Europa’s planned Venus exploration mission will depend on a challenging aerobraking procedure to lower the orbiter, which will test the thermal resistance of the spacecraft’s materials to their limits.
The EnVision missionexpected to launch in the early 2030s, will study the geology and atmosphere of Venusthe hellish planet that once could have looked quite like the earth but transformed into a scorched hostile world due to an escape greenhouse effect.
To get EnVision to its target orbit, 310 miles (500 kilometers) above Venus’ surface (which is so hot it would melt lead), it will take thousands of passes through the planet’s thick atmosphere over a period of two years, the European Space Agency (ESA) said in a statement (opens in a new tab).
“EnVision as currently conceived cannot take place without this long phase of aerobraking,” ESA’s EnVision study leader, Thomas Voirin, said in the statement.
Related: How Venus went to Hell, and how Earth is next
The space vehicle the size of the van, which will be launched towards Europe’s future Ariane 6 rocket, will not be able to carry enough fuel to decelerate in Venus’ orbit using onboard propulsion. Instead, it will use the aerobraking procedure and follow a highly elliptical path that will periodically take it to within 80 miles (130 km) of Venus’ surface at its closest and about 155,000 miles (250,000 km) from the planet at its furthest point .
ESA previously used aero braking to slow down ExoMars Track the Gas Orbiter before it entered its scientific orbit March. But Mars’ atmosphere is much thinner than Venus’s, and its gravity is much lower, which affects the speed of the orbiting spacecraft.
“Aerobraking around Venus is going to be much more challenging than for the Trace Gas Orbiter,” Voirin said. “The gravity of Venus is about 10 times that of Mars. This means that velocities about twice that of the TGO will be experienced by the spacecraft as they pass through the atmosphere, and heat is generated as a velocity cube.”
ESA briefly tested aerobraking around Venus during the past few months 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 the mission, spacecraft controllers did not worry about the damage to the spacecraft caused by the heat. EnVision, on the other hand, will be expected to explore Venus for at least four years.
Engineers are already busy devising the right materials that will enable 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 found in the upper layers of Earth’s atmosphere, which consists of a single oxygen atom. Atomic oxygen, a nemesis of all low soil orbiting spacecraft, burned thermal blankets on several NASA spaceship mission in the 1980s.
Observations from previous Venus missions showed that atomic oxygen is present in the upper layers of the Venusian atmosphere in concentrations similar to those around Earth.
“The concentration is quite high. With one round it doesn’t mean much, but over thousands of times it starts to accumulate and ends up with a level of atomic oxygen fluence we have to take into account, similar to what we experience in low Earth orbit, but at higher temperatures,” Voirin said.
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 being eroded and also maintain their optical properties — meaning they don’t degrade or darken, which can have a negative effect in terms of their thermal behavior, because we have delicate scientific instruments that must 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 their similar sizes, has recently been somewhat sidelined the solar system explorers such as the potentially more habitable Mars (which is likely to contain traces of life) have become the favourite. But a 2020 study that discovered molecules that can be traces of living organisms in the planet’s sulphur-rich clouds sparked a new wave of interest in Venus.
In addition to Europa, NASA has plans to send orbiters to the fiery planet: DAVINCI+ and VERITAS missionwhich is expected to be launched between 2028 and 2030. Currently a lone spacecraft, Japan’s Akatsukiorbits Venus and studies its dense atmosphere in an attempt to unravel the mysteries of its harsh climate.