US or China: Whose rocket is about to hit the Moon?

News sites around the world, including us, reported on a Falcon 9 upper stage that was on a collision course with the Moon, with an impact expected on March 4. Except… new evidence (or rather, reobserving old evidence) points to the fact that this rocket stage is not actually the Falcon 9 upper stage from the DSCOVR mission, but instead a rocket stage from the Long March 3C that launched China’s Chang’e 5-T1 mission.

As first reported by Ars Technica, Bill Gray, the astronomer who first discovered that this man-made object was headed on a course for the Moon, has since updated his website, mentioning an error in his initial identification.

This error was discovered thanks to an email by Jon Giorgini at NASA’s Jet Propulsion Laboratory, “inquiring about my statement that ‘DSCOVR (and this rocket stage with it) passed close by the moon on 2015 February 13, two days after it was launched. Jon pointed out that JPL’s Horizons system showed that the DSCOVR spacecraft’s trajectory did not go particularly close to the moon.”

This email prompted Gray to search back through his records to figure out why he had first categorized the object as from the Falcon 9 rocket that launched that DSCOVR mission.

Gray noted the difficulty of identifying space junk:

Identifications of high-flying space junk often require a bit of detective work, and sometimes, we never do figure out the ID for a bit of space junk; there are some UOOs (Unidentified Orbiting Objects) out there.

Rather than SpaceX’s Falcon 9 upper stage, there was a different candidate for the upper stage that Gray spotted back in 2015, China’s Chang’e 5-T1 mission.

The preceding candidate launch was the Chang’e 5-T1 mission, launched at 18:00 UTC on 2014 October 23. Its booster was (we thought) never seen…

Running the orbit for WE0913A further backward, I got a lunar flyby on 2014 October 28,[…]which is a quite close lunar flyby at about the right time. 

According to Gray, the object was in the “usual lunar transfer orbit,” which lined up with the orbit the stage from Chang’e 5-T1 was expected to be in.

Gray continues, noting that Astronomer Jonathan McDowell sent over the orbital information of a small cubesat that was a rideshare on the booster, and the orbits line up.

It seems rather likely that Elon Musk is not to blame for the space junk that is about to hit the Moon, though even Gray found it important to note that all of the evidence for this object’s identity is still circumstantial.

Space Explored’s take

We noted this when we first reported on the object’s collisions course, but I think it’s worth mentioning again:

Many mission’s spent stages have been used to impact the Moon in the past. Most notably during Apollo, NASA would impact both the S-IVB (Saturn V third stage) and Lunar Module’s ascent stage into the surface. Then seismometers would record the “moonquakes” that would occur.

While the Lunar Reconnaissance Orbiter team won’t go out of their way to observe the impact, this is far from the first time a space-junk has been discarded onto the surface of the Moon, and the risk of this impact causing issues with any of the robotic missions on the Moon are basically zero.

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