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Falcon 9 rocket consumes approximately 30 tons of fuel for the first 15 seconds of flight while it's still less than 350 meters in altitude.

Is it possible to build a giant tower near the launchpad, so the rocket can be refueled during the first seconds of flight? If so, what would be the main technical challenge of that idea?

user3715778
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    Whether or not it is possible, it would also be possible to build the launch pad at a location that is already at 350 meters altitude.. – Andrew Thompson Apr 22 '16 at 01:56
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    The point of that idea is to have fully fuelled rocket while it already has some kinetic energy, not to launching it from the top of the 350 meters tower. – user3715778 Apr 22 '16 at 02:05
  • If the flow is "guaranteed", then it could be just one of the propellants. It would be a heck of a lot easier to pump the RP-1 (kerosene) than it would be to keep 2 tons of LOX per second from boiling while passing really really fast through hundreds of meters of hose. – uhoh Apr 22 '16 at 07:16
  • May be it will be easier to lift additional tank directly attached to the side of the rocket on some kind of crane or elevator and separate it as soon as it drains out. – user3715778 Apr 22 '16 at 07:40

2 Answers2

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The main technical challenges with this idea:

  1. You've got a giant hose (2 tons/s capacity) hanging off one side of the rocket, making the weight distribution very unsymmetrical. You could relieve the weight by suspending the hose from a winch, but then you'd have to synchronize that exactly with the movement of the rocket.

  2. You'll need to keep that hose out of the exhaust, so you need to reel it in/out during liftoff. That's not easy to do while the hose is full of pressurized liquids, one of which is cryogenic.

  3. Clean separation gets difficult. You have no time to properly drain the hose, so you have to eject the (heavy) hose from the rocket while making sure it doesn't bang into the rocket after separation.

Hobbes
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  • Roughy speaking, how big/heavy would the hose actually be? Compared to a mass of 1.2 million pounds with a vectorable thrust of 1.5 million pounds, is it even a 1% effect, quantitatively speaking? – uhoh Apr 22 '16 at 07:11
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    @uhoh the issue is more puncturing the thin rocket body than disturbing its orientation. – Antzi Apr 22 '16 at 08:02
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  • One way to do this easily is to use a smaller rocket to lift the hose as it clears the pad. Then you could feed the hose from a small tank on the smaller rocket. Oh wait...did we just invent cross feed staging?
    • – Aron Apr 22 '16 at 08:08
  • @uhoh The mass of the hose is the least of your worries. Its the impulse/momentum that you should be worried about. As Antzi says, it should easily punch straight through your rocket. – Aron Apr 22 '16 at 08:11
  • @Aron Thanks! I like your answer. I'm mostly worried by the use of words like like "large" and "small" without accompanying numbers or at least a shared understanding (e.g. "Law of Large Numbers"). I worked out the transverse force for a 12 inch ID hose in this comment. The image of implementing such a hose is worrying, the transverse momentum transfer not so much. – uhoh Apr 22 '16 at 09:25