Circus registry 331/3 (called by its operators Thirty-Three and A Third) is a Universal Standard Transport LS1517 series Space Hauler. The LS1517 series is often used as a pilot engine for a train of container pods with the primary motive power coming from a secondary drive at the end.
The series is an older design with a higher crew (or more sophisticated nonspohont mind) than new models and only one axis of container attachment, but it has better armaments (ostensibly "space debris protection") and a more powerful engine.