Author Topic: Introducing Firefly Space Systems  (Read 340674 times)

Offline R7

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Re: Introducing Firefly Space Systems
« Reply #80 on: 05/08/2014 02:23 pm »
Those were all high performance, high Isp pump fed systems.

XRS-2200 wasn't particularly stellar performance wise, 58bar Pc 428/338 Isp vac/sea level. SSME beats these with flying colors, RS-68A looses 14s in vac but beats sea level 24s.

The latest Firefly aerospike seems to be somewhat compromised; there are discrete small bell engines instead of just combustion chambers feeding the spike.
« Last Edit: 05/08/2014 02:23 pm by R7 »
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Offline Helodriver

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Re: Introducing Firefly Space Systems
« Reply #81 on: 05/08/2014 02:39 pm »
With a small lightweight and simple rocket, I wonder if they will be going after the "launch from anywhere, anytime" market that the Pegasus, Taurus, and Falcon 1 were originally shooting for. The DOD has long had their eyes on responsive space launch but all the vehicles that came along still never quite met that goal. It will be interesting to see if DARPA throws some money their way in the near future and a transportable expeditionary infrastructure and processing flow develops. Firefly to Omelek anyone?

Offline butters

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Re: Introducing Firefly Space Systems
« Reply #82 on: 05/08/2014 02:46 pm »
With a small lightweight and simple rocket, I wonder if they will be going after the "launch from anywhere, anytime" market that the Pegasus, Taurus, and Falcon 1 were originally shooting for. The DOD has long had their eyes on responsive space launch but all the vehicles that came along still never quite met that goal. It will be interesting to see if DARPA throws some money their way in the near future and a transportable expeditionary infrastructure and processing flow develops. Firefly to Omelek anyone?

I think SpaceX demonstrated that the logistics of launching from Omelek just weren't worth it. Maybe it would be more reasonable with solids, but liquid rockets and their ground support equipment don't travel very well.

Offline Elmar Moelzer

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Re: Introducing Firefly Space Systems
« Reply #83 on: 05/08/2014 03:13 pm »
XRS-2200 wasn't particularly stellar performance wise, 58bar Pc 428/338 Isp vac/sea level. SSME beats these with flying colors, RS-68A looses 14s in vac but beats sea level 24s.

Well, the comparison is not quite fair. First of all the XRS-2200 had a vac Isp of 436, not 338. Second, IIRC, it was a much simpler gas generator engine, while the SSME is a staged combustion engine.
The RS 68 looses 26 in vac from all I know.
The bigger RS 2200 was supposed to have even better values (also quite amazing for a gas generator engine):
Isp was 347 at sea level and 466 in a vacuum, which would have been almost equivalent to the SSME with a  simpler and more robust gas generator engine and a higher throttle range (down to 20%).

Offline baldusi

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Re: Introducing Firefly Space Systems
« Reply #84 on: 05/08/2014 04:20 pm »
XRS-2200 wasn't particularly stellar performance wise, 58bar Pc 428/338 Isp vac/sea level. SSME beats these with flying colors, RS-68A looses 14s in vac but beats sea level 24s.

Well, the comparison is not quite fair. First of all the XRS-2200 had a vac Isp of 436, not 338. Second, IIRC, it was a much simpler gas generator engine, while the SSME is a staged combustion engine.
The RS 68 looses 26 in vac from all I know.
The bigger RS 2200 was supposed to have even better values (also quite amazing for a gas generator engine):
Isp was 347 at sea level and 466 in a vacuum, which would have been almost equivalent to the SSME with a  simpler and more robust gas generator engine and a higher throttle range (down to 20%).
XRS-2200 was an expander cycle. The whole point of making it lineal was that you could get the surface to volume sort of fixed and thus could scale thrust a lot more than a traditional expander. Thus, you should compare its values not to SSME, but to RL10. And don't forget to add the T/W, which was the critical measure that killed that engine.

Offline Elmar Moelzer

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Re: Introducing Firefly Space Systems
« Reply #85 on: 05/08/2014 04:37 pm »
XRS-2200 was an expander cycle. The whole point of making it lineal was that you could get the surface to volume sort of fixed and thus could scale thrust a lot more than a traditional expander. Thus, you should compare its values not to SSME, but to RL10. And don't forget to add the T/W, which was the critical measure that killed that engine.
It was not me who did the comparison to SSME, but R7. Hmm, all sources I find state that XRS2200 was a GG cycle, like the J2. Maybe the XRS 2200 was an expander, but RS2200 was meant to be a gas generator, at least according to Astronautix. The RL 10 is an amazing engine, but expander cycles cant scale beyond a certain size from what I understand (unless they use linear aerospikes).
« Last Edit: 05/08/2014 04:56 pm by Elmar Moelzer »

Offline A_M_Swallow

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Re: Introducing Firefly Space Systems
« Reply #86 on: 05/08/2014 05:23 pm »
Interesting... But I'm surprised they bother to have two different stage diameters, if they are so close. But I suppose this helps reduce the fairing mass, and I can't imagine a 400kg payload needing a 6ft fairing.

400 kg payload should permit the launching to LEO of 100-200 cubesats.

