Half a croissant, on a plate, with a sign in front of it saying '50c'
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This would work fine, except in terms of success.

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Rockoon 2

A balloon lifting a rocket for a high-altitude launch, Plus
  [vote for,

The balloon is filled with hydrogen gas. At high altitude there is still plenty of oxygen in the air. So, the first stage of the rocket should actually be a jet engine, burning the balloon's hydrogen with atmospheric oxygen. Thus the balloon essentially provides both an initial lift and an initial velocity, before the regular rockoon engine is fired, which allows either the payload to be slightly bigger, or the rocket to be slightly smaller, than in an ordinary Rockoon.
Vernon, Sep 25 2013

Rockoon 1 https://en.wikipedia.org/wiki/Rockoon
For anyone interested [Vernon, Sep 25 2013]

Prior Art Big_20Bang_20to_20Outer_20Space
[MechE, Sep 25 2013]

Internal Flame Hydrogen Balloon Internal_20flame_20hydrogen_20balloon
More lift! [bungston, Sep 25 2013]

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       [+] for brevity   

       [-] for won't work   

       Scenario 1: Rocket screams along, dragging a deflating and fragile balloon, near its burst altitude, behind (in the exhaust plume)   

       Scenario 2: Pump Hydrogen into tank on the rocket. Extra weight/complexity and as you are pumping, you are falling under a deflating balloon
Klaatu, Sep 25 2013

       On the other hand, [Klaatu], either of those scenarios would make for great film footage.
pertinax, Sep 25 2013

       Hang on - air-breathing engines have mostly been ruled out for ground-based launches, because jet engines are so much heavier than rocket engines that it's usually best just to carry extra oxidiser. Won't being above most of the atmosphere make it even worse?   

       I still think you should fill the balloon with a stoichiometric mix of H2 and O2. It will only need to be about 1œ times as big.
spidermother, Sep 25 2013

       For degreasing things, absolutely.
bungston, Sep 25 2013

       Klaatu, I think you are ignoring the rate at which a jet engine can consume fuel. I suspect the balloon would be empty before it could be dragged. :)   

       Which makes the Idea properly HalfBaked, of course!
Vernon, Sep 25 2013

       One of the N-Prize teams planned to re-use the balloon's hydrogen as rocket fuel (with onboard oxidiser, I think). I think the fundamental problem came down to the difficulty of compressing the hydrogen sufficiently to feed it into the rocket's combustion chamber.   

       If you use the hydrogen as jet fuel relying on atmospheric oxygen, you reduce the need to compress the hydrogen but, as pointed out, the weight and complexity don't justify it.   

       Also, a hydrogen balloon can take you up to something like 30km, at which point jet engines aren't a great option anyway.   

       You might get somewhere using a pulse-rocket, in which fuel and oxidiser are fed into the combustion chamber under low pressure, then ignited; then the cycle repeats. This again reduces the need to compress the hydrogen.
MaxwellBuchanan, Sep 25 2013


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