Accuracy Requirements for Cannon-Launched Space Missions

Cannon launch has been proposed on several occasions as a comparatively inexpensive means of earth-to-space propulsion. In most of these proposals, an initial boost is given to a spacecraft by an electric or light gas gun, followed by a rocket burn that places the spacecraft into a stable orbit. In this study, we examined the accuracy needed to successfully achieve missions based on primarily ballistic trajectories, avoiding midcourse corrections to the extent possible. The results for four different missions are presented. First, launch of a payload from the moon's surface to a "catcher" at Lagrange points 1 and 2, previously studied by Heppenheimer. Next, launch from the earth to a catcher at L1, and, finally, launch from the earth directly to the moon. It was found that the accuracy required in launch speed is within the realm of possibility for electromagnetic launch methods that include feedback control of speed; for example, the accuracy requirement for earth to moon launch is + or –45 m/s at 12 km/s, or + or –0.4%. The acceptable error in launch time for this mission is quite large as well. Assuming an exact speed at the time that the projectile leaves the atmosphere, the launch can occur within a window of approximately one hour. The prospects for achieving these missions with developing electromagnetic launch technology are also presented.