is a good ‘old fashioned ion drive, good enough?
It is good enough that we use it. They have a reasonable fuel economy, as your spacecraft doesn't have to be made of mostly fuel, and a high enough thrust that your orbit can be significantly altered within a couple of months.
The first three of your drives are operating on known physics, which makes it possible to make some statements about them. For instance, none of them are suitable for take off and landing. The dipole drive doesn't work within an atmosphere, the quantized inertia drive doesn't have enough thrust to support its own weight, and the thermonuclear micro bomb drive pollutes very significantly. For use in space, none of these are in theory a game stopper.
Each of them also have traditional equivalents, that come without some of their disadvantages, and are emerging technologies that may bring significant changes to space travel.
- A dipole drive can be compared to a solar sail, which does not require power.
- A quantized inertia drive can be compared to an ion drive, which offers much larger thrust.
- A micro bomb drive can be compared to a nuclear thermal rocket, which does not scatter large amounts of nuclear debris.
The next four drives are harder to gauge, as they rely on currently unknown physics. Or rather, they say that if certain effects exist, we know of a way to use them for propulsion. But we have yet to observe these effect.
Consider these two possibilities:
- The effects don't exist, or are too small to be used in any meaningful way.
- The effects do exist, and are so important that they change everything about how we do space travel.
Notice how they are almost the complete opposite of each other, and we can't rule out any of them. They may not have any roots in reality at all, or future readers on their weekend tour to Saturn in a pitch drive ship will laugh at this post that considers ion drives "practical". And anything in betwen.