July 30, 2021

ESA selects radar probe to join armada of Venus missions

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The EnVision mission to Venus will explore why Earth’s closest neighbor is so different. This artist’s concept shows the spacecraft superimposed on global views of Earth and Venus. Credit: NASA / JAXA / ISAS / DARTS / Damia Bouic / VR2Planets

A week after NASA selected two robotic missions for launch to Venus in the late 2020s, the European Space Agency has announced its own orbiter will launch to Venus as soon as 2031 with two radars and three spectrometer instruments to comprehensively study the planet from its core to the atmosphere.

ESA announced June 10 that the EnVision mission will become the fifth medium-class, or “M-class,” mission in the agency’s Cosmic Vision program, which selects future space science projects in large, medium and small cost classifications.

“A new era in the exploration of our closest, yet wildly different, solar system neighbor awaits us,” said Günther Hasinger, ESA’s director of science. “Together with the newly announced NASA-led Venus missions, we will have an extremely comprehensive science program at this enigmatic planet well into the next decade.”

EnVision’s selection by ESA came eight days after NASA announced it will launch two robotic “Discovery-class” missions to Venus around 2029.

One of NASA’s missions, named DAVINCI+, will send a probe through the super-hot atmosphere of Venus to collect data as it descends through sulfuric acid clouds. Suspended under a parachute for an hour-long descent, the probe will measure the composition of Venus’s atmosphere and take high-resolution pictures of its surface before touching down in a mountainous region called Alpha Regio.

The DAVINCI+ entry probe could return data from the surface of Venus for a few minutes before succumbing to intense pressures and scorching temperatures near 900 degrees Fahrenheit (480 degrees Celsius).

The other NASA mission to Venus is called VERITAS. It will consist of an orbiting spacecraft fitted with an X-band radar to peer through the blanket of clouds hiding the planet’s landscape from cameras taking pictures in visible light. VERITAS will create a global map of Venus’s surface significantly better than the one produced by NASA’s Magellan radar mission in the early 1990s.

DAVINCI+ and VERITAS will be NASA’s first missions dedicated to Venus observations since 1994, when the Magellan mission ended.

The EnVision mission will be ESA’s second spacecraft to orbit Venus, following the Venus Express spacecraft, which observed the planet from orbit between 2006 and 2014.

Japan’s Akatsuki spacecraft is the only active spacecraft currently orbiting Venus. Akatsuki’s science instruments are focused on observing the planet’s atmosphere.

The selection of the EnVision mission ends the competition for ESA’s fifth medium-class Cosmic Vision mission. The other finalist for the fifth M-class mission was THESEUS, an astronomy probe that would have monitored gamma-ray bursts, giant stellar explosions, to shed light on the lives of stars in the earliest billion years of the universe.

EnVision could launch as soon as 2031 on a European Ariane 6 rocket, according to ESA. There are other launch opportunities available in 2032 and 2033.

After a 15-month cruise, the EnVision spacecraft will maneuver into orbit around Venus, eventually settling in a quasi-polar orbit with an altitude between 136 miles and 335 miles (220-by-540 kilometers).

Like the NASA missions, EnVision will attempt to help scientists better understand why Venus ended up a radically different planet than Earth, its nearest neighbor in the solar system. Venus and Earth about the same size and composition, and Venus may have once harbored oceans of liquid water.

But Venus now has a crushing, toxic atmosphere with a surface air pressure more than 90 times thicker than Earth’s. Knowledge of Venus’s evolution could tell astronomers more about the environments of exoplanets — distant worlds around other stars.

EnVision will host three spectrometers sensitive in infrared and ultraviolet wavelengths. The spectrometer will measure the composition in the atmosphere of Venus and search for volcanic gas plumes. The spectrometers will also analyze the chemical make-up of the surface, looking for changes that could be signs of recent volcanic eruptions, according to ESA.

The European spacecraft will also have a high-frequency radar sounder to map underground layers to a depth of 3,300 feet, or 1 kilometer, ESA said. The sounder will look for evidence of buried geologic boundaries.

NASA is also supplying an S-band synthetic aperture radar, called VenSAR, to be mounted on the EnVision spacecraft.

The X-band radar on the VERITAS mission will collect data to generate a global map of Venus’s topography. EnVision’s radar will focus only on certain parts of Venus, but at higher resolution. The European mission will also carry more instruments than VERITAS, which has two science payloads.

Measurements using radio signals passed between EnVision and ground stations will also yield insights into the interior structure of Venus, the planet’s gravity field, and the structure of its atmosphere, ESA said.

ESA did not disclose the projected cost of the EnVision mission, but the agency’s M-class projects come with a cost cap of 550 million euros, roughly $665 million at current exchange rates. The cost cap does not include contributions from other space agencies, such as NASA.

Lori Glaze, director of NASA’s planetary science division, said the EnVision, VERITAS, and EnVision missions are complementary.

“ESA’s EnVision mission will provide unparalleled high-resolution imaging and polarimetry capabilities,” she said in a statement. “High-resolution images of many dynamic processes at Mars profoundly changed the way we thought about the Red Planet and images at similar scales have the potential to do the same for Venus.”

“The combined results of EnVision and our Discovery missions will tell us how the forces of volcanism, tectonics and chemical weathering joined together to create and sustain Venus’s runaway hothouse climate,” said Tom Wagner, NASA’s Discovery program scientist.

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Follow Stephen Clark on Twitter: @StephenClark1.

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