Do you have additional ideas? I would prefer a game with slight fantasy influences like the
old D&D Buck Rogers.
In no particular order:
1) Any generic-ishy ruleset should work- HERO and GURPS both have Sci-Fi settings into which you can drop fantasy elements. While not technically a generic ruleset, M&M has many of the same characteristics as one, and should do just fine.
2) Spaceship Zero. Its based on shows like Buck Rogers & Flash Gordon.
3) Star Wars (any version- FASA, WotC, etc.)- a classic Space Opera meld of sci-fi and fantasy. The Dune RPG would have similar elements in its mix.
4) Dragon Star- its D&D in space- 'nuff said.
5) A hard sci-fi game like Traveller (any version) would be cool, but you'd need to flesh out the fantasy elements of the game yourself. Alternity or its D20 Future conversion takes care of that if you use material drawn from Urban Arcana, Dark*Matter, as well as Green Ronin's Modern Magic and the Psychic's Handbook)
6) Fading Suns has a D20 version.
7) Depending upon your setting's timeline, you might want something more Victorian, like Space:1889- gaming in a Wellsian/Vernian campaign world.
8) With some tweeking, the WW2 Supers game Godlike could get you what you want. Ditto the FRPG, Iron Kingdoms.
9) Shadowrun and RIFTS both combine sci-fi and fantasy. The former has a lot to offer, but you'd have to tweek it for that Buck Rogers feel. The latter's mechanics are not well loved- and for good reason- but its incredibly creative. Good for source material if nothing else.