In the Simpsons Psp game how do you get on the UFO

It took me a while to figure this out so here is how, Once you've started the level, go through using the helium to make Homer float by pulsing the X button and making Bart use Bartman's powers. Firstly Bartman has to climb the wall and Homer has to float up and over the trailer or whatever that thing is then you must use Homer to allow Bartman through by using helium to go over the gaps and pulling the levers to make steam to allow Bartman to glide over then once you've reached where the smashed down wall, get Homer and Bartman to stand on the the black mat-like things which have lights above them and the doors will open, allowing you to pass into the UFO and save Cledus! :') Hope it helps!