Spaceflight Now by Stephen Clark August 9, 2018
The NASA manager overseeing development of Boeing and SpaceX’s commercial crew ferry ships says the space agency has approved SpaceX’s proposal to strap in astronauts atop Falcon 9 rockets, then fuel the launchers in the final hour of the countdown as the company does for its uncrewed missions.
The “load-and-go†procedure has become standard for SpaceX’s satellite launches, in which an automatic countdown sequencer commands chilled kerosene and cryogenic liquid oxygen to flow into the Falcon 9 rocket in the final minutes before liftoff.
“From a program standpoint, we went throgh a pretty extensive process where we laid out the different options for loading the crew, and assessing how the vehicles have been designed, and what the trades were,†said Kathy Lueders, NASA’s commercial crew program manager, in an interview Friday. “That came to the program in June, and after looking at it, we felt like the current baseline plan for how SpaceX plans to load the crews meets our requirements.â€
Other liquid-fueled rockets, such as United Launch Alliance’s Atlas 5 launcher, typically receive their propellants earlier in their countdowns. The Atlas 5, which will be used to launch Boeing’s CST-100 Starliner capsule, consumes the same propellants as the Falcon 9.
But SpaceX’s Falcon 9 rocket, which will power the company’s Crew Dragon spacecraft into orbit with astronauts on-board, burns a mix of kerosene and liquid oxygen chilled to near each fluid’s freezing point. The densified propellant allows more fuel to be loaded into the Falcon 9’s tanks, and it gives the rocket’s Merlin engines a thrust enhancement.
Filling of the Falcon 9 rocket in the final stages of the countdown is timed to give the super-chilled propellant minimal time to warm up before liftoff, which would reduce the rocket’s lift capability.
On some more demanding launches, the lost lift capacity from warmed propellant would prevent the Falcon 9 from satisfying mission requirements.
On crewed launches, ULA plans to finish loading propellant a couple of hours before liftoff, then slowly replenish liquid oxygen as it boils off in the warm ambient environment on Florida’s Space Coast. Ground support crews will help the astronauts board the CST-100 crew capsules, then evacuate the pad for the terminal countdown.
The space shuttle followed a similar pre-launch timeline, with fueling occurring first, followed by the strap-in of the astronauts.
More:
https://spaceflightnow.com/2018/08/09/nasa-signs-off-on-spacexs-load-and-go-procedure-for-crew-launches/
