|A dirigible approaches an outpost in the atmosphere of Venus. Image credit: NASA.|
There's no award for "Most Imaginative Space Engineer," but if there were, Geoffrey Landis would certainly be a top contender. In fact, if such an award is ever created, it should perhaps be named the Geoffrey, in parallel with science fiction's Hugo Award, which owes its name to pioneering author, editor, and publisher Hugo Gernsback. Not incidentally, Landis owns a pair of Hugos; he received his first in 1992 for "A Walk in the Sun," a short story set on the Moon, and his second in 2003 for his story "Falling Onto Mars."
Landis is an engineer at NASA's Glenn Research Center (GRC) in Cleveland, Ohio. Much of his NASA work has centered on energy systems, with an emphasis on solar photovoltaic power.
In a brief paper prepared for the February 2003 Space Technology and Applications International Forum in Albuquerque, New Mexico, Landis made a compelling case for Venus, not the Moon, nor Mars, nor a twirling sphere, torus, or tube in open space, as the ideal place to establish an off-Earth human settlement. Specifically, he set his sights on the Venusian atmosphere just above the dense sulfuric-acid clouds. Landis called it "the most earth-like environment (other than the Earth itself) in the Solar System."
Most people think of Venus as a hell planet because they think only of its surface. By about 1960, scientists using Earth-based instruments had determined that Venus had a temperature of 342° C (648° F). Many, however, refused to believe that Venus could be so hot. Some tried to find a loophole: they hypothesized that the Venusian atmosphere was hot while its surface was cool enough for liquid water and life.
Mariner 2, the first successful interplanetary spacecraft, flew past Venus in December 1962. Its crude scanning radiometer found a lower temperature — around 230° C (450° F) — though one still much higher than most planetary scientists expected. Mariner 2 also determined that air pressure at the Venusian surface was at least 20 times Earth sea-level pressure.
For more than two decades, Venus was the Soviet Union's favorite Solar System exploration target. The Venera landers determined that its surface is made of basalt, a volcanic rock. They also found that the mean atmospheric pressure at the surface is 96 times Earth sea-level pressure and that the surface temperature averages about 462° C (863° F) with relatively modest day/night, latitude, and altitude variations.
The Venusian atmospheric temperature, on the other hand, was found to vary significantly with altitude, a fact that the Soviet Union would put to good use. In June 1985, the Vega 1 and Vega 2 spacecraft released armored landers and lightly constructed rubber balloons as they flew past Venus on their way to Comet Halley. The Vega 1 lander touched down but returned minimal data. Vega 2 landed successfully and survived the hellish surface conditions for 56 minutes.
The twin three-meter-diameter, helium-filled balloons deployed between 50 and 55 kilometers (31 and 34 miles) above the Venusian surface — that is, just above the cloud-tops, in the zone Landis saw as promising for human settlement. Their small instrument payloads transmitted data for approximately two days — until they exhausted their chemical batteries.
In that time, the balloons rode the carbon dioxide winds from their deployment points over the nightside into bright Venusian daylight. The Vega 2 balloon travelled about 11,100 kilometers (6900 miles) and the Vega 1 balloon travelled 11,600 kilometers (7210 miles). When their instrument payloads exhausted their batteries, the balloons carrying them showed no sign of imminent failure. They might have lasted for months or even years.
|Vega-type balloon on display at the National Air and Space Museum's Udvar-Hazy Center in northern Virginia, just outside Washington, DC. Image credit: Geoffrey A. Landis.|
The fragile balloons could last so long because 50 kilometers above Venus, just above the cloud tops, the temperature ranges from between 0° C to 50° C (32° F to 122° F) and the atmospheric pressure approximates Earth sea-level pressure. A thin fabric cover was sufficient to shield each balloon from sulfuric acid droplets drifting up from the cloud layer.
Venus settlers would float where Vega 1 and Vega 2 floated, but Landis rejected helium balloons. He noted that, on Venus, a human-breathable nitrogen/oxygen air mix is a lifting gas. A balloon containing a cubic meter of breathable air would be capable of hoisting about half a kilogram, or about half as much weight as a balloon containing a cubic meter of helium. A kilometer-wide spherical balloon filled only with breathable air could in the Venusian atmosphere lift 700,000 tons, or roughly the weight of 230 fully-fueled Saturn V rockets. Settlers could build and live inside the air envelope.
The air envelope supporting a settlement would not necessarily maintain a spherical form. Lack of any pressure differential would allow the gas envelope to change shape fluidly over time. It would also limit the danger should the envelope tear. The internal and external atmospheres would mix slowly, so the settlement atmosphere would not suddenly turn poisonous, nor would the settlement rapidly lose altitude.
