With all the talk about sending humans to the moon and eventually Mars, it can be easy to forget there are other planets worth exploring. But a team of researchers at NASA has set its sights on Venus, Earth’s closest neighbor and one of the least understood planets in the solar system.
Since the first (crash) landing on Venus in 1966, by a Soviet probe, spacecraft have only survived a total of a few hours on the planet’s surface. But NASA’s new probe is being designed last up to 60 days on the punishing Venusian surface. Known as the Long-Lived In-situ Solar System Explorer, or LLISSE, each of the probe’s components is specially engineered to withstand the high temperature, high pressure, and reactive atmosphere that define that infernal planet.
Venus has rightfully earned a reputation as Earth’s “evil twin.” Their mass and size are roughly the same, and scientists believe that Venus was once a water-rich paradise that may have hosted elementary life. Today, however, conditions on its surface are downright hellish. Temperatures are high enough to turn a block of lead into a puddle, and the atmospheric pressure is similar to what you’d find diving thousands of feet deep into the ocean. If that’s not enough, winds whip around the planet at tornado-like speeds, and during the day thick clouds of sulphuric acid blot out the sun. Once night falls, it lasts for over 100 Earth-days.
The going theory is that Venus once had a vast, shallow ocean of liquid water that the sun eventually boiled off. As the ocean evaporated and hydrogen escaped into space, the carbon dioxide-rich atmosphere fueled a runaway greenhouse effect and turned the planet into the hellscape we see today. But the planet’s thick atmosphere limits the amount of information that spacecraft can collect as they orbit or fly by. To learn what happened on Earth’s neighbor, scientists need to get to the surface.
At the center of NASA’s renewed Venus ambitions is Tibor Kremic, chief of the space science project office at Glenn Research Center in Ohio. Unlike the car-sized rovers NASA drops on Mars, LLISSE is small because it will have to hitch a ride with other spacecraft headed to the neighborhood. It’s a cube less than 10 inches to a side, and it’s packed with instruments to test everything from the Venusian atmosphere to its geology.
Shoring up LLISSE for the extremes of Venus has been an all-consuming task. Because the carbon dioxide-rich atmosphere contains trace amounts of sulfur, crystals quickly form on normal electronic components. So Kremic and the LLISSE team designed and built hardened chips out of silicon carbide, a synthetic material found in sandpaper and fake diamonds. Every sensor on the probe also has to be similarly hardened. But LLISSE’s size constraints mean it won’t carry some instruments you might find on other spacecraft—like cameras. “If there’s a way for us to put a camera on LLISSE, you bet we’ll try, but it’s a little small for that,” says Kremic.
One of the biggest challenges, says Kremic, was figuring out how to power the probe for a full 60 days. Many deep space missions rely on small nuclear reactors to generate power, but LLISSE will use a heat-activated thermal battery similar to the kind found in missiles. Limiting power flow from the battery so it doesn’t drain too quickly is an ongoing engineering challenge.
As they build the probe’s components, Kremic and his team methodically test each one for up to two months inside a chamber that perfectly replicates the conditions on Venus. Kremic and his team want the probe to last that long so it can witness the transition between night and day. If they land late in a Venusian day, which lasts almost four Earth months, they think they can eke out enough battery life to make that happen. “We don’t have any data on how the conditions change from day to night on Venus,” says Kremic. “We’re trying to capture as much of that as possible.”
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