We’ve been to the moon. Mars is easy. But landing on Venus? That’s tough.
- By Sam Kean
- Air & Space magazine, September 2010
(Page 3 of 4)
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.
Insulation won’t be enough. Long-duration (weeks-long) landers will require “active” cooling—refrigeration—says planetary scientist Mark Bullock of the Southwest Research Institute in Boulder, Colorado, who heads the team designing SAGE’s camera. Future Venus landers would basically be Frigidaires, devoting 70 percent or more of their power to staying cool. They will more than likely need multi-stage cooling: fridges within fridges. The only way to achieve that, says Bullock, is with nuclear power.
Other scientists have speculated beyond rovers to Venus aircraft. To investigate how a planet that rotates so slowly can generate such powerful winds, some suggest penetrating the acid clouds with a Teflon-coated helium-filled balloon. Scientists like Geoffrey Landis at NASA’s Glenn Research Center in Ohio have proposed sending an autonomous airplane with the rover. Landis points out the advantages of this one-two combination: The airplane would fly in the cooler upper atmosphere, which is friendlier to electronics. If most of the computer brain power were placed on the airplane, it could direct the rover from above.
With these kinds of tools, scientists could really start to unravel the mysteries of Venus: Why the planet doesn’t have plate tectonics, what happened to its water, and the Big Question: Could the same runaway greenhouse effect happen on Earth? It’s still not clear which one of the twin planets is the anomaly, says Smrekar. “We have two end members of [the spectrum of] Earth-like planets, and it will be interesting to see which is more common.”