BROOMFIELD, Colo. — As commercial suborbital vehicles capable of carrying both payloads and people prepare to enter service, NASA officials say they’re willing to consider allowing agency-funded researchers to fly on those vehicles.

In an interview after a speech at the Next-Generation Suborbital Researchers Conference here Dec. 19, Steve Jurczyk, NASA associate administrator for space technology, said the agency would be open to allowing researchers funded by NASA’s Flight Opportunities program to fly on suborbital spacecraft to carry out their experiments.

“As principal investigators propose, both internal to NASA and external, we’ll do the same kind of process that we do with Zero G,” he said, referring to the company that performs parabolic aircraft flights. Zero G flies investigations as part of the Flight Opportunities program, with researchers flying on the aircraft with their experiments.

Zero G’s aircraft, a Boeing 727, is regulated by the Federal Aviation Administration. Jurczyk said that, in addition to the FAA oversight, NASA’s Armstrong Flight Research Center performs an evaluation of the aircraft for investigations selected by the Flight Opportunities program for flights on it. “It just ensures that our grantees and contractors are safe to fly, and then we allow them to go fly,” he said in a speech at the conference.

A similar procedure is not yet in place for suborbital vehicles, but Jurczyk said the agency would be open to finding some process analogous to that used for Zero G. “Moving forward, as these capabilities start coming online, we’ll figure it out,” he said in the interview.

His comments come four and a half years after another agency official opened the door to flying people on commercial suborbital vehicles through the Flight Opportunities program. Speaking at the same conference in June 2013, Lori Garver, NASA deputy administrator at the time, said that past prohibitions about flying people would be lifted.

“We absolutely do not want to rule out paying for research that could be done by an individual spaceflight participant — a researcher or payload specialist — on these vehicles in the future,” Garver said then. “That could open up a lot more opportunities.”

That announcement took the program by surprise, with the program’s managers saying at the time they had yet to craft a policy for allowing people to fly with their experiments. Development of such a policy suffered years of delays, in part because of Garver’s departure from NASA just a few months after her announcement as well as extended delays in the development of commercial suborbital vehicles capable of carrying people.

“It mostly resulted in a bunch of ostriches sticking heads in the sand for a few years,” said Erika Wagner, business development manager at Blue Origin, during a panel discussion at the conference Dec. 18.

Blue Origin’s New Shepard vehicle is already carrying research payloads, including for Flight Opportunities, but without people on board. However, the vehicle will be able to support missions carrying payloads and people in the future. Virgin Galactic’s SpaceShipTwo vehicle will also fly research payloads accompanied by a payload specialist.

Wagner said she has seen some progress as both companies’ vehicles advance through flight testing. “The heads are back out. They’re looking around trying to understand what really are the barriers, what is the liability regime.”

Those liability issues today, she said, prevent NASA civil servants from flying on the Zero G aircraft, even though outside researchers whose experiments are funded by NASA are able to do so. Jurczyk, in his speech at the conference, said that’s because they would have to sign a liability waiver to do so. “Right now, that’s just NASA policy. We don’t have a strong mission need to do that,” he said. “That’s current policy. I’m not saying it’s going to be policy forever and ever.”

Scientists who would like to fly experiments on suborbital vehicles argue that such missions are analogous to fieldwork — oftentimes hazardous — performed in other fields. “Marine biologists and marine geologists get to put themselves in that very same operationally risky environment by going to the bottom of the ocean, to a deep sea vent,” said Dan Durda, a planetary scientist at the Southwest Research Institute, during the Dec. 18 panel. “These vehicles offer us, as space scientists, that opportunity to get into the field the way that biologists and geologists do.”

Advocates of commercial suborbital research, such as the Commercial Spaceflight Federation’s Suborbital Applications Research Group, have been pushing to allow NASA to fund human-tended experiments.

“They’re working quietly to get the word out that there are very definite needs for human-tended payloads,” said Steven Collicott, a Purdue University professor, in a conference speech Dec. 19. “We’ve heard some encouraging words and we’re working quietly to try and move that ahead.”

Others at the conference noted a decades-old precedent that suggests existing barriers to flying NASA-funded researchers on commercial suborbital vehicles can be overcome. In the 1980s, several payload specialists flew on the space shuttle, including Charles Walker, a McDonnell Douglas engineer who was part of three shuttle missions.

Walker, in the Dec. 18 panel discussion, noted that on those shuttle missions he and his family signed liability waivers. He supported similar approaches to allow researchers to fly on commercial suborbital vehicles.

“The environments opened up by suborbital flight and, at a greater scale, orbital flight, are laboratory environments,” he said. “You should be there to maximize the answers that are coming out of the conduct in that environment.”