Author Topic: Rocket Engine Q&A  (Read 382953 times)

Offline Tommy OSullivan

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Re: Rocket Engine Q&A
« Reply #700 on: 01/03/2016 08:37 pm »
Hey, I was wondering if anyone could help me out with this project I've started working on. I want to put together a full flow methane mockup engine with a fully fleshed out interior and exterior, I have made a first rendition but I want the mark.2 to be more realistic.

Link to the full post is here http://forum.nasaspaceflight.com/index.php?topic=39200.msg1468297#msg1468297 (sorry to be advertising it).

But I was just wondering if anyone could help me with how the turbopumps and preburners work internally and how they operate with one another in full flow engines like the SSME.

Thanks!

Offline gin455res

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Re: Rocket Engine Q&A
« Reply #701 on: 05/13/2016 06:12 am »
Are there any piston pump designs based on 2-stroke geometries, specifically stepped piston designs where the crank case compressor volume is multiple  times as large as the power cylinder and massive short circuiting is promoted?

Two of these massively short circuiting engines, One running oxidizer rich , and one running fuel rich  might be equivalent to a full flow staged combustion turbo pump .

Offline gin455res

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Re: Rocket Engine Q&A
« Reply #702 on: 06/01/2016 10:29 pm »
Have any pumps been built that can switch between combustion chambers?
(like below - is it feasible)


And what configurations might be most interesting?
below:

Offline Jim

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Re: Rocket Engine Q&A
« Reply #703 on: 06/02/2016 03:14 am »
Have any pumps been built that can switch between combustion chambers?


no

Offline baldusi

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Re: Rocket Engine Q&A
« Reply #704 on: 06/02/2016 04:53 pm »
I remember an NPO Energomash paper stating that the RD-170 could (not sure if can) shutoff individual chambers. And then you have cases like the RD-0110 that feeds the main chambers and the vernier chambers from the same TP. But generally speaking the combustion chamber and nozzle are really heavy and duplicating the mass is simply not worth it for the possible increase in isp.

Offline gin455res

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Re: Rocket Engine Q&A
« Reply #705 on: 06/02/2016 06:48 pm »
I remember an NPO Energomash paper stating that the RD-170 could (not sure if can) shutoff individual chambers. And then you have cases like the RD-0110 that feeds the main chambers and the vernier chambers from the same TP. But generally speaking the combustion chamber and nozzle are really heavy and duplicating the mass is simply not worth it for the possible increase in isp.

Any differences between a normal expendable booster thrust profile, and an F9 style RTLS profile.  I'm wondering if improved isp on the boost back  improves or exacerbates the chamber and nozzle mass issue?

Offline baldusi

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Re: Rocket Engine Q&A
« Reply #706 on: 06/03/2016 08:36 pm »
Given how little time is needed for the boostback, I seriously doubt that it would ever be worth it. In any case, you could work on an extendable and retractable nozzle. But again, I seriously doubt it is worth it.

Offline gin455res

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Re: Rocket Engine Q&A
« Reply #707 on: 06/04/2016 10:24 pm »
I guess I'd need to model it to truly convince myself. I was imagining a system where the second stage is smaller; payload smaller; and staging at a much higher speed.

And consequently the rocket would  spend more time throttled back on two high isp chamber/nozzles on the way up and on the deceleration and re-entry burn.

Say, staging at mach 14? then decelerating to mach 5? for re-entry, before  a barge landing. With a small cheap pressure-fed disposable upperstage.

Offline nicp

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Re: Rocket Engine Q&A
« Reply #708 on: 07/01/2016 11:58 am »
I have an unusual and pointless question.
What does a liquid fueled rocket engine sound like? And I don't mean the hypersonic exhaust hitting the atmosphere, the huge roar we are all familiar with (at least second hand).

Mullane in 'Riding Rockets' describes the SSMEs ('three Rocketdyne beauties..') as smooth as glass (or similar, it's been a while since I've read it) after the SRBs have separated. Now there's some distance between the flight deck and the engines and probably lots of sound insulation.  (I'm not sure he actually describes them as quiet, perhaps only smooth).

So.. subtracting anythng from the engine bell, would they sound like a jet engine perhaps?
For Vectron!

Offline PahTo

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Re: Rocket Engine Q&A
« Reply #709 on: 07/01/2016 05:54 pm »
I have an unusual and pointless question.
What does a liquid fueled rocket engine sound like? And I don't mean the hypersonic exhaust hitting the atmosphere, the huge roar we are all familiar with (at least second hand).

