost of sending astronauts to asteroids and other deep space destinations. But legislation moving through Congress this year would provide substantially less than NASA has proposed spending to mature promising technologies for manned missions to asteroids and other destinations.

“Advanced propulsion makes it much more efficient in terms of how much mass you put in space to go do this mission,” Cooke told reporters during a two-day workshop here on the exploration of asteroids and other near-Earth objects. “Efficiency in propulsion translates to the amount of fuel that you end up having to launch.”

Laurie Leshin, NASA deputy associate administrator for exploration, agreed. “Mass is money, and that’s the key here,” she told reporters attending the workshop. “The capabilities that we really need to develop are such that we can make this program affordable. We obviously have been challenged in the past. The key is to try and make a few of those really key investments like cryogenic storage and fluid management to allow us to be able to launch less mass out of our huge gravity well here on Earth.”

Cooke said NASA would work with Congress to influence the outcome of authorization and appropriations bills that lawmakers are expected to take up in September when they return from campaigning in their districts. Measures in both the House and Senate reduce funding for robotic precursor missions, space technology and propulsion development while requiring NASA to immediately begin work on a new heavy-lift rocket that would incorporate solid-rocket motor technology that would otherwise be abandoned under Obama’s manned spaceflight plans.

Although Cooke said NASA would like greater flexibility in determining the type of heavy-lift vehicle that could most efficiently and effectively deliver astronauts beyond low Earth orbit, in the end, boosting astronauts to a near-Earth object in 2025 using solid-rocket motors remains a viable option.

“There are different concepts that can do the same type of mission; it’s a matter of efficiency and cost,” he said. “Those components can do the job; we’ve studied that before. It’s a matter of whether or not through a competitive process, potentially, we come up with the best approach that gives us the best capability for the money.”

Cooke said once NASA develops the space transportation system needed to send astronauts on missions to near-Earth objects, that same capability could be used to launch astronauts to Mars.

“It’s a very similar trip,” he said. “In terms of the exact approach that we’re going to take on the vehicle infrastructure, we’re still working through internal studies, but basically these trips to near-Earth objects tend to be very similar — they can be shorter or longer — but they tend to be very similar to a Mars transit mission.”

Cooke said a manned mission to an asteroid would not require a lander like would be needed to reach the martian surface, but that “basically, the in-space transit part of it requires a lot of the same components in terms of propulsion, habitation for the crew and entry vehicle for when you come back.”

NASA hopes that in addition to keeping an open mind on heavy lift, Congress will restore some of the funding it trimmed from proposed robotic precursor missions that could visit near-Earth objects.

“We’d want to get up close and personal with a few of these things to really make sure we understand the environment that the humans would be operating in,” Leshin said. “One thing that’s becoming really clear through this conversation is the need for robotic precursors.”

Leshin said if at all possible, NASA would prefer to send precursor robots to the asteroid humans would ultimately visit.

“Visiting the one that humans would target is very important, but you can reasonably ask the question, ‘Is it reasonable to pick one for a mission that’s 15 years away and maybe there’ll be a schedule slip, maybe there’ll be a technical problem?’ So you need to have backups,” Leshin said, adding that NASA already has a plethora of remotely gathered data on near-Earth objects, and that sending robots on precursor missions to even a single asteroid could help scientists make better sense of it.

“We have a bunch of remote sensing observations of asteroids,” she said. “It’s hard to interpret those if you don’t spend a lot of time with a few asteroids. Once you do that, you can interpret your remote sensing data on lots of asteroids much better. So the idea of one is very compelling.”

In addition to launching robots and eventually humans to a handful of specific asteroids, the agency is considering sending small spacecraft on reconnaissance missions to a variety of near-Earth objects.

Cooke said small satellites deployed on a single launch vehicle “could, over a period of time, go out and gauge a number of near-Earth objects so you get a broader sample on what you might expect.”

Cooke said if and when the money becomes available, NASA would like to send its first robotic precursor to a near-Earth asteroid, though he is not sure which one.

“Actually, we don’t really have to decide right now,” he said. “I think we’ll go through a process to make sure we have our best understanding of the best one to go to, and if we end up with a mission with multiple payloads going to multiple destinations, then actually in that scenario we’ve done enough work to know that you can actually change the destination during the mission, so there’s some flexibility there.”