NASA advisers are continuing to express concerns about a SpaceX fueling process known as “load and go,” in which chilled fuel is loaded onto the rocket just 30 minutes before a scheduled launch. This week the agency’s Aerospace Safety Advisory Panel strongly encouraged NASA top management to “scrutinize” this issue as part of an annual report on safety concerns in US spaceflight, which could have significant implications for the commercial crew program.

SpaceX has gained notoriety during the last 13 months for landing the first stage of its Falcon 9 rocket on land, and at sea aboard an autonomous drone ship. One critical component to this success has been the use of a new fueling process that chills liquid oxygen to below -200 degrees Celsius, allowing more of this denser oxidizer to fit within the rocket’s fuel tanks. The additional fuel has provided SpaceX the margin needed to fly its boosters back to Earth after they delivered their payloads into space, especially those bound for geostationary orbit.

Because this super-chilled oxygen can warm quickly after it is loaded onto the rocket, SpaceX has adopted the “load and go” strategy. After implementing the new fueling process in December, 2015, SpaceX had been working toward using the same fueling methods when beginning crew flights to the International Space Station next year.

Despite SpaceX’s early success with this fueling process, however, NASA had retained concerns about it, as historically neither the crew nor any other personnel have been allowed in or near a booster during fueling operations. These concerns were magnified after the September 1 accident when, during fueling of the Falcon 9’s second stage for a prelaunch test, both the rocket and its satellite were lost in an explosion. (SpaceX founder Elon Musk has said the Dragon's launch abort system would have saved the astronauts, had this happened during a crewed mission).

In December the chairman of NASA’s advisory committee on the space station, Gen. Thomas Stafford, expressed his panel’s fears about the safety of load and go to the agency’s senior management. “There is a unanimous, and strong, feeling by the committee that scheduling the crew to be on board Dragon spacecraft prior to loading oxidizer into the rocket is contrary to booster safety criteria that has been in place for over 50 years, both in this country and internationally,” Stafford wrote.

“Steep hill to climb”

Now the agency’s overall safety panel (ASAP) has weighed in, too, citing concerns about unknowns with the new, dynamic fueling process. Although SpaceX finalized its investigation of the September 1 mishap earlier this month and plans a return-to-flight mission as early as Saturday, the aerospace panel is calling for a wider investigation.

“We believe that the focus of the investigation must not be solely to identify and fix the specific cause of this mishap,” the report states. “It must focus also on improving the understanding of how the system functions in the dynamic thermal environment associated with ‘load and go’ so that other previously unidentified hazards can be discovered. This is not a trivial effort. Despite testing at the component and sub-assembly level, systems often display ‘emergent’ behavior once they are used in the actual operational environment.”

The ASAP panel urged NASA to weigh the benefits of load and go with the “large” uncertainties and additional risk it entails. There is some evidence NASA’s commercial crew program managers are doing just that. One official familiar with deliberations at Johnson Space Center told Ars, “Prelaunch is a phase of flight that is scrutinized as much as any other with safety being our top priority. Load and go has had a great deal of interest within NASA a long time before last September’s accident and any ASAP discussions.”

Another Houston source directly involved in the review said load and go operations for crewed Dragon flights were not yet entirely off the table, but the concept had a “steep hill to climb” to get NASA's acceptance.

NASA already faces some schedule pressure to get its commercial crew providers flying. Although it has bought Soyuz seats for US crew flights to the space station through 2018, further development delays with the Boeing Starliner and SpaceX Dragon vehicles would require the purchase of additional seats in 2019. Politically this would be a bitter pill for the agency to swallow, after it has told Congress repeatedly that crew flights would probably begin from US soil by the end of 2017 and certainly in 2018.