 For years, the dream of conquering the space frontier has continued to become reality. An increased level of operations in this challenging environment will require frequent docking of orbiting vehicles. To achieve this, a safe rendezvous and docking mechanism is essential. An accurate docking sensor would minimize plume impingement, increase fuel efficiency, simplify docking mechanisms, and increase safety and reliability. More importantly, the system would be capable of operating in a fully autonomous mode. This would minimize the necessary crew interaction during docking. Various optical docking sensors have been proposed which provide information on range, bearing angles, attitude, and their respective rates. Accuracies for these sensors are fairly stringent. As a result, a system is being designed by the Tracking and Communications Division at NASA's Johnson Space Center to test the accuracies of these docking sensors. This system, designated the Six Degree of Freedom or Six DoF system, provides six degrees of movement by using five rotational stages and one linear stage. Range, bearing angles, attitude, and the respective rates are provided. Range is furnished by a granite rail 12 meters in length with a carriage floating on three air bearings. The maximum change in range travel distance is 10.5 meters, while rates can vary from 5 millimeters per second to 400 millimeters per second. Mounted inside the granite rail is a linear encoder with a resolution of five microns. The gratings on the encoder are photo-electrically scanned and counted to keep track of absolute position. Two rotational stages on top of the range carriage provide azimuth and elevation, referred to as the sensor gimbal mount. This entire assembly can safely support a sensor weighing up to 40 kilograms. Here, a laser is mounted on the sensor gimbal mount to simulate a docking sensor prototype. A separate movable granite table designated the target gimbal mount is offset from the granite rail. Three rotary stages provide yaw, roll, and pitch. All five rotational stages contain rotary encoders that possess a resolution of one one thousandth of a degree. A retro reflector assembly would be a typical target attached to the target gimbal mount. A 19-inch rack houses the equipment necessary to operate the six-dough stages. Included is a computer containing the control software which drives the stages through a central interface. The six-dough subsystems are also contained in this rack, including a global positioning system time receiver and a rate meter. These instruments provide time tagging and calculation of absolute and relative rates of each of the stages. Operation of the six-dough system is based on knowing the initial coordinates of 14 reference points on the two gimbal mounts and commanding the stages to move to a desired range and attitude at a specified rate. In order for all position and rate measurements to be relative to each other, a common coordinate system was defined. A digital metrology system is used to shoot individual targets and calculate position coordinates. These coordinates are then entered into the control computer software. The stages are commanded to move. The laser spot searches for the target. The proximity of the laser spot to the desired target determines the accuracy of the sensor prototype. In a typical testing scenario, static and dynamic accuracies will be tested on a candidate optical docking sensor. Position information taken from the sensor will be compared to the true six-dough position. Dynamic information is provided by comparing the tracking capability of the docking sensor to that of the more accurate six-dough system. Future enhancements of the six-dough system include a proposed expansion into an autonomous rendezvous and docking test facility. Here, docking scenarios will be set up to gain knowledge on docking sensors. This will enable development of an optimum docking sensor that could be used in a multitude of docking applications. A potential application of the six-dough system would support the shuttle and space station docking simulator. Currently, astronauts practice docking the shuttle to the space station by using visual cues. If this system was connected to the simulator, it could move using the relative range, bearing angles, and attitude as calculated by the six-dough system. This would enable the simulator to operate in a completely autonomous mode, from enhancing astronaut training to docking with space station freedom to aiding orbital assembly. The accuracy of the six-degree of freedom system will provide an important service as we continue to reach out beyond Earth's boundaries.