NASA Drops Promised Radar for ESA's Envision Venus Probe as Science Budget Fight Bites

The European Space Agency is moving ahead alone on a key piece of its Venus mission after NASA signaled it probably can't deliver hardware it agreed to provide two years ago.

ESA's Envision orbiter is designed to map the surface of Venus at ten times the resolution of NASA's last Venus radar mission in the 1990s. Because Venus is wrapped in thick sulfuric acid clouds, radar is the only practical way to see its surface and hunt for signs of active volcanism.

Under a memorandum of understanding NASA and ESA signed in 2024, NASA was supposed to supply Envision's synthetic aperture radar, the mission's primary science instrument, plus tracking support through NASA's Deep Space Network. In return, ESA agreed to build the spacecraft, launch it on an Ariane 6 rocket, and give US researchers seats on the science team.

"At the moment, we are finalizing our agreement with NASA, but it is looking like they are not able to provide the radar," ESA's Camilla Straume-Lindner told Ars Technica. "So that is why we are going full steam ahead with the European solution."

A NASA spokesperson told Ars that conversations with ESA on Envision "are ongoing." ESA isn't waiting. Officials have already pushed Envision's launch back a year, to 2032, to give European teams time to build a replacement radar from scratch.

Where the money went

The root cause is NASA's own budget fight. The Trump administration proposed cutting NASA's science division funding nearly in half for fiscal years 2026 and 2027. Congress rejected most of that, passing a 2026 budget that gives NASA's planetary science division $2.54 billion, well above what the White House asked for, but still about $220 million short of the prior year's level.

That gap is forcing NASA managers to choose. According to Ars Technica, the agency is prioritizing its own missions and cutting funding for operating spacecraft well past their design life and for international partnership commitments. Envision's radar fell into that second bucket.

NASA's own DAVINCI mission, an entry probe meant to plunge into Venus's atmosphere, survived the cuts. So did the Rosalind Franklin Mars rover, a European-built mission that Congress's restored funding allowed NASA to lock in a SpaceX launch contract for, targeting 2028, after the Trump administration had sought to cancel NASA's role entirely.

Not everything survived intact. NASA's own VERITAS radar orbiter to Venus, once planned for the late 2020s, has slipped to no earlier than 2031 and remains in limbo due to funding problems at NASA and the Jet Propulsion Laboratory. The joint NASA-ESA Venus Science Coordination group has been suspended outright, which Straume-Lindner attributed to "changes to the budgetary situation in the US."

LISA and New Athena also exposed

The Envision radar isn't the only US commitment now in question. NASA was set to provide lasers and stabilized telescopes for LISA, the first space mission designed to detect gravitational waves, and X-ray sensor hardware, a cryocooler, and a vibration isolation system for New Athena, a planned successor to the Chandra X-ray Observatory. Both were on track for launches in the late 2030s before NASA's contributions came into doubt. ESA is now assessing how to cover those roles itself.

ESA's science director, Carole Mundell, struck a diplomatic tone about NASA despite the disruption. "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," she said.

The China question

As US commitments wobble, Europe is deepening ties with China in space science. ESA already flew its first 50-50 joint mission with China this year, the SMILE spacecraft studying solar wind interactions with Earth's magnetic field, launched on Europe's Vega rocket. A European instrument also rode to the lunar surface aboard China's Chang'e 6 mission in 2024. Mundell confirmed China has invited ESA onto more of its missions and said Europe is "exploring" that.

A NASA that can't reliably deliver on signed agreements pushes allies toward Beijing by default, not by preference. But nothing in ESA's own statements suggests a pivot away from Washington. Human spaceflight cooperation, through the International Space Station and the Orion capsule for Artemis Moon missions, remains intact, and ESA officials frame the China outreach as supplemental exploration, not a replacement partnership.

None of this is resolved. NASA still hasn't sent ESA the formal notification on Envision's radar that both sides say is coming. Whether Congress's 2027 budget closes the remaining $220 million gap, or widens it, will determine whether LISA and New Athena face the same fate as Envision's radar did.