A NASA safety advisory group weighed in Thursday on SpaceX's highly scrutinized proposal to load rocket propellants while astronauts are aboard, saying it appears to be a "viable option."
Several members of the Aerospace Safety Advisory Panel said that as long as potential hazards can be controlled, loading crew before fueling is finished could be acceptable.
"My sense is that, assuming there are adequate, verifiable controls identified and implemented for the credible hazard causes, and those which could potentially result in an emergency situation … it appears load-and-go is a viable option for the program to consider," panel member Capt. Brent Jett Jr. (Ret.) said during Thursday's meeting.
SpaceX and Boeing Co. each have NASA contracts to develop separate crew capsules to transport astronauts to the International Space Station. Both SpaceX and Boeing are scheduled to conduct uncrewed flight tests of their vehicles in August, with crewed flight tests set for several months later.
SpaceX's rocket fueling procedure, known as "load-and-go," has come under scrutiny, most recently earlier this year when the issue came up during a meeting of the House Committee on Science, Space and Technology.
Hawthorne-based SpaceX uses super-chilled liquid oxygen to maximize the amount that can fit in the tank and increase the rocket's power at liftoff. But the extremely cold temperature means it must be loaded right before launch, and in a flight with a crew, that means astronauts would be aboard.
In 2016, a SpaceX Falcon 9 rocket exploded on a Florida launch pad while propellant was being loaded into the vehicle. The explosion damaged the pad and destroyed a communications satellite SpaceX was set to launch.
An investigation later found that "buckles" had developed in the inner lining of one of three composite overwrapped pressure vessels located in the rocket's second-stage liquid oxygen tank. SpaceX said at the time that the tank likely failed after the super-chilled liquid oxygen gathered in those buckles. "Breaking fibers or friction" could then ignite the oxygen in the carbon overwrap, the company said.
SpaceX has since redesigned the pressure vessels and NASA has started a "rigorous" test program to understand how they react to the extremely cold environment, according to an Aerospace Safety Advisory Panel report released in January.
During the space shuttle era, astronauts boarded the shuttle after propellants were loaded.
The Aerospace Safety Advisory Panel previously flagged the proposed SpaceX method in a report released in January 2017, saying it was concerned the potential risks were not "adequately understood."
But SpaceX executives have said they believe this quicker fuel-loading process is safer than traditional methods because it minimizes the time that crew are exposed in a fuel-loaded rocket. It also has tested a capsule emergency abort system that is designed to rocket astronauts away to safety if there's an explosion.
Before the recent launch of SpaceX's upgraded Falcon 9 rocket, company Chief Executive Elon Musk said he thought the issue was "overblown," and noted that airplane passengers don't necessarily wait for the aircraft to finish fueling before boarding.
The Aerospace Safety Advisory Panel said the NASA Commercial Crew program is expected to make a decision soon on the appropriate sequence for loading crew and fuel into SpaceX's Falcon 9 rocket.