The Cosmo Jetter is the Jetters main transport. It's a large ship that is able to travel in space. It also can carry the containers that hold the other Jetters vehicles.
In episode 33, Mujoe accidently super combines the Cosmo Jetter and Ein into Jetter Ein Bomber.
Another view of the Cosmo Jetter
The Cosmo Jetter about to travel in light years