Thursday, 14 September 2006

Flying microwave-ovens!

(Slightly post-dated and pseudo-physics heavy) A reaction less, microwave powered drive that that could replace rockets, wheels, wings and rails seems a little too good to be true! I'd normally pass such claims over in a quick and disappointed sigh, given a fairly thorough education in physics and all...

However, it came to my attention in the form of a cover feature in New Scientist (9 Sept 2006), and is the work of the highly respectable Roger Shawyer. Having worked on several military/space industry projects (including an important role consulting for the Galileo Project), his current research is UK government funded and his recent publications have brought big interest form the US and China (while Europe remains disinterested in general).

The reason the concept has such a stigma is that it seems to 'fly in the face' of Newton's ever trusty Third Law: "Every action has an equal and opposite reaction" (i.e. to accelerate an object in one direction you much push off another object which will tend to accelerate in the other direction). However, Newton's laws are outmoded by General and Special Relativity which must be invoked to deal with the microwave photons travelling at near light speed in the experimental apparatus used.
James Clerk Maxwell figured that light should exert a force on any surface it hits way back in 1871 (clever bloke, though this is something most A-level physics teachers will probably still deny in my experience). The trick is that microwaves bouncing end-to-end of an almost cylindrical metal 'cavity' are caused to exert unequal forces on the end surfaces, as the narrower topology of the cavity towards one end restricts them to move slower, imparting less momentum to that narrower cylinder face.
Basically, it all involves such complex physics/mathematics, that the whole concepts tantamount to witch-doctory, even to other microwave engineers (let alone the average Joe), so there are obviously some opponents of it's validity. Shawyer's tabletop size experiments demonstrate a measured force of up to 300 millinewtons (about equivalent of a 30 gram weight) using your standard power 1 Kilowatt microwave generator (as found in your kitchen). This is tiny, but highly useable in the space industry for satellite position for example. Currently half the weight of satellites is 'reaction mass' for the thrusters used to keep the device in a stable orbit until it runs out. With launch cost still around $10'000 per kilogram, this technology could replace all that bulky fuel, saving billions in a few years.
Then there's the prospect of higher efficiency "Emdrive"s: the current technology is highly inefficient; the metal walls of the cavity dissipate the microwave energy off as heat fairly rapidly, before the rays can bounce off more than an average of 50'000 times. Shawyer hopes to use superconducting materials (already commonly used and well studied in particle accelerator magnets) to massively improve this performance within a couple of years, allowing an equivalent apparatus to produce forces strong enough to lift a car (in principle) using the same energy input. In my opinion this should tie in nicely with recent advances towards room temperature supercontuctors.
This is where things become *really* exciting! It doesn't take much imagination to envisage Fifth Element style hover-cars running off hydrogen fuel cells or improved "Bullet Train" style maglev without the overly restrictive need for really expensive tracks. It even makes some of the more fictional seeming 'sci' of Ian M. Banks immediately more plausible: solid, head sized (or smaller), human intelligence (with personality), flying 'drones'! Hence my excitement.
This kind of potential technological revelation takes me back to the heady days of young ‘teenagedom’ when I was convinced I’d work as a scientist to develop FTL (faster than light) travel technology. I’ve long since shrugged off the desperate need for such technology, with the idea of an inevitable, technological Singularity: the product of an isolated Earth, negating the need to “boldly go” (as it’s incorrectly stated) anywhere but the infinetely more interesting future, here! That naustalgic feeling is partly why I anticipate disappointment with this development.
Also, trying to imaging a vehicle *actually* hovering there, with no measurable support seems unrealistic, especially knowing that no energy was being used to actually propel the device (all input energy lost as waste heat)! However, something as simple as a patio widow might seem unintelligible to a person before the common use of glass, let alone video screens/helicopters ("Any sufficiently advanced technology is indistinguishable from magic.") . And no energy need be input to a rope supporting a heavy mass in order that it maintain itself against gravity; there is merely the need for potential energy stored as tension in the rope’s strands. Perhaps that is a better way to view the nature of the force from this drive.

General info links: 1 | 2| 3
(information sorced from New Scientist Magazine hard copy, speculation and interpretation from myself)

1 comment :

  1. I obviously can't comment on the science much, but this is a really nice entry in just your enthusiasm and helpful links (And to see you using that brain before it goes all squidgey) well done.

    ReplyDelete