In the wake of the historic detection of gravitational waves by a terrestrial US experiment, a space-borne European effort is drawing interest from a range of parties. But although advisers to the European Space Agency (ESA) recommended increasing international contributions to the billion-euro gravitational-wave detector on April 12, regulatory hurdles may hinder proposed partnerships with the United States and China.

In February, researchers working on the US-based Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)announced that they had detected ripples in space-time that had been produced by the merger of two black holes. The space-based observatory planned by ESA would be able to detect ripples with much lower frequencies than would be possible on Earth, bringing into view a greater variety of astronomical events, including mergers between supermassive black holes.

Such a detector is widely seen as “the best thing you could do in gravitational waves”, says Robin Stebbins, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. After a mission to test crucial technologies for the observatory proved successful, the ESA advisory team last month concluded that not only are the agency’s plans feasible, but also that the launch could even be brought forward, from 2034 to 2029.

Initially, NASA and ESA were partners in the effort, but funding issues led NASA to pull out in 2011. The US space agency has since stated that it wants only a minor role in the observatory. But excitement around the LIGO findings mean that US scientists are keen for NASA to become an equal partner again, says Rainer Weiss, a physicist at the Massachusetts Institute of Technology in Cambridge who was instrumental in creating LIGO.

Stebbins expects that the committee tasked with assessing progress on the US decadal review, which decides the priorities of NASA and other funding agencies,will express support for a larger role in the ESA observatory later this month. But such a role might require NASA to find more money before the next review, in 2020, and that would mean either diverting money away from other projects or persuading the US Congress to give it more.

Any plan to cooperate with ESA on an equal footing could also come up against ESA’s policy of capping international contributions to large missions at 20% to stop projects from falling apart if a partner pulls out. It is too early in discussions to know whether the policy will present a problem, says Fabio Favata, head of science planning and community coordination at ESA.

The United States is not the only country seeking to capitalize on the LIGO breakthrough. Japan’s gravitational-wave community is also looking for a way to contribute to the ESA mission. And Chinese scientists have expressed interest for several years now, says Stebbins. They could provide financial or in-kind contributions to the ESA mission in exchange for technical know-how, he says.

US participation could also complicate any potential collaboration between ESA and China. An amendment to US law introduced in 2011 blocks NASA scientists from working directly with Chinese counterparts under almost all circumstances. Stebbins’s superiors have told him that the law applies to bilateral collaboration, so it might not apply to a collaboration with ESA that also includes China.

But Congress might try to prevent this kind of collaboration anyway, says Brian Weeden, the technical adviser for the Secure World Foundation in Washington DC, which promotes the peaceful use of outer space. And Congress’s scepticism of collaboration with China could stop NASA scientists from even trying to participate. That the gravitational-wave detector is purely a science mission may reassure Congress, Weeden adds. “There may be less concern over that type of cooperation than there would be on cooperation with a more political component, such as human spaceflight.”

China is a growing space power—it is scheduled to launch several high-profile space-science missions this year—so the United States will eventually work with China in some capacity, Weeden says. And that would probably be through some kind of multilateral project, he thinks. “The challenge is finding a topic that both the United States and China want to work on. I think the gravitational-wave detector could be one of those.”

This article is reproduced with permission and was first published on May 4, 2016.