PTHC

Pressure, Temperature, Humidity Control.
Abbreviation used (mainly) in science fiction when describing the process of terraforming a planet i.e. making a planet more "earth-like", improving its chances of supporting Life.
Humidity refers to atmoshperic density, not concetration of vapor (H2O) gas.

The 2008 Maxis game "Spore" has comprehensive PTHC tools.

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