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 also 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.
That’s enough to start work on a European radar for Envision, even as ESA still awaits a formal notification from NASA on the status of its contribution to the mission. “NASA conversations with ESA regarding Envision are ongoing,” a NASA spokesperson said.
But time is of the essence if Envision is to launch in the early 2030s. ESA officials have already delayed Envision’s launch by one year until 2032 to give teams in Europe more time to deliver the radar.
“At the moment, we are finalizing our agreement with NASA, but it is looking like they are not able to provide the radar,” Straume-Lindner said in response to a question from Ars. “So that is why we are going full steam ahead with the European solution.”
Cancellations and delays
A complementary mission to Envision, NASA’s VERITAS radar orbiter, was supposed to launch in the late 2020s, but funding woes at NASA and the Jet Propulsion Laboratory forced a delay until no earlier than 2031. Its development remains in limbo. The DAVINCI mission, led by NASA’s Goddard Space Flight Center, continues working toward a launch in the early 2030s.
The work of the Venus Science Coordination group, established jointly by NASA and ESA, has also been suspended due to “changes to the budgetary situation in the US,” Straume-Lindner said.
Meanwhile, ESA is also assessing how it can fill the roles of NASA on LISA and New Athena. On LISA, NASA was to provide lasers and ultra-stable telescopes for the mission’s three formation-flying spacecraft. The US space agency was on the hook for X-ray sensor hardware, a cryocooler, and a vibration isolation system for New Athena.
The Trump administration also sought to cancel NASA’s role in ESA’s Rosalind Franklin rover mission to Mars, set for launch in 2028. NASA has a longstanding agreement with ESA to pay for the launch of the European-built rover, and funding restored by Congress last year allowed the space agency to sign a contract with SpaceX to launch Rosalind Franklin in 2028.
“ESA is a very reliable partner, and we always deliver on our commitments and our promises, and we appreciate the difficulty that they’re in right now,” Mundell said, referring to NASA.
Europe has other places to look for cooperation in space, but NASA is the agency’s most enduring partner. In human spaceflight, ESA and NASA cooperate closely on the International Space Station and the Orion spacecraft used for Artemis missions to the Moon.
ESA launched its first 50-50 joint science mission with China earlier this year. The SMILE spacecraft, built in China and launched by Europe’s Vega rocket, is studying the connection between the solar wind and Earth. The first ESA instrument to land on the Moon arrived on the lunar surface in 2024 aboard China’s Chang’e 6 mission.
Mundell said China has invited ESA to join more Chinese-led science missions. “That is something that we’re exploring,” she said.
