Just a minor tip for everyone on the Little Rocket Man achievement: It's a lot easier to just manually get out of your car and shoot the gnome forward with the gravity gun, drive up to it, quickly get out and use the train cars as cover when necessary, shoot it forward again, repeat. It's not as tedious as it sounds and overall isn't too bad of an achievement. I even managed to take the gnome with me when getting the ant lion extract when I didn't need to and that was probably more difficult than the helicopter chase.
With that out of the way...yeah. Mile High Club.