[AlexanderHowl]

Do you want an impactor to take over ten years to reach its destination? Chemical rockets are only able to get to Saturn through gravitational assists and Hoffman transfers, which take forever. Considering the orbital radius of an artificial satellite will vary by as much as 0.1% per year in a complex system like Saturn's just due to the gravitational interactions, you may be off by quite a bit when you final get to Saturn if you do not want to risk detection by using additional rockets.

Anyway, an impact going to Saturn through using chemical rockets has to expend 12.5 mps just to account for differences in orbital velocity. Since it is nearly impossible for chemical rockets to get to that delta-v through staging, you need the gravitational assists to gain the required delta-v. At best, it might be able to have another 1 mps of delta-v to allow it to ram at 1 mps.