Abstract:
The European Space Agency (ESA) is accelerating the "EnVision" Venus exploration mission, but this mission, which was originally jointly implemented by Europe and the United States, may now have to be completed independently by Europe. As the National Aeronautics and Space Administration (NASA) is affected by budget pressure, it has become increasingly difficult to fulfill its commitment to provide core synthetic aperture radar for EnVision. Europe has now launched an alternative plan to develop a radar system with similar functions.
EnVision is a Venus orbital exploration mission led by ESA. Its main goal is to comprehensively study the geology, internal structure, surface and atmospheric environment of Venus, and try to answer a question that has long puzzled planetary scientists: why Venus, which is very similar to the Earth in size and composition, eventually evolved into a "hell world" with extremely high surface temperatures, a dense atmosphere, and clouds of sulfuric acid.
The surface of Venus is completely wrapped in thick sulfuric acid clouds, and ordinary optical cameras cannot directly observe its surface from orbit. Therefore, radar has become a key means to detect the surface of Venus. EnVision originally planned to carry VenSAR, a synthetic aperture radar provided by NASA, to perform high-resolution imaging of the surface of Venus. The resolution will reach about 10 meters, which is about an order of magnitude higher than the radar image of Venus obtained by NASA's "Magellan" probe in the 1990s.
Through this high-resolution radar observation, scientists can not only draw a more detailed topographic map of Venus, but also look for signs of changes on the surface, and focus on investigating whether there is still active volcanic activity on Venus. Previous missions such as Venus Express have discovered some clues that may be related to recent volcanic activity, and EnVision is expected to further verify these findings through repeated imaging and more refined topographic measurements.
According to the cooperation agreement signed between NASA and ESA in 2024, NASA was originally responsible for providing the VenSAR synthetic aperture radar and at the same time providing tracking and communication support for the mission through the NASA Deep Space Network. Europe is responsible for building the EnVision detector body and other scientific instruments, and launching the detector using the Ariane 6 launch vehicle. In exchange, U.S. researchers will participate in the EnVision science team.
But this transatlantic collaboration is now severely affected by NASA's budget crisis. The Trump administration has previously proposed to significantly reduce NASA science project funding in fiscal years 2026 and 2027, with the reduction once being close to half. Although the U.S. Congress ultimately rejected most of the cuts and allocated a budget of $2.54 billion for NASA's planetary science department in 2026, this figure is still about $220 million less than the previous year.
The budget ultimately did not allow NASA to cancel some of its own key planetary missions, including the DAVINCI mission, which planned to drop a probe into the atmosphere of Venus. However, NASA management still needs to cut spending on science projects, with one focus being on long-term missions and projects implemented with international partners.
EnVision is one of the European projects most directly affected. As of 2025, NASA has invested more than $50 million in its work related to EnVision. However, as the U.S. government requires reexamination or even cancellation of some international scientific cooperation projects, whether NASA can continue to fulfill its previous commitments has become increasingly uncertain.
Faced with this situation, ESA has begun to take action. Since it cannot continue to wait for NASA's final decision, Europe has issued contracts to relevant institutions and companies to start the technical development of independent radar payloads. Industrial teams in the UK and Italy are currently studying different radar designs, hoping to create a European version that can meet the main performance requirements of NASA's original VenSAR plan.
Anne Grete Straume-Lindner, ESA EnVision project scientist, said that the European side has not yet determined the final radar design, but because the new radar needs to meet the same scientific mission requirements as the original plan, the research team expects to still be able to complete basically the same scientific work. The new system will have the same working model as the original NASA solution, but there may be differences in specific technical details.
Europe currently has the technical capabilities to develop such radar on its own. In fact, EnVision's radar was initially considered to be undertaken by European companies, but after NASA joined the cooperation, the United States was ultimately responsible for VenSAR. Now that ESA has restarted the European program, it means that Europe needs to undertake a key task originally responsible for NASA within a relatively limited time.
