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Venus is considered Earth’s sister planet because they are roughly the same size and have a similar composition. However, the similarities end there. After scientists took a close look at Venus, they were greeted with a hot hellish landscape of sulfuric acid clouds. The European Space Agency (ESA) is planning a new mission to Venus, where its EnVision probe can conduct detailed science never before possible. First, engineers must figure out how to prevent the spacecraft from falling apart as it descends into the planet’s fierce atmosphere.
ESA announced its selection of EnVision last year, and in recent days has provided an update on the probe’s design and construction. The plan is for EnVision to perform an air-stop maneuver in orbit around Venus, allowing it to gradually lower its orbit while scanning the surface. The agency has experience with this process from the Trace Gas Orbiter (TGO) as well as Venus Express. In the latter case, ESA attempted an air-stop only at the end of the mission in 2014 and burned up in the atmosphere. With EnVision, ESA must surf the corrosive soup stuck to Venus before it can start doing science.
Specimens for simulated air suspension tests.
Venus’ atmosphere is 92 times denser than Earth’s, is composed almost entirely of carbon dioxide, and probably does not support life. Crushing pressure is complemented by temperatures that reach 864 degrees Fahrenheit (462 degrees Celsius). For the record, that’s several hundred degrees above the melting point of lead. This makes it so difficult to study Venus up close, but EnVision was designed specifically for these conditions.
EnVision will most likely launch in the early 2030s on an Ariane 6 rocket. ESA says it can’t predict enough mass to give the orbiter fuel to lower its orbit, so it will rely on an airdrop . The mission will launch into a very high orbit of 250,000 kilometers (155,000 miles) and, through successive passes through the atmosphere, will drop to a 500-kilometer (310 miles) polar orbit for science operations — it will not land on the surface.
ESA plans to slow it down with EnVision. Since the heat is generated as the cube of the velocity, it will spend about twice as much time decelerating as the TGO. Engineers are also hard at work testing different air suspension materials. They have to contend with extreme temperatures, and Venus’ atmosphere is also high in reactive atomic oxygen. Fortunately, ESA has a facility that can generate atomic oxygen at energy levels that are equivalent to orbital velocity. They test insulation materials, antennas, star trackers, and more. These materials must resist erosion while maintaining their optical properties, ensuring that the probe’s sensitive instruments work once it reaches its intended orbit. The team expects to receive the results of this testing by the end of this year.
When EnVision settles into its final orbit, it will map the planet in more detail than ever before. Scientists hope that by studying Venus, which may be a victim of the greenhouse effect, we can gain insight into what is happening on Earth.
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