In Civ2 I always built up a large treaury so I could rush-build my spaceship, but that doesn't seem to work in Civ3. However, it is possible to switch from a wonder to a spaceship component. So as you research the techs needed for a spaceship, keep building wonders large and small in all your big cities. When a tech is complete, look for an incomplete wonder with the right number of shields accumulated,then switch. Then restart the wonder. If you do this skillfully, you can win the game on the same turn that you get the final sapceship technology. I haven't checked whether you can almost complete a battleship by disbanding and lumberjacking, then switch to a wonder for a few turns, then switch to spaceship component.