Corrected identification of object about to hit the moon

UPDATE : resulting impact crater has been imaged

Note : I keep getting questions that cause me to realize I should explain something else, or that I explained something poorly. Click here for a list of recent changes. Last modified 2015 Mar 05 16:00 UTC. Here's the original story about this object.

Short version : back in March 2015, I (mis)identified this object as 2015-007B, the second stage of the DSCOVR spacecraft. We now have good evidence that it is actually 2014-065B, the booster for the Chang'e 5-T1 lunar mission. (It will, however, still hit the moon within a few kilometers of the predicted spot on 2022 March 4 at 12:25 UTC, within a few seconds of the predicted time. In fact, we've gotten more observations refining the impact point slightly.)

The full story

This morning (2022 Feb 12), I received an e-mail from Jon Giorgini at the Jet Propulsion Laboratory. JPL doesn't track space junk, but they do keep careful track of a lot of active spacecraft, including DSCOVR.

Jon inquired 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. It would be a little strange if the second stage went right past the moon, while DSCOVR was in another part of the sky. There's always some separation, but this was suspiciously large.

Prompted by Jon's e-mail, I dug into my e-mail archives to remind myself why I had originally identified the object as the DSCOVR stage in the first place, seven years ago. I did that digging in full confidence it would prove that the object was, in fact, the DSCOVR second stage.

How the object was originally (mis)identified as the DSCOVR second stage

On 2015 March 14, about a month after DSCOVR was launched, the Catalina Sky Survey found a possible near-earth asteroid. As is the usual practice, they posted their observations on the NEOCP (Near-Earth Object Confirmation Page). This is where astronomers post data about objects they've found that might be near-earth asteroids or comets; the idea is that others can then try to observe them as well and say "I found it, too, at the following location" or "Hmmm, can't find that one." The discoverers, thinking they had a rock, gave it the temporary name WE0913A.

These data are publicly available, and shortly thereafter, an astronomer in Brazil noted on a newsgroup that the object was orbiting the earth, not the sun, suggesting it might be a human-made object. I replied to confirm this, and wrote that I thought it was either DSCOVR or some bit of hardware associated with it, but that I was having problems finding any data on DSCOVR's trajectory.

Further data confirmed that yes, WE0913A had gone past the moon two days after DSCOVR's launch, and I and others came to accept the identification with the second stage as correct. The object had about the brightness we would expect, and had showed up at the expected time and moving in a reasonable orbit.

Essentially, I had pretty good circumstantial evidence for the identification, but nothing conclusive. That was not at all unusual. 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 a couple of unidentified bits of junk out there. (At least, not identified yet.)

Why I'm now sure it's actually the Chang'e 5-T1 booster

In hindsight, I should have noticed some odd things about WE0913A's orbit. Assuming no maneuvers, it would have been in a somewhat odd orbit around the earth before the lunar flyby. At its highest point, it would be near the moon's orbit; at its lowest (perigee), about a third of that distance. I'd have expected the perigee to be near the earth's surface. The perigee seemed quite high.

However, rocket hardware often does strange things in its early days in space, with leftover fuel leaking out and pushing it around. That causes changes in the orbit, so that when you try to figure out where the junk came from, you get a wrong (or at least altered) answer. Such things happen routinely, but in this case, it would have required an unusual (though possible) sort of leakage, occurring several days after the lunar flyby. And it would have had to be a pretty substantial amount of leakage. Also, I didn't have a trajectory for DSCOVR at the time, and the lunar flyby seemed quite plausible (spacecraft often use a lunar flyby to adjust their orbits).

So matters stood, until I received Jon's e-mail. That prompted me to look for earlier space missions that might account for the object. It couldn't have been up all that long before, because this is a large, bright object; somebody would have seen it. So it had to have been launched not long before March 2015, in a high orbit going past the moon. Few objects go that high; most stay relatively near the earth.

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.

