Firefly Space Systems unveils Alpha launch vehicle design with aerospike engine


July 13, 2014

The Firefly Alpha uses methane fuel and a plug-aerospike engine

The Firefly Alpha uses methane fuel and a plug-aerospike engine

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The signs of a healthy industry isn't just growth or innovation, but a tendency to reach out and fill niche markets. A case in point is the small satellite launch company Firefly Space Systems, which recently unveiled its planned Alpha launcher. Aimed at the small satellite launch market, it's designed to launch satellites into low-Earth orbit (LEO) at very low cost with an unconventional aerospike engine. It is also the first orbital launcher to use methane as fuel.

The Firefly Alpha is a specialized design to launch light satellites at low cost into low Earth and Sun-synchronous orbits for broadband communication and Earth observation missions. Designed to carry payloads of up to 400 kg (880 lb), the Alpha features carbon composite construction and uses the same basic design for both of its two stages to keep down costs and simplify assembly.

The launcher uses methane and liquid oxygen as propellants, which Firefly says is a first for orbital launchers, though methane has been proposed for landers. Methane was chosen because it’s cheap, plentiful, clean-burning and, unlike more conventional fuels, self-pressurizing, so it doesn't require a second pressurization system.

However, the interesting thing is that when you look at the first stage, you see a curious bulge at the base ringed with rocket burners rather than the usual cluster of rocket engines. That’s because, while the second stage uses conventional rocket engines, the first stage uses a more exotic plug-cluster aerospike engine putting out 90,000 lb (400.3 kN) of thrust.

Aerospike engines have been under development since the 1960s, though, until now they've never got much past the design phase. The idea behind them is that rockets with conventional bell-shaped nozzles are extremely efficient, but only at a particular altitude. Since rockets are generally used to make things go up, this means that an engine that works best at sea level will become less and less efficient as it rises.

The plug aerospike is basically a bell-shaped rocket nozzle that’s been cut in half, then stretched to form a ring with the half-nozzle now forming the profile of a plug. The clever bit is that the open side of the rocket engine is now replaced with the air around it. As the rocket fires, the air pressure keeps the hot gases confined on that side like the wall of the bell nozzle did. As the craft rises, the change in air pressure alters the shape of the “nozzle;” keeping the engine working efficiently.

One of Alpha's rocket burners

The result of this arrangement is a lighter rocket engine that works well across a range of altitudes. Because the second stage operates in a near vacuum, it uses conventional rocket nozzles.

"What used to cost hundreds of millions of dollars is rapidly becoming available in the single digit millions," says Firefly CEO Thomas Markusic. "We are offering small satellite customers the launch they need for a fraction of that, around US$8 or 9 million – the lowest cost in the world. It’s far cheaper than the alternatives, without the headaches of a multi manifest launch."

Source: Firefly via New Scientist

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

O.K. then, how about explaining for us dummies out here: "How's a methane rocket going to not add greenhouse gasses to the atmosphere??? I know there's someone out there whose smarter than me!!!


This is cool, SpaceX should incorporate this areospike tech in there rockets.

Ryan Gibbons

Ryan, While it is possible this idea is not patented I wouldn't bet on it. SpaceX could do something similar or license this tech, possibly even if it is patented.


There has to be a limit regarding the number of small satellites that we can put into orbit if we are going to guarantee that they will not collide with each other and in doing so, increase the danger to all satellites. As it is, the poles are extremely congested.

Mel Tisdale

I have never got around the question, "How is fire pressing against air going too provide the containment too accelerate the reaction mass to the rear enough to matter?" It looks to me like putting a muzzle brake on a rocket. I think putting a thrust augmenter around the whole engine grouping would do more good.


I eventually stopped visualizing a horizontal cut in the bell, but I still don't get the "stretch" and "plug" at all. What is the function of the central vent? Do the rockets aim out, and then in? Did an illustration or a paragraph go missing?

Bob Stuart

@katgod - This version of the aerospike might be. The Aerospike itself has too much prior art to issue a blanket patent that would stick. SpaceX could freely design its own variant and then put it to production so long as their design is clearly not based on the design firefly uses.

@Slowburn - This is one of those cases where physics does not follow common sense. Aero spikes have been successfully tested many times. NASA even tested their version that was to go into the space plane successfully accross the intended operational range. It wasn't the aerospike that killed the project, it was the fuel tanks. The new lighter composites could not withstand lift-off vibrations while containing cryogenic fuels. So they were going to have to drop back to heavier aluminum, which reduced the cargo fraction to a point where its viability was in question. Since it was over budget they killed the space plane rather than redesign the entire vehicle.


