October 17, 2019

IF IT SOUNDS TOO GOOD TO BE TRUE… Near-infinite specific thrust from drive that ignores physics.

The basic idea of the Helical Drive, according to the author of that link, is simple. Imagine that you have a mass in a cylinder that is oscillating back and forth. Every time the mass hits the end of the cylinder, it will impart some momentum, accelerating it. Because the mass sequentially collides with each end of the cylinder, the net force is zero, and the only outcome is that the cylinder gets a massive headache.

But, what if—you’re going to love this—you could magically increase the size of the mass when it was traveling in one direction and decrease the mass when it was traveling in the other direction? If the velocity of the mass is kept the same, the force imparted at one end would be greater than at the other. You would have a net force: the cylinder would continuously accelerate in one direction.

Now we just have to fill in the magic part: how do we magically change the mass? The answer here is special relativity. If something is moving at close to the speed of light, its mass will increase. Indeed, the closer the object is to the speed of light, the larger its mass.

So, the answer, apparently, is simple. If we use a very strong magnetic field along the length of the cylinder, then alpha particles (helium atoms with the electrons stripped off) will start to corkscrew around the field. An accelerator in one section can accelerate the ions to as close to the speed of light as possible, while in a different section a countering accelerator will slow them back down. At each end, the ions reflect, imparting momentum to the cylinder.

Even better, the energy lost in accelerating the ions can be recovered when you slow them down, so it’s nearly free acceleration.

There’s just one problem:

Even though the author does a very nice simulation, he has left out the fields that do the accelerating. When we accelerate ions using a magnetic or electric field, the ions push back on the field. There is an equal and opposite force exerted on the electrodes and coils that produce the fields, and those just happen to be in the spaceship, too.

Oops.

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