NASA Study Proposes Airships, Cloud Cities for Venus Exploration

Image: NASA Langley Research Center

It has been accepted for decades that Mars is the next logical place for humans to explore. Mars certainly seems to offer the most Earth-like environment of any other place in the solar system, and its closer to Earth than just about anyplace else, except Venus. But exploration of Venus has always been an enormous challenge: Venuss surface is hellish, with 92 atmospheres of pressure and temperatures of nearly 500 C.

The surface of Venus isnt going to work for humans, but what if we ignore the surface and stick to the clouds? Dale Arney and Chris Jones, from the Space Mission Analysis Branch of NASAs Systems Analysis and Concepts Directorate at Langley Research Center, in Virginia, have been exploring that idea. Perhaps humans could ride through the upper atmosphere of Venus in a solar-powered airship. Arney and Jones propose that it may make sense to go to Venus before we ever send humans to Mars.

To put NASAs High Altitude Venus Operational Concept (HAVOC) mission in context, it helps to start thinking about exploring the atmosphere of Venus instead of exploring the surface. The vast majority of people, when they hear the idea of going to Venus and exploring, think of the surface, where its hot enough to melt lead and the pressure is the same as if you were almost a mile underneath the ocean, Jones says. I think that not many people have gone and looked at the relatively much more hospitable atmosphere and how you might tackle operating there for a while.

At 50 kilometers above its surface, Venus offers one atmosphere of pressure and only slightly lower gravity than Earth. Mars, in comparison, has a sea level atmospheric pressure of less than a hundredth of Earths, and gravity just over a third Earth normal. The temperature at 50 km on Venus is around 75 C, which is a mere 17 degrees hotter than the highest temperature recorded on Earth. It averages -63 C on Mars, and while neither extreme would be pleasant for an unprotected human, both are manageable.

Whats more important, especially relative to Mars, is the amount of solar power available on Venus and the amount of protection that Venus has from radiation. The amount of radiation an astronaut would be exposed to in Venuss atmosphere would be about the same as if you were in Canada, says Arney. On Mars, unshielded astronauts would be exposed to about 0.67 millisieverts per day, which is 40 times as much as on Earth, and theyd likely need to bury their habitats several meters beneath the surface to minimize exposure. As for solar power, proximity to the sun gets Venus 40 percent more than we get here on Earth, and 240 percent more than wed see on Mars. Put all of these numbers together and as long as you dont worry about having something under your feet, Jones points out, the upper atmosphere of Venus is probably the most Earth-like environment thats out there.

Its also important to note that Venus is often significantly closer to Earth than Mars is. Because of how 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: 110 days out, a 30-day stay, and then 300 days backwith the option to abort and begin the trip back to Earth immediately after arrival. That sounds like a long time to spend in space, and it absolutely is. But getting to Mars and back using the same propulsive technology would involve more than 500 days in space at a minimum. A more realistic Mars mission would probably last anywhere from 650 to 900 days (or longer) due to the need to wait for a favorable orbital alignment for the return journey, which means that theres no option to abort the mission and come home earlier: If anything went wrong, astronauts would have to just wait around on Mars until their return window opened.

HAVOC comprises a series of missions that would begin by sending a robot into the atmosphere of Venus to check things out. That would be followed up by 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.

The defining feature of these missions is the vehicle that will be doing the atmospheric exploring: a helium-filled, solar-powered airship. The robotic version would be 31 meters long (about half the size of the Goodyear blimp), while the crewed version would be nearly 130 meters long, or twice the size of a Boeing 747. The top of the airship would be covered with more than 1,000 square meters of solar panels, with a gondola slung underneath for instruments and, in the crewed version, a small habitat and the ascent vehicle that the astronauts would use to return to Venuss orbit, and home.

Getting an airship to Venus is not a trivial task, and getting an airship to Venus with humans inside it is even more difficult. The crewed mission would involve a Venus orbit rendezvous, where the airship itself (folded up inside a spacecraft) would be sent to Venus ahead of time. Humans would follow in a transit vehicle (based on NASAs Deep Space Habitat), linking up with the airship in Venus orbit.

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NASA Study Proposes Airships, Cloud Cities for Venus Exploration