Venus isn't exactly the best place for humans to inhabit. In fact, it's a hellish place with scorching hot temperatures and crushing air pressure. Temperatures at the surface are enough to melt lead. The atmospheric pressure is also comparable to the pressure 3,000 feet below the surface of the ocean.

The extreme condition on the surface of Venus explains why scientists have been favoring Mars as the next extraterrestrial world for humans to explore -- and possibly inhabit -- regardless of the fact that Venus is the closest planet to Earth.

It appears, however, that there are NASA scientists who have not yet given up on the possibility of sending manned missions to Venus. In fact, the idea of setting up a cloud city in the solar system's hottest planet is currently being explored.

Dale Arney and Chris Jones from NASA's Systems Analysis and Concepts Directorate's Space Mission Analysis Branch had been pondering on humans riding through and possibly dwelling in Venus' upper atmosphere in a solar-powered airship, citing that despite the tempestuous conditions on the surface of the planet, at about 50 kilometers above the surface, the atmosphere thins and cools to one comparable to what can be found on Earth.

The potentially habitable condition above Venus is where the idea for NASA's High Altitude Venus Operational Concept (HAVOC) comes in. HAVOC involves a number of missions that would start with a robot being deployed to Venus' atmosphere to assess things, followed by a 30-day manned mission to the planet's orbit.

A mission that involves a month-long stay at the planet's atmosphere would then come next, followed by missions with longer durations of stay until there would be a permanent human presence in what could become a floating cloud city.

"If one does see humanity's future as expanding beyond just Earth, in all likelihood, Venus is probably no worse than the second planet you might go to behind Mars," Arney said. "Given that Venus's upper atmosphere is a fairly hospitable destination, we think it can play a role in humanity's future in space."

The vehicle that would be used for the mission is an airship with more than 1,000 square meters of solar panels on its top to harness the power of the sun. The robotic version of the helium-filled aircraft would be 31 meters long, but the version carrying a crew would measure nearly 130 meters in length, which is about the size of two Boeing 747 airplanes.