Offline R7

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Re: Introducing Firefly Space Systems
« Reply #87 on: 05/08/2014 06:11 pm »
all sources I find state that XRS2200 was a GG cycle, like the J2.

Yes, it used J2 derived turbomachinery. I had incorrect source for XRS vac Isp. My previous point was not to compare engine cycles but note that there were existing comparable conventional engines so what's the benefit? Aerospikes don't seem inherently cheaper and XRS-2200 had a weight problem.
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Offline baldusi

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Re: Introducing Firefly Space Systems
« Reply #88 on: 05/08/2014 07:26 pm »
XRS-2200 was an expander cycle. The whole point of making it lineal was that you could get the surface to volume sort of fixed and thus could scale thrust a lot more than a traditional expander. Thus, you should compare its values not to SSME, but to RL10. And don't forget to add the T/W, which was the critical measure that killed that engine.
It was not me who did the comparison to SSME, but R7. Hmm, all sources I find state that XRS2200 was a GG cycle, like the J2. Maybe the XRS 2200 was an expander, but RS2200 was meant to be a gas generator, at least according to Astronautix. The RL 10 is an amazing engine, but expander cycles cant scale beyond a certain size from what I understand (unless they use linear aerospikes).
You were right. I don't know where did I got that it was RL derived. Probably some comments that linear aerospike could solve the expander scale limitations. BTW, they state that they used the J-2S turbomachinery. But I understood that it was a tap-off cycle. While they clearly speak of a gas generator. Now I'm confused.

Offline rklaehn

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Re: Introducing Firefly Space Systems
« Reply #89 on: 05/08/2014 07:41 pm »
I think an aerospike engine is a way to get acceptable Isp out of low chamber pressure like what you get with a pressure fed design. Once you go to pump-fed and higher chamber pressure, the advantage of the aerospike is less pronounced. And if you go to very high chamber pressures like the RD-170 engine family, there is no advantage whatsoever in using an aerospike.

So the aerospike and the pressure-fed design kind of go together.
I am confused. How does this fit in with the aerospike engines developed (or at least envisioned) for various RLV programs, like the X33. Those were all high performance, high Isp pump fed systems.

Any of the real rocket experts correct me if I got this wrong:

An aerospike buys you altitude compensation. So while it can not magically improve your Isp if you have low chamber pressure and high ambient pressure, it will adjust (increase) its expansion ratio continuously as you get into thinner air. So you get a much better average Isp over the flight profile of a typical first stage.

For an SSTO like X-33 was supposed to evolve into, altitude compensation is even more important: it is a way to get a very high expansion ratio, like an upper stage engine, during the majority of the flight that happens in vacuum, while still retaining the ability to work at sea level.

But this is only really relevant if you have a low to medium chamber pressure. If you have a high chamber pressure, you can have a large expansion ratio even at sea level.

Offline Elmar Moelzer

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Re: Introducing Firefly Space Systems
« Reply #90 on: 05/08/2014 07:59 pm »

Any of the real rocket experts correct me if I got this wrong:

An aerospike buys you altitude compensation. So while it can not magically improve your Isp if you have low chamber pressure and high ambient pressure, it will adjust (increase) its expansion ratio continuously as you get into thinner air. So you get a much better average Isp over the flight profile of a typical first stage.

For an SSTO like X-33 was supposed to evolve into, altitude compensation is even more important: it is a way to get a very high expansion ratio, like an upper stage engine, during the majority of the flight that happens in vacuum, while still retaining the ability to work at sea level.

But this is only really relevant if you have a low to medium chamber pressure. If you have a high chamber pressure, you can have a large expansion ratio even at sea level.
That is what I understood as well, which is why I was confused by the comments by rklaehn.

Offline RanulfC

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Re: Introducing Firefly Space Systems
« Reply #91 on: 05/08/2014 09:17 pm »
The latest Firefly aerospike seems to be somewhat compromised; there are discrete small bell engines instead of just combustion chambers feeding the spike.

Not really "compromised" as it's much easier to cluster small engine 'bells' into a clustered-plug-nozzle configuration than it is to cluster combustion chambers. Speaking of which the set up reminds me of the clustered-plug-nozzle Garvey tested last year for an "un-named" company...

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Offline dror

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Re: Introducing Firefly Space Systems
« Reply #92 on: 05/09/2014 12:41 pm »
400 kg payload should permit the launching to LEO of 100-200 cubesats.

Falcon9 -> $56.5m, 13,150kg
Firefly -> 400 kg -> $1.7m
Do you think they can get so low?

At 100 cubesats its 17,000$ a piece.
At 200 cubesats its 8,500$ a piece.
?
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Offline A_M_Swallow

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Re: Introducing Firefly Space Systems
« Reply #93 on: 05/09/2014 11:26 pm »
400 kg payload should permit the launching to LEO of 100-200 cubesats.

Falcon9 -> $56.5m, 13,150kg
Firefly -> 400 kg -> $1.7m
Do you think they can get so low?

At 100 cubesats its 17,000$ a piece.
At 200 cubesats its 8,500$ a piece.
?

I do not know sufficient about the firm to know if they can meet the $1.7m price and make a profit.