Mullane in 'Riding Rockets' describes the SSMEs ('three Rocketdyne beauties..') as smooth as glass (or similar, it's been a while since I've read it) after the SRBs have separated. Now there's some distance between the flight deck and the engines and probably lots of sound insulation.  (I'm not sure he actually describes them as quiet, perhaps only smooth).

So.. subtracting anythng from the engine bell, would they sound like a jet engine perhaps?


Correct--smooth, not quiet.  Remember the HPFT is spinning at (36,000?) rpm and HPOT at a good clip too.  One cannot have that much compression/impeller force without plenty of sound.

Offline the_other_Doug

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Re: Rocket Engine Q&A
« Reply #710 on: 07/01/2016 06:21 pm »
I have an unusual and pointless question.
What does a liquid fueled rocket engine sound like? And I don't mean the hypersonic exhaust hitting the atmosphere, the huge roar we are all familiar with (at least second hand).

Mullane in 'Riding Rockets' describes the SSMEs ('three Rocketdyne beauties..') as smooth as glass (or similar, it's been a while since I've read it) after the SRBs have separated. Now there's some distance between the flight deck and the engines and probably lots of sound insulation.  (I'm not sure he actually describes them as quiet, perhaps only smooth).

So.. subtracting anythng from the engine bell, would they sound like a jet engine perhaps?


Correct--smooth, not quiet.  Remember the HPFT is spinning at (36,000?) rpm and HPOT at a good clip too.  One cannot have that much compression/impeller force without plenty of sound.

Yeah, the engines definitely made some noise, which was transmitted through the structure of the orbiter.  After going supersonic, none of the sound the engines make in the air gets up to the cabin, of course, and then shortly thereafter there wasn't enough air to carry a lot of sound, anyway.  And consider that the crews regularly reported the OMS firings as sounding like howitzers going off, you have the think the SSMEs generated sound that carried through the structure, as well.

The only description I've ever heard of the sound of an engine firing while the spacecraft was in space was of the LM ascent engine.  It literally sat about two feet behind the crew station, the guts of the engine and the combustion chamber all inside a little can in the back.  With that small engine, the crews reported it sounded like the wind blowing in the distance -- very little sound, almost no vibration.  So, while an engine is going to generate some noise in a vacuum, it won't necessarily be a big, loud noise.  It all depends on the type of engine -- the SSMEs were pump-fed, so the pumps would generate more noise than a pressure-fed engine.

Of course, most of the classic sound of a rocket engine we hear on Earth is caused by the rapid displacement of air by the exhaust.  That sound doesn't exist in space, but most definitely, sound travels through the spacecraft structure.

I know that every simulation of the RCS engines firing in Apollo I have ever heard, both in the LM and the CSM, sounded for all the world like someone opened up a high-pressure steam valve for just a moment, so perhaps some of the engine sounds you'd encounter in a spacecraft would sound more like that, and less like the roar we're used to...
-Doug  (With my shield, not yet upon it)

Offline Proponent

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Re: Rocket Engine Q&A
« Reply #711 on: 07/02/2016 11:09 am »
I recall a presentation by Firestar, the company that was behind the NOFBX monopropellant, that said non-hypergolic bi-propellant engines tend to be noisier than hypergols which in turn tend to be noisier than monoprops.  I believe the claim was that the smoothness of mixing of fuel and oxidizer was a factor in noisiness.

Offline PahTo

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Re: Rocket Engine Q&A
« Reply #712 on: 07/02/2016 07:37 pm »
I recall a presentation by Firestar, the company that was behind the NOFBX monopropellant, that said non-hypergolic bi-propellant engines tend to be noisier than hypergols which in turn tend to be noisier than monoprops.  I believe the claim was that the smoothness of mixing of fuel and oxidizer was a factor in noisiness.

Thanks for that, Proponent.  I was pondering the mass of material passing through multiple pintles, and figured that would itself generate significant vibration (sounds), and then of course there's the actual "intermixing"...

Offline the_other_Doug

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Re: Rocket Engine Q&A
« Reply #713 on: 07/03/2016 02:50 am »
ISTR that Mike Collins described the sound and feel of the S-IVB on Apollo 11 as "crisp and rattly," though how much of that was a vibration felt more than heard is hard to say.  I'd say that most of the astronauts who have ridden rockets into space would be hard pressed to separate their perceptions of sound vs. those of vibrations felt through the seat of their couch...
-Doug  (With my shield, not yet upon it)

Offline Proponent

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Re: Rocket Engine Q&A
« Reply #714 on: 07/04/2016 06:00 pm »
By the way, we also have the negative evidence from Gemini 8.  That it took the crew a while to realize that the gyrations the spacecraft was undergoing were caused by a thruster that was stuck open indicates they couldn't hear thrusters in operation.  I do recall being told in another thread, however, that the opening and closing propellant valves on the Shuttle was very noisy. 

