Design Space Pruning Heuristics and Global Optimization Method for Conceptual Design of Low-Thrust Asteroid Tour Missions

Paper number

IAC-08.C1.2.3

Author

Ms. Kristina Alemany, School of Aerospace Engineering, Georgia Institute of Technology, United States

Coauthor

Dr. Robert D. Braun, Georgia Institute of Technology, United States

Year

2008

Abstract

Electric propulsion has recently become a viable technology for spacecraft, enabling shorter flight times, fewer required planetary gravity assists, larger payload masses, and/or smaller launch vehicles.  With the maturation of this technology, however, comes a new set of challenges in the area of trajectory design.  Because low-thrust trajectory optimization has historically required long run-times and significant user-manipulation, mission design has relied on expert-based knowledge for selecting departure and arrival dates and gravitational swing-bys.  These choices are generally based on known configurations that have worked well in previous analyses or simply on trial and error.  In the conceptual design stage, however, the ability to explore the full extent of the design space is imperative to locating the best solutions in terms of mass and/or flight times.

In 2006, the 2nd Global Trajectory Optimization Competition (GTOC2) posed a difficult mission design problem: to design the best possible trajectory, in terms of final mass and total mission time, that would rendezvous with one asteroid in each of four pre-defined groups.  In addition to the 41 billion possible discrete asteroid combinations, continuous design variables included Earth departure date, hyperbolic excess velocity at Earth departure, times of flight, and the stay times at each asteroid.  Even with recent advances in low-thrust trajectory optimization, a full enumeration of this problem was not possible.

This work presents a two-step methodology for determining the best set of solutions to the above problem, in terms of final mass and total time of flight.  First is a pruning step that uses a heuristic sequence to quickly reduce the size of the design space.  Second, a genetic algorithm is combined with a low-thrust trajectory optimization method to locate the best solutions of the reduced design space.  The resulting methodology is capable of obtaining a set of conceptual design solutions across the full extent of the design space.  A subset of the full GTOC2 problem is solved by discretizing the design space and evaluating all possible asteroid combinations.  The proposed methodology is then validated by comparing its results to the known set of best solutions of this sub-problem.  The methodology developed provides the first organized search technique for low-thrust, asteroid tour mission design.  It enables better solutions to be found, in a shorter period of time.  Therefore, a larger set of trajectories with shorter flight times and greater final masses are available to carry into the detailed design phase.

Abstract document

IAC-08.C1.2.3.pdf

Manuscript document

IAC-08.C1.2.3.pdf (🔒 authorized access only).

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