I just thought of a spring launch. There's this large spring stretching to the end of the launch, and the end of the spring has locks that grip to teh cars. It "rides" on 2 rails that keep it in the track, then, a few "riders" that are also hung on rails grab onto the end of the spring unit, then, powered by a cable, move back to the station and let's the end spring unit lock onto the cars. Then, the "riders" release and the giant spring pushes the train. Tell me some minor problems with this idea and I will explain it.
Who knows, maybe it is better than a hydralic launch. Just kidding.
Sorry, I have all these wierd ideas, such as this pipeline suspended hearlined swinging coaster I mentioned a while ago.