Offline envy887

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Re: Rocket Engine Q&A
« Reply #715 on: 07/13/2016 05:26 pm »
I guess I'd need to model it to truly convince myself. I was imagining a system where the second stage is smaller; payload smaller; and staging at a much higher speed.

And consequently the rocket would  spend more time throttled back on two high isp chamber/nozzles on the way up and on the deceleration and re-entry burn.

Say, staging at mach 14? then decelerating to mach 5? for re-entry, before  a barge landing. With a small cheap pressure-fed disposable upperstage.

Trading thrust for ISP is generally a bad idea on first stages. Every second the 1st stage has to burn is almost 10 m/s of gravity losses. Over 30% of the F9's first stage performance is just fighting gravity losses.

And the F9 can't get to Mach 14 at MECO with ANY reserves for boostback, no matter what ISP gains you theorize. It simply doesn't have the mass fraction after gravity losses (and reducing thrust will make those worse).

Offline gin455res

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Re: Rocket Engine Q&A
« Reply #716 on: 07/13/2016 09:28 pm »
I guess I'd need to model it to truly convince myself. I was imagining a system where the second stage is smaller; payload smaller; and staging at a much higher speed.

And consequently the rocket would  spend more time throttled back on two high isp chamber/nozzles on the way up and on the deceleration and re-entry burn.

Say, staging at mach 14? then decelerating to mach 5? for re-entry, before  a barge landing. With a small cheap pressure-fed disposable upperstage.

Trading thrust for ISP is generally a bad idea on first stages. Every second the 1st stage has to burn is almost 10 m/s of gravity losses. Over 30% of the F9's first stage performance is just fighting gravity losses.

And the F9 can't get to Mach 14 at MECO with ANY reserves for boostback, no matter what ISP gains you theorize. It simply doesn't have the mass fraction after gravity losses (and reducing thrust will make those worse).


Yes, I was surprised when I first read of the t/w of rockets at take-off. 


I would still have to model it to believe it, not saying you are wrong, but that it is not self evident. Those mach numbers were plucked out my b@tt, they are not definitive. If those numbers are unrealistic, this doesn't mean others are not (or for that matter are). I would have to model it. I don't have the time or inclination right now (I need to get on with my phonics apps).


I would model a tri-core falcon 5 with a modified central core that has 3 sea level falcons and start with a single falcon feeding 6 chambers for higher ISP (this might be too heavy, and illustrate the need for a new smaller pump, or just kill the concept entirely). This is complicated and we would have to map the whole space of solutions before declaring there isn't one.


Additionally, it is not just about payload fractions. There are unknowns such as how much cheaper re-usability might make the ratio between the cost of the upper expendable stage and the marginal cost of the tri-core. This is not so easy to analyse/predict/guess.

Offline Nicolas PILLET

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Re: Rocket Engine Q&A
« Reply #717 on: 07/17/2016 12:54 pm »
Little historical question...
S1.5400, built in OKB-1 for Molniya launch vehicle, was the first staged combustion engine.
But what was the first American staged combustion engine ? SSME ?
Thanks !
Nicolas PILLET
Kosmonavtika : The French site on Russian Space

Offline baldusi

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Re: Rocket Engine Q&A
« Reply #718 on: 07/18/2016 01:48 pm »
Little historical question...
S1.5400, built in OKB-1 for Molniya launch vehicle, was the first staged combustion engine.
But what was the first American staged combustion engine ? SSME ?
Thanks !
Non classified and production, yes. We don't know about all military engines, and regarding experiments. But yes, the Americans needed 21 more years to fly a staged combustion engine than the Russians. And the Russians started with an oxidizer rich version. Granted, SSME is clearly the most difficult, complex, expensive and sophisticated of the two debuts.

Offline Nicolas PILLET

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Re: Rocket Engine Q&A
« Reply #719 on: 07/18/2016 04:07 pm »
the Americans needed 21 more years to fly a staged combustion engine than the Russians

But SSME was a bit more reliable than S1.5400, which is a good thing for shuttle crews ! :D
Nicolas PILLET
Kosmonavtika : The French site on Russian Space

 

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