all you have to do is just take a ghost go through the building with it (the one near the end of the level)(the marine camand post) as soon a you get to top (where the sarge says "i asked for reenforcements but i didnt think they'd send a spartian we got trouble." well dont even stop by him just keep boosting past and you should land by the scorpian just kick the marine out and jum in! not really much use after that but you saved a life!