Abstract: Access door pallets for an external tank of a Shuttle Transportation System are provided. Access door pallets replace one or more access doors on the external tank. In addition to carrying out the original function of the replaced access door, they provide a means for attaching a payload to the external tank. The payload can be mounted on either side of the door. For example, thrusters, maneuvering devices, guidance and attitude control systems can be mounted on the exterior; measuring instruments, chemical release devices, transmitters, extensible solar collectors, and pressurized chambers can be mounted on the interior.