This variant of the Shuttle PB is used by the ODST(Orbital Drop Shock Trooper) units of the UNSC(United Nations Space Command) as a light all-purpose spacecraft. It's small size makes it an ideal escape vehicle, and after several reinforcements it can withstand very high tempratures during atmospheric entrance. Flying to orbit is usually done with the help of a launcher, even though the Shuttle PB can do it alone despite its low lift power and fuel capacity.
Note - The Shuttle PB does not appear in any of the Halo games or books. It's a skin I made for fun.