You know you’re living in the space age when a rocket hits the moon and the industry as a whole points skyward and like an angry teacher holding a paper airplane asks “Who started that?! ” Really, that’s what happened this week when an unidentified (!) rocket stage slammed into the lunar surface, forming an interesting new crater and leaving us all wondering how it’s possible we don’t know what that happened.
The short version of this story is that skywatchers led by Bill Gray had been tracking an object for months that they calculated would soon impact the moon. It was obviously rocket junk (rockets produce a ton of junk), but no one stepped in to say “yeah, that’s ours, sorry about that”.
Based on their observations and discussions, these self-proclaimed object trackers (though by no means lacking in expertise) determined that it was likely a piece of a 2015 SpaceX launch vehicle. But SpaceX didn’t adapt to it, and after a while Gray and others, including NASA, decided it was more likely the Chang’e 5-T1 launch in 2014 from China. China has denied that is the case, saying the launcher in question burned up during re-entry.
Maybe they’re telling the truth; maybe they don’t want to be responsible for the first completely unintended lunar impact in history. Other spacecraft have hit the moon, but it was on purpose or as part of a failed landing (in other words, the impact was intentional, just a little harder than intended) – not just a piece capricious of space debris.
Maybe we’ll never know, and really, that’s the weirdest part of all. With hundreds of ground-based telescopes and radars, space sensor arrays and cameras pointing in every direction – and that’s only space surveillance as we know it! – it seems amazing that an entire rocket stage managed to stay in orbit for six or seven years, finally making it to the moon, unidentified.
I thought someone from LeoLabs, which has been building a new network of debris tracking radars around the world, might have a little insight. Darren McKnight, senior technical member there, had the following answers to my questions.
How is it possible that we don’t know the identity and trajectory of such a large, relatively recently launched object?
Tracking abandoned objects in cislunar orbit is probably not a priority for government sensors when they can spend that time observing satellites or space junk closer to Earth. However, tracking and monitoring operational satellites in cislunar orbit is indeed critical to strategic intelligence, as this is new high ground.
Would such confusion be possible for an object thrown now?
Yes, it could happen again now because the technology used by the US government to track space objects has not changed for many years.
Are there likely to be more of these “mystery objects” impacting here and there over the next few years?
It’s possible that an accidental moonstrike like this could happen again in the future, depending on the number of missions that place rocket bodies in those orbits and a sufficient lead time (years or decades). But events like this should generally remain extremely rare.
And as Bill Gray notes in his article:
…High altitude trash hasn’t worried anyone outside of asteroid surveys, and even we haven’t been that worried about it. Objects of this type are not tracked by the US Space Force; they (mostly) use radar, which is “myopic”: it can track four inch/10cm diameter objects in low orbits, but cannot see large rocket stages like this when they are as far as the moon. You need telescopes for that.
Strange as it may seem (to me, anyway), orbits are only calculated for such objects by me, in my spare time.
It’s remarkable in a way, but as anyone in the space surveillance world will tell you, there’s a lot to watch out there and you have to choose your targets. A rocket-sized object halfway to the moon is not straightforward or easy to get a good image.
Our best clue as to the object’s identity may actually be the crater it left behind when it hit. The impact location was photographed shortly afterwards and it has a curious double O shape: two overlapping craters, one 18 meters in diameter and the other 16 meters. Here is the before and after:
“The double crater was unexpected and may indicate that the rocket body had large masses at either end. Typically, a spent rocket has mass concentrated at the engine end; the rest of the rocket stage mostly consists of an empty fuel tank,” NASA’s Mark Robinson wrote.
While it’s an alluring mystery, the truth is that there doesn’t seem to be much reason to devote serious resources to uncovering it. Stranger things happen in space than a piece of rocket flying at exactly the angle and speed needed to finally hit the moon. And as far as we know, someone out there is well aware of what this strange, double-ended piece of space junk is, but prefers to keep it quiet.