  Space debris have been becoming exceedingly dangerous over the years as the
number of objects in orbit continues to rise. Active debris removal (ADR)
missions have garnered significant attention as an effective way to mitigate
this collision risk. This research focuses on developing a multi-ADR mission
that utilizes controlled reentry and deorbiting. The mission comprises two
spacecraft: a Servicer that brings debris down to a low altitude and a Shepherd
that rendezvous with the debris to later perform a controlled reentry. A
preliminary mission design tool (PMDT) is developed to obtain time or fuel
optimal trajectories for the proposed mission while taking the effect of $J_2$,
drag, eclipses, and duty ratio into account. The PMDT can perform such
trajectory optimizations within computational times that are under a minute.
Three guidance schemes are also studied, taking the PMDT solution as a
reference, to validate the design methodology and provide guidance solutions
for this complex mission profile.
