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SpaceX Plan To Fuel Rockets With People Aboard Raises Alarm Bells (fortune.com)
Several space industry experts that advise NASA have told the US space agency there are safety risks in a proposal by Elon Musk's SpaceX to fuel its rockets while astronauts are on board. From a report on Fortune: "This is a hazardous operation," Space Station Advisory Committee Chairman Thomas Stafford, a former NASA astronaut and retired Air Force general, said during a conference call on Monday. Stafford said the group's concerns were heightened after an explosion of an unmanned SpaceX rocket while it was being fueled on Sept. 1. The causes of that explosion are still under investigation. Members of the eight-member group, which includes veterans of NASA's Gemini, Apollo and space shuttle programs noted that all previous rockets that have flown people into space were fueled before astronauts got to the launch pad. "It was unanimous ... Everybody there, and particularly the people who had experience over the years, said nobody is ever near the pad when they fuel a booster," Stafford said, referring to an earlier briefing the group had about SpaceX's proposed fueling procedure.
SpaceX is using densified (highly cooled) LOX to increase peformance by cramming more fuel into the same-sized tank. That super-cooled LOX will only sit in the tank for so long before it starts to warm up and expand, so for best performance they need to be fueling up until just a few minutes before launch.
Probably the Falcon 9 could still lift the Dragon without supercooled LOX, but it would have lower launch margins.
NASA may have done the bulk of the fueling before loading astronauts, but they kept topping up the tanks against boil-off right up until a few minutes before launch, so there's a bit of an exaggeration here.