h a l f b a k e r y
This would work fine, except in terms of success.
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A balloon lifting a rocket for a high-altitude launch, Plus
The balloon is filled with hydrogen gas. At high altitude
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
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.
For anyone interested [Vernon, Sep 25 2013]
[MechE, Sep 25 2013]
Internal Flame Hydrogen Balloon
More lift! [bungston, Sep 25 2013]
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||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
||On the other hand, [Klaatu], either of those scenarios would make for great film footage.
||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.
||For degreasing things, absolutely.
||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!
||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.