After months of heated debate and leaked documents, NASA’s long-awaited EM Drive paper has finally been peer-reviewed and published. And it shows that the ‘impossible’ propulsion system appears to work. Tests carried out by both NASA and independent researchers confirmed that the drive was able to produce thrust in a vacuum that would allow us to reach the moon in just four hours, Mars in 70 days, and Pluto in just 18 months.
You can read the abstract summary of NASA’s NASA Eagleworks Laboratory paper: Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum. Read here.
The EM Drive, or Electromagnetic Drive, is a propulsion system first proposed by British inventor Roger Shawyer back in 1999 based on the theory of special relativity, electricity converted into microwaves and fired within a truncated cone-shaped closed metal cavity causes the microwave particles to exert more force on the flat surface at the large end of the cone (there is less combined particle momentum at the narrow end due to a reduction in group particle velocity), generating thrust.
In order to minimise the internal Doppler shift (the change in frequency or wavelength of a wave for an observer moving relative to its source), circular polarisation and a phase-locked loop control the microwave input to the thruster, which maximises thrust as it accelerates.
Critics say that according to the Newton’s law of conservation of momentum, EM Drive theory cannot work as in order for a thruster to gain momentum in one direction, a propellant must be expelled in the opposite direction, while the EmDrive is a closed system.
Shawyer claims that following fundamental physics involving the theory of special relativity, the EmDrive does in fact preserve the law of conservation of momentum and energy. Instead of using heavy, inefficient rocket fuel, it bounces microwaves back and forth inside a cone-shaped metal cavity to generate thrust that it could power NASA to Mars in just 70 days.
The NASA release is similar to the paper that was leaked online earlier this month and, most notably, shows that the drive does indeed produce 1.2 millinewtons per kilowatt of thrust in a vacuum:
To put that into perspective, the super-powerful Hall thruster, a type of ion thruster in which the propellant is accelerated by an electric field, generates force of 60 millinewtons per kilowatt, an order of magnitude more than the EM Drive. But the Hall thruster requires propellants, and that extra weight could offset the higher thrust, the team concludes. The Hall-effect thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the ions in the plume.
Light sails on the other hand, which are currently the most popular form of zero-propellant propulsion, only generate force up to 6.67 micronewtons per kilowatt – two orders of magnitude less than NASA’s EM Drive, says the paper.
But the Eagleworks team stress that they were trying to prove whether or not the drive really works, rather than optimiizing performance in the tests, which means the EM Drive could get a lot more efficient with future testing.
The team also offers a hypothesis about how the drive actually works without contradicting the laws of physics: “[The] supporting physics model used to derive a force based on operating conditions in the test article can be categorised as a nonlocal hidden-variable theory, or pilot-wave theory for short.”
Pilot-wave theory is a controversial interpretation of quantum mechanics that differs from th e Copenhagen interpretation of quantum mechanics that states that particles do not have defined locations until they are observed, suggesting that particles do have precise positions at all times, but in order for this to be the case, the world must also be strange in other ways – which is why many physicists have dismissed the idea.
The NASA team suggests pilot-wave theory can help explain how the EM Drive produces thrust without appearing to propel anything in the other direction: “If a medium is capable of supporting acoustic oscillations, this means that the internal constituents were capable of interacting and exchanging momentum,” the team writes.
“If the vacuum is indeed mutable and degradable as was explored, then it might be possible to do/extract work on/from the vacuum, and thereby be possible to push off of the quantum vacuum and preserve the laws of conservation of energy and conservation of momentum.”
Beyond the true-believers of the NASA team, the world’s scientific community is hugely skeptical: a Motherboard article on the EM Drive, for example, was deleted by the moderators of the popular subreddit r/Physics because they “consider the EM Drive to be unscientific.”
The next step for the EM Drive is for it to be tested in space, which is scheduled to happen in the coming months, with plans to launch the first EM Drive having been made back in September.