Introducing Firefly Space Systems

[Silversheep2011]

FuseUpHereAlone & go4mars:

Thanks for adding graphics "a picture says a thousand words"

-And thanks to Wikipedia,    - lets do the compare thing-

Yes in my view, there is 'low pressure' at the base of the truncated cone
See attached image

[LeighM]

Just a general comment about aerospike engines.

I always thought that the advantage was not necessarily about the efficiency of the engine per se, but the weight savings that it would give because of:-
a) the ability, at least with an annular design, to vector the thrust, dispensing with heavy gimballing structures and
b) the much simpler path for transmitting the thrust from the engine to the payload i.e. not having to go from effectively a point source on a traditional bell-nozzle engine to the cylindrical structure of the rocket. With an annular engine the thrust goes straight from the engine to the structure.

Regardless, all very interesting - I wish them well and look forward to seeing how it all pans out.

[Robotbeat]

I think aerospikes are over-rated but I do like the idea of air-augmentation. Not that I think it's a slam-dunk approach by any measure, but it does indeed increase the effective specific impulse by a lot, and it's something that no one has really explored this area of the trade space with an actual launch vehicle... That is, assuming it gets to flight.

[john smith 19]

I thought there was an aerospike or plug nozzle Q&A but in case there isn't.

The #1 benefit of such nozzles is reduction of losses. Bells nozzle deliver perfect expansion IE exhaust pressure has dropped to exactly the ambient atmospheric pressure at exactly 1 altitude.

Looking up the text book nozzle losses that loss is the worst major loss at about 15% (although I can't recall if that's Isp or thrust).

If you look at graphs comparing plugs with bells you see a huge skirt of lost performance where the bell is much below the plug but (slightly) exceeds the plug at it's design altitude.

BTW people have spec'd plugs for upper stages as well because they are so much shorter than the 100:1 + expansion ratio nozzles, so you don't need a long interstage (which adds surprisingly large mass).

Eliminating gimbals is a potential benefit but as I said the only flight weight plug nozzle I'm aware of was gimballed for TVC.

Sadly due to the wrong brazing alloy used to join parts of the combustion chambers a sizeable part of it was destroyed in ground test. The rest is presumably sitting in a warehouse at the AFRL. Still the best example of a dual LO2/LH2 expander cycle tested to date AFAIK.

[Proponent]

In the simple 1-D rocket-engine model, the difference between vacuum and sea-level thrust is simply exit area times sea-level atmospheric pressure.  If thrust density (newtons per square meter of exit) of a conventional nozzle is high (basically, if chamber pressure is high), then the pressure losses are relatively small.

[Davidthefat]

Follow up question: what do these 3 components represent on the truncated Aero spike center.
1. looks like a cylindrical center piece, function unknown?
2. looks like a heating transfer grid of come sort? - or is a flame arrest?
3. looks like an internal nozzle, again function unknown?

In a truncated aerospike, there's a low pressure zone where the the spike is truncated. It makes the hot gases recirculate in that zone and makes the engine lose some thrust. That center piece looks like it's for some kind of gas to flow out of to create a slightly high pressure to prevent that gas re-circulation.


The only paper I've seen on thrust differential on an annular aerospike uses throttling of the nozzles, not gimbals.

Interesting point. The two papers on plug nozzles that I know that were actually built were a GE pressure fed in the 50's and the one built by Rocketdyne in the 70's for the USAF AFRL under Dr Huang (that's the co-author of "Modern Engineering for the Design of Liquid Propellant Rocket Engines"

The former was a ground test engine where some of the chambers were 15% below nominal (IIRC the rest ran at normal pressure) to give a 5degree shift in the angle of the thrust.

The latter was the only known flight weight plug nozzle I've ever seen. It did use a gimbal mounting of the whole structure (the base plate was a key part of the design and was made of 2 layers of Ti plate machined into a waffle pattern perforated to evenly spread what I think was some of the expander exhaust. The whole engine hung from 4 upside down V shaped supports which in a vehicle would be the gimbals.

