Is it safe to use a coilgun or railgun as an engine inside the solar system?

Question

Given a large iron body and a coilgun or railgun to impart thrust, You can turn an asteroid into a fuel tank (sort of).

Sending large or small bits of iron at high speed towards someone is likely to be considered unfriendly at best. Obviously using this form of propulsion in or near earth orbit would be BAD.

Could it safely be used anywhere in the solar system?

Answer 1

It could be used anywhere, with the following conditions:

1. You fire those bits of iron at greater than solar escape velocity and aim the trajectory so that they won't hit anyone on the way out of the solar system
2. You fire them in such a way that they will deliberately hit something (eg. the Moon) in such a way that they are then easily mine-able
3. You fire them on a trajectory that ultimately ends in the sun

All of these require calculation of the trajectory carfully to ensure they won't hit anything they aren't supposed to.

I would expect that of these 3 options, number 2 would be best, as it doesn't waste resources, but to be honest they are all a bit fraught with danger.

Instead, why not use the asteroid as a base to launch your space craft from? The mass ratios work much better this way.

Answer 2

You are actually just turning the asteroid into your source of reaction mass. Your real propulsion source is whatever energy source you are using to power the railgun. Unless you are using charged particles, your railgun will have a pathetic specific impulse too.