Introducing Firefly Space Systems

[Proponent]

Thanks, R7 -- that's interesting.

It's a nice looking rocket!
Not air augmented though.
So what advancement does it represent?

In addition to the aerospike, the propellant combination will be nearly novel if if flies before a Raptor does, which seems quite possible (Europe's first liquid-propellant rocket, by Max Valier in the 1930s, and a recent rocket by Garvey Space have burned lox/methane, though neither of those was anywhere near being LEO capable).  Is the all-composite design also novel for an orbital launch vehicle?

EDIT:  Typo.

[R7]

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.

[Proponent]

I'm a little surprised the sea-level Isp for the aerospike is only 305 s.  I thought the aerospike's big attraction was its ability to atltiude-compensate.  Maybe the advantage in this application is low weight.  Or could the first-stage Isp be the result of a trade of Isp against propellant density?  Or maybe it allows lower-pressure engines, which would be quite an advantage in a pressure-fed first stage?

I also wonder a bit about the choice of methane.  As far as I can tell from Raptor discussions, methane really shines when used in a staged-combustion cycle, because of its high mass-specific heat capacity.  In a pressure-fed engine, I would think higher-density hydrocarbons -- propane or propylene (used by Garvey) would look relatively attractive.  Maybe it's to do with the autogenous pressurization.

[OK, I'll stop thinking out loud now.]

[Elmar Moelzer]

Hmm, unless I am misunderstanding the concept, this looks more like an aeroplug than an aerospike (honest question here)?
I presume that the lower Isp is due to the fact that it is pressure fed and not pump fed?
Now I am the one who is speculating...

[JBF]

Hmm, unless I am misunderstanding the concept, this looks more like an aeroplug than an aerospike (honest question here)?
I presume that the lower Isp is due to the fact that it is pressure fed and not pump fed?
Now I am the one who is speculating...

The aeroplug design is technically a truncated aerospike.  I'm attaching a paper that goes through the analysis of how much a spike you really need. This paper is directed more toward airplanes the rockets but the principle is the same. What it generally comes down to is how big of an engine you are talking about; the weight and space trade-off of a full spike or a truncated spike vs the efficiency.

Here is the link to a program if you want to experiment with various lengths.  http://aerospike.software.informer.com/2.6/

*grammar correction*

[Lampyridae]

Must say, I like the name. It's shiny.

[Proponent]

Hmm, unless I am misunderstanding the concept, this looks more like an aeroplug than an aerospike (honest question here)?
I presume that the lower Isp is due to the fact that it is pressure fed and not pump fed?
Now I am the one who is speculating...

The aeroplug design is technically a truncated aerospike.

I thought the whole point of calling in an aerospike was that the solid part of the spike was truncated, leaving the rest of the spike to be made up of gas (the "aero").  In this view an engine with a complete solid spike would be simply a spike engine.

Oh, and thanks very much for the paper!

[JBF]

I thought the whole point of calling in an aerospike was that the solid part of the spike was truncated, leaving the rest of the spike to be made up of gas (the "aero").  In this view an engine with a complete solid spike would be simply a spike engine.

Looks like you are correct.

From Wikipedia:

The terminology in the literature surrounding this subject is somewhat confused—the term aerospike was originally used for a truncated plug nozzle with a very rough conical taper and some gas injection, forming an "air spike" to help make up for the absence of the plug tail. However, frequently, a full-length plug nozzle is now called an aerospike.

[Elmar Moelzer]

Interesting info, guys! So I guess the answer is it is an aerospike and an aeroplug depending on who you ask?
One more thing: From the graphic, the plug/spike seems to be more truncated than the 60% cited as optimum in the document provided by JBF, or am I seeing this wrong?

[Lars_J]

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.

[Vultur]

400kg to LEO is kinda tiny... Reminds me of Falcon 1.

Works as a practice rocket, of course. SpaceX started the same way.

Well, there seems to be a lot of interest in small satellites, so I'm not sure there'd be anything "wrong" with being a specific-to-small-payloads launch service, for stuff that would otherwise be a secondary payload. I think that's what LauncherOne is supposed to be too...

[Jarnis]

...also starting small for a new company probably gives them a few more tries at getting it right if/when they run into teething problems.

[Coastal Ron]

Interestly they have chosen to setup their R&D in Hawthorne, maybe they are looking at recruiting a few SpaceX staff.

They are on the same street as SpaceX. Walking distance

If you're looking for the type of people that like to work on cutting edge stuff, then why not be located near a large employer of such people.  It cuts down on your hiring costs, either for employees of SpaceX that decide to join (don't have to pay relocation costs) or for potential new recruits being flown in to interview at SpaceX and then walking down the street to do a second interview at Firefly.

Happens all the time.

[Coastal Ron]

...also starting small for a new company probably gives them a few more tries at getting it right if/when they run into teething problems.

Yes, like another NewSpace company we've all been following...

[simonbp]

Composite tanks are really interesting. Plug nozzle is also interesting.

If they can get to orbit with pressurized engines on this (and make a bit of profit), then they have a built-in easy upgrade path by converting to turbo engines and substantially increasing the payload.

[DJPledger]

Composite tanks are really interesting. Plug nozzle is also interesting.

If they can get to orbit with pressurized engines on this (and make a bit of profit), then they have a built-in easy upgrade path by converting to turbo engines and substantially increasing the payload.

Why not simply scale up the design for greater payload capability while keeping the simplicity of a pressure fed system?

[TrevorMonty]

One article on aerospike engine gave a 23 % LEO payload improvement over contemporary 1st stage engines. If true it is worth the effort of developing this type of engine.

[rklaehn]

Composite tanks are really interesting. Plug nozzle is also interesting.

If they can get to orbit with pressurized engines on this (and make a bit of profit), then they have a built-in easy upgrade path by converting to turbo engines and substantially increasing the payload.

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.

[Elmar Moelzer]

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.

[go4mars]

It seems to me that on a future iteration, aerospike would be advantageous on re-entry too.  Exo-atmospheric/re-entry burns, then final propulsive landing should be more efficient.  I'm still curious whether/if there is much formal connection with SpaceX (shareholders).   

I like their homepage "[email protected]"