The Onager was a 439SL Class 7 Excavator Vessel originally used by colonists of Hadley's Hope on Acheron for drilling ore, ferrying cargo to low orbit for pickup, and not much else. But it could get off the surface, which was enough for some of the colonists of Hadley's Hope who used the Onager as a makeshift escape vehicle to ferry themselves off planet when the colony was infested by Xenomorphs in 2179.