Designs for a device called a microwave thruster, which could power spacecrafts without the need for propellant, have been proposed since 2006. While the engine follows the principles of relativity theory in converting electrical energy into force to produce thrust, it has been dismissed as impossible in practice since it defies the law of conservation of momentum. But a team from NASA has just successfully trialled their own version of the engine, which changes everything.
Several years ago British scientist Roger Shawyer presented his EmDrive microwave thruster engine to the scientific community. It used microwaves bounced off reflectors in a sealed container to produce small amounts of force and thereby achieve propulsion via propellant-free thrust. Its possibilities for long-distance spaceflight were extraordinary, but while it was groundbreaking there was one catch: it defied the law of conservation of momentum and was therefore deemed theoretically flawed. In 2012, scientists in China successfully repeated Shawyer's development, but still most of the scientific community didn't pay much attention to the results.
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Now a team at NASA has tested the Cannae Drive developed by U.S. scientist Guido Fetta. It too is a microwave thruster and it was presented as a successful test at the recent 50th Joint Propulsion Conference in Cleveland, Ohio. The drive produced 30 to 50 micronewtons of thrust, which was decidedly less than the Chinese team's reported 720 millinewtons or Shawyer's 16 to 30 millinewtons. The NASA team's report stated: "Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma." I believe that translates as, "We are not entirely sure why, but it works."
However, if like NASA we choose to focus on the results and not the method for the moment, what could be the implications of a microwave thruster-powered spacecraft? The device is so interesting because it does away with the need for lugging along a fuel supply that is about equivalent in weight to the craft it is propelling. Using solar energy to generate the power to create the microwaves in the first place becomes an option too. This would mean the engine could continue indefinitely, at least until mechanical failure brought it to a halt, though it would also limit the craft's range to proximity to a source. For now, however, NASA's development doesn't even provide enough thrust to propel a peanut through space, so there is still a way to go to scale up to a mission to Mars.
Photos by EmDrive and NASA via Wikimedia Commons