Now I'm not 100% on the science involved, this is a theory. The idea is using magnetic energy powered by the sun or eventually other stars to send objects (ships, cargo) etc. Through space on a magnetic rail like a sling shot, Magnets work perfectly in the vacuum of space and in the absence of a gravitational field. They don't depend on any "environment" or "medium". And the electromagnetic force is independent of gravity.

A rail-launch system, propelled by electromagnetic force is quite feasible to reduce propellant use in getting about - assuming this takes place in orbit. Ofc, the launcher will require a much greater mass than what you're lauching via this method, possibly thrust equal to the force of the launch system moving, and hitting the stop at the end(if there is one) or the ship'll stand still and you'll throw the launcher.

Might be good for getting ships out of a larger facility, but I'd most envision ships docking up at designated zones, not flying in and parking.

EyeR is correct, it would need to be quite big. You wouldn't be able to use it for populated ships or anything not designed to be launched, due to the massive acceleration. The other problem is you only save half the fuel, you still have to carry enough to slow down when you near your destination.

Half saved is still twice as much to use. Massive acceleration is possible, but it's also possible to apply this "slowly". Keeping it under 6G should be "survivable" for people and most well packaged fragile cargo.

My napkin working says you'd need to have 18km of track if you're accelerating at 6Gs and you want to make Mars. A typical human will black out at 4-6Gs, more if they're trained.

This kind of stuff is perfect for cargo, and it's a lot more achievable.

I was working on six G with flightsuits for citizens - it's not uncommon for pilots to take more. Six G is still enough - Unsure where the Mars target came from, but it's as good as any I suppose. 18km isn't unfeasible. The thermal dissipation systems for the long term habiational stations will likely be bigger than that, so again, by virtue of being able to provide for our populous providing the materials for such a project will be trivial.

You could use a centrafugal launcher, and get a similar effect with a lot less mass I'd wager.

Though these things are achievable, I do prefer to keep things at least within a reasonable timeframe away. Building an 18km long railgun in space is pretty far off, with the cost per kg to LEO being around $4k.

For cargo transport, you can make the acceleration much higher, and therefor the length(and mass) more reasonable.

Again, ignore cost to LEO - it's not happening that way, this is something we can clearly both be in agreement over. You'd also want it higher most likely. Just the materials cost, let alone design time and assembly would sincerely suggest such a project could not possibly be entertained until first supermassive resources are obtained - like those littering the solar system.

Certainly, it's unlikey to start fabrication tomorrow there's far too much infrastructure that'd need to be in place. Floor lift or stellar harvest. It doesn't hurt none to start working through what would be involved in doing it, however, so when we are better able to do so all the pieces are in place and most if not all problems rectified before anyone actually does anything. Drastically reduces devel costs for such a system.

With regards to making mass more reasonable, a simple electical motor with a rotor arm and counterweight. Spin it up and release it at the "right" point in it's arc and you can "throw" things. And actually put them where you'd intend. It'd possibly not have the range of a 18km oversized railgun, but a series of them could be built with the same or similar mass.