Like gnoodlemeier said:
The ship, in order to reverse, must stay in the same hex(es) for on turn, then can back up at 1/2 forward speed (Rounding down).
Or, since it isn't easy to stop a mass that quickly, the Lev takes three turns to stop and reverse
Turn 1: the Lev 'coasts' forward 1/2 its regular movement,
Turn 2: Comes to a stop
Turn 3: starts moving backwards
There could be a "Emergancy reverse" In which the ship stops and backs up in the same ture, but there should be some sort of roll to reflect the harshness of this on the engine (player must make a breech roll against the engines with a certain set of dice)
Craig