An anonymous reader writes: NASA has tested an electrical space drive what uses no propellant – and found it works even when it is designed not to.
The system uses microwave energy reflected around a specially designed chamber to produce thrust. The idea first appeared as the Emdrive by British inventor Roger Shawyer in 2001, who designed a system which he showed could produce power in this way. But critics scoffed, saying it would violate the laws of momentum.
The EmDrive generates thrust by using the properties of radiation pressure. An electromagnetic wave has a small amount of momentum which, when it hits a reflector, can translate that into thrust, Shawyer found, and this can be used to power flight in the near-frictionless environment of space.
The idea languished, but a decade later the Chinese Academy of Sciences published a paper saying that it too had built an EmDrive-like which, when fed 2.5kW, generated 720mN of thrust. This got the attention of NASA, which in 2013 commissioned a series of tests on the drive and got some surprising results.
In an eight-day trial held by US engineering firm Cannae the researchers found that by using a reflective chamber similar to that proposed by Shawyer the team was able to use solely electrical inputs to generate 30-50 micro-Newtons of thrust.
"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," the team reported in a paper to the 50th Joint Propulsion Conference in Cleveland, Ohio, at the end of July.
Being scientists, the Cannae team also built a second chamber which was designed not to work as a control mechanism, or a "null test article". To their surprise they found that this control engine also generated thrust, although nowhere near as much as the first design.
The system isn’t perfect – it requires manual control of the microwave emissions to get the best results, but the Cannae team said that an automatic controller was under development and could be used in a scaled-up system.
If a larger-scale engine works in the same way as the test system the design could revolutionize space travel as we know it. Potentially it could get us to Mars in weeks rather than the nine months or so currently projected.
The weight and cost of fuel needed for rocket motors is one of the key limiting factors in space travel – simply getting one pound of fuel into orbit costs thousands of dollars in launch costs. Spacecraft then need to carry enough fuel to accelerate to their target, and a similar amount to slow down at the other end of the trip, but a fuel-less drive system like EmDrive changes that equation.
Instead of firing a controlled engine burn to get up to speed, then coasting towards the target and firing rockets again to slow down, the EmDrive could fire constantly until the midpoint of the mission, powered by solar power cells. At the midway point the engine can then be rotated and fired again constantly to slow down the spacecraft.
The challenge now is to scale a system like the EmDrive up to full size and see exactly how much thrust can be generated within a given solar power input envelope. Hopefully it won't take NASA another 12 years to try out the system.