This website says that launching a cubesat costs over $100,000 so a new firm launching a U2 for $17,000 is probably very competitively priced.
http://www.diyspaceexploration.com/what-are-cubesats

A secondary payload on the Falcon 9 has to go into nearly the same plane as the main payload.  The Firefly can go into a very different plane from say the ISS, minimising the chance of a crash.

Offline Patchouli

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Re: Introducing Firefly Space Systems
« Reply #94 on: 05/10/2014 03:54 pm »
Autogenous pressurization = no helium. Pressurant gases are the propellants themselves.

Looks like what Beal Aerospace should have started with, a "small dumb booster".

400kg is two OG2s. If the price is right and service on time there will be Orbcomm-like customers who would love to be treated as real customers instead of practice ones getting bumped to right for years.

In theory getting rid of the helium pressurization system could be a big cost saver.

More interesting would be seeing an aerospike actually fly on something capable of going into orbit.

I heard of talk of their advantage over bell nozzles for years it would be interesting to see it in practice.


Offline Robotbeat

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Re: Introducing Firefly Space Systems
« Reply #95 on: 05/10/2014 11:35 pm »
I think an aerospike engine is a way to get acceptable Isp out of low chamber pressure like what you get with a pressure fed design. Once you go to pump-fed and higher chamber pressure, the advantage of the aerospike is less pronounced. And if you go to very high chamber pressures like the RD-170 engine family, there is no advantage whatsoever in using an aerospike.

So the aerospike and the pressure-fed design kind of go together.
I am confused. How does this fit in with the aerospike engines developed (or at least envisioned) for various RLV programs, like the X33. Those were all high performance, high Isp pump fed systems.

Any of the real rocket experts correct me if I got this wrong:

An aerospike buys you altitude compensation. So while it can not magically improve your Isp if you have low chamber pressure and high ambient pressure, it will adjust (increase) its expansion ratio continuously as you get into thinner air. So you get a much better average Isp over the flight profile of a typical first stage.

For an SSTO like X-33 was supposed to evolve into, altitude compensation is even more important: it is a way to get a very high expansion ratio, like an upper stage engine, during the majority of the flight that happens in vacuum, while still retaining the ability to work at sea level.

But this is only really relevant if you have a low to medium chamber pressure. If you have a high chamber pressure, you can have a large expansion ratio even at sea level.
Yup! But I think aerospikes and plug nozzles aren't necessarily worth the hassle. I'd like to see a dual-bell or something, too.

I must say I'm a little disappointed they got rid of air-augmentation. I'm not an air-breathing amazing people, but I was interested that someone seemed to be genuinely attempting it in order to expand the overall trade space. I hope they try it anyway.
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Offline DJPledger

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Re: Introducing Firefly Space Systems
« Reply #96 on: 05/11/2014 07:56 am »
Autogenous pressurization = no helium. Pressurant gases are the propellants themselves.

Looks like what Beal Aerospace should have started with, a "small dumb booster".

400kg is two OG2s. If the price is right and service on time there will be Orbcomm-like customers who would love to be treated as real customers instead of practice ones getting bumped to right for years.

In theory getting rid of the helium pressurization system could be a big cost saver.

More interesting would be seeing an aerospike actually fly on something capable of going into orbit.

I heard of talk of their advantage over bell nozzles for years it would be interesting to see it in practice.


Also getting rid of the helium pressurization system gets rid of all the problems associated with it and so Firefly's LV should theoretically be more reliable than ones with it. Just look at other companies' LV's which have had helium problems.
« Last Edit: 05/11/2014 07:57 am by DJPledger »

Offline Proponent

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Re: Introducing Firefly Space Systems
« Reply #97 on: 05/11/2014 10:59 am »
I must say I'm a little disappointed they got rid of air-augmentation. I'm not an air-breathing amazing people, but I was interested that someone seemed to be genuinely attempting it in order to expand the overall trade space. I hope they try it anyway.

Ditto.  It seemed like a good way of taking advantage of the atmosphere without letting wings-and-wheels thinking completely hijack the project.  I'll bet they had a good reason for dropping it, and it would be really interesting to know how their analysis went.

Offline dcporter

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Re: Introducing Firefly Space Systems
« Reply #98 on: 05/11/2014 07:59 pm »
I must say I'm a little disappointed they got rid of air-augmentation. I'm not an air-breathing amazing people, but I was interested that someone seemed to be genuinely attempting it in order to expand the overall trade space. I hope they try it anyway.

Ditto.  It seemed like a good way of taking advantage of the atmosphere without letting wings-and-wheels thinking completely hijack the project.  I'll bet they had a good reason for dropping it, and it would be really interesting to know how their analysis went.

"Yikes. No wonder this has never been done before."

Offline simonbp

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Re: Introducing Firefly Space Systems
« Reply #99 on: 05/12/2014 12:31 am »
"Yikes. No wonder this has never been done before."

Which is another way of saying it's more trouble that it's worth.

On the other hand, large carbon-fibre tanks have even less "heritage", but they must be worth their trouble.
« Last Edit: 05/12/2014 12:32 am by simonbp »

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