Docking is vital for the mission objectives of the Crew Transfer Vehicle. Today, it has been practiced hundreds of times, manned and unmanned. Pressurized docking is much more complicated than a simple, structural 'hard dock', but over the years an international standard has been developed for both categories.

    The Shuttle's Universal Docking System is perfect for the orbiter in its existing state. Some structural supports, designed for the Shuttle's payload bay, have to be removed for installation in the orbiter, but the essential hardware remains the same. However, the docking module servers three functions: hatch, for entering and exiting the vehicle while on the ground, docking module, for docking with either the International Space Station or the Space Shuttle, and airlock, for the capacity to conduct emergency EVAs while in orbit.

    Two windows, one on the port side of the vehicle, the other on starboard, are located directly aft of the docking module, allowing for manual docking ability should the guidance system, coupled with active radar, is unable to dock the vehicle automatically.

    In the aftermath of Columbia, the ability to rescue a stranded shuttle crew was added to the orbiter's mission objectives. This leads to an additional module attaches on top of the Universal Docking Module. This component will be discussed in more detail in the Shuttle Rescue Subsystems Report.