A repair crew would not require pressure suits, Landis explained. They would, of course, need air-tight face masks to provide them with oxygen and keep out carbon dioxide; adding goggles and unpressurized protective garments would keep them safe from acid droplets.
Acid droplets in the Venusian atmosphere would no doubt be annoying, but Venus would lack the frequent toxic dust storms of Mars. Orbiting nearly twice as close to the Sun as does Mars, a Venusian solar farm would have available four times as much solar energy at all times — and with no dust storms to get in the way. Landis noted that solar panels could collect almost as much sunlight reflected off the bright Venusian clouds as they could from the Sun itself.
Mars, the Moon, and free-space habitats all must contend with solar and galactic-cosmic ionizing radiation. A settlement 50 kilometers above Venus, by contrast, could rely on the Venusian atmosphere to ward off dangerous radiation. Radiation exposure would be virtually identical to that experienced at sea level on Earth.
Many aspiring space settlers assume that humans and the plants and animals they rely on (or simply like to have around) will be able to live in one-sixth or one-third Earth gravity — the gravitational pull felt on the Moon and on Mars, respectively — with no ill effects. The hard reality, however, is that no one knows if this is true. It is possible that astronauts living in hypogravity — that is, gravity less than one Earth gravity — will experience health effects similar to those they experience during long stays in microgravity (for example, on board the International Space Station).
Venus is nearly as dense and as large as Earth, so its gravitational pull is about 90% that of humankind's homeworld. The likelihood that hypogravity will make long-term occupancy unhealthful might thus be reduced.
The Venusian atmosphere is rich in resources needed for life and the Venusian surface, while hellish, would lay only 50 kilometers away from the settlement at all times. Landis suggested that Venus settlers might use a suspended super-strong cable to lift silicon, iron, aluminum, magnesium, potassium, calcium, and other essential chemical elements to the floating settlement. He noted that laboratory experiments aimed at producing robots hardy enough to function on Venus for long periods had already begun; operators might use such rovers to remotely mine the surface from the comfort of the floating settlement.
Landis pointed to the Main Asteroid Belt between Mars and Jupiter as a potential source of resources for Venus. He noted that any given asteroid in the Main Belt is easier to reach from Venus than from the Earth or Mars. A spacecraft launched from Venus on a minimum-energy trajectory can, for example, reach resource-rich 1 Ceres, the largest asteroid, in a little less than an Earth year; a minimum-energy trip from Earth to 1 Ceres would need a little more than an Earth year.
|Image credit: NASA.|
The large Main Belt asteroids are in fact generally located farther away from each other than they are from Venus. They also orbit the Sun much more slowly: 3 Vesta needs 1325 Earth days to circle the Sun once; 1 Ceres needs 1682 Earth days; 2 Pallas, 1686 Earth days; and 10 Hygeia, in the outer part of the Main Belt, 2035 Earth days. This means that minimum-energy transfer opportunities between Main Belt asteroids occur years or even decades apart. Opportunities for minimum-energy transfers between Venus and any Main Belt asteroid, on the other hand, occur about once per Venus year (that is, about once every 225 Earth days).
As the journeys of the twin Vega balloons illustrate, Venus atmosphere settlements would ride fast winds. Those near the equator would circle the planet every four days. This would mean, Landis explained, that they would experience a day/night pattern of two days of darkness followed by two days of light. He expected that settlements eager for a more Earth-like lighting pattern could migrate to the Venusian circumpolar regions, where a circuit around the planet would be shorter.
If many "cloud cities" were eventually established in the atmosphere of Venus, then a preference for the poles might lead to crowding. If, on the other hand, any latitude were fair game, then Venus would offer for settlement a total area 3.1 times Earth's land area — that is, more than three times greater than the surface area of Mars. Landis wrote that, eventually, a "billion habitats, each one with a population of hundreds of thousands of humans, could. . . float in the Venus atmosphere."
Mariner Venus 1962 — Final Project Report, NASA SP-59, NASA Jet Propulsion Laboratory, 1965.
Soviet Space Programs 1980-1985, Nicholas L. Johnson, Volume 66, Science and Technology Series, American Astronautical Society, 1987, pp. 186-188.
"Colonization of Venus," Geoffrey A. Landis, Space Technology and Applications International Forum (STAIF) 2003, Albuquerque, New Mexico, 2-5 February 2003; American Institute of Physics Proceedings 654, Mohamed S. El-Genk, editor, 2003, pp. 1193-1198.