I'd quote a reference but I've just tried to used the ARC AIAA search function and it seems to have gone down the toilet (has AIAA sold it's collection to some private company?). 

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050217125.pdf

That's the paper that I was referring to. It's from 2003.

[TrevorMonty]

From the drawings earlier in this thread steering seems to be by having one privot point per engine/ nozzle and moving it in or out. Simple design by rocket standards and should be lot cheaper to manufacture than gimbal mount.

If aerospike development proves impossible they can still do a mini F9 using 2nd stage engine.

Could this engine be scaled by increase diameter and adding more engines/nozzles eg 16?.

[edkyle99]

In my view, the most important parts of this design are the use of all-composite tanks and structure and of LOX/methane propellants.  Firefly has a chance to be the first to orbit using such a setup.  The aerospike is interesting, but its effect is offset by the use of a pressure fed propulsion system.  These latter two elements of the design seem to me selected to keep costs low for what is likely only a precursor test variant. 

 - Ed Kyle

[Proponent]

I think the aerospike and pressure-feed sort of go together.  Pressure feed forces one to relatively low-pressure engines.  Low-pressure engines, in turn, benefit much more from aerospike nozzles than do high-pressure engines.

[simonbp]

I may be even simpler than that. They are cribbing SpaceX's concept of the first stage being a cluster of second stage engines, and if you have that many small first stage engines, arranging them around a plug is an efficient packing. So it's not so much that they set out to design an aerospike first stage, they just already had a ring of engines on the first stage, and stuck an aerospike on there.

[Tomness]

Do they really have research and development operations in Hawthorne, CA just down the road from SpaceX rocket factory? Crazy, I wouldn't be surprised if SpaceX sold them their Falcon 1 Tooling.

I hope they are able to provide a viable product.

[dasmoth]

Do they really have research and development operations in Hawthorne, CA just down the road from SpaceX rocket factory? Crazy, I wouldn't be surprised if SpaceX sold them their Falcon 1 Tooling.

Falcon 1 tooling is unlikely to be helpful when building a composite vehicle.

I do wonder if FRE-1 might be just a little bit Kestrel-inspired, though...

[Silversheep2011]

Firefly-B photos. note the x4 nozzles on outer boosters

[Silversheep2011]

And this one,
How to Interpret what's going on?
Looks like a Falcon heavy doesn't it, painted in black and fluoro green logo.
Bruce Wayne Enterprises perhaps,
but where's Batman?

[Crispy]

Is there a sensible reason for the slightly mismatched booster diameters?

[Prober]

In my view, the most important parts of this design are the use of all-composite tanks and structure and of LOX/methane propellants.  Firefly has a chance to be the first to orbit using such a setup.  The aerospike is interesting, but its effect is offset by the use of a pressure fed propulsion system.  These latter two elements of the design seem to me selected to keep costs low for what is likely only a precursor test variant. 

 - Ed Kyle

you forgot using methane to provide the pressure.   

[Prober]

Sadly due to the wrong brazing alloy used to join parts of the combustion chambers a sizeable part of it was destroyed in ground test. The rest is presumably sitting in a warehouse at the AFRL. Still the best example of a dual LO2/LH2 expander cycle tested to date AFAIK.

maybe someone will pull this out of storage, and 3D print (shameless plug) a new test part.   Lot's of test programs can be revisited now at a much lower cost.

[Zed_Noir]

And this one,
How to Interpret what's going on?
Looks like a Falcon heavy doesn't it, painted in black and fluoro green logo.
Bruce Wayne Enterprises perhaps,
but where's Batman?

The rocket logo more likely related to the Firefly TV series. The rocket is shiny. 

[Silversheep2011]

The rocket logo more likely related to the Firefly TV series. The rocket is shiny. 

Quite apt>.....

Find a Crew.
Find a Job.
Keep Flying.

[Proponent]

Firefly-B photos. note the x4 nozzles on outer boosters

Reminiscent of the old Falcon 9-S5.