iMessage connection issue satellite internet

HI everyone.

I work on a ship that travels worldwide. We have Internet access via a slow satellite internet connection. (256k) I have a wireless router attached that I pull wifi to my US based iPad, iPhone and an a second unlocked iPhone. When we leave the states, I will keep my iMessage connection for a few days on the U.S. based equipment and it will continue to work. After a few days I lose the iMessage connection and cannot regain it via the wifi. Does anybody know why this is? I'm thinking speed of the network or foreign satellite. I cannot regain the connection on US based equipment OR unlocked iPhone. Please advise. Thanks. -Zach