A team led by Heegyeong Kim has proposed HARP, a planner that helps one drone take over tracking a target from another. The incoming drone has not yet seen the target, so it uses the outgoing drone's prediction to decide whether to turn, move or look around an obstacle, without blocking its partner's view. In simulation it found the target in all 49 standard trials and 15 of 16 stress tests, and two-drone field trials backed up the approach. Preprint, not yet peer-reviewed.