How long would it take to reach the ground? Because IIRC the deck of a spelljammer is technically something capable of supporting the rod for the purpose of being a valid target for conjuration spells. The problem is choosing an altitude where it will land in less than 1 round per caster level.It's D&D Adamantine rods not tungsten.
I think the velocity alone is similar to a nuclear bomb when it hits.
They actually planned that out but getting a 20 ton rod into orbit and aiming it are impractical.