You might not want to expose humans to more than a reasonable transverse G loading, say 6-10 Gs and preferably less. Transverse G loading is across the chest, typically from front to back, as opposed to positive (head to foot) or negative G loads. That's why astronauts are sitting on their backs during liftoff (and reentry in capsules).

The lower the G load, the longer the track has to be to accelerate to a given velocity. That means the challenge of developing the maglev launcher becomes a lot harder and more expensive. If all you're talking about are non-sensitive things like ice, you could crank up the Gs and have a track under 100 feet long if you wished. To reach lunar escape velocity with a human on board, your track might have to be kilometers long. Even if the track is circular as you suggested, G loading is the critical factor, and that's keyed to the final velocity and the radius of the track. To reach lunar escape velocity, you need to reach roughly 6,000 MPH. Even at a steady speed, you'd be pulling Gs due to inertia (not centrifugal force, which is an illusion), so your radius would have to be quite large to reach escape velocity and keep the loads to safe levels for humans.