An object roughly 15 meters long and 3 meters wide was forecast to hit the far side of the Moon at about 2.58 km/s, on March 4, 2022, within a few seconds of 12:25 UTC. For a few weeks, the working assumption was that it was a leftover SpaceX Falcon 9 upper stage. Then the identification changed.
The first claim, published in early February 2022, was that the stage came from the 2015 launch of NOAA’s DSCOVR climate observatory. Falcon 9 had put DSCOVR around the L1 Lagrange point, about 1.5 million kilometers from Earth. The upper stage ended up pointing away from Earth into interplanetary space, which ruled out a deorbit burn, and it lacked the speed to leave the Earth-Moon system. It was left in a chaotic orbit around the Sun near the two bodies. The estimated mass was about 3 tons.
On February 15 came a correction. Further analysis by citizen-scientist Bill Gray and colleagues at NASA’s JPL indicated that the object expected to hit the Moon was not the stage that delivered the earlier US solar monitoring mission to L1. The impact point stayed within a few kilometers of the predicted spot. Whose hardware it actually was remained unsettled in the update.
A gap in the rules
Human-made objects have hit the Moon before, but on purpose. Apollo upper stages were crashed in the lunar program to set off moonquakes for surface seismometers. ESA’s Smart-1 was crashed in 2006, NASA’s LCROSS in 2009, where the debris plume revealed water, and LADEE on the far side in 2013. The March event would have been the first unintentional strike by a human-made object.
ESA staff said the case sits at the edge of what anyone tracks. Tim Flohrer of ESA’s Space Debris Office said it was “a little beyond our usual area of interest,” because his team watches low-Earth and geosynchronous orbits. Detlef Koschny, who heads the Planetary Defence Office, said telescopes there mainly follow natural objects but occasionally pick up man-made ones such as lunar spacecraft remnants and objects returning from Lagrange points.
No clear international guidelines cover disposal of spacecraft or spent stages sent to Lagrange points. Crashing into the Moon or burning up in Earth’s atmosphere have been the easiest default options. Holger Krag, head of ESA’s Space Safety Program, said the episode showed the need for a regulatory regime that also covers the Moon, and that it “would take international consensus.”
Europe’s own rockets offer a contrast. The Ariane 5 that carried the James Webb Space Telescope to L2 used its remaining fuel after separation to escape the Earth-Moon system into a stable orbit around the Sun. ESA’s Vega, Ariane 6 and Vega C can all reignite to bring their upper stages back for burn-up in the atmosphere.
