Optimized Solutions for the Kistler K- 1 Branching Trajectory Using MDO Techniques

Abstract

Fully reusable two-stage-to-orbit vehicle designs that incorporate 'branching' trajectories during their ascent are of current interest in the advanced launch vehicle design community. Unlike expendable vehicle designs, the booster of a reusable system must fly to a designated landing site after staging. Therefore, both the booster return branch and the orbital upper stage branch along with the lower ascent trajectory are of interest after the staging point and must be simultaneously optimized in order to achieve an overall system objective. Current and notable designs in this class include the U. S. Air Force Space Operations Vehicle designs with their 'pop-up' trajectories, the Kelly Astroliner, the Kistler K-l, the two-stage-to-orbit vehicle Stargazer, and NASA's proposed liquid flyback booster designs (Space Shuttle booster replacement). The solution to this problem using an industrystandard trajectory optimization code (POST) typically requires at least two separate computer jobs — one for the orbital branch, from the ground to orbit, and one for the flyback branch, from the staging point to the landing site. These jobs are coupled and their data requirements are interdependent. These requirements must be taken into consideration when optimizing the entire trajectory. This paper analyzes the results of branching trajectory optimization for the Kistler K-l launch vehicle with respect to computational efficiency and data consistency for various solution methods. In particular, these methods originate from the field of Multidisciplinary Design Optimization (MDO).