WASHINGTON — A group of planetary defense advocates is asking European governments to fund a mission to a near Earth asteroid, three years after a similar mission failed to win approval.

At a press conference in Berlin Nov. 15, backers of the proposed Hera mission said more than 1,200 scientists and other supporters had signed a letter calling on European Space Agency member states to fund the mission at their ministerial meeting later this month in Spain.

Hera, as currently designed, will launch in October 2024 and arrive at the near Earth asteroid Didymos and its small moon, informally called “Didymoon,” in December 2026. That moon will be the target — literally — of NASA’s Double Asteroid Redirect Test (DART) spacecraft, which will collide with Didymoon in 2022 to demonstrate the ability of “kinetic impactors” to change the orbit of an asteroid.

“What Hera wants to do is measure precisely the effect of this impact,” said Patrick Michel, principal investigator for Hera, at the press conference. That includes detailed studies of Didymos and its moon, in particular examination of the crater made by DART’s collision with the body.

Those studies have benefits both for planetary defense and broader planetary science research, he argued. Japan’s Hayabusa2 spacecraft fired a small impactor, weighing only a couple kilograms, onto the surface of the asteroid Ryugu. Models predicted the impact would leave a crater one to two meters across, but images instead revealed a crater 10 meters across.

“This is both important for planetary defense, because the momentum transferred to the target depends on this, and it’s also important for science, because the way we date the surface is by counting the craters and measuring their sizes,” he said. “This relies on the relationship between the crater size and the projectile size.”

“Without Hera, we wouldn’t see the crater, wouldn’t see the properties of the body and wouldn’t know the mass,” said Kai Wünnemann, head of the department of impact and meteorite research at the Museum für Naturkunde Berlin, “all these things that are absolutely crucial for making progress in terms of our modeling predictions.”

The public advocacy of Hera is unusual for a European mission, where debates usually take place at the national rather than grassroots level. This effort seeks to avoid a repeat of three years ago, when a similar mission, the Asteroid Impact Mission (AIM), failed to win funding at ESA’s last ministerial meeting. AIM would have launched earlier and been able to observe DART’s impact with Didymoon.

ESA’s leadership acknowledged that the agency did not do a good job convincing member states to fund AIM. “Last time, we developed the AIM mission internally, and then we gave the information to our delegations,” Jan Woerner, director general of ESA, said in a June 2018 interview. That information, he said, was provided to delegations just a few months ahead of the ministerial.

ESA has been more active this time in promoting Hera. “Since the last ministerial in 2016, we are raising awareness to politicians of the possible danger of an asteroid impact,” Woerner said last year. “By doing that, we will change the narrative.”

ESA has been actively promoting the mission in recent months, including releasing a video narrated by rock star-turned-astrophysicist Brian May and highlighting support for it from former Apollo astronaut Rusty Schweickart, a long-time advocate of planetary defense efforts.

Hera is part of ESA’s “safety and security” initiative, one of four pillars that agency has organized its activities around ahead of the Space19+ ministerial meeting Nov. 27–28 in Seville, Spain. Other projects in that initiative range from space weather monitoring to efforts to monitor and reduce the amount of space debris.