Europe will go it alone on Venus mission after NASA yanks radar instrument

The European Space Agency is moving “full steam ahead” with development of a robotic mission to Venus after NASA officials determined they were unlikely to fulfill a commitment to provide a US-built radar instrument for the spacecraft, the mission’s project scientist said.

The European orbiter, named Envision, will map the Venusian surface at 10 times higher resolution than the last radar mission sent to Venus by NASA in the 1990s. The planet is enshrouded in a blanket of thick clouds of sulfuric acid, rendering its mysterious surface unseen by optical cameras in orbit. Radar is the most effective way to penetrate the clouds of Venus to reveal the terrain below, and scientists will use Envision to look for signs of active volcanism.

NASA and ESA signed a memorandum of understanding in 2024 outlining their partnership on Envision. NASA agreed to supply a US-made synthetic aperture radar instrument, Envision’s primary means of mapping the surface of Venus, along with providing tracking and communications support through NASA’s Deep Space Network. In exchange, ESA would include US researchers on Envision’s science team. Europe would build the Envision spacecraft and the rest of its science instruments and provide the launch on an Ariane 6 rocket.

But NASA’s budget for science missions is under the gun from the Trump administration, which proposed slashing the agency’s science funding nearly in half in fiscal years 2026 and 2027. Congress rejected most of the cuts in 2026, when lawmakers passed a budget with $2.54 billion for NASA’s planetary science division, far above the White House’s request, but about $220 million shy of last year’s funding.

That saved several key science missions from the chopping block, including one of NASA’s own Venus missions, called DAVINCI, designed to send an entry probe into the planet’s crushing atmosphere. But the shortfall is forcing NASA managers to make tough decisions. The primary targets for cuts in science are NASA’s funding for operating missions, especially those well beyond their original design lives, and support for partnerships on international missions.

Reneging on a pledge

Most prominent among the cuts in the latter category are NASA’s contributions to three European-led science missions. Two of the missions are big, new space-based observatories, LISA and New Athena. LISA will be the first space mission to measure gravitational waves, ripples in the fabric of spacetime emanating from cataclysmic cosmic events like mergers of black holes. New Athena will be the largest X-ray telescope ever built, a successor to NASA’s Chandra X-ray Observatory, still operational after launching in 1999.

Before NASA’s contributions were in doubt, LISA and New Athena were on track for launches in the late 2030s.

But the most pressing impact for ESA is how to fill the void left by NASA in the Envision mission, which was supposed to launch in 2031. NASA and ESA signed an agreement in early 2024 detailing each partner’s role on Envision, and contracts were awarded for construction of the Envision spacecraft and its instruments. NASA had spent more than $50 million on its contributions to the mission as of 2025, when the Trump administration first proposed canceling it.

With NASA’s fulfillment of its part of the agreement in doubt, ESA officials issued contracts to begin technology development on a European radar payload for Envision. Industrial teams in the United Kingdom and Italy are now studying radar designs under contract with ESA, with the goal of delivering a radar for Envision with similar capabilities as the NASA-funded radar, which was to be built at the Jet Propulsion Laboratory in California.

“We don’t know what the final design will be, but we have the same requirements, so we’re expecting that we can do exactly the same science,” said Anne Grete Straume-Lindner, ESA’s project scientist for Envision, in a presentation at the Europlanet Science Congress. “We’ll have the same modes, but in detail, of course, there can be differences.”

Carole Mundell, ESA’s director of science, told Ars earlier this year that the agency’s 23 member states committed “unprecedented” funding for ESA science at a meeting of government ministers last year. The member states agreed to increase ESA’s science budget by 3.5 percent per year through 2028, plus inflation. Still, ESA’s science budget is a fraction of that of NASA, averaging out to about 750 million euros (less than $900 million) each year.