Seminars

Explore is a global multiple gravity assist (MGA) trajectory tool based on a grid-search algorithm operating on a given encounter sequence. An efficient sequential tree search eliminates v-infinity discontinuities and prunes trajectories. Where computational resources prohibit an exhaustive search, one or more performance indices are used to further prune the search. Multiple objectives are handled by allowing a performance index to change along the different trajectory segments and by pruning with a Pareto-optimality ranking. The MGA search is extended to include deep space maneuvers (DSM), v-infinity leveraging transfers (VILT) and low-thrust (LT) transfers. In addition, rendezvous or n-pi sequences can patch the transfers together, enabling an automatic augmentation of the MGA sequence.

Details of the VILT segments and n-pi sequences are presented: A boundary-value problem (BVP) VILT formulation based on a one-dimensional root-solve allows the inclusion of an efficient class of maneuvers with runtime comparable to solving ballistic transfers. Importantly, the BVP VILT enables the calculation of velocity-aligned apsidal maneuvers (VAM), including inter-body transfers and orbit insertion and departure maneuvers as well as VILTs. An automated method for the inclusion of n-pi transfers such as resonant returns and back-flip trajectories is introduced. This method poses a BVP on the v-infinity sphere and solves it by one or more n-pi transfers which may additionally be used to fulfill specified science objectives. The n-pi sequence BVP is implemented in the context of the broader search, combining n-pi and other transfers in the same trajectory.

To aid in proximity operations around small bodies, analytical methods are used to investigate stability regions in the presence of significant solar radiation pressure (SRP) and body oblateness perturbations. The interactions of perturbations from even zonal gravity terms and SRP allow for heliotropic orbits, a stable family of low-altitude orbits investigated in further detail. A novel constrained double averaging technique enables the investigation of inclined heliotropic orbits. This type of knowledge is uniquely valuable for small body missions where SRP and irregular body shape are very important and where target selection is generally a free parameter in the mission design.