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martyb [soylentnews.org] writes:

According to SpaceFlight Now, SpaceX's SES-9 [ses.com] launch was again aborted in the final minutes [spaceflightnow.com]. But why? Well, this IS rocket science for one. For background, please refer to the eminently readable explanation written by a Space Shuttle astronaut: The Tyranny of the Rocket Equation [nasa.gov]. (In short, something like 90%-95% of the rocket's launch mass is fuel and oxidizer.) In order to increase the lifting capacity of the Falcon-9, SpaceX is using fuel and liquid oxygen that have undergone additional chilling. The SpaceFlight Now article explains it well:

The modified Falcon 9 consumes a super-chilled propellant mix that allows engineers to load additional fuel into the rocket. The cryogenic liquid oxygen is chilled closer to its freezing point, from minus 298 degrees Fahrenheit [90 Kelvin] to minus 340 degrees [66 Kelvin] , while the Falcon 9’s RP-1 fuel — a refined form of kerosene — is cooled from a standard room temperature of about 70 degrees Fahrenheit to 20 degrees, according to Elon Musk, SpaceX’s founder and CEO.

The change essentially allows engineers to load more propellant mass into the the volume of the Falcon 9 fuel tanks, which are also slightly enlarged on the upgraded rocket. The denser fuel mix flows faster into the rocket’s Merlin engines, adding extra thrust to haul heavier satellites into orbit and leaving leftover fuel to attempt landings of the booster for future reuse.

The first stage’s nine Merlin 1D engines collectively generate 1.5 million pounds of thrust at sea level, up from 1.3 million force-pounds on the earlier version of the Falcon 9. All told, the changes allow the Falcon 9 to deliver about 30 percent more mass to orbit without extra thrust from strap-on boosters or other major additions to the booster, according to SpaceX.

[...] SpaceX engineers struggled to master the handling of the super-cold densified propellants at the Falcon 9 launch pad before the maiden flight of the upgraded rocket in December, but the rocket successfully took off the first time it received propellants on a real launch attempt.

The launch team updated the Falcon 9’s countdown procedures to account for the sensitivity of the super-chilled propellants.

Instead of loading the propellants three hours before liftoff, the upgraded Falcon 9 receives its fuel in the final 30 minutes of the countdown to minimize the time the cryogenic liquid sits inside the rocket tanks and warms up in the mild ambient temperatures of Florida’s Space Coast.

Bear in mind that the rocket still needs to withstand the acceleration, vibration, and aerodynamic drag of launch all while keeping its payload on target and without breaking up (or exploding) in the process!

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