Skylon Spaceplane Design Passes Key Review 136
gbjbaanb writes "A revolutionary UK spaceplane concept has been boosted by the conclusions of an important technical review. Skylon is a design for a spaceplane that uses engines that work as normal jets near the ground and switch to rocket propulsion in the upper atmosphere. The concept means the plane will not have to carry as much fuel and so will not need disposable stages. It is estimated (by its developers) that the Skylon will drop the cost of delivering payloads to orbit from $15,000 per kilo to $1000."
Hate to rain on the hype parade (Score:5, Informative)
This spaceplane is still in the concept phase. They're not even planning to build it until the 2020's. Right now it's all just fund-raising and hype. All this review says is "Well, it COULD work."
In fact, this thing has apparently just the latest version of a spaceplane that has been in the development stage since 1982 (no, that's not a mistake--1982), and has already went through quite a bit of government and private money, with little more to show for it than some concept art and promises. Add to this the fact that they're emphasizing cause-du-jour selling points like "the environmentally-friendly green rocket" in their promotional literature, and I'm a little skeptical.
More power to them if they can build it though. The real first test will come when they're supposed to actually build a test engine this summer. Deliver something to me in the real world that actually works, and you'll get my attention.
Re:PopSci != Tech Breakthrough (Score:5, Informative)
"The 10 or 20 kilometers that you can save by using this kind of design is really a small fraction of the distance to cross"
Distance isn't the problem for getting to orbit, velocity is.
By running as a plane you don't have to burn thrust to support the weight of the craft and fuel, you can accelerate up to Mach 5 (as they plan to) using the atmosphere to support you. That's a truly massive gain, for reference the first stage of the Saturn V got you up to just over mach 6. Now I don't know what percentage of their fuel they burn to get to that speed but to not have to support that weight with thrust for such a long period is a huge gain. Remembering as well that during this phase they are air breathing too which is another massive gain.
Fine you say mach 5 is 1/5th of the way to mach 25. so at best they've saved 20%, better but still not amazing.
Not quite because you get a weird multiplier effect, because (when you are at say mach 5) you have accelerated the fuel you carry to mach 5 so it effectively has more energy that when it was at rest on the ground. If you run the numbers for a multistage rocker you'll find that they can't reach orbit unless you take this effect into account. Trying to find a good source for this, will hopefully reply to this later with said source...
Re:America : Number Four! (Score:4, Informative)
Space planes are not a new idea. The SR-71, while it never flew in space, was still considered by many engineers to be proof that a space plane was possible.
"...NASA couldn't even make the Aerospike work either..."
"After we lost our German scientists, America went back to black powder and cannon to launch rockets."
A gross characterization. Lockheed Martin made aerospike technology workable while developing Venture Star, a canceled successor to the Space Shuttle. They made three aerospike engines but only had the chance to test one of them (successfully) before the cancellation of the X-33 test vehicle. While the engine concept was sound there were budget issues, fuel tank failures, and political pressure to stay with the Space Shuttle.
http://www.aerospaceweb.org/design/aerospike/figures/test02.jpg [aerospaceweb.org]
Instead of pouring tons of cash into a 40 year of design like the Space Shuttle the US is embracing simpler, more affordable rocket technology. Commercial rocket launch companies like SpaceX can do it cheaper than NASA. They have a proven track record and are now building their first heavy class rocket.
For all the Space Shuttle's accomplishments it's initial purpose was to make the cost per pound of cargo cheaper, something it never did.
Re:PopSci != Tech Breakthrough (Score:2, Informative)
You were not entirely wrong and your perfectly right that this is an energy problem.
The fuel would not have "more energy" in the way that it would burn hotter or give more thrust, but I think the point is that it now is flying at mach 5 and does not have to be accelerated from zero.
This is the real reason multistage rockets are so frickin huge, you do not only have to accelerate the payload into orbit but also all the fuel not yet burnt and the oxidizer also. And I think this is your "multiplier effect".
The point is well illustrated by the Saturn V, it spends all of the first stage just to reach mach 6-7, and that stage ALONE is easily heavier than stage 2, 3 and the payload combined.
I have not seen the numbers but would not be surprised if the potential fuel savings with a spacecraft that can accelerate to mach 5 as an airplane would be more like 50-60% and not 20%.