To date, there is no theoretical consensus as to how a resonant cavity can provide for the direct conversion of electrical energy to thrust without the need to expel any propellant.
I love just about anything to do with space. I really wish that I could travel around the universe on an Orville-class starship to visit far-flung star systems, walk on alien planets, and observe wondrous celestial phenomena.
I’m also constantly amazed by the weird and wonderful ideas that people come up with. Take the Interplanetary Transport Network (ITN), for example. When most people think about sending something like a space probe to another planet in our solar system (say, Saturn), they typically consider using a honking big rocket. The problem is that traditional rocket engines require a lot of fuel. One way around this — and to shorten the duration of the mission — is to fly our space probe close to another planet that’s on the way, like Jupiter, and to use a gravitational slingshot effect to accelerate the spacecraft and modify its path.
If you don’t mind how long it takes to reach the target destination, then the Interplanetary Transport Network provides an alternative mechanism. If you take two large bodies in space, like Earth and the moon, for example, then there are five locations called Lagrangian points, or Lagrange points, where a smaller object like a space probe can maintain its position relative to the two larger objects.
Where things really start to become interesting is when you combine chaos theory with three or more bodies, such as planets and other objects forming our solar system. In this case, we can map flight paths between the various Lagrange points, where we can visualize these paths as being tubes in space.
Once we get our space probe to one of the Earth-moon Lagrange points, then — using the Interplanetary Transport Network — it would be possible to transport it almost anywhere in the solar system using very little energy. The downside to this approach is that it could take a long, long time to get there.
But that’s not what I wanted to talk to you about. This column was sparked by my running across developments in NASA’s futuristic EM Drive (also known as the EmDrive), which is based on an RF resonant cavity thruster.
The problem here is that traditional rocket engines are reaction engines that obtain thrust by expelling mass in accordance with Newton’s third law, which can be summarized as, “For every action, there is an equal and opposite reaction.” Most of us think about rockets based on the use of liquid propellants or solid fuel, but even in the case of an ion drive, the engine creates thrust by accelerating and expelling ions.
By comparison, the EmDrive features a microwave cavity that produces thrust from an electromagnetic field inside the cavity. Originally hypothesized by British engineer Roger Shawyer in 2001, the EmDrive did not, at first, gain much traction. Many theoretical physicists say that the device is “impossible” because it appears to violate the laws of physics as they are currently understood.
To date, there is no theoretical consensus as to how a resonant cavity can provide for the direct conversion of electrical energy to thrust without the need to expel any propellant. This made it all the more interesting (or embarrassing, depending on your point of view) when NASA successfully tested an EmDrive in 2014.
One possibility is that the EmDrive is leveraging quantum effects, like using the fleeting electromagnetic waves and virtual particles that pop into and out of existence in the quantum vacuum. While this may sound a tad esoteric, let’s not forget that all sorts of weird and wonderful effects happen at the quantum level, including quantum entanglement and quantum teleportation.
On the one hand, I’m extremely proud of all that we (the human race) have discovered and accomplished. At the end of the day, however, I’m left thinking that we still understand very little compared with all the things there are to know. As usual, the Bard of Avon nailed it in Hamlet, when Hamlet says to Horatio, “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”