Chinese scientists appear to have validated a propellentless space propulsion technology previously branded as impossible. Based on earlier British research, it is averred that the EmDrive concept provides sustained thrust at low cost and weight, but this has yet to be accepted even as a workable theory by the wider propulsion community.Either this is a massive fraud, or it will have major impact on satellite launches.
The EmDrive story started in 2001 when engineer Roger Shawyer set up Satellite Propulsion Research (SPR) to exploit his new concept in electrical propulsion. He was helped by a modest grant from the U.K.'s now defunct Trade and Industry Department.
Space propulsion relies on Newton's laws of motion: propellant is ejected backward at high velocity, and the craft is pushed forward with equal and opposite momentum. Even with high exhaust velocity, such as ion drives ejecting particles at 30 km per second (more than 62,000 mph), the mass of propellant is a limiting factor.
Shawyer's EmDrive does not have any exhaust. It consists of a tuned cavity shaped like a truncated cone into which resonating microwaves are channeled. Like other radiation, these exert a tiny pressure when reflected off a surface. According to Shawyer, the pressure exerted on the large end of the cavity is greater than the pressure on the small end, producing a net thrust.
The result , 720 mN, is just 2.5 oz. of thrust, but satellites often work with less. Boeing's advanced XIPS thruster , which fires out Xenon ions at high speed, achieves 165 mN of thrust from 4.5 lb. It weighs 35 lb., more than an equivalent EmDrive, and the propellant for prolonged operation can weigh much more.
XIPS and EmDrive can both run off solar electricity, but the EmDrive never runs out of propellant. Propellant to maintain satellite position is a major weight contribution; Shawyer suggests that the EmDrive could halve the cost of geostationary satellites .
For interplanetary probes, it could be revolutionary, cutting times and costs by something like an order of magnitude.
I'd wait for more independent verification though. The Chinese seem to be playing their results pretty close to the vest, which in and of itself is suspicious.