Precisely. I would like to get an answer to this one too.

Better yet, is Cap Kirk (from StarTrek) greedy? He's not working for salary (as I've never seen that he is paid for what he does) nor do they show any kind of money in any of the movies. How about Scotty? Why is he showing up for work every day, risking his life repairing the space ship that always seems to break down in the worst possible moment?

In fact StarTrek crew are by evidence communists: they work for government, no money or possession (Federation = government owns starship Enterprise), no private sector or private enterprise (there are no companies), health care is free, so is food ( and drinks ) in starhip caffe. They do not trade except where they perform trading on behalf of Federation = government. There are no courts except for the military tribunals and no lawyers.

I know these are fictional characters but we all dreamed to "go where no man has gone before" when we were kids right? So we approve of their life style and intuitively understand their motivation. But are they doing all that out of greed?

Certainly we (as kids) did not see their actions as a result of greed. I would go further and say that they seem to do it out of curiosity.

One can't just say every human motive stems from greed. That is greed is not synonymous with motive.