Why Comet Tempel 1?
Tempel 1 is the comet that best satisfies a variety of constraints for a launch within the 2-year window for which the team was allowed to propose. Constraints require the comet to be large enough to sustain a crater, to have a low rotation rate (so the newly formed crater doesn’t rotate out of view before the flyby spacecraft can get pictures!), to have a trajectory that allows natural intercept at high speed and an approach from the sunward side by the spacecraft, and to be observable from Earth at the time of impact. If the launch were to take place at a different time, a different target would have been chosen.
