Aug 01 2014

NASA Tests EM Drive

I’m skeptical. I know, you’re shocked. When you recover, take a look at this article about NASA “validating” an allegedly impossible drive.

The bottom line is that I just don’t believe it. I could be wrong. I hope I’m wrong. I don’t necessarily think the results of NASA’s test are untrue, just that I don’t think they have “validated” that the propellantless drive is what proponents say it is.

My reaction is identical to the claim made in 2011 that a team of researchers found that neutrinos travel faster than light. I didn’t believe those results either. The researchers were very careful, they rigorously reviewed every aspect of their experiment, and only announced the results when they were confident they ruled out all error. The physics community didn’t believe it, but they did their due diligence. After further analysis, it was found that the results were an error – an artifact introduced in the experimental setup. Initial skepticism was vindicated.

The claims made for a machine that can provide thrust without propellant is as unlikely and at variance with the laws of physics as neutrinos traveling faster than light or free energy machines. Sure, it’s always possible that our understanding of the universe is incomplete in a way that allows for one of these phenomena to be true, but our current understanding calls for extreme initial skepticism. Such a stance has a very good history to support it.

At the same time, I wouldn’t invest a dime of my own money in a company claiming to have invented a free energy machine, and I don’t think our taxes should fund such research either. It’s worse than playing the lottery.

Producing thrust without propellant is similar. It seems to violate the conservation of momentum. Conservation laws in physics are among the most reliable and solid of the laws of the universe that we have discovered. Scientists should not idly speculate about violating them.

The idea here is to create a drive that converts energy into thrust without the need for accelerate propellant in the opposite direction. This would transform space travel, and make things like hovercars a reality. Perhaps the biggest limitation of space travel is that you have to carry around your fuel and propellant with you. This means you have to accelerate the fuel and propellant also, and the fuel for accelerating that fuel, etc. Most of the energy spent in getting to orbit is lifting the fuel you need to get into orbit.

For most rockets used today, the fuel is the propellant. There are drives, however, that generate energy to accelerate a separate propellant, such as an ion drive. There are also designs that do not need propellant, such as solar sails or using a laser to push a spaceship. Ram drives are designed to scoop up their propellant as they go (from the thin hydrogen gas in space). Many of these are theoretical technologies or provide very little thrust.

Imagine, however, if we had a device that could turn energy directly into thrust without the need for propellant, by exploiting some exotic feature of physics. That is what some people claim they have developed.

NASA has recently tested one design and published the results in a paper entitled: Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum. In the paper they do not speculate about the physics involved, just test the drive. They found: “Approximately 30-50 micro-Newtons of thrust were recorded from an electric propulsion test article consisting primarily of a radio frequency (RF) resonant cavity excited at approximately 935 megahertz.”

They are correct to term this “anomalous thrust,” which just means they don’t know where it is coming from. They are not concluding it is propellantless thrust or that that their test confirms the speculation of proponents. I also find it highly significant that that anomalous thrust is teeny tiny – 30-50 micro-Newtons. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. So this thrust is 30-50 millionths of a Newton.

It is hard to draw any firm conclusions from such tiny anomalies. The fact that the force is so small means that even very subtle errors in the experimental setup, or unknown factors affecting the measurement, could be sufficient to explain the results. You can’t simply extrapolate from such small effects and assume they will scale up. That is the perpetual mistake of perpetual motion machine claimants – they find tiny anomalies and naively believe they will scale up.

The other possibility is that the anomalous thrust is genuine and is produced by some subtle physical effect, so subtle that this is all you are going to get and it won’t scale up. There may not be more thrust to be had.

Proponents argue that even a tiny thrust is useful in space and over years can provide a significant cumulative acceleration. This, of course, would also provide the ultimate test. If engineers can build a ship using this form of thrust and actually use it to accelerate a probe, that would be impressive evidence. This is similar to my challenge to free energy gurus – call me when you are running your home, or even a large motor, off your device (actually doing work, without any “supplemental” energy source).

For now my attitude toward the NASA test of this alleged propellantless drive is the same as it was toward the faster-than-light neutrinos. I think it is far more likely that this will turn out to be some experimental artifact than a truly new phenomenon. This will need careful independent replication, enough to get the physics community excited, before I will get excited too.

I do sincerely hope that I am wrong. I want my flying car just as much as the next guy.

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