Science fiction writers often fail to understand the cost in energy and resources of getting hardware into space. No sane nation would risk nontrivial spacecraft in combat; they're simply too valuable, and this will likely always be true because the escape velocity of the planets in our solar system isn't going to change.
Even if there were spacecraft designed for combat, they wouldn't be crewed in general: the maintenance of human life in space is outrageously resource-intensive and would place unreasonable limitations on the duration and nature of combat missions. Artificial intelligence would be the likely solution. No life support means smaller ships with less mass which means less fuel consumption which means longer missions which means higher mission success rate, etc..
For the same reason, armor on spacecraft would be irrelevant. If your spacecraft gets hit by any nontrivial weapon, it won't survive, so what's the point? Not only that, but armor of any sort will add mass. Relative velocity is a superior quality (consider a rough analogy, for example, in the history of bombers in World War 2).
Unlike in Earth's atmosphere, friction is not an issue. Momentum, however, is. Should your craft ever wish to change direction, that's going to cost fuel. Depending on how drastic you want the change to be, it may cost a lot of fuel.
Only in the very far future would large quantities of armored, crewed spacecraft even begin to be a remote possibility.