This third round of rocketry startups sounds a bit more robust than the first two, and of course SpaceX is demonstrating an amazing ability to execute their agenda.
When the big aerospike hoopla over the Regan era NASA Space plane (good discussion here: http://books.google.com/books?id=UaUGpW8M_KMC&pg=PA52#v=onep...) which talked about these engines 20 years ago. It would be super awesome for them to add another voice to the space 'race' but I'm suspicious about ideas that keep coming up and keep not actually coming out. That pattern usually means there is a 'gotcha' in there somewhere that isn't obvious on the surface.
How does one go about starting a space startup? A lot of YC companies are tech companies where one can go into Ruby on Rails or Java, crank something out with virtually zero capital, get the hockey stick growth and then it's a company but with space startups this definitely isn't the case. What would I need to convince investors?
You can start making money once you can get a customer's payload into low earth orbit. You want to achieve this initial revenue as soon as possible, by making the simplest orbit-capable rocket you possibly can, which would be a 2-stage (probably non-reusable) rocket with 1 engine per stage. An additional trade-off you can make if your company only wants to carry cargo, not people, is you could use solid instead of liquid fuel to simplify your rocket at the expense of danger.
I would start by planning your rocket architecture and your series of equipment builds, ground tests, and test flights, and leaving plenty of margin for when things inevitably go wrong (SpaceX's first 3 launches failed, so I wouldn't assume you yourself can do any better than 3 failed launches before your first success). Plan out the total cost of all of these builds and tests (including healthy (2X?) margin on the cost), and plan how much revenue you can generate once you start having paying customers. Expect to self-fund most of your initial builds and tests, since I'd guess investors won't believe in you until you've at least built a working engine. Also always apply to any possible government-backed competitions or incentive programs that can provide grant or debt-based financing.
- First gen: NASA, governments
- Second gen: Lockheed, Boeing, Raytheon, General Dynamics etc. as contractors
- Third gen: SpaceX, Orbital, Virgin Galactic as private companies
- The first gen was NASA and their subcontractors Boeing, Lockheed, Rocketdyne,
and other military contractors.
- The second gen arrived with 'Star Wars' and the need to put lots of
things in orbit, Rotary Rocket, the DC-X, and a host of other
Single-stage-to-orbit companies.
- The third stage is SpaceX, Virgin Galactic, Blue Origin, Armadillo, Etc.
Their explanation of why aerospikes aren't used isn't very convincing.. ie: that they ere worked on in 1969; that nasa already has old rockets in stock; etc.
There have been new rockets since 1969, yet they didn't include an aerospike in the design.
Does anyone know: Is this just an experimental idea that hasn't been tested? Or why aren't these on every new rocket design in the past 40 years?
I mean, the article makes it sound like this is an easy win -- more efficient at lower altitudes, and only slightly less efficient at higher altitudes. Makes me think they are leaving something big out of the article.
> Makes me think they are leaving something big out of the article.
I'm certainly not leaving anything out on purpose!
Speculating, though, I imagine it's a question of risk versus reward. There have definitely been advances in rocket designs since the 1960s—the RS-25 is a great example of a more modern high-efficiency, high-performance design (the MSFC propulsion engineers I interviewed a couple of years ago for my F-1 piece likened the RS-25 to a Ferrari, while the F-1 is more like a giant Mack truck).
But developing rocket engines has until relatively recently been the domain of big aerospace companies on big government contracts, and under those circumstances it's often far more short-term cost efficient to go with the sure thing and either use an existing rocket or design one with a conventional bell nozzle.
Rocketdyne in fact proposed an annular aerospike engine for the space shuttle when the program was in early development, but the technology wasn't considered mature and the RS-25 was designed instead.
R&D funding for rocketry has been very sparse, and large scale rocketry has consistently been extremely risk averse. Because of that there have only been a few different rocket engine designs which have been advanced towards production suitable for use on orbital launch vehicles. In the US, for example, there was a period of development on LOX/Kerosene engines in the US during the Apollo program but then the Hydrogen fad came along with the Shuttle program and that largely stopped until SpaceX came along. The SSME, RS-68, and SpaceX's engines are the only rocket engines with more than 500 kN of thrust that have been developed in the US in decades. That gives you a sense of how sparse the development landscape for rocket engines has been.
We simply have not explored much of the design space for rocket engines as of yet. We haven't even explored many of the most promising propellants (LOX/Methane being one example), let alone most of the rocket engine designs. Pursuing a new engine design and scaling it up to a size suitable for orbital rocketry is typically incredibly expensive and difficult, which is why it has been done so rarely.
Additionally, government backed R&D has often suffered from a bit from "Wile E Coyote" engineering. If a project works on something new and that project fails, or sometimes merely ends, then whatever was being worked on is often abandoned and treated as though it's impossible. Just look at the failure to followup on the DC-X work, despite the program overall being quite successful. Yet now there are several companies who are following up on those design principles (VTVL reusability) such as SpaceX, Blue Origin, and now Firefly. Aerospikes have a lot of potential but also a lot of difficulties, nobody has ever put in sufficient work to figure out whether those difficulties are surmountable.
In theory, aerospike engines are pretty efficient at nearly any altitude. It has to do with the pressure and temperature variations as the rocket travels through the atmosphere. (There are pockets of isothermal regions, or regions where the temperature is the same in the atmopshere, and there are pockets where the temperature varies; therefore the Mach number varies). The atmospheric pressure and temperature affect the flame of the aerospike and act like a "variable" nozzle.
Aerospikes aren't as popular because,
1) they're heavy. more deadweight mass on a launch vehicle is a big no no. By deadweight I mean everything on the launch vehicle that doesn't contain the a) payload b) propellant. Because once you burn out (or run out of propellant), usually that's when you stage (or separate) your payload from the launch vehicle. At that point, the launch vehicle is useless; deadweight.
2) they require a massive amount of cooling: you're basically heating up a piece of metal to launch temperatures during the launch sequence. You have to make sure your "spike" doensn't melt.
3) There is a bunch of research and development into other cheaper alternatives, and we already have cheaper and efficient alternatives. This basically pushed aerospikes to the "novelty" category. I'm sure if there was a big technological "push" for aerospikes I'm sure we could get something that's more efficient but that research and time will cost more than to just use the rockets we have now.
You can shape Laval nozzles to have peak efficiency at a specific altitude/pressure/velocity. If you are committed to multi-stage rockets - and there are many reasons to do this - then you can have a different shaped nozzle for each stage. This can lessen the advantage of an aerospike and make the extra weight and inefficiency more of an issue.
For example, the nozzles on the shuttle's solid boosters were optimized for low atmospheric use, but they were discarded relatively quickly. The nozzles on the shuttle's main engines were most efficient out of the atmosphere.
Aerospikes are rocket nozzles that are very efficient across a wide range of altitudes because at different altitudes you have different pressures and temperatures. Normal rocket engines usually compensate for this with variable geometry nozzles.
Alpha is going to send 500 kg to orbit, while Beta - "which will likely be made up of a number of Alpha bodies in parallel staging" - 1100 kg. Sounds like a less mass-efficient design?
When the big aerospike hoopla over the Regan era NASA Space plane (good discussion here: http://books.google.com/books?id=UaUGpW8M_KMC&pg=PA52#v=onep...) which talked about these engines 20 years ago. It would be super awesome for them to add another voice to the space 'race' but I'm suspicious about ideas that keep coming up and keep not actually coming out. That pattern usually means there is a 'gotcha' in there somewhere that isn't obvious on the surface.