Those were all high performance, high Isp pump fed systems.
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?
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.
Quote from: R7 on 05/08/2014 02:23 pmXRS-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.
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.
all sources I find state that XRS2200 was a GG cycle, like the J2.
Quote from: baldusi on 05/08/2014 04:20 pmXRS-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).
Quote from: rklaehn on 05/08/2014 08:58 amI 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.
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.
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.
The latest Firefly aerospike seems to be somewhat compromised; there are discrete small bell engines instead of just combustion chambers feeding the spike.
400 kg payload should permit the launching to LEO of 100-200 cubesats.
Quote from: A_M_Swallow on 05/08/2014 05:23 pm400 kg payload should permit the launching to LEO of 100-200 cubesats.Falcon9 -> $56.5m, 13,150kgFirefly -> 400 kg -> $1.7mDo you think they can get so low?At 100 cubesats its 17,000$ a piece. At 200 cubesats its 8,500$ a piece.?
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.
Quote from: Elmar Moelzer on 05/08/2014 01:42 pmQuote from: rklaehn on 05/08/2014 08:58 amI 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.
Quote from: R7 on 05/05/2014 11:14 amAutogenous 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.
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.
Quote from: Robotbeat on 05/10/2014 11:35 pmI 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."