It's a very simple system really. I don't know the exact ins and outs of the hydraulic launch, but.
The train is attached underneath (second car back I think, but it may be the third) to a "catch car". This is a simple hook kind of device which runs on a trolley, down the centre of the launch track. The train is maneuvered forwards over the catch car, then back to that the "hook" engages". I don't think it's an actual hook, more a block really.
When it gets ready to launch, you feel the train move slightly forwardsa nd back, that's it getting onto the catch car.
Liquid Nitrogen is pumped into a hydraulic system and put under immense pressure.
This is released through a winch mechanism, which pulls the catch car at incredible speeds. The train, being attached, follows along. About halfway down the launch track, the catch car trough dips downwards, so the catch car releases from the train. Magentic brakes stop the catch car. the train carries on along the launch track, over the winch and hydraulics house and up into the ride.
The magnets are used entirely for braking systems. Before launch, two rows of metal "fins" come up down the launch section. These are powerful magnetic plates. If the car should launch prematurely, or with fault, the fins bring the train to a damn quick stop.
Just before the train launches, the fins lower back into the track, and the train sales over them. There's another set on the hill at the far side where you stop. Again, powerful magnets which stop the train.
I think that's about it really
I'm sure you'll love Alton if you've not been there for a good few years. I can recommend the hotels if you can get a good deal. We stopped a couple of years back as a treat (even though we only live 15 or so miles away) and it was fantastic. The kids have had a few birthday parties in Cariba Creek too and they were superb. Plus, you get two days in the park, so it's a good opportunity to have a relaxed couple of days soaking it all in.