Since the levels don't seem to be numbered and I haven't been counting, I'll try to describe the level I'm stalled on.
I'm stuck at the end of the level just past where you push the red control button and you can see the ship through the window. There is an X on the ceiling near the bottom of some stairs. You go up the stairs and look down into a pit that has an X on a slab. I gather you need to get across the gap from the top of the stairs over the pit to finish the level.
I first tried to just jump the gap, but never really came close. I then had trouble getting a portal to even open on the slab at the bottom of the pit, but finally managed to do it. Placing a portal on the X on the ceiling at the bottom of the stairs quickly made no sense, so I placed it on the floor below the X on the ceiling. I then go to the top of the stairs and jump in the portal at the bottom of the pit. I don't get near enough height or momentum to carry me the other side, and even if I did since there is very little, if any control when you come out of the portal I'm pointing in all directions at seemingly at random. I even reversed it & tryied jumping in the portal at the bottm of the stairs & not even close. I've got to be missing something obvious here but don't have a clue after so many attempt. Any help?