Author Topic: New methane SC engine.  (Read 407912 times)

Offline go4mars

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Re: New methane SC engine.
« Reply #40 on: 10/07/2011 10:34 pm »
Even though propane might be a great rocket fuel. I believe methane might be a safer option.

If Oil and gas service companies can do large-scale propane frac's (they have started to in the last couple of years) then it should be very doable as a rocket fuel.  Propane is actually relatively stable.  My friend drove a propane fueled pick-up truck when I was in high school, and propane is pretty well distributed through many other mundane uses in society.
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Offline Zed_Noir

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Re: New methane SC engine.
« Reply #41 on: 10/07/2011 11:12 pm »
I think most of the fork-lifts use for warehousing are run on propane. 

Offline docmordrid

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Re: New methane SC engine.
« Reply #42 on: 10/08/2011 01:07 am »
We have propane powered buses & municipal vehicles around here (SE Michigan). See 'em all the time.
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Online oldAtlas_Eguy

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Re: New methane SC engine.
« Reply #43 on: 10/08/2011 09:45 pm »
baldusi, where did you get the value of 44,178kg for RP-1 US?

The values I dug up in an old NASA report showed max propelant loads of 27600 L of LOX or ~31,491kg and 17,400 L of RP-1 or ~ 19,853kg for a total of 51,345kg for the current F9 US.

Offline baldusi

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Re: New methane SC engine.
« Reply #44 on: 10/08/2011 10:29 pm »
baldusi, where did you get the value of 44,178kg for RP-1 US?

The values I dug up in an old NASA report showed max propelant loads of 27600 L of LOX or ~31,491kg and 17,400 L of RP-1 or ~ 19,853kg for a total of 51,345kg for the current F9 US.

May be I didn't made this clear enough, but this is not an exact replica of the Falcon 9. This is more of a comparison of technologies. This is also why the payload of the RP-1 doesn't fits the Falcon 9's. Neither Merlin 1C's nor D's. I was more trying to do comparison between the technologies.
The methodology that I choose, was to set a given T/W of the stack without payload (1.4), and an engine thrust (140klbf are 667kN, or 5.6MN for the FS), and change the propellant mass fraction and isp of each stage. I don't really know if this is the correct way of doing this comparison, but I felt this was one way.
As usual, all you care is about the cost to put a certain payload on orbit. So having fixed the total stack weight might or might not have been a valid comparison. But it was something to start a discussion. I did made this numbers trying to fit new methane engines in the current tank tooling.
What I meant was that the methane version, having 28% extra volume, would roughly fit on the extended Falcon 9 of 16tonnes to LEO that SpaceX briefly had on their website. The problem I had there was that such version, at the expected weight of 480tonnes, had a T/W of less than 1.2. So I played some numbers with Shillings, and used a weight that fit withing that volume limitation (60m tall, 3.65m wide). Then I played the cross feeding and single stick with a single US. And reach an optimum if the US was 7.5 smaller than the FS. At that relationship, we are reaching a very good balance between high energy and low energy. Having those parameters, I just did the variations I've explained previously.
If you know how Shilling's work, it's very sensitive to the T/W. And it doesn't take into considerations the Drag. My approach kept all the biases and systematic errors the same for every modeled version. So, as I said, it's good to estimate relative performances.

Offline Prober

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Re: New methane SC engine.
« Reply #45 on: 10/09/2011 12:32 am »
NASA has no need to pay for the Grashopper RLV.

bet part of the LAS program pays for the Grashopper RLV.
 
 
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Offline Jason1701

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Re: New methane SC engine.
« Reply #46 on: 10/09/2011 12:52 am »
NASA has no need to pay for the Grashopper RLV.

bet part of the LAS program pays for the Grashopper RLV.
 
 

They are completely unrelated. Grasshopper is powered by a Merlin. Are there Merlins on Dragon Crew? The first Dragon Crew flights will splash down, not land, so they don't require propulsive landing GNC work right away.

Offline baldusi

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Re: New methane SC engine.
« Reply #47 on: 10/09/2011 02:09 am »
Please let's keep the topic on the methane engine. One extra advantage that I can see, is that the delta-v that you gain from leaving a certain fraction of fuel for boost back stage is significantly more with these levels of isp (around 350s vacuum). So, may be they want to use the Merlin 1D to develop the basic technology, but will really take advantage with a high efficiency methane.

