Nasa plans to send solar-powered airships to explore Venus' atmosphere and to eventually establish a permanent human colony in a floating cloud city above the Earth's nearest planetary neighbour.
Dale Arney and Chris Jones, from the Space Mission Analysis Branch of Nasa's Systems Analysis and Concepts Directorate at Langley Research Center, in Virginia, have proposed that it may make sense to go to Venus before we ever send humans to Mars.
Nasa's High Altitude Venus Operational Concept (HAVOC) mission aims to explore the atmosphere of Venus instead of exploring the surface.
The researchers believe the upper atmosphere of Venus is "probably the most Earth-like environment that's out there."
At 50 kilometres above its surface, Venus offers one atmosphere of pressure and only slightly lower gravity than Earth.
Astronauts would also be protected from radiation in Venus's atmosphere, researchers said. The planet's proximity to the Sun provides it 40% more solar power than the Earth gets, and 240% more than that seen on Mars.
Since the orbits of Venus and Earth align over time, a crewed mission to Venus would take a total of 440 days using existing or very near-term propulsion technology, 'IEEE' reported.
But getting to Mars and back using the same propulsive technology would involve more than 500 days in space at a minimum.
HAVOC involves a series of missions, including a robotic mission first and then a crewed mission to Venus orbit with a stay of 30 days, and then a mission that includes a 30-day atmospheric stay.
Later missions would have a crew of two spend a year in the atmosphere, and eventually there would be a permanent human presence there in a floating cloud city.
A helium-filled, solar-powered airship would explore the planet's atmosphere. The robotic version would be 31 metres long while the crewed version would be nearly 130 metres long.
The crewed version would come with a small habitat and the ascent vehicle, a winged two-stage rocket slung below the airship, that the astronauts would use to return to Venus's orbit and home.