Author Topic: dual tripropellant for energy efficiency in reusable VTVL 2STO  (Read 2806 times)

Offline Funchucks

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« Last Edit: 08/14/2013 06:49 PM by Funchucks »

Online Robotbeat

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Lithium, fluorine, and hydrogen. If you're going to do it, do it right. :)

More practically, a tripropellant using dense hydrocarbon (subcooled propylene), hydrogen, and oxygen makes sense if you want SSTO. Or a very high performance stage in a multi-stage rocket.
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Offline R7

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Lithium, fluorine, and hydrogen. If you're going to do it, do it right. :)

Hey, the idea appears to be to aim for low Isp, althought I miserably fail to get why.  ;D

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Online hkultala

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Lithium, fluorine, and hydrogen. If you're going to do it, do it right. :)

Hey, the idea appears to be to aim for low Isp, althought I miserably fail to get why.  ;D
If higher specific impulse was always better, all of our rockets would be flashlights.

The bigger the difference between exhaust speed and vehicle speed, the lower the energy efficiency.  Ideally, we would begin by pushing off from an infinite mass, and match exhaust speed to vehicle speed perfectly after that.

But energy efficiency is the wrong target to optimize for.

Lowering the isp artificially just to get better energy efficiency does not make sense.

Offline Tass

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In a world, where rockets are cheap and completely reusable without maintenance cost, and energy is somehow terribly expensive, it does make sense.

But I have a hard time imagining that world.

Online Robotbeat

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Thrust-augmentation may make sense at times.

Some missiles use fluid-injection for thrust-vector control, and it does slightly increase the thrust. I wonder if they intentionally add some extra fluid right at launch (where gravity losses are highest)?

Some drop-tanks tanks of pressurized water for injection just after the engine's throat may increase thrust at the critical lift-off stage of flight. But it's probably not even close to worth it.
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Offline R7

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Thrust-augmentation may make sense at times.

Wide term. What you use for augmentation?

convergent-divergent ejector tube to suck in ambient atmosphere, heat it up with plume and let it expand inside the tube producing more thrust? Makes sense (at least as a concept)

TAN? altitude compensation and increased liftoff thrust, makes sense.

Watering down reaction chamber with inert stuff to get more thurst but crappy overall Isp ... sure would like to see the math that makes that sensible.
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Online Robotbeat

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I don't think it does make sense. But if you have oxygen-rich combustion, injecting some kerosene right past the throat can help you get extra thrust and can prevent gross over-expansion at sea level. Neat idea. Aerojet has studied it.
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Offline R7

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Neat idea. Aerojet has studied it.
That's the TAN part in my post  ;)
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Online Robotbeat

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Neat idea. Aerojet has studied it.
That's the TAN part in my post  ;)
I thought so, but wasn't sure.

Strangequark, what do you think of TAN?
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0