[lightknight]

So...launch some floating cities, send them to Venus, send the astronauts later on. There's more than enough energy in the atmosphere to run machinery, and unless there are some truly violent lightning storms, the cities should stay afloat. As tech advances, a cable can be dropped to the surface (or several of them), and colonization take place.

Pity the atmosphere is so inhospitable, the surface so bland, and the utter lack of lifeforms. But a little work, and it will probably resemble Earth.

As for Mars, Mercury, and the Moon...Mercury is a surprising read. Mars would need nuclear reactors, I agree, or some other process for creating energy (anything in the soil that could react chemically with something else?). And the Moon...hmm. There's just a lack of data here, for all of them.