Some building types may be upgraded as replacements are researched.
Solar Power Plants may be upgraded to Nuclear Power Plants.
Nuclear Power Plants may be upgraded to Fusion Power Plants.
Planetary Mines may be upgraded to Lunar Mines.
Lunar Mines may be upgraded to Asteroid Mines.
Civilian Residences may be upgraded to Skyscrapers.
The cost to upgrade is one-half the current build cost. An upgrade takes approximately
half as long as building a new building.
You can see the status of upgrades by clicking on the My Status link in the left menu,
then on Construction Status.