> Colonists to Venus would not build on the planet's surface; they would, in theory, set up a floating "cloud city" in Venus’s atmosphere. Of course, Venus-bound missions would "require big policy changes at NASA," writes Elizabeth Lopatto for The Verge. But two scientists, Dale Arney and Chris Jones, of NASA’s Systems Analysis and Concepts Directorate at Langley Research Center in Virginia, point out that about 31 miles above the surface, the gravity and pressure is Earth-like, temperatures stay near the more manageable 167 degrees F and the colony would be more shielded from the Sun’s radiation than Mars.

It is easier to heat something than cool something. A permanently flying vessel [which is essentially what Venus requires] isn't safe except as a robotic design. It is a fatal mechanical failure waiting to happen.

There is a reason planes need so much maintenance and it isn't "saving money". A plane that would never have to land or need maintenance would be cheaper.

Sure, the ISS can manage it and you could probably set up something similar on Venus. But it wouldn't be a permanent, expandable settlement like you might be able to do on Mars.

Venus with a sun shield at L1! We're technologically far from being able to do it, but the physics seem straightforward. Venus has proven, at least, that it can hold onto an atmosphere.

From Kim Stanley Robinson's 2312 http://en.wikipedia.org/wiki/2312_%28novel%29.

The L1 point is unstable, however. (Saddle point). Though you already have a solar sail...

Better hope your control loop is well and truly stable.

I sounds like a nice control theory problem to see if you can stabilize an orbit near L1 with a solar sail and a minimal gyro, while fullfilling the role of blocking radiation maximally; I'm not very qualified though. I think you'd need to place the object not actually at L1 but at an orbit closed to the sun so that mean reflective impulse at the sun-veanus direction generated by the sail cancels out the extra gravity.

I love this kind of proposal because it's hard to tell off the top of your head whether it's absurd or completely plausible, given some technological level. You have to look at the basic numbers.

According to this link we already have satellites at Earth's L1 and L2 points (!):

http://map.gsfc.nasa.gov/mission/observatory_l2.html