Offline ArbitraryConstant

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Re: New methane SC engine.
« Reply #48 on: 10/09/2011 05:22 am »
What we had said, was that the cost of development for an engine like the RD-191 was simply too much for the extra performance, given SpaceX's cost consciousness. But since they have stated that they are working an a "super efficient staged combustion" rocket engine, it's clear that they have found a way to develop it at a reasonable cost.
I don't think it is clear. Certainly not that they've matched the better Russian engines in every respect. They almost certainly haven't.

If you look at Merlin 1D, its chamber pressure is still nowhere near the better Russian engines. They cut a lot of weight leading to an excellent T/W, but it makes no sense for them to do this if they are both capable of matching the Russians, and of a mind that it is economical to do so. If they were willing and able to do so, 1D would be better than it is.

Far more likely is the idea that the new SC engine will have a chamber pressure similar to Merlin 1D, it'll have a very good ISP due to SC and the large expansion nozzle, and a mediocre T/W that will be acceptable on US engines.

I've no doubt it's operationally simpler for SpaceX to have the same fuel and similar engines on both stages, but the fact is they had to build a complete rocket on a relative shoestring and that contributed to their design decisions. Now they have real cash flow and much larger first stages to deal with, and that can quite easily lead to different decisions than before.

Offline mlorrey

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Re: New methane SC engine.
« Reply #49 on: 10/09/2011 07:10 am »
The initial use of Grasshopper, IMHO, will be as a SpaceX version of Little Joe to do a live test of the LAS. As such, it will likely get billed to LAS project funding.
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Offline strangequark

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Re: New methane SC engine.
« Reply #50 on: 10/09/2011 07:42 am »
Far more likely is the idea that the new SC engine will have a chamber pressure similar to Merlin 1D, it'll have a very good ISP due to SC and the large expansion nozzle, and a mediocre T/W that will be acceptable on US engines.

I don't see the point of going staged combustion and keeping the chamber pressure low. One of the reasons you get such good Isp with staged combustion engines is the higher chamber pressure.

SpaceX went with a gas generator on Merlin because it's a simple, well understood design, and for kerosene SC you need to run an ox-rich preburner, which is a big, expensive materials challenge. A staged combustion methane engine with a fuel rich preburner is going to be a lot easier to develop than either a hydrogen or kerosene staged combustion engine.
« Last Edit: 10/09/2011 07:48 am by strangequark »

Offline baldusi

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Re: New methane SC engine.
« Reply #51 on: 10/09/2011 02:24 pm »
If you look at Merlin 1D, its chamber pressure is still nowhere near the better Russian engines. They cut a lot of weight leading to an excellent T/W, but it makes no sense for them to do this if they are both capable of matching the Russians, and of a mind that it is economical to do so. If they were willing and able to do so, 1D would be better than it is.
They are not able to match the Russians. At least they are not in an RP-1 engine. Please remember, the Merlin 1D was their first turbopump. They don't have experience in developing oxygen rich gas generators (the metallurgy is a very difficult task). The Merlin 1D was a perfect way of doing incremental improvements. In fact, much of the revolutionary things that they did where on the production and manufacturing side, not on the technological. There's a reason nobody had done an 160 T/W engine. Currently that means a gas generator, and even at lower T/W, the good SC give better performance.
What's more, just to put an example of the Russian technology, the RD-191 loses 4s of when throttling to 50%. Ask SpaceX how much will they lose when doing 70%. Tip: the Merlin 2 was supposed to lose 15s. Energomash has something like 60 years of designing rockets engines. You don't get that level of sophistication in a decade.
I would go as far as postulate that the Merlin 1D was a fundamental step in developing what they are developing now. Without it's experience, they would have never been able to develop it.

