Altair Descent and Ascent Reference Trajectory Design and Initial Dispersion Analyses

The Altair Lunar Lander is one element of NASA’s Constellation Program for human return to the Moon. The Altair lander is responsible for several critical maneuvers on the way to and returning from the lunar surface. Since propellant to perform these maneuvers constitutes 50% (cargo) to greater than 60% (piloted) of the total lander mass, it is important to characterize the magnitude of these maneuvers as accurately as possible early in the design process. The Altair Lander descent module main engine performs the lunar orbit insertion burn(s), the low lunar orbit plane change burn when necessary, and the powered descent burn to lunar touchdown. The descent module also performs all trajectory correction maneuvers en route using a storable reaction control system as well as all attitude control functions. The Altair ascent module main engine performs the single, continuous ascent burn from the moon after the seven-day lunar surface mission to the low lunar orbit phasing ellipse. The ascent module then performs all rendezvous, proximity operations and docking maneuvers using the ascent module reaction control system. This paper describes the Altair performance characteristics and results determined thus far from the first four design and analysis cycles and presents the results of analysis and simulation work defining the Altair vehicle’s required maneuvers as well as statistical analyses of anticipated dispersions in performance parameters.