Europe’s planned Venus exploration mission will depend on a difficult aerobraking procedure to lower its orbit, which will test the thermal resilience of the spacecraft’s materials to their limits.
The Envision Missionscheduled for launch in the early 2030s, will study the geology and atmosphere of Venusthe hellish planet that may have once looked quite like the earth but turned into a hostile burnt world due to a runaway Greenhouse effect.
To get EnVision to its target orbit, 310 miles (500 kilometers) above the surface of Venus (which is so hot it would melt lead), it will take thousands of passes through the the thick atmosphere of the planet over a two-year period, the European Space Agency (ESA) said in a statement (opens in a new tab).
“EnVision as currently designed cannot take place without this long aerobraking phase,” ESA’s EnVision study leader Thomas Voirin said in the statement.
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The van-sized spacecraft that will launch into the future of Europe Ariadne 6 rocket, will not be able to carry enough fuel to slow down in the orbit of Venus thanks to the onboard propulsion. Instead, it will use the aerobraking procedure and follow a highly elliptical orbit that will periodically bring it within 80 miles (130 km) of the surface of Venus at its closest point and approximately 155,000 miles ( 250,000 km) from the planet at its furthest point.
ESA previously used aerobraking to slow the ExoMars Trace Gas Orbiter before it enters its scientific orbit around March. But the atmosphere of Mars is much finer than that of Venus, and its gravity is much lower, which affects the speed of the spacecraft in orbit.
“Airbraking around Venus is going to be much more difficult than Trace Gas Orbiter,” Voirin said. “The gravity of Venus is about 10 times greater than that of Mars. This means that speeds about twice as high as for TGO will be felt by the spacecraft as it passes through the atmosphere, and heat is generated under the shape of a speed cube.
ESA briefly tested aerobraking around Venus during the last months of the Venus Express mission, which eventually spiraled toward the planet and burned up in the atmosphere in 2014. As Venus Express was already at the end of its mission, spacecraft controllers were unconcerned about the damage to the spacecraft caused by heat. EnVision, on the other hand, is expected to explore Venus for at least four years.
Engineers are already busy finding the right materials that would allow EnVision to withstand the extreme conditions. In addition to the heat experienced during the aerobraking procedure, the spacecraft will also be exposed to very high concentrations of highly reactive atomic oxygen. Atomic oxygen is a form of oxygen present in the upper layers of earth’s atmosphere, which consists of a single oxygen atom. Atomic oxygen, an enemy of all low ground spacecraft in orbit, thermal blankets burned on several NASA spaceship assignments in the 1980s.
Observations from previous Venus missions have shown that atomic oxygen is present in the upper layers of Venus’ atmosphere at concentrations similar to those around Earth.
“The concentration is quite high. In one pass it doesn’t matter that much, but after thousands of times it starts to build up and ends in a level of atomic oxygen fluence that we have to consider, equivalent to what we feel in low Earth orbit, but at higher temperatures,” Voirin said.
ESA is currently testing materials for their ability to withstand both the heat and the atomic oxygen concentration expected during EnVision aerobraking and hopes to have selected candidate materials by the end of this year. .
“We want to verify that these parts resist erosion, and also maintain their optical properties – i.e. they don’t degrade or darken, which could impact their thermal behavior, because we have delicate scientific instruments that have to maintain a set temperature,” Voirin said. “We also have to avoid scaling or outgassing, which leads to contamination.”
Venus, sometimes considered Earth’s twin due to their similar sizes, has recently been somewhat sidelined by solar system explorers because potentially more habitable Mars (which is more likely to harbor traces of life) has become the favorite. But a 2020 study that detected molecules that could be traces of living organisms in the planet’s sulfur-rich clouds has sparked new interest in Venus.
In addition to Europe, NASA plans to send orbiters to the burning planet: the DAVINCI+ and VERITAS missionsscheduled for launch between 2028 and 2030. Currently only one spacecraft, Japan Akatsukiis orbiting Venus, studying its dense atmosphere in an attempt to unravel the mysteries of its harsh climate.