In terms of funding, although ESA is far less powerful than NASA, member states have significantly increased their investment in European aerospace science projects in recent years. ESA's science program budget is expected to grow by 3.5% annually until 2028, with adjustments for inflation. ESA's science budget currently averages about 750 million euros per year, less than one-tenth the size of NASA's similar budget.
This amount of money is enough to allow Europe to start the development of replacement radars, but it is still not enough to make the entire process proceed without stress. ESA is still waiting for NASA to officially notify it of its final position on the EnVision project, while NASA said that communication between the two parties regarding EnVision is still continuing.
Time pressure is particularly acute. EnVision was originally scheduled to launch in 2031, but in order to give the European team more time to complete the new radar, ESA has postponed the launch by one year to 2032. Project scientists said that ESA is still finalizing cooperation arrangements with NASA, but judging from the current situation, NASA is likely to be unable to provide the radar as originally planned, so Europe will "advance at full speed" with its own solution.
EnVision is not the only major European science mission affected by changes in NASA's budget. ESA is also considering how to fill the void left by NASA's possible withdrawal from two other large projects, including the laser interference space antenna LISA and the New Athena X-ray observatory. LISA plans to fly in formation with three spacecraft, and will directly detect gravitational waves from violent cosmic events such as black hole mergers for the first time; New Athena will become the largest X-ray space telescope in history, replacing the still-operating "Chandra" X-ray Observatory.
In the LISA project, NASA was originally responsible for providing key equipment such as lasers and ultra-stable telescopes; New Athena involves NASA providing X-ray detector hardware, cryogenic refrigerators, and vibration isolation systems. If the United States eventually withdraws, Europe will also need to find alternatives.
Meanwhile, NASA's own Venus mission is not entirely free from budget and schedule issues. The VERITAS Venus radar orbiter, originally planned to be launched in the late 2020s, has been postponed to no earlier than 2031 due to financial difficulties at NASA and the Jet Propulsion Laboratory, and the project is still in a state of uncertainty. Another mission, the DAVINCI mission managed by NASA's Goddard Space Flight Center, is still striving to launch in the early 2030s.
Even the Venus Science Coordination Group jointly established by NASA and ESA has been affected. This coordination mechanism is currently suspended due to changes in the budget environment in the United States.
The cooperation between NASA and ESA extends far beyond scientific exploration missions. The two parties have long-term cooperation in operating the International Space Station, and ESA is also an important partner of the "Orion" spacecraft in NASA's "Artemis" program. However, changes in U.S. space policy and budgets in recent years are prompting Europe to rethink its reliance on a single partner.
In fact, ESA has begun to expand space cooperation with other countries. Earlier this year, ESA and China launched the first joint scientific mission, the Solar Wind-Magnetosphere Interaction All-Sky Imager (SMILE), in which each holds a 50% share. The probe was built in China and launched aboard a European "Vega" rocket to study the interaction between the solar wind and the Earth's magnetosphere.
In addition, ESA's first lunar landing scientific instrument has also arrived on the moon in 2024 aboard China's Chang'e-6 mission. As European and American space cooperation faces new uncertainties, China is becoming another important space partner that Europe can consider.
Carol Mondel, ESA science director, said that China has invited ESA to participate in more scientific exploration missions led by China, and Europe is currently studying the possibility of such cooperation. She also emphasized that the United States remains one of ESA's longest-term and most important partners.
Therefore, the changes in the EnVision project not only mean that a radar is switched from American to European manufacturing, but also reflect the changing pattern of global aerospace science cooperation. For Europe, independently undertaking the development of EnVision's key radar can prevent an important planetary exploration mission from being stalled due to changes in U.S. budget policies. It also means that ESA is being forced to improve its ability to independently conduct deep space science missions.
If Europe ultimately succeeds in completing its radar replacement plan, EnVision is still expected to set off to Venus around 2032. By then, this mission, which originally symbolized European and American deep space scientific cooperation, may become a representative project for Europe to independently carry out high-level Venus exploration.
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