# Speculation on the concept of in-space magnetic ring/rail launcher for a spaceship?

This is in reference to the question If human space travel is limited by the G force vulnerability, is there a way to counter G forces?

Which, by my limited understanding, seems to point at the problem of space travel as: not being able to accelerate in space efficiently, hence it takes so long to get to Mars, etc.

Just out of curiosity, what would be the immediate problems with magnetic rings (in space, rail launcher), a ship passes through and is accelerated away, perhaps even flying through several rings to increase its acceleration?

Fictional reference: Cowboy Bebop

• Step 1 for any hypothetical space acceleration system: Get it out of the Earth's atmosphere. As for whether or not it'd work depends on a variety of factors (none of which I know). Neat question though. Apr 5, 2019 at 19:33
• Possible duplicate of space.stackexchange.com/questions/31886/…. Apr 7, 2019 at 21:18

The main constraint with any system that boosts payloads on their way is the equal and opposite reaction element. So if you build your hypothetical launcher in earth orbit then each time you launch a mars mission through it boosting 'up' (increased orbital velocity) you push your launcher 'down' (lower orbital velocity).

Traveling between orbital stations or to the moon there are ways to model shots that equal out or 'catch' incoming payloads but for a mars shot that does not work as neatly so you end up needing similar fuel loads being boosted to orbit anyway, though you can potentially use a single high efficiency/low thrust engine on your launcher in place of multiple lower efficiency/high thrust engines on your payload which may make for some gains.

Placing your launcher on the moon has a number of advantages here as you get access to materials and a massive launch platform that in human terms can be considered immovable.

Regardless of location such a launcher will be massive, the months longs mars transits involve DV of 3km/s from and up from LEO so your system muzzle velocity needs to be 3km/s. At 5G that means accelerating for just over a minute and a length of around 100kms. Doubling to 10G acceleration around about halves the system length to 50km. That is a substantial structure to build, keep straight against tidal forces and keep pointed accurately.

Also note your launch system in LEO will be a highly effective weapon against anybody in the earth/moon system so politically exciting to have around.

Framing question in little better way - how feasible is accelerating satellites in space in using Rail Guns?

After accelerating a payload in space, the Rail Gun will accelerate in the opposite direction. To work in practice efficiently using this kind of propulsion, the Rail Gun mass should be at least an order of magnitude larger than the object being accelerated. By inertia, If you push a ball weighing 1kg, it gets moved. If you push a ball weighing 1 Ton, you get moved.

Coming to practical, nobody wants to invest in a few big rail guns in space. Not sure whether any rocket is currently capable of putting these systems into orbit. Because the rail guns decelerate every time they accelerate something is space, sometime in future they need to be accelerated again, defeating the original purpose. These systems would require more power than can reasonably be delivered by a solar panel. Such a magnetic field may mess up with electrical parts in payload. If a cluster of magnetic rings are accelerating a payload, then such an arrangement can only accelerate the payload in one direction.

Ion thrusters do better job in accelerating satellites in space compared to Rail guns.