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The European Space Agency wants to partner with NASA on a mission to Uranus (left) and Neptune, last visited by Voyager 2 in the 1980s.


Fleets of flying telescopes and returning samples from Venus among Europe’s space hopes

European space scientists' most ambitious dreams are about to meet reality. Earlier this year, the European Space Agency (ESA) asked a committee to invite researchers to pitch ideas for Voyage 2050, a 20-year program of missions beginning in 2035. "We want to know what their dreams are," says astronomer Linda Tacconi of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who chairs the committee. It received almost 100 proposals, including scientific quests that would require an orbiting radio telescope the size of several city blocks, a fleet of formation-flying telescopes to study exoplanets, and a robotic odyssey to bring back samples from Venus. Next week, scientists will gather in Madrid for a workshop to debate the merits of the different science themes, after which the committee will spend about 1 year choosing which ones to recommend to ESA for the program.

Günther Hasinger, ESA's director of science, says the agency is looking to lead three large billion-euro missions, and five or six medium missions costing less than half a billion euros—an agenda similar to its current science program, called Cosmic Vision. Voyage 2050 will also include a series of "fast" missions, with budgets less than €150 million, launching every 3 years. This year, ESA picked the first of those, the Comet Interceptor, which after launch in 2028 would park itself beyond the Moon and wait for a pristine comet to enter the Solar System.

Tacconi's committee will settle on the themes for the three large missions and a menu of about a dozen for medium missions. Calls for specific mission proposals to fit the themes will come later. Hasinger says the long lead time will help ESA get a head start on technology development for the missions.

Many of the proposals submitted for the workshop call for exoplanet science, Hasinger says. One envisions a few midinfrared telescopes orbiting in formation about 150 meters apart and combining their light to get sharp views of Earth-like exoplanets. Another calls for a parasol-shaped starshade orbiting in space, which would create brief eclipses of distant stars so that ground-based telescopes can discern the faint light of planets around them.

Leon Koopmans of the University of Groningen's Kapteyn Astronomical Institute in the Netherlands heads a team that wants to probe the universe's dark ages, before the light of the first stars. Because Earth's atmosphere blocks radio signals from that era, the team envisions a giant orbiting radio antenna with a collecting area of 1 square kilometer and, later, an array of antennas on the radio-quiet far side of the Moon. "It's been treated as an exciting and original idea. But there is stiff competition," Koopmans says.

Other ambitious proposals have targets closer to home. One would retrieve samples from the surface of Venus through a complex choreography of two orbiters, multiple landers, a balloon high in the atmosphere, and a return rocket.

Constraining those ambitions is ESA's science budget, which all 22 member countries must contribute to in line with their gross domestic product. It has been flat for the past couple of decades. As inflation erodes its value, the gaps between missions have grown longer. Hasinger points out that no medium-size science mission has launched in more than 10 years.

Next month, government ministers from the 22 member nations will meet in Seville, Spain, to hash out the agency's budget for the next 5 years or so. The science directorate is asking for a funding boost of between 10% and 20%. "This is absolutely necessary. A flat budget is not healthy," says Athena Coustenis, a planetary scientist at the Paris Observatory and chair of the European Space Sciences Committee, an advisory body. "There's almost unanimous support that there has to be an increase, but the devil is in the detail," Hasinger says. "We may not get as much as we asked for."

Hasinger has other items on his wish list for Seville. He will also ask ministers for extra funding for Cosmic Vision, so ESA can launch one of its large missions, the Laser Interferometer Space Antenna, a gravitational wave detector, earlier than its scheduled 2034 date. That way, it can fly at the same time as another large ESA mission, dubbed Athena, an x-ray observatory due for launch in 2031. "They both study the same phenomena but with different eyes and ears," Hasinger says, explaining that the cosmic collisions that generate gravitational waves can also unleash blasts of x-rays.

ESA also wants to join NASA in sending a probe to Uranus and Neptune, the first visit to the ice giants since Voyager 2 in the 1980s. Around 2030, the planets will be aligned with Jupiter so it can act as a gravitational slingshot to fling a spacecraft onward. This maneuver saves so much fuel that the spacecraft can be five times bigger than without the boost, Hasinger says. Final approval for the ice giants mission will likely have to wait until the next ministerial meeting after Seville, because the NASA team is also seeking support, from the U.S. space science community.