It's unclear when the Chang'e 5-T1 booster would have gone by the moon, but four days after launch would be a reasonable ballpark estimate. Running the orbit for WE0913A further backward, I got a lunar flyby on 2014 October 28 :

Orbital elements:  WE0913A = DSCOVR object = 2015-007B = NORAD 40391
   Perilune 2014 Oct 27.9200390 +/- 0.000152 TT = 22:04:51.37 (JD 2456958.4200390)
A1: 4.24e-9 +/- 4.51e-11   A2: 7.59e-11 +/- 3.01e-11
A3: -6.33e-10 +/- 4.72e-11 AU/day^2 [1/r^2]
Epoch 2014 Oct 28.0 TT = JDT 2456958.5                        Find_Orb
q  6826.0085634 +/- 99.4            (J2000 ecliptic)
H   27.4  G 0.15                    Peri.  110.9433956 +/- 0.14
                                    Node     7.0878255 +/- 0.13
e   2.054713052 +/- 0.0151          Incl.  119.1718318 +/- 0.13
71 of 85 observations 2015 Mar. 14-July 14; mean residual 0".553

...which is a quite close lunar flyby at about the right time. But even more impressively, the orbit before the flyby has it in the "usual" lunar transfer orbit. If we assume that perigee was just above the atmosphere (as it usually is), then it happens about half an hour after launch time, and the ground path starts out near the launch site in China and proceeds almost due East. In short, it looks exactly like a Chinese lunar mission ought to look in every particular.

Orbital elements:  WE0913A = DSCOVR object = 2015-007B = NORAD 40391
   Perigee 2014 Oct 23.7643109 +/- 0.00152 TT;  Constraint: q=6500k
A1: 3.78e-9 +/- 2.24e-11   A2: 3.65e-10 +/- 2e-11   A3: -6.45e-10 +/- 6.51e-11 AU/day^2 [1/r^2]
Epoch 2014 Oct 24.0 TT = JDT 2456954.5                        Find_Orb
M   8.3102144356 +/- 0.053          (J2000 equator)
n  35.2592288110 +/- 0.0058         Peri.  141.9756875 +/- 0.14
a198802.40474 +/- 21.8              Node   301.7804670 +/- 0.15
e   0.967304355 +/- 4.7e-6          Incl.   27.0705663 +/- 0.16
P  10.21d                  H 27.4   G  0.15   U  9.3
q 6499.9727089 +/- 0.115    Q 391104.83678 +/- 44.1
71 of 85 observations 2015 Mar. 14-July 14; mean residual 0".848

To add to the new evidence, Jonathan McDowell has sent orbital elements for an amateur radio cubesat that got a "ride share" with the booster, and it's a very close match.

Also, students at the University of Arizona studied the composition of this object, and confirmed that it resembles similar Chinese boosters, not Falcon 9 boosters. (Which is not specific enough to say which Chinese lunar booster it is, and there are plenty out there. It's a bit like saying a crime suspect has blond hair. It does mean that you cross brunettes and redheads off your list of suspects -- in this case, we can cross the SpaceX DSCOVR booster off our list -- but it leaves us with a long list of blonds/Chinese boosters. We've essentially used the trajectory data to figure out which blond we're talking about.)

In a sense, all this remains "circumstantial" evidence. But I would regard it as fairly convincing evidence, the sort where the jury would file out of the courtroom and come back in a few minutes with a conviction. So I am persuaded that the object about to hit the moon on 2022 Mar 4 at 12:25 UTC is actually the Chang'e 5-T1 rocket stage.

Why did China's Foreign Ministry say this isn't the Chang'e 5 booster?

On 2022 Feb 21, China's Ministry of Foreign Affairs said this object is not the Chang'e-5 upper stage. I think the Ministry of Foreign Affairs simply got two different, but similarly named, lunar missions mixed up. (Here's the original statement from the MFA. If you search for 'booster', you'll find the relevant bit.)

The Chang'e 5-T1 lunar mission launched in October 2014. The upper stage of that mission is the one that'll hit the moon this March, and is the subject of this Web page.

Separately, there was a Chang'e 5 lunar mission launched in November 2020. A different mission, with a booster that did re-enter over the Pacific Ocean a week after it was launched.

I originally identified this object as the 5-T1 upper stage based on very strong orbital element (trajectory) data. That only got stronger with the added data about the amateur radio satellite attached to the 5-T1 booster and the spectral analysis. So I don't really have any reason to doubt the identification.

