NASA Is Concerned About SpaceX's Rocket Fueling Practices It's worried that SpaceX will put crews at risk by topping up while they're aboard.

NASA is a little nervous about SpaceX's future crewed flights.

The Wall Street Journal has obtained a letter from December 2015 showing that an agency International Space Station committee has been worried about the safety of SpaceX's planned fueling strategy. While the nature of SpaceX's Falcon 9 rockets will require that it fill up while the crew is aboard (it has to supply the supercooled fuel 30 minutes before launch), that goes against "50 years" of booster safety practices around the world, according to the letter.

The committee raised the issue again with NASA officials days before SpaceX's launchpad explosion, but hadn't heard anything for weeks afterward.

This isn't to say that those officials or SpaceX have ignored the jitters. SpaceX tells us that it has worked with NASA on a "detailed analysis" of every potential danger for the past year and a half, and its safety controls were approved by a NASA board in July. There's "continued work ahead" to both prove that these controls are in place and adjust them (if necessary) following its explosion investigation, the company says. SpaceX is mainly counting on its Crew Dragon launch abort system to rescue astronauts if there's a failure during the fueling process. You can read the full statement below.

NASA, meanwhile, says it has a "rigorous review process" for fueling crewed Falcon 9 rockets, and that SpaceX's investigation will play a part in that review. It adds that a separate advisory panel is its main independent adviser for commercial spaceflight, not the ISS committee.

Will the concerns play havoc with SpaceX's plans? Probably not. However, they show that SpaceX still has its share of doubters at NASA, even as it improves the reliability of its rockets. It needs to demonstrate that a different fueling process isn't necessarily more dangerous, and it may not completely eliminate those fears until it has a rock-solid record of sending people to space.

"SpaceX has designed a reliable fueling and launch process that minimizes the duration and number of personnel exposed to the hazards of launching a rocket. As part of this process, the crew will safely board the Crew Dragon, ground personnel will depart, propellants will be carefully loaded over a short period, and then the vehicle will launch. During this time the Crew Dragon launch abort system will be enabled. Over the last year and a half, NASA and SpaceX have performed a detailed analysis of all potential hazards with this process. The hazard report documenting the controls was approved by the NASA's Safety Technical Review Board in July 2016. As with all hazard analyses across the entire system and operations, controls against those hazards have been identified, and will be implemented and carefully verified prior to certification. There will be continued work ahead to show that all of these controls are in place for crewed operations and that the verifications meet NASA requirements. These analyses and controls will be carefully evaluated in light of all data and corrective actions resulting from the anomaly investigation. As needed, any additional controls will be put in place to ensure crew safety, from the moment the astronauts reach the pad, through fueling, launch and spaceflight, and until they are brought safely home."