This circular slide rule computes the relationship among the various parameters of a rocket-propelled space mission: the specific impulse of the rocket motor, the paylod weight, the desired trajectory, and velocity. It would not have been accurate enough for an engineer to use in planning a mission; they used detailed mathematical formulas, evaluated by digital computers. But the slide rule would have been very useful for managers, members of the trade press, news media, and government funding agencies, who needed to know the basics of a space mission.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.