Manned spacecraft will require maintenance robots to inspect and repair components of the spacecraft that are accessible only from the outside. This paper presents a design of a novel free-flying maintenance robot (known as a MaintenanceBot.) The MaintenanceBot uses Control Moment Gyros (CMGs) for manipulator arm and attitude control. This architecture provides high authority control in a compact low power package. Relative position and attitude determination is accomplished with an RF system supplemented by a vision system at close range. When not docked to the manned vehicle (which must be done periodically to refuel and recharge batteries or when the manned vehicle performs orbit changes) the MaintenanceBots fly in formation using a cold gas thruster system and formation flying algorithms that permit dozens of MaintenanceBots to coordinate their positions. The use of CMGs is a prominent feature of this design. An array of CMGs can exchange angular momentum with the spacecraft body to effect attitude changes, as long as certain mathematical singularities in the actuator Jacobian are avoided. The proposed maintenance robot benefits dramatically from the dynamics and control of a multibody robotic arm whose joints are driven by CMGs. In addition to high power efficiency, another advantage of this concept is that spacecraft appendages actuated by CMGs can be considered reactionless, in the sense that careful manipulation of the CMG gimbal angles can virtually eliminate moments applied to the spacecraft body. This paper provides a preliminary design of the MaintenanceBot. Analysis of the formation flying and close maneuver control systems is included. Simulation results for a typical operation is provided.