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Good luck to 'em. But I don't know that I would have picked several never-flown techniques as the basis for my least-cost rocket. I count at least four: aerospi
by jccooper 12y ago
Good luck to 'em. But I don't know that I would have picked several never-flown techniques as the basis for my least-cost rocket. I count at least four: aerospike nozzle, methane fuel, autogenous pressurization (whatever they mean by that), and all-composite structure. That would seem to be a path to spending lots of time and money on research.
To be fair, composites and aerospikes are well-tested, and methane has some good qualities and no obvious problems as a rocket fuel. (I don't know what they intend for pressurization; perhaps they want to boil both fuel and oxidizer to create pressure? Seem like a non-standard technique anyway.) And it's not like you can buy rocket hardware OTS, so everything you do is a development project. But none has flown on a real vehicle. Picking one would be ambitious. Four just seems like compounded risk.
Scaled Composites has had plenty of trouble with their seemingly-simple hybrid engine. You may think a technology is researched enough or simple enough to use without much danger, but rocketry is an extreme environment and can hold lots of surprises at scale and in the margins.
SpaceX, on the other hand, has only done one really revolutionary thing: cost discipline. Mostly through simplicity. Which is a pretty important contribution to the world of rocketry. Much more important than any particular nozzle or engine improvement.
The Firefly Alpha should be a nifty rocket if they can get it flying without spending too much money--but the history of rocket development doesn't suggest that'll be easy.
- ozi 12y agoNo inert pressurant is needed for Methane; the fuel itself is used to provide the working pressure for the engine.
- api 12y agoMethane is simpler in some ways -- no helium, for example. The big question marks here are composites and aerospike. Aerospikes have been tested but have not (as far as I know) flown. Composites haven't flown at this scale as far as I know. So yeah they have their work cut out for them! BTW: SpaceX has done some revolutionary things around reusability, but I mostly agree -- other than their reusability efforts everything else they've done is good old fashioned rocket science + cost control.
- chucknelson 12y ago> autogenous pressurization (whatever they mean by that) From their Vehicle page: "Firely's engines are actually self-pressurized (AKA autogenously pressurized), so that the fuel itself is used to provide the working pressure for the engine. This simplifies the design and saves weight."
- jccooper 12y agoProbably I'm hung up on "Firely's engines are actually self-pressurized". If they actually mean that, it's some sort of novel system. If they actually mean self-pressurizing tanks then that's a bit more normal--though I still would want to know if it's a blowdown system or if they are using some sort of gas generator (perhaps using heat from the cooling system) for regulated pressure. Either one requires a reasonably strong tank, but maybe that's not a problem for a small rocket due to minimum gauge issues. It's a nice cheap way to go, but still somewhat unusual in launch systems. More common in upper stages and manuevering thrusters.
- InclinedPlane 12y agoMethane pressurization is easy, it's the same method used as with LOX. Getting rid of Helium simplifies the process enormously and is also the same route that SpaceX is going down, though at much larger scales. Also, a lot of people called out Scaled Composites on their choice of engine for Space Ship 1/2 as being a risk. Hybrids seem easy on paper and at small scale, but they have a lot of special difficulties once you scale up. The engines they're building out to be fairly simple, and lots of companies have built engines that size and actually with greater complexity without having prior experience.