Vespene is a heavy gas. It is under the crust of the planet. It is formed closer to the core, much deeper than metal or minerals. To extract it commercially, refineries must be drilled. Develop refineries, drill deeper and produce more. Vespene is needed as fuel for ships. It is needed for almost all research and viewing of the galaxy, as well as for using by the sensor phalanx.
+ 6 * level * 1.1 to the power of level * (1.28 - 0.002 * maximum temperature of the planet)
- 20 * level * 1.1 to the power of level