Europa’s planned Venus exploration mission will rely on a challenging aerobraking procedure to lower its orbit, which will test the thermal resistance of the spacecraft’s materials to their limits.
The EnVision missionwhich is expected to launch in the early 2030s, will study the geology and atmosphere of Venusthe hellish planet I could once have it looked quite down to Earth but it became a hostile world burned because of an escape greenhouse effect.
Getting EnVision into its target orbit, 310 miles (500 kilometers) above the surface of Venus (which is so hot it would melt lead), will require thousands of passes through the the thick atmosphere of the planet for a period of two years, said the European Space Agency (ESA) in a statement (opens in a new tab).
“EnVision, as currently conceived, cannot take place without this long aerobraking phase,” ESA EnVision study lead Thomas Voirin said in the statement.
Related: How Venus became hell, and what the next Earth looks like
The spaceship the size of a van, which will be launched into the future of Europe Ariane 6 rocket, it won’t be able to carry enough fuel to stop itself in Venus orbit using 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 about 155,000 miles (250,000 km ) of the planet at its farthest point.
ESA previously used aerobraking to slow down the speed ExoMars Trace Gas Orbiter before it entered its scientific orbit March. But the atmosphere of Mars is much thinner than that of Venus, and its own gravity is much smaller, which affects the speed of the spacecraft in orbit.
“Aerobraking around Venus will be much more difficult than for the Trace Gas Orbiter,” Voirin said. “The gravity of Venus is about 10 times that of Mars. This means that the spacecraft will experience velocities about twice that of TGO as it passes through the atmosphere, and the heat is generated as a cube of velocity.”
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. Since Venus Express was already at the end of its mission, spacecraft controllers were not concerned about the damage that the spacecraft was suffering from heat. EnVision, on the other hand, is expected to explore Venus for at least four years.
Engineers are already busy crafting the right materials to allow EnVision to withstand 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, a nemesis of all low ground orbiting spacecraft, burned thermal blankets at several NASA space shuttle missions of the eighties.
Observations from previous Venus missions showed that atomic oxygen is present in the upper layers of Venus’ atmosphere at concentrations similar to those around Earth.
“The concentration is quite high. With one pass it doesn’t matter that much, but over thousands of times it starts to build up and ends up with a level of atomic oxygen fluence that we have to take into account, equivalent to what we experience in orbit low terrestrial, but at higher temperatures,” said Voirin.
ESA is currently testing materials for their ability to withstand both the heat and concentration of atomic oxygen expected during EnVision’s aerobraking and hopes to have some candidate materials selected by the end of this year.
“We want to check that these parts are resistant to erosion and also maintain their optical properties, that is, they do not degrade or darken, which could have side effects in terms of their thermal behavior, because we have “delicate scientific instruments. This has to maintain a set temperature,” Voirin said. “We also need to avoid flaking or outgassing, which leads to contamination.”
Venus, sometimes considered Earth’s twin due to its similar sizes, has recently been somewhat on the sidelines due to solar system explorers, as the 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 led to a new surge of interest in Venus.
In addition to Europa, NASA has plans to send orbiters to the scorching planet: The DAVINCI+ and VERITAS missionswhich is expected to launch between 2028 and 2030. Currently, a lone spacecraft, the Japanese Akatsukiis orbiting Venus, studying its dense atmosphere to try to unravel the mysteries of its harsh climate.
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