Lots of solar power, too, and lightsails and magsails have more to work with. (I was thinking of free-space skyhooks, exchanging momentum between inbound and o

Lots of solar power, too, and lightsails and magsails have more to work with. (I was thinking of free-space skyhooks, exchanging momentum between inbound and outbound trips, but the ones for planets are also cool. Just harder when the planet is heavy like Earth and Venus.)