INTRODUCTION THE Lunagem is a conceptual high-speed lunar exploration vehicle which is intended for Apollo Follow-on or future post-Apollo lunar missions. As shown in Fig. l, this vehicle is a ground effects machine which utilizes storable liquid rocket propellants to provide both lift and propulsion. Propulsion is provided by two small rocket thrusters. Steering is accomplished by the use of thrust vector control and adjustable drag skids. The vehicle is supported by a of gaseous exhaust products which result from the combustion of the rocket propellants within a gas generator. These cushion gases leak through the small peripheral gap between the ground and the flexible skirt at a rate which is equivalent to the flow rate required for a small (i.e., 1-5 lb thrust) rocket thruster. Such small leakage rates are due to the extremely low absolute cushion pressure required to support this light weight craft. During the development of the Lunagem, it became apparent that a complete mission analysis was necessary to evaluate the feasibility of this concept. A crucial factor in this analysis was the effect of vehicle dynamics on the ability of the vehicle to maintain high average speeds while traveling over the rough lunar terrain. Therefore, a theoretical model of the Lunagem dynamic characteristics was developed to assist in this evaluation. This paper presents the salient features of the mathematical model.