On the Silent Cartographer level, go anywhere where there is an overshield, and bring a warthog with you. It's best to do this in co-op because it's easier to collect the grenades and "initiate launch-off". Get as many grenades as you can, and have your partner kill you, and vice-versa to get the grenades into one big pile. (Make sure this is *near* an overshield.) Drive the warthog onto the grenades and try to position it to where it would fly up on top of the level. Before you do anything else, make sure you get a checkpoint. Have your buddy pick up a grenade and toss it under the warthog, and RIGHT as he throws it, pick up the overshield and get into the warthog quick. If you get into the warthog while the overshield is charging, you should get blasted upward unharmed. You should reach the top of the level. If not, reposition the warthog, or get more grenades. When you're up there, kill your friend with the plasma pistol from long range, and he should appear up there with you. Have fun!