A rocket silo with a small circuit to enable counting launches. Due to the game's inability to track this natively anymore (RIP rocket launch counter window) and the Rocket Silo's inability to output a usable signal, it works by keeping track of how many times the inventory of the silo has been reset to 0 after being loaded.
Note that this means that you cannot use it on silos that are automatically unloaded, like for Gleba resources or biter eggs.
Set it up by placing the rocket silo blueprint, then connecting a green wire from the output of the last R / R combinator to whatever you want. Multiple silos will automatically sum, so you can connect everything to the same circuit (or have clusters of silos connected to their own radars). Remember that radars only work for the same surface you're on; you cannot beam a signal from, say, Fulgora to Nauvis without mods.
This book includes a copy of Monkfish's Numerical Display, which can be found here: https://factoriobin.com/post/srewzg I've modified it slightly to add a radar and making it ready for tracking rocket launches.