Whether it be social, recreational, or professional, some of what represents me is here. Post a comment, or contact me at should you so desire.

The posts are in reverse chronological order, and are pegged by topic on the links to the left. For more of an introduction, please see the About this site page listed above.

Thursday, 30 July 2015

"Impossible" Rockets? The EM Drive and the Cannae Drive

Welcome back, space fans! Today, we're going to look at a new, experimental, "exotic" type of propulsion, known as a Radio Frequency Resonant Cavity thruster, electromagnetic thruster, or RF/EM drive, for short. 

These thrusters have been making news, for better or for worse, as "impossible" rocket thrusters that could get us to the far reaches of the Solar System incredibly quickly AND apparently will do so without fuel.

In today's post, we will explore a little of what this means, what is true, what is not, and why this is important.

Before we begin, I'll just say that this post is not about ion thrusters. This type of propulsion system was first launched in 1964, routinely used in maintaining the orbits of military and commercial satellites in the 1970s, and reinvigorated for deep-space missions including NASA's Deep Space 1, Japan's Hayabusa, Europe's SMART-1, and NASA's Dawn mission. 

Ion thrusters work by ionizing (charging) particles of a gas (such as xenon) and using magnetic fields to accelerate the particles away from the spacecraft, producing thrust in the opposite direction.

In the above diagram, electrons and the propellant are injected into the chamber. The propellant is charged (ionized) by losing or gaining electrons. Magnets along the chamber produce magnetic fields which accelerate the particles outside of the chamber, producing thrust. Additionally, electrons (negatively charged) are released behind the craft so that the protons (positively charged) do not create an imbalance in the space environment, as this could cause problems for the spacecraft.

Rocket thrust can be very simply thought of as just a measure of how much and how fast you throw something behind you. The more you throw, the faster you go!

Ion thrusters have been well-proven and have so far worked well in space missions. They produce low amounts of thrust (because single particles are very low-mass) but this can add up over time, using low-mass fuel, theoretically achieving much higher top speeds than using a traditional chemical rocket. 

Contrary to the above, the RF drives, specifically the EM Drive and Cannae drive, claim to operate without the use of propellant. What is more interesting is that no one is sure the drives work and, if they do, no one is able to explain why or how! This has led to some rather suspect journalism and some sensational news stories.

The Cannae Drive
There have been numerous articles written about the "impossible" rockets that can "get us to the Moon in four hours" instead of days and all this hope, and hype, have been confusing a lot of people.

Now, I found this really excellent review of what we do know about the thrusters, and you can read it here. It also includes a list of sources at the end and was a refreshing find after scouring the internet for such information, myself. I should point out that this review is 3 months old and recent statements made in more recent articles are more confident about the results. However, as of yet, no peer-reviewed paper has been published, and while I am very hopeful, I am skeptical.

To summarize the review, basically the EM Drive has been tested at numerous locations, and an independent team from China even made their own, producing similar results. The Cannae drive has only been independently tested at NASA's Johnson Space Center, (JSC).
All of the tests reveal that a very small amount of thrust has been produced, but the inventors, test scientists/engineers, and scientific community cannot verify that the thruster itself is even producing the thrust, and even if it is, how it is doing so. There have been theories as exotic as bouncing microwaves off the cavity chamber, to possibly pulling in super-tiny particles from higher dimensions and thrusting them out the back. Many of the news stories covering these thrusters claim they have "violated the laws of physics" but that's not yet proven to be true. The fact is, no one understands how the thrusters work, if they do, and until we do, we cannot verify exactly what laws of physics are being broken or adhered to.

When I interned at JSC, I overheard numerous discussions over these drives. The engineers wanted to create tests which could more definitively and accurately prove that the drives were working. However, no one could agree on how the drives worked, even in theory. Without this knowledge, it was very difficult to account for other variables which could be affecting the tests. While the process of testing is very involved, it reminds me of the Improbability Drive from The Hitchhiker's Guide to the Galaxy that could only work when someone asked the drive itself to figure out how it worked.

So far, these thrusters are still in the testing stage. It is very possible that the drives do not work at all and that their results are due to errors in the test or the measurements. However, it is also possible that the drives do work and that the way they work could change our understanding of physics.

Traditional rockets work under Newtonian mechanics (the more you throw, the faster you go) using large, controlled explosions to create thrust. These drives, and others like it, are attempts at working under Quantum mechanical principles. Not warp drive (bending space and time, although that is being worked on), but by other means. I personally favour the idea that it could be possible to pull in small particles from "higher dimensions" and thrust them out the back, which would appear to be propellant-less (as you put no propellant in), but would not actually be so. I favour this option because there have been numerous issues with quantum mechanics and my, albeit limited, understanding of it leads me to believe that subatomic particles may lose/gain energy, dropping in and out of our observable universe. 

Earlier in the summer, some very good friends of mine and I had a lengthy, involved, animated discussion about these thrusters. We discussed different possibilities for how they may work and what it may mean. The reason behind all the excitement and controversy concerning these thrusters is that they could open up new opportunities. Propellant-less vehicles could possibly provide a more environmentally-friendly alternative to the vehicles we use today. For space travel, spacecrafts using these drives may be capable of great things, including faster travel to the Moon and beyond, and could being new opportunities for science and exploration.

The RF thruster is a very interesting, and possibly exciting, development in propulsion technology. Rather than understanding the physics and then creating an engine which profits from it, these thrusters are coming at it from the other side, producing results and then trying to understand why. If successful, the drive could not only open new opportunities for propulsion but expand our knowledge of physics. If the thrusters are not successful, understanding why will be just as important and should help in making new discoveries in the future!

So, when you hear about these thrusters in the news, be excited, but skeptical, as all good scientists should be!

Thanks for reading!

1 comment: