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Electric Space Plane Propulsion Systems

Posted by: GrumpyDog22 - Mon Apr 01, 2013 11:22 pm
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Electric Space Plane Propulsion Systems 
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Post Electric Space Plane Propulsion Systems   Posted on: Mon Apr 01, 2013 11:22 pm
Currently there aren't a lot of electric propulsion systems, and few could feasibly power a space plane, or anything else that isn't in the vacuum of space(ion drive). My idea was to have an electric jet engine, heated by an induction coil, with a titanium/ceramic rod in the center. The coil super heats the metal, which in turn heats the surrounding air being brought in by the intake. The ceramic is infused in the titanium is so the rod doesn't all melt at once, but gives a specific impulse. Coupled with solar panels, a plane equipped with this could be the ultimate "green machine" This is my first post, please give feedback,

Thanks, GrumpyDog


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Post Re: Electric Space Plane Propulsion Systems   Posted on: Thu Apr 11, 2013 6:15 pm
Hi, welcome!

It sounds nice in theory, but the problem is the power requirements. For example, to get a metric tonne of payload to low Earth orbit, you need a delta-v of about 8km/s. That corresponds to a kinetic energy of 1/2 * 1000kg * 8000m/s * 8000m/s = 3.2*10^10 J. Your typical rocket takes about 10 minutes to get into LEO, so you'd need a power output of at least (due to losses, no engine is perfectly efficient) 3.2*10^10 / 600 = 5.3*10^8 W = 530MW.

That's about the power output of the under-construction Desert Sunlight Solar Farm, which weighs considerably more than 1000kg. By comparison, the ISS' big solar wings produce a combined total of about 250kW, which is a factor 2000 too little (and they weigh more than 1000kg together as well, not to mention the aerodynamic drag they'd incur.)

So, in short, you're never going to be able to produce nearly enough electrical power to power your engine. Likewise, storing 32GJ of energy in batteries is going to require a much too heavy bank of them. The idea is nice, but unfortunately, the laws of physics prohibit it :-(.

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Post Re: Electric Space Plane Propulsion Systems   Posted on: Thu Apr 11, 2013 6:47 pm
Yup. The closest we have gotten has been some of the radiothermal (nuclear) jet concepts, where the energy to heat and expand the intake gas came from fission decay.

That obviously isn't... practical these days.


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Post Re: Electric Space Plane Propulsion Systems   Posted on: Thu Apr 11, 2013 7:38 pm
If the guys at MIT have got their sums right the EHD toy might eventually become a serious player but as i tend to assume that Lourens has his sums right it might be only when we have viable a broadcast energy system or a huge acreage of spray on efficient solar cells considering the size needed to make it efficient.

http://www.gizmag.com/mit-ionocraft/26908/

Mind you i think it would be quite nice to have huge airships moved by solar powered EHD ion drives which might be one way to make the tech viable. I wonder if this is what JP Aerospace plans to do for propulsion when they get their high altitude airships sorted and in production. I had considered using an inflatable silver mylar Rogallo wing reflecting onto a very thin film or even paint on solar cell with the satellite and ion drive as its counterweight as the final stage of our N-Prize teams entry but as we are still working on the first stage and unlikely to be ready before the competition ends. I thought i would stick this bit out in the public domain as i think as IIRC all the individual bits of this are out of patent and unlikely to be patentable as a whole and it would be nice to see it fly even if i don't profit from it.

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Post Re: Electric Space Plane Propulsion Systems   Posted on: Thu Apr 11, 2013 10:26 pm
I've seen suggestions to use a Solar Thermal powered airship to reach orbit. Perhaps with an afterburner system, trading Isp for thrust, it could work. Or maybe using solar panels and an electrically-enhanced chemical engine.

I doubt you could make it all the way to orbit with it, but if you can get to 4km/s, you can stage there and use a disposable upper stage to put perhaps 200kg in LEO. Not much, but you could get a probe into that, as well as a tank of supplies. If you can make the first stage reusable, to the point where you're essentially refuelling and doing it again, then you've only got the cost of the upper stage, which doesn't have to be much more than a solid rocket stage. Let the payload circularise it's own orbit.


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Post Re: Electric Space Plane Propulsion Systems   Posted on: Fri Apr 12, 2013 1:37 am
Why not beam power? from earth and from space :)

Space
high power laser = low scattering due to thin atmosphere + sunlight(same panel)

Earth Based
Many low energy beams all targeting the ship with a spectrum that is not absorbed by water, or atmosphere - like Laser/H.E.R.F

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Post Re: Electric Space Plane Propulsion Systems   Posted on: Fri Apr 12, 2013 10:30 am
Well yes, that's another possibility. A while back I thought about the idea of using nearspace stations to beam power to launch vehicles - at 40km altitude the horizon is over 700km away, so with a few stations spaced out above the Atlantic you should be able to manage it. If you were good on the targeting, you could possibly do it with just one...


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Post Re: Electric Space Plane Propulsion Systems   Posted on: Sun May 19, 2013 3:03 pm
We don't have any induction coils capable of that kind of output that would last that long. You're basically talking about a Resistor with Heat as a by product. So, it loses a lot of energy turning current into heat inefficiently, then transfering that from the element to the air (Or other reaction mass.)

I was thinking more like a Plasma Torch as a reacive nozzle. My fuel is ANAS, Ammonium Nitrate in Aqueous Solution, or basically dissolved chemical fertilizer. In a dense enough saturation, it's vaporized, and the chemicals react to sustain it, so you don't have to carry the reaction mass, and energy seperately.

That's the other problem with an all electric designs, we don't have the storage media to make a car capable of competing with Gasoline in performance AND range. Now, compound that discrepancy to the point of accellerating a skyscraper to 5 miles per second within 100 miles straight up against gravity, and air resistance. I think we're going to be stuck with Chemical Propellant for generations without a breakthrough. That's going to have to come in the Battery long before we start to design an Engine to work with it.

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