Battlelords of the 23rd. Century 7th. Edition.
I was looking to see if anyone here mentioned this.
The setting is pure space opera, but the rules are hardcore. To be honest I'm surprised people don't use it for a game like
Traveller. People claim they like the hardcore setting of traveller, and BL has a very hardcore setting under it's space opera cover. It's rules for sensors, comms, active systems vs passive ones, electronic warfare, etc should make it a dream system for traveller fans.