Things like this have happened to me before. Did you get some kind of message as soon as you landed on the outpost saying the marines were taking over, or just nothing at all? If you got the message, then you have completed the mission and need to find the next one. But if nothing happened, then you didn't do everything you needed to do, meaning a Voinian ship probably got away. In this case, abort and go back to where you got it and you should be able to get the mission again. This time, when you think you've killed all the Voinian ships, hit "tab" repeatedly to cycle through all the ships in the system and make sure no Voinians are left. Also, you have to DESTROY all the ships, so make sure you haven't left any disabled. Then land the marines and you should be fine.
Nothing to abort, you say, go to the system with Krotun. There should be three stellars: two planets and a moon, I think. I believe you can land on one of them even if it is Voinian space. If not, go back to Obron. Check your starmap, if you completed the mission, Obron should have changed to a UE system when you jumped out of it. Land at what is now Outpost Sigma and go to the bar, where d'Erlon might have another mission for you. If this doesn't work, try Earth and Luna.
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The last time I was on this board, the price of dumb questions was really high.
(This message has been edited by StarStrafer (edited 03-14-2001).)