Mine Shaft Gap is a free science fiction board game. From the description:
Mine-Shaft Gap simulates a battle for resources on, above, and under the surface of a lifeless but treacherous planetoid. Players must seek out valuable metals and fuel materials and mine them, using the materials to feed their home planets, and inch closer to victory, while at the same time allocating resources to maintain or strengthen their armed forces and fortifications. Drill tanks tunnel beneath the surface of the planet while drilling stations pound away from above. Drilling stations are faster and more efficient, but are vulnerable to attack from above and even capture by enemy troops. But tunnels can cave in… And market forces are unpredictable. The resource making your planet rich today might be better off greasing the treads of your tanks tomorrow!