Aerospike Engines - Why Aren't We Using them Now?

We Don't Do Vegetables said:
My sabre engine design had the single most complicated launch profile of any vehicle I'd ever designed in the program though. I can't imagine how difficult an actual one would be for actual pilots. Basically you have to accelerate to absurd speeds in atmosphere, to the point where you are stressing the limits of the vehicle, in order to build as much velocity as humanly possible using the highly efficient airbreathing mode. To altitudes where there's barely enough air for the engines to even function, but at speeds such that the craft is burning up even in the thin atmosphere, similiar to reentry.

Then you turn on the rocket mode, and try to point nose up as much as possible to build enough vertical momentum to get you into orbit without losing that horizontal momentum and coming crashing to the ground. Bearing in mind that it is extremely difficult to maneuver a vehicle like that under such high aerodynamic stress. It's a very difficult needle to thread.

And it would be much more difficult in Earths atmosphere actually, KSP makes kind of goes easy on your and gives the home planet a weaker atmosphere and weaker gravity than Earth. LEO on KSP takes a speed of about 3500 m/s to get into, whereas on Earth it takes about 7000-8000 m/s. That extra 4000 is a bitch to get. The game became orders of magnitude more difficult when I installed a mod that gave the home planet similiar parameters as Earth.
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Looks like REL has two serious heavyweights Rolls Royce and Boeing on board, the precooler is just mental. Cooling an airstream at 1000C down to -150C in less than 1/100th of a second is just incredible.

REL is developing what it calls the Sabre engine. This power plant is designed to push a vehicle from a standing start all the way to orbit in a single step.

It would work like a conventional jet engine up to about Mach 5.5 (5.5 times the speed of sound) before then transitioning to a rocket mode for the rest of the ascent.

Key technologies include a compact pre-cooler heat-exchanger that can take an incoming airstream of over 1,000C and cool it to -150C in less than 1/100th of a second. This would permit Sabre to use oxygen direct from the atmosphere for combustion instead of carrying it in a tank with the weight penalty that implies.

Although Sabre is usually talked about in the context of an orbiting spaceplane, it could also be fitted to a vehicle that flies at very high speed from point to point on the Earth's surface.

This is an application that clearly interests Boeing, whose investment arm, HorizonX Ventures, is driving the tie-up in what is its first investment in a UK-based company.

"As Reaction Engines unlocks advanced propulsion that could change the future of air and space travel, we expect to leverage their revolutionary technology to support Boeing's pursuit of hypersonic flight," said HorizonX vice president, Steve Nordlund.
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https://www.bbc.co.uk/news/science-environment-43732035
 
We Don't Do Vegetables said:
My sabre engine design had the single most complicated launch profile of any vehicle I'd ever designed in the program though. I can't imagine how difficult an actual one would be for actual pilots. Basically you have to accelerate to absurd speeds in atmosphere, to the point where you are stressing the limits of the vehicle, in order to build as much velocity as humanly possible using the highly efficient airbreathing mode. To altitudes where there's barely enough air for the engines to even function, but at speeds such that the craft is burning up even in the thin atmosphere, similiar to reentry.

Then you turn on the rocket mode, and try to point nose up as much as possible to build enough vertical momentum to get you into orbit without losing that horizontal momentum and coming crashing to the ground. Bearing in mind that it is extremely difficult to maneuver a vehicle like that under such high aerodynamic stress. It's a very difficult needle to thread.

And it would be much more difficult in Earths atmosphere actually, KSP makes kind of goes easy on your and gives the home planet a weaker atmosphere and weaker gravity than Earth. LEO on KSP takes a speed of about 3500 m/s to get into, whereas on Earth it takes about 7000-8000 m/s. That extra 4000 is a bitch to get. The game became orders of magnitude more difficult when I installed a mod that gave the home planet similiar parameters as Earth.
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It is not intended for manned flight for the foreseeable future, maybe later?
 
Havana Moon said:
Looks like REL has two serious heavyweights Rolls Royce and Boeing on board, the precooler is just mental. Cooling an airstream at 1000C down to -150C in less than 1/100th of a second is just incredible.



https://www.bbc.co.uk/news/science-environment-43732035
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Crap I didn't realize that they needed it at cryogenic temperatures! Yeah that makes things a ton harder. They're basically trying to make an airbreathing engine with rocket type parameters.
 
Havana Moon said:
It is not intended for manned flight for the foreseeable future, maybe later?
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Manned flight would probably almost always be automated in practice. But they'd still have to learn the entire flight profile by heart ofc. For a first time SSTO, yes, I imagine they would go with automated launch. Just to save on all the weight they'd otherwise have supporting the humans.
 
I reinstalled KSP with realism overhaul (which adds a bunch of real life engines and fuels and realistic parameters for them), and then threw together an aerospike SSTO, based on the XRS-2200 linear aerospike engine from the X-33.

DQZl4WI.jpg


Looks kind of goofy but it works pretty well. Way simpler than my SABRE based SSTO. And it still has a bunch of Delta V left so it can probably carry quite a load (have no calculated exactly how much). I think I'll try and program kOS to launch this and retrieve it in an automated fashion, then I can put together a refueling depot and orbital NERVA nuclear engine based interplanetary "tug", and carry out all those interplanetary missions I had wanted too in the past.
 
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