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Mr Monkeybat

Rectenna Powered Airbreathing VASIMR Spaceplane

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I was reading an article about space based solar power and it got me thinking how useful wireless power could be for planes. So how plausible do you think the title of this post is? Ground stations connected to the grid along the launch path from the space port transmit wireless power to a microwave rectennas in the wings. I tsucks in air to ionise into plasma for tyhe first stage up to about mach 6 in the upper atmosphere then it switches to its own tanks for reaction mass to propel it to orbit still powered by microwaves from the ground stations. Not needing any fuel in the atmosphere and need no oxidizer and having the high impulse of VASIMR to orbit it should have a higher payload fraction than any other SSTO proposal out there.

 

Or more modestly even ordinary commercial flights spend allot of their fuel lifting fuel, but with rectennas in their wings they can carry no fuel and run electric fans instead, or an air breathing VASIMR for high speed planes. If covering all the major flight paths with Magnetron ground stations is still less infrastructure intensive than roads or railway lines or you can use those space planes to put up space based solar powered satellite transmitters.

 

The best microwave magnetrons and transmitters are over 90% efficient so what are the major obstacles?

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Magnetrons and transmitters can be as efficient as you wish, but propagation losses of radio frequencies render any long distance delivery unuseable.

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it all boils down to power density.

this has been achieved with lasers due to low loss. these were powerful lasers and a very small craft (size of tin can).

what it boils down to:

how well can you focus the transmission at variable distances

how efficient is the antennae

how much of the load do you lose due to atmospheric conditions

 

lasers are a much more economical alternative but even they have problems with light scatter over long distances. this is the reason that you don't really see long distance laser weapons. they have a fairly short effective range and are vulnerable to weather conditions.

i will not say that you cannot do it but i will say there will be loss in the system and it will be great.

 

masers are getting much better. i wonder if this is a possibility to decrease some of the loss. a second laser could be used to probe the atmosphere and control adaptive optics for the maser but this is just speculation.

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Just a thought. Doesn't the definition of "spaceplane" rather rule out "air breathing"?

In space, no one can hear you complain about the lack of air.

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Did you 2 read the whole post or just the title?

 

What power? How?

The wikipedia definition of a rectenna is:

"A rectenna is a rectifying antenna, a special type of antenna that is used to convert microwave energy into direct current electricity. They are used in wireless power transmission systems that transmit power by radio waves."

 

So the power is any ground based power station via ordinary electricity pylons. And if it can reduce the cost of putting things into space enough Space based solar power transmitters.

 

Just a thought. Doesn't the definition of "spaceplane" rather rule out "air breathing"?

In space, no one can hear you complain about the lack of air.

 

The idea of a space plane is to make getting from the surface of the Earth to orbit and back easier. For example the plan of Skylon has an "air breathing rocket engine" which makes use of atmospheric oxygen until it reaches mach 6 in the upper atmosphere when it switches to its own oxygen tanks which are smaller than if it had to rely on its tanks from ground level. Instead of using the oxygen I just want to use the atmosphere as reaction mass in a VASIMR type plasma engine until it reaches its top speed in the upper atmosphere when it switches to on board tanks, if you have a better term for this than "air breathing" I am all ears.

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I did read the post, and that's exactly why I ask and re-ask:

What power? How?

which, because engineering is all about figures, means:

How much power do you need? How do you transmit that much mower?

and also: how much thrust do you need, how much does the Vasimr provide?

As a side question: what sort of ions can the Vasimr use? Does it accept oxygen?

 

To be clearer, your suggestion fails at this. But I had preferred to formulate it as a question.


In space, no one can hear you complain about the lack of air.

 

:)


Just a thought. Doesn't the definition of "spaceplane" rather rule out "air breathing"?

 

Many attempts want to breathe air when at "low" speed (for a launcher) and altitude, then switch to a normal rocket. I dislike them all, because

(1) They cumulate several technologies, hence cumulate the worries

(2) A medium rocket weighs 600t at lift-off, an A380 400t. All wheeled and winged attempts need to be huge hence heavy, take giant runways, possibly fly very fast at take-off with all associated drawbacks.

(3) The speed they bring is small! Mach 6 is only 2km/s, launching just to low-Earth orbit needs like 9km/s. The remaining 7km/s are uncomfortably much for a single rocket stage, even more so if the air-breathing stage isn't separated, while two-stage rockets reach Leo easily.

(4) The commercial business is Geosynchronous transfer orbit (or even geosynchronous orbit). 2.5km/s aren't attainable by an airbreathing plus a rocket stage, while several launchers do it in two stages. Reusing the lower stage will work with standard rockets.

(5) Imagine the airbreathed 2km/s come for completely free: this gains only a factor of 2 on the launching mass. Launch costs result from complexity in design and operation, not from kerosene amounts. Rockets can't afford the same development effort as airliners.

(6) But reusing an already developed aircraft as a carrier is more sensible. Only for a small launcher, with a small gain, the interesting part being to launch from the Equator without paying a spaceport. The tiny Pegasus already needed a B-52; a MiG-21, F-4 Phantom or SR-71 would carry nothing.

 

I understand Skylon as a technically very interesting attempt at a faster airliner, disguised as a launcher because Esa is only a space agency as opposed to Nasa. Presently, their take-off speed bans them from commercial airports and airlines.

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I have not done that much research yet, it was just a thought I had the other day. My web searches for rectenna etc powered aircraft did not bring up many previous examples. But today I stumbled upon these people called Escape Dynamics working on a very similar idea. They dont mention using the atmosphere for reaction mass though and their website does not seem have the kind of details and figures that would satisfy Enthalpy, or me for that matter.

http://escapedynamics.com/

http://singularityhub.com/2014/05/11/escape-dynamics-aims-to-eliminate-single-use-rockets-in-space-flight/

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Take an engine that accelerates air from 2000m/s to 3000m/s (a Vasimr is bad for that). At 20% efficiency, audacious incoming 100MW treat 8kg/s air. This pushes 8kN. Without any acceleration nor climbing, just from overoptimistic lift-to-drag = 5, it lets fly a 4t aircraft, oh good.

 

Just for the landmark, an RD-171 rocket engine

http://www.lpre.de/energomash/RD-170/index.htm

burns 2393kg/s of propellants, of which 659kg/s (more than one bathtub per second) are kerosene and the rest oxygen, so the thermal power (producing much CO) is around 23GW or 17 nuclear power plants.

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