The Space Crawler series was one of the earliest series of ships constructed by Centauri Spaceworks. They were designed to support planetary exploration missions. They were named for the long solar panels on the sides which resembled tank treads.
Space Crawler I was the first design it was limited to carrying Apollo Command Modules because of the proximity of the solar panels to the docking ports. It also had poor maneuverability and never made it past the flight trials.
Space Crawler II was designed to be carry the larger LK Lander. It was retrofitted with Voyager X engines to try and solve the poor maneuvering and rotation control.
Space Crawler III worked around the limited rotational speed by adding an ATV module with forward-facing engines. This allows the the Space Crawler III to enter and leave orbit without having to changes its orientation. Space Crawler III was put into service and made successful flights to RED and GRN.