Author Topic: Parallel Staging  (Read 59880 times)

Offline DonPMitchell

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Re: Parallel Staging
« Reply #15 on: June 07, 2009, 12:29:36 PM »
I'm not sure if the combustion volume/surface area makes it harder or easier to cool.  Isn't more heat dumped into a smaller surface area?

Is the F-1 the biggest engine every used?  I've read that it just barely achieved combustion stability, and the Saturn V had real problems with pogo oscillation.  The modern trend seems to be more combustion chambers that are smaller, like the RD-170 on Zenit.

F-1 ------ 7.7 million Newtons,  265 sec Isp (304 vacuum)
RD-170 -- 7.9 million Newtons,  309 sec Isp (337 vacuum)

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Offline jdbenner

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Re: Parallel Staging
« Reply #16 on: June 07, 2009, 01:35:07 PM »
The temperature inside the big engine should be the same as the temperature inside a small engine.  More coolant is available per unit engine surface area.

Actually the same equations that govern cooling also govern heating.
Joshua D. Benner Associate in Arts and Sciences in General Science

Offline DonPMitchell

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Re: Parallel Staging
« Reply #17 on: June 07, 2009, 02:06:47 PM »
It's not temperature you have to worry about, it is heat.  The number of calories being generated increases as the cube of the dimension, and radiation and convection are transporting that to the walls.

In any case, I don't believe you could achieve combustion stability.  Sea Dragon looks like a hand waving design proposal that never really got to a serious engineering stage.  Maybe you could build a rocket that big with clusters of engines -- I don't understand why they even proposed building a giant rocket engine, that seems very naive.
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Offline ijuin

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Re: Parallel Staging
« Reply #18 on: June 07, 2009, 11:21:14 PM »
I would expect that ten million newtons or so is as high as we can go with current methods, and we will probably have to come up with a novel combustion chamber architecture to exceed this ten meganewton per chamber level.

Offline DonPMitchell

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Re: Parallel Staging
« Reply #19 on: June 08, 2009, 10:55:58 AM »
I haven't been paying close attention to the Ares heavy lift designs.  Are folks still debating SSME vs. RS-68?

I imagine the SSME is vastly more expensive, although more efficient:

SSME --- 3.2 mega Newtons, 485 sec. Isp
RS-68 --- 3.3 mega Newtons, 420 sec.

So they're talking about putting four or five engines like this on a first stage.

Just to point out, if you reverse Tsiolkovsky's equation, the mass of fuel you need is an exponential function of specific impulse, so there is a real reason the Russians went crazy getting close-cycle engines to work.  And these modern engines are hugely superior to the F-1, both because of LH2 and because of better design.

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Offline Bob B.

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Re: Parallel Staging
« Reply #20 on: June 08, 2009, 12:23:14 PM »
I haven't been paying close attention to the Ares heavy lift designs.  Are folks still debating SSME vs. RS-68?

I thought it was a settled issue a couple years ago that they were using the RS-68, but I've heard a recent rumor that they may be reconsidering the SSME.  Prior to that I think I heard they were changing from five R-68s to six.  Apparently it is still a work in progress and I don't know what the status is.

Offline DonPMitchell

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Re: Parallel Staging
« Reply #21 on: June 08, 2009, 01:55:40 PM »
The bigger question is, what will they do with such a large rocket.  I don't really think we, or anyone, is going to spend the money and risk to send men to the Moon again.  Is there a more realistic project requiring superheavy lift?

I think America needs a major rocket launch on the equator.  Maybe get more serious about the Omelek Island base.  We've completely lost the commercial comsat launch market, despite having rockets that are superior to the Ariane and Proton. 
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Offline Satanic Mechanic

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Re: Parallel Staging
« Reply #22 on: June 08, 2009, 02:08:46 PM »
I too have heard the rumors about going away from the RS-68 and going with the SSME.  A couple of reasons why they are talking about it is there will be 60 SSMEs available after the retirement of the shuttle and the heat from the SRB's might interfere with the RS-68 engine. I know there was talk about about making a RS-68 with regenerative cooling (RS-68B?) to compensate for the heat and of course there has been talk about a disposable version of the SSME.  But that is what it is, talk.

SM

P.S. I do not hear much about Ares-V anymore, just talk about Ares-I, Direct and believe it or not Shuttle-C!

Offline jdbenner

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Re: Parallel Staging
« Reply #23 on: June 08, 2009, 06:01:06 PM »
It's not temperature you have to worry about, it is heat.  The number of calories being generated increases as the cube of the dimension, and radiation and convection are transporting that to the walls.


Heat transfer rates are dependent on temperature.  If the small engines do not cool the gas appreciably then How is it a lack of heat energy that is responsible for keeping the engines from melting?
Joshua D. Benner Associate in Arts and Sciences in General Science