Reachability analysis to design zero-wait entry guidance

This paper presents a novel reentry guidance architecture that aims to improve cur- rent mission safety by enabling zero-wait orbital aborts. To do so, an on-board trajectory planner based on Adaptive Multivariate Pseudospectral Interpolation (AMPI) is devel- oped. This planner generates mathematical approximations of the reference trajectory to be tracked by comparing the vehicle-state information at the entry point against a pre-computed trajectory database that is stored on-board. Such a trajectory database is populated by systematically solving a number of optimal-control problems, which ulti- mately generate a set of reference angle-of-attack and bank-angle profiles that feed a Linear Quadratic Regulator trajectory tracker. The architecture proposed in this paper is tested using a scaled-down version of the X-38, SPHYNX, a small lifting-body reentry vehicle developed by the European Space Agency. The proposed on-board trajectory planner is able to generate reference commands in the order of a few milliseconds, thus proving the ability to run the system in current ight-hardware. Furthermore, a Monte Carlo test campaign showed that the trajectory database can be compressed with a loss-less process without having a detrimental impact on the landing dispersions and constraint compliance, achieving database sizes as low as 18 MB. Finally, the presented architecture allows for easy targeting of any landing site, as long as reference guidance commands are stored in the database.Astrodynamics & Space Mission