COntinue buying upgrades when completed the campaign

Im sorry Im fairly sure this is me being a moron but I have just completed the campaign and am going back to do more achievments and such that I did not complete through the first time, however I cannot seem to find a way to purchase more upgrades in order to complete that achievement. All I recieve is a list of missions instead of being aboard the hyperion.

Is there anyway without starting a new campaign to do this? If I have to start over again and do a complete play through then I will I just wondered?

Cheers

 

You can not do all upgrades in one campaign you must pay through at least one more time if not two (ie save money save get up reload get other ups)

 

So what do I do now

So what do I do at this point now? Do I start a new campaign and I will have all my old upgrades etc? or do I need to do something diffeent to keep my current upgrades?