I've researched it, built it, fed it with parts, everything is ready, but I don't understand how do I select a destination. When I choose "Deliver cargo", only the space platforms in current orbit show up as valid destinations, but not other planets

Hello! The two primary ways of launching an ICBM/IPBM/ISBM, are either manually with the ICBM-remote shortcut that is unlocked after completing the ICBM research (presently no hotkey for it; can add one if needed/desired); or via a circuit-network circuit connected directly to the silo.

• If firing/targeting manually, simply have the ICBM-remote in your cursor and select where you want it to target.
• If firing/targeting via a circuit-network, connect the rocket-silo to a circuit network; after connecting, when the rocket-silo GUI is opened, a new window should appear to the right with the relevant target selection information.

Also, the only accepted payloads are presently the atomic-bomb (default disabled), the atomic-warhead, "Rods from God", "Jericho[s]", and "Mjölnir[s]". The above methods will only initiate a launch if one of the aforementioned payloads are present - anything else and it won't launch (allowing payloads to accept any ammo and/or capsule is presently in progress).

Hope that helps, let me know if you have any other questions!