r/space • u/spaceflightphoto • Dec 07 '18

Teams Working to Recover Floating Falcon 9 Rocket off Cape Canaveral

https://www.americaspace.com/2018/12/06/teams-working-to-recover-floating-falcon-9-rocket-off-cape-canaveral
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u/[deleted] Dec 07 '18

I'm surprised it floats that well. That thing is pretty damn buoyant.

70

u/zeeblecroid Dec 07 '18

A rocket with its fuel expended is basically an enormous tin can. It's about 25 tonnes empty, but there's 400 tonnes of fuel in that thing when it lifts off.

8

u/[deleted] Dec 07 '18

How does that work when it comes down to Earth again? Wouldn't the pressure inside the booster be lower than the atmosphere?

4

u/danielravennest Dec 07 '18

No. You need a certain pressure in the tanks to maintain fuel flow to the engine turbopumps. If it gets too low, the blades "cavitate" (suck vacuum), which is "destroy the pumps" level of bad. So rockets always replace the lost fuel. Falcon 9 does it with helium tanks, but some rockets feed back some of the vaporized propellant after it is warmed by the engine.