I don't think anyone is even considering to use TCP for interplanetary communication. You would use other protocol to communicate between planets and then only

I don't think anyone is even considering to use TCP for interplanetary communication. You would use other protocol to communicate between planets and then only on earth you would switch to TCP or other protocol (depending what you would like to do) for fetching data from internet. Then get the data through proxy on earth and deliver it through this protocol to the other planet.