design space pruning heuristics and global optimization method for ...

elative to the asteroid at arrival and v ast
is the heliocentric velocity of the asteroid.
GTOC2 required participants to design a low-thrust trajectory that rendezvous with one
asteroid in each of four predefined groups, while maximizing the ratio of final mass to
total time of flight. 8,9
For this problem, no gravity assists were allowed. GTOC3 also
involved a multiple-asteroid rendezvous mission, but in this case the goal was to design a
low-thrust trajectory that would rendezvous with three asteroids out of a single group of
140 and then return to Earth. 10 Gravity assists of Earth were allowed and the objective
function was to maximize a weighted combination of mass ratio and the minimum stay
time at the three asteroids. Most recently, the GTOC4 problem asked participants to
maximize the number of asteroids visited (via a flyby) en route to a rendezvous with a
final asteroid, without the use of any gravity assists. 11
There were 1436 candidate
asteroids for participants to choose from.
In light of the recent developments in electric propulsion and emerging scientific
interest in asteroids, this work will focus on the development of a methodology for
solving a multiple-asteroid rendezvous low-thrust mission design problem at the
conceptual design level. Two specific types of asteroid rendezvous problems are
considered. First is the case of rendezvousing with one asteroid from each of a given
number of predetermined groups, as presented in the GTOC2 problem. This type of
mission would be relevant if the goal were to visit asteroids with different scientific
properties. The second type of problem is to rendezvous with several asteroids out of a
single group, such as the Near Earth Asteroids (NEAs). In either case, a spacecraft could
return to Earth at the end of the mission duration, which would be representative of a
sample return mission. Because the target application is conceptual design, the goal will
be to identify a large set of good solutions to a given multiple-asteroid rendezvous
mission. Unlike the GTOC competitions, which required only a single best solution to be
submitted, the result of the methodology will be a suite of solutions that could then be
carried forward into the more detailed design phases, where higher fidelity analysis with
3