The following story is of interest as it challenges some longstanding laws of physics. It should be remembered that a published paper does not conclusively prove or disprove anything, but it does put it out there for the science community to scrutinize.
In 1687, Sir Isaac Newton published three laws of motion that formed the foundation for classical mechanics. Over the intervening three centuries, those laws have held true.
The EmDrive violates Newton’s third law, which states that for every action, there is an equal and opposing reaction.. This is why jet engines generate thrust: As the engine expels hot gases backward, the plane moves forward.
The EmDrive doesn’t expel anything at all, and isiniolationof Newton’s third law. If the EmDrive moves forward without expelling anything out the back, then there’s no opposing force to explain the thrust. It’s a bit like arguing that a person inside a car could propel it forward by repeatedly hitting the steering wheel, or that the crew of a spaceship could fly the craft to their destination simply by pushing on the walls.
WHAT’S AN EMDRIVE?
First proposed nearly 20 years ago by British scientist Roger Shawyer, this incarnation of the EmDrive has been developed and tested by engineers at NASA’s Advanced Propulsion Physics Research Laboratory, informally known as Eagleworks.
Put simply, the Eagleworks EmDrive generates thrust by bouncing around electromagnetic energy (in this case, microwave photons) in a closed, cone-shaped chamber. As those photons collide with the chamber’s walls, they somehow propel the device forward, despite the fact that nothing is released from the chamber. By contrast, ion drives now in use on some NASA spacecraft create thrust by ionizing a propellant, often xenon gas, and shooting out beams of charged atoms.
What this means, if the EmDrive withstands further scrutiny, is that future vehicles could hurtle through space without needing to carry literal tons of propellant. In space travel, staying light is crucial for fast and cost-effective trips over long distances.
the NASA team behind the EmDrive has published the results of their experiments in a peer-reviewed journal. While peer review doesn’t guarantee that a finding or observation is valid, it does indicate that at least a few independent scientists looked over the experimental setup, results, and interpretation and found it all to be reasonable.
In this paper, the team describes how they tested the EmDrive in a near vacuum, similar to what it would encounter in space. Scientists placed the engine on a device called a torsion pendulum, fired it up, and determined how much thrust it generated based on how much it moved. Turns out, the EmDrive is capable of producing 1.2 millinewtons per kilowatt of energy, according to the authors’ estimates.
That’s not a lot of thrust compared to more traditional engines, but it’s far from insignificant considering the completely fuel-free setup. And to put that in perspective, light sails and other related technologies—which are propelled by the push of photons—only generate a fraction of that thrust, between 3.33 and 6.67 micronewtons per kilowatt.
Before now, one of the major criticisms about the EmDrive is that it warmed up while activated, which some scientists suggested could heat the surrounding air and generate thrust. Testing the device in a vacuum resolved some of that criticism, though there are still loads of caveats that need addressing.
A vacuum test campaign that used an updated integrated test article and optimized torsion pendulum layout was completed. The test campaign consisted of a forward thrust element that included performing testing at ambient pressure to establish and confirm good tuning, as well as subsequent power scans at 40, 60, and 80 W, with three thrust runs performed at each power setting for a total of nine runs at vacuum. The test campaign consisted of a reverse thrust element that mirrored the forward thrust element. The test campaign included a null thrust test effort of three tests performed at vacuum at 80 W to try and identify any mundane sources of impulsive thrust; none were identified. Thrust data from forward, reverse, and null suggested that the system was consistently performing at which was very close to the average impulsive performance measured in air. A number of error sources were considered and discussed. Although thermal shift was addressed to a degree with this test campaign, future testing efforts should seek to develop testing approaches that are immune to CG shifts from thermal expansion. As indicated in Sec. ,II.C.8, a modified Cavendish balance approach could be employed to definitively rule out thermal. Although this test campaign was not focused on optimizing performance and was more an exercise in existence proof, it is still useful to put the observed thrust-to-power figure of in context. The current state-of–the-art thrust to power for a Hall thruster is on the order of . This is an order of magnitude higher than the test article evaluated during the course of this vacuum campaign; however, for missions with very large delta-v requirements, having a propellant consumption rate of zero could offset the higher power requirements. The performance parameter is over two orders of magnitude higher than other forms of “zero-propellant” propulsion, such as light sails, laser propulsion, and photon rockets having thrust-to-power levels in the (or ) range.