Expert: Ray Wilkinson - 2/9/2009

Question
I am currently doing some conceptual designs, which could replace the current propulsion systems for aircrafts. Using a solar power station,it is possible to transmit microwave power to Earth. However, I am thinking that if it is possible to transmit miocrowave power from a geostationary satellite to aircrafts and then using rectenna on the aircraft to get around 2Mw of power. The main concern, of course is the antenna sizing. Do you think that this idea can work or will work? If yes, what do you think about the antenna sizing? Is it possible to set an atenna on the aircraft? What about the aerodynamics of the aircraft?
I appreciate all your time and effort in answering my questions.

With all respect,

Cyrus

Answer
Hi Cyrus

This is probably one of the most unusual questions I've ever received, and an interesting concept.

There are a few examples of large antennae on aircraft, especially for military surveillance - the Boeing E3 Sentry being one of the most obvious, although there's also a Saab 340 with an Ericsson radar antenna on top - check out http://en.wikipedia.org/wiki/Airborne_Warning_And_Control_System So from an aerodynamic point of view, this is probably not a major issue. I'm not an electronics or systems engineer, so I can't advise on antenna sizing, sorry.

What would be of major concern is the prospect of beaming a couple of megawatts of microwave power onto an aircraft full of people, from two respects. Firstly, and most obviously, the effect on the occupants themselves. Aircraft skins are thin aluminium alloy (typically around 2mm) and increasingly of composites (up to maybe 5mm thick. Secondly, though, the EMC issue might be a problem. Aircraft contain several miles of cable, and the avionics don't take kindly to being irradiated with powerful sources such as you suggest. I think there would be a big problem protecting the avionics and their interconnections from the microwaves. In the 1980s an RAF Tornado was lost because it flew through the radio waves from the Radio Free Europe transmitter broadcasting propaganda into East Germany. The cause was determined to be electrical interference from the powerful radio waves.

What about any microwave energy that misses the aircraft? Can you guarantee that the beam will always stay focused within the confines of the aircraft, and that nothing will pass by and reach the ground? The Failure Modes and Effects Analysis would make interesting reading!