SpaceX engineers believe that failure most likely started when liquid oxygen propellant froze in a buckle or void between the aluminum liner and carbon overwrap of one of the COPVs. SpaceX is also redesigning high-pressure helium tanks, or composite overwrapped pressure vessels, blamed for the September 2016 accident. The abort thrusters will be activated and armed before fueling of the Falcon 9 during crewed launches. Officials from SpaceX said the Crew Dragon’s escape system, comprising a set of high-thrust SuperDraco engines around the circumference of the capsule, would be quick enough to push the spacecraft and its crew away from such an explosion during fueling. The fiery accident occurred in the final minutes of a countdown while propellants were flowing into the rocket before a hold-down engine firing, destroying the launcher and an Israeli-owned communications satellite on-board. SpaceX’s “load-and-go” procedure raised concerns after a Falcon 9 rocket exploded on its launch pad at Cape Canaveral in September 2016. That really helped us with that decision.” “So it’s really about understanding the differences in the vehicles, and how each one flies the best. There were recirculation pumps and stuff like that that you can’t do with the SpaceX vehicle,” she said. “There are things that you could do with the shuttle. Even though it looks different, it’s different because it’s not the shuttle. “That also really helped us in the assessment because we really understand now why SpaceX was doing what they’re doing. “Our teams have been following along with their normal operations, so we have a pretty good understanding of how their vehicle operates,” Lueders said. SpaceX proposed using its normal countdown timeline, which calls for propellant loading to commence at T-minus 35 minutes with the company’s Falcon 9 Block 5 rocket, the same model that will be used for crewed launches.Īstronauts will be in their seats, the Crew Dragon’s hatch will be closed, and the closeout team will be a safe distance away from launch pad 39A at NASA’s Kennedy Space Center before fueling begins. The space shuttle followed a similar pre-launch timeline, with fueling occurring first, followed by the strap-in of the astronauts. Ground support crews will help the astronauts board the CST-100 crew capsules, then evacuate the pad for the terminal countdown. 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. Artist’s concept of SpaceX’s Crew Dragon spacecraft. On some more demanding launches, the lost lift capacity from warmed propellant would prevent the Falcon 9 from satisfying mission requirements. 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.įilling 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. ![]() The Atlas 5, which will be used to launch Boeing’s CST-100 Starliner capsule, consumes the same propellants as the Falcon 9.īut 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. Other liquid-fueled rockets, such as United Launch Alliance’s Atlas 5 launcher, typically receive their propellants earlier in their countdowns. “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.” “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. 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. 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. A prototype of SpaceX’s Crew Dragon capsule completed a pad abort test at Cape Canaveral in May 2015.
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