Forbidden Planet- page 3 | Space | Air & Space Magazine
Most pictures of the Venus surface are synthetic, like this view of a volcanic region called Eistla, created from Magellan orbital radar data. The SAGE lander would take actual photos from ground level. (NASA/JPL)

Forbidden Planet

We’ve been to the moon. Mars is easy. But landing on Venus? That’s tough.

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(Continued from page 2)

Back in the 1970s, Soviet scientists were shocked by the softness of the weather rind—one Venera probe took just two minutes to drill down an inch. The soft Venusian crust can conceal bits of harder material, however—nuts in the brownie—and robotic drills have been known to struggle with differences in rock density. So the SAGE drill may have to work harder to get to the soil underneath. The depth of the weather rind is in fact one of the things the mission will try to determine.

What scientists really want to know about Venus—beyond what the rocks are made of—is how the air, volcanoes, and surface interacted to bring the planet to its current boil. In other words, how the planet works as a system, and how that system went awry. “Venus is like the Earth, but has taken a different evolutionary path,” says Esposito. “And everything from its center to the top of the atmosphere plays into and contributes to those different evolutionary paths.”

Answering the question requires lots of data, and the lander will have to gather its information without human supervision. The pictures and other data will arrive at Earth only after the lander has finished its work on the surface.

To ensure its survival on Venus, the SAGE lander will have to endure grueling trials in several test chambers, some new and some old. NASA’s Venus test chambers from the Pioneer days simulated the surface temperature just fine, but didn’t bother duplicating the carbon dioxide atmosphere, on the assumption that it posed no threat to spacecraft. No one is making that mistake this time around; the new chambers are toxic kilns.

So far, Smrekar’s team has tested mechanical parts and materials in chambers up to two feet in diameter, sometimes observing them through small windows. (Nothing has failed yet.) To simulate the spacecraft’s aerodynamic stability in the upper atmosphere of Venus, the engineers will test it in a wind tunnel. For simulating the lower atmosphere, they will place it in a water tank.

One item of vital concern is the communications antenna. The thick clouds around Venus muffle radio waves, and SAGE won’t have much lung power to begin with. Nor will it have orbiting satellites to communicate with, as the Mars rovers do. All the lander’s data will be beamed up to the spacecraft that dropped it off, and from there relayed to Earth. As with the rest of the SAGE hardware, the communication system has to work in terrific heat.

Unfortunately, beyond a certain temperature—about 250 degrees Fahrenheit—commercial silicon electronics crap out, and the temperatures on Venus are hundreds of degrees higher than that. Semiconductors made of silicon blended with carbon, or gallium blended with nitrogen, might be hardy enough.

Or, the engineers could revive a technology from the 1950s, says Sanjay Limaye, a University of Wisconsin planetary scientist. Vacuum tubes turned out to be impractical for computers for a number of reasons, one being that they blazed so hot that they eventually popped in air that was many degrees cooler. But that heat makes them perfect for Venus, with its higher ambient temperature.

“We used to know how to do high-temp electronics when we had vacuum tubes,” says Limaye. And even though some of that knowledge has been lost after decades of using silicon circuits, he thinks tubes could be adapted for Venus radios—provided they’re smaller than the ones used in 1955 Zenith TVs.

ANY VENUS LANDER launched in the near future will live on the surface five hours, at most. Whether that’s long enough “depends on what your perspective is, whether you’re a glass half-full or half-empty person,” says Limaye. Even three hours gives a spacecraft time to collect data, take pictures, and do a little drilling. But to really understand how the Venus system works over time—that requires longer missions and new technologies.

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