Firefly and SpaceX are aiming at very different markets. The aerospike engine sounds great at first, but it has been tried and failed many times since the 1960's. It has two major problems: 1) The engine is very heavy, and 2) additional cooling is required for the engine. Both of these come at a cost of "throw-weight" or "throw distance." That is why Firefly is targeting Very Low Earth Orbit, low weight satellites. In the long run, aerospike does not look to be scalable much beyond what Firefly is doing.

SpaceX on the other hand is scalable and has several unique features: A) The SpaceX first stages will eventually be reusable. They will return to Earth and a soft landing. B) The second stage is restartable, something that no other production rocket can currently do. This allows efficient missions that can drop off satellites at various orbits and altitudes. C) The SpaceX first stage is seminal technology for future Lunar and Mars manned landers. D) As soon as the Air Force quits impeding it, the SpaceX capsule will be man-rated and able to replace both the Space Shuttle and Soyuz with something bpoth cheaper and more reliable.

There are niches for lots of innovation in space.


Because if the methane were in the atmosphere, it would be a much more powerful greenhouse gas than the carbon dioxide and water vapor to which it would be oxidized? I guess that would be a net loss of greenhous-ery. (Yes, I know that the methane almost certainly wasn't in the atmosphere to begin with, but you did ask how.)


SpaceX announced in 2012 development of methane/LOX Raptor engine


@ WhasaMatterYou?:

Another name for methane is "farts," which paints quite a picture of this rocket being propelled into space. The most common sources are cattle and termites from the digestion of cellulose. Swamp gas, melting frozen methane ice at the bottom of some oceans and the gas that's leaking out of defrosing tundras are other major free-release sources. Another name for the material is "natural gas," which is pumped out of the ground .

While methane is a much more powerful greenhouse gas, it is also absorbed into the ecosystem much faster than CO2. If I recall correctly, it's something like a few months compared to about a century or so. For a full explanation and hard numbers, check out "Global Fever," by William H. Calvin.

A Methane molecule is composed of one carbon atom, attached to four hydrogen atoms. When methane fuel is burned, this carbon atom is released into the atmosphere, where it binds with to Oxygen atoms to become CO2.

Whether or not this rocket fuel is a "green" application depends on where the methane came from. If it's natural gas, a fossil fuel, then the carbon atom entering the atmosphere is a new one and adds directly to the atmosphere's carbon load.

If it is derived from the digestion of wood scraps or switchgrass or bamboo etc., then the carbon atom was already in the system, so it's being recycled.

Recycled carbon is always best. Using it is not going to stop global warming nor reduce the atmosphere's carbon load. But, it will not make the problem worse. Every carbon atom that we recycle results in a fossil carbon atom that remains safely locked away underground. That makes it carbon-neutral.

Most likely, though, the company is using fossil carbon in its fuel, since that's a lot easier and cheaper to obtain.


There's many thousands of boats & ships zig-zagging their way across the oceans at the same exact altitude, namely zero. Satellites travel in straight lines at a range of altitudes. There's plenty of room for many more. The current - and growing - problem isn't the satellites, it's debris.


Mere rockets will not add much to the excess CO2 problem, but they are so expensive that it probably wouldn't hurt to "go green" and use advanced high temp nuclear made methane as the ultimate CO2 recycler so as to get the ball rolling towards an advanced nuclear powered world where we would never have to worry about fossil fueled depletion into an overheated biosphere (and resource wars). I like the idea of different rocket concepts for different applications.

Robert Bernal

Sorry to disagree Bobcat but the Linear Aerospike engine out performed the bell rocket engines at every turn. It was not tried and failed. It has never been tried. With all its advantages, including 25 to 30% fuel savings at low altitude where much of the fuel is used, it's unbelievable that NASA has not demanded it be developed and used to save money on launches.

Before the X-33 was killed (doomed on purpose with the impossible, composite tanks), they should have at least put the aluminum tanks in, lit the thing up and showed the capabilities of the Linear Aerospike engine in flight.

I know..., we've been doin' it this way for 60 years. Why change things now. If it ain't broke, don't fix it. Stupid, stupid logic.

Larry Pope
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