Plausible mid-future Space Marine*:
The main weapon is computer-controlled and aim wherever the user is looking. I figured that a few hundred years from now and we wouldn't be trusting our notoriously unreliable meat** to aim weapons anymore.
*I'm not a fan of the term Space Marine, simply because it's so heavily freighted with baggage. Orbital Marine doesn't really cover it, Vacuum Marine is probably more accurate but has strange cleaning connotations. Astro-Anything just sounds weird.
**I realize that eyes are still technically meat.