This has been causing a stir lately. See:
http://www.emdrive.com/
http://www.wired.com/dangerroom/2009/10/impossible-drive-designers-dream-flying-cars-stealth-missiles/
QUOTE from website:
A New Concept in Spacecraft Propulsion
Satellite Propulsion Research Ltd (SPR Ltd) a small UK based company,
has demonstrated a remarkable new space propulsion technology. The
company has successfully tested both an experimental thruster and a
demonstrator engine which use patented microwave technology to
convert electrical energy directly into thrust. No propellant is used
in the conversion process. Thrust is produced by the amplification of
the radiation pressure of an electromagnetic wave propagated through
a resonant waveguide assembly.
- Jed