Quote
Far more likely is the idea that the new SC engine will have a chamber pressure similar to Merlin 1D, it'll have a very good ISP due to SC and the large expansion nozzle, and a mediocre T/W that will be acceptable on US engines.
How are they going to achieve such level of isp with 100bar? The RD-191 that I quote in the paper had close to 300! And they played with taking advantage of the methane lower viscosity and density to do fuel regen and film cooling. This saved them 73% of the pump need for those reasons alone! You not only don't get those performance numbers with RP-1, you've got a lot of coking problems. And the methane is a very special case, because the gains of lower density are bigger than the losses of extra volume. If they had gone with the hydrogen case, that would not have been the tradeoff. In fact, when you read the Energomash paper, they had to use quite a few tricks to actually get that level of performance. Use less than what they did, and you'd find yourself with, at best, same performance.
The reason this works is because you trade 50% extra dry mass for 50 seconds of extra isp. Fifty! The whole RS-68A was to get some five seconds or so. I'm not surprised the Russian will never implement a methane engine. If I had used RD-191 numbers (they proposed to design a 25% more powerful version, now), the methane version would have been swept under the rug. So, this only work if you start from where SpaceX is now.

Quote
I've no doubt it's operationally simpler for SpaceX to have the same fuel and similar engines on both stages, but the fact is they had to build a complete rocket on a relative shoestring and that contributed to their design decisions. Now they have real cash flow and much larger first stages to deal with, and that can quite easily lead to different decisions than before.
They don't have so much cashflow, yet. They have a lot of obligations and they have hardly covered the bare minimum. What I proposed was to make a minimum change to their current design and tooling.
You can use the same LOX tank for the LCH4. Same piping, etc. No change in the 3.65m tooling, aerodynamic profile, etc. Same number of engines of the same thrust. The only strong assumption is they are developing the fuel rich SC CH4 engine. Once they have that, and given the work they did for the FH, they would have a similar effort on the design side for the methane version.
They would need a new cryogenic tank for the methane at the pad(s). And they would need to revise their ground infrastructure and operations. It's an expense, but nothing different from working with LOX. So you've got to requalify and such, but it's not a completely new technology.
« Last Edit: 10/09/2011 02:25 pm by baldusi »

Offline clongton

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Re: New methane SC engine.
« Reply #52 on: 10/09/2011 02:41 pm »
They are not able to match the Russians. At least they are not in an RP-1 engine.

They don't need to match the Russians. If they are aiming at a Methane SC engine, then it will be fuel rich in lieu of oxidizer rich, which requires no new metallurgy.
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Offline ugordan

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Re: New methane SC engine.
« Reply #53 on: 10/09/2011 02:47 pm »
Please remember, the Merlin 1D was their first turbopump.

What source do you have for this claim? Or indeed any such claim that they are actually actively producing their own turbopumps now instead of Barber-Nichols, just because they said they would do that at one point? Also, development and manufacture are two different things.

Offline krytek

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Re: New methane SC engine.
« Reply #54 on: 10/09/2011 10:24 pm »
A quick search came up with this, although this is NOT listed on their site.
http://www.startuphire.com/job/turbo-pump-designer-hawthorne-ca-spacex-147175

Offline Robotbeat

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Re: New methane SC engine.
« Reply #55 on: 10/10/2011 03:48 am »
A quick search came up with this, although this is NOT listed on their site.
http://www.startuphire.com/job/turbo-pump-designer-hawthorne-ca-spacex-147175

I've definitely seen turbopump designers on the SpaceX website a while ago.
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Offline krytek

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Re: New methane SC engine.
« Reply #56 on: 10/10/2011 04:29 am »
A quick search came up with this, although this is NOT listed on their site.
http://www.startuphire.com/job/turbo-pump-designer-hawthorne-ca-spacex-147175

I've definitely seen turbopump designers on the SpaceX website a while ago.
Double checked. There are currently 3-4 turbo machinery related jobs listed.

Offline ugordan

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Re: New methane SC engine.
« Reply #57 on: 10/10/2011 08:01 am »
I'll ask again. Does that prove they are actively building their own M1d turbopumps?

This is how rumors and unconfirmed information turns into a "fact" later.

Offline Comga

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Re: New methane SC engine.
« Reply #58 on: 10/10/2011 10:22 pm »
I'll ask again. Does that prove they are actively building their own M1d turbopumps?

This is how rumors and unconfirmed information turns into a "fact" later.

Perhaps not definitively, but didn't Musk state that they wanted to bring in-house the turbopump design and manufacture?
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline ugordan

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Re: New methane SC engine.
« Reply #59 on: 10/10/2011 10:27 pm »
Yes, he did. Doesn't mean they *have* done it yet and doesn't mean M1d already uses inhouse turbopumps.

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