to send smaller and cheaper probes using the thousands of missiles America has rotting in silos across the mid west?
They already HAVE done the equivalent of that with Red-stone missiles that had a nasty habit of blowing up either on the launch pad or soon after launch. The first satellite the USA tried to launch into space was on top of a Red-stone rocket that blew up on the launch pad at take-off. I STILL have vivid memories of watching it LIVE on black and white TV when I only 4.5 years old.
The reasons you need big rockets is to get out of the Earth's gravity well or at least to a stable orbit. A ballistic missile will *always* fall back to earth. They are exactly the size they need to be to just get out of the atmosphere, travel a bit then drop back to the planet. If you want to get to orbit or further you need substantially bigger rockets.
Some of the first 'Propaganda' satelites were such launches. ICBMs are SUB-orbital vehicles, and due to economics, a lot of design work went into making their payloads light. The probes they could boost into orbit would be too light to be worth much.
the Russians were using older submarine launched ballistic missiles to put small payloads in orbit. the u.s. wanted to do the same with minuteman 1 missiles. i know at least one payload was launched from a russian sub. the minuteman usage is unknown to me.