I should note that many have gotten these two missions mixed up before at one time or another. (Picture my hand raised here.) Given that, I think this was probably an honest error on the part of the Foreign Ministry.

But Space-Track/18SPCS says the Chang'e 5-T1 booster hit the earth's atmosphere long ago!

We did have a small mystery, in that the 18th Space Control Squadron listed this booster (the same one I'm saying will hit the moon) as having instead hit the earth's atmosphere in October 2015, almost a year after launch. Note that 18SPCS has revised that listing and says the Chang'e 5-T1 upper stage did not actually re-enter the atmosphere. They now list the decay date as 2022 March 4.

I was skeptical of the 18SPCS listing from the beginning. If 18SPCS had actually tracked the object over the following year, they probably would have posted an updated trajectory publicly. They're usually quite reliable about that.

The only trajectory data they provided was for shortly after launch. If that's all they had to work with, then the re-entry date is a prediction a year ahead of time and is not particularly meaningful. (Sort of like trying to predict weather a year ahead of time.) The object was at high altitudes for most of that year, beyond the likely reach of radar. Asteroid observers did keep track of it several times over that year, and in the years afterward, such that I was able to say it would hit the moon in March.

In defense of 18SPCS, I should say that they do quite a good job of tracking anything relatively close to the earth, down to objects ten cm across in low-earth orbit. (Which is where 100% of the concern has been.) But objects at really high altitudes are not something they tend to track. In fact, the only real reason I've been computing orbits for high-altitude space junk (such as this object) is because 18SPCS basically can't. They rely on radar, which is not a particularly useful tool for deep-space objects.

How did this mistake get past everybody? Aren't others tracking junk like this?

As mentioned on my original page about this object, high-altitude junk has been of no concern to anybody outside the asteroid surveys, and even we haven't been all that fussed about it. Objects of this sort are not tracked by the US Space Force; they (mostly) use radar, which is 'near-sighted' : it can track objects four inches/10 cm across in low orbits, but can't see big rocket stages like this when they're as far away as the moon. You need telescopes for that.

Strange as it seems (to me, anyway), orbits are computed for objects of this sort only by me, in my spare time. Which leads to the question...

Should high-flying space junk be better tracked? Perhaps by an 'official' agency of some sort?

In the past, the limited work I did was probably sufficient. For the reasons described above, tracking deep-space junk wasn't all that major of a concern. (Though I should note that it appears that 18SPCS now plans to start tracking cislunar objects.)

But many more spacecraft are now going into high orbits, and some of them will be taking crews to the moon. Such junk will no longer be merely an annoyance to a small group of astronomers. A few fairly simple steps would help quite a bit.

First, anybody launching objects into high orbits ought to make the last known state vector (where the object was and where it was going) publicly available, to some agreed-upon, centralized location that has some funding to do the job. SpaceX did have such a vector for the DSCOVR second stage, but it didn't get much distribution; I only learned of it very recently. (If I'd had it back in 2015, I probably would have recognized my mistake quickly.) The amateur radio community put together a state vector and orbital elements for the Chang'e 5-T1 stage, but that didn't get much distribution either and was also unavailable to me at the time.

Second, that centralized location ought to be the clearinghouse for observational data on high-orbiting junk, and should keep track of where such objects are going and make that data publicly available. (Basically, I'm asking for somebody to take over the job. They can use my software, which is all freely available, but I'm busy with asteroids.) This would be somewhat similar to the way in which the Minor Planet Center gathers observations of asteroids and figures out where they're all going.

I'd also advocate for attacking the problem on an international basis. This isn't just a US (or Chinese) problem.

Third, some thought should go into Keeping Outer Space Clean. (This already happens for low-orbiting objects, but everyone has been quite blasé about high-altitude junk.) The most recent Chinese lunar mission, Chang'e 5, put the booster into an orbit where it went past the moon, came back, and re-entered into the middle of the Pacific, far from any land mass. I hope that means CNSA has decided to dispose of space junk properly. (I don't know that they have; it could just have been sheer luck. If the upper stage of their next lunar mission goes into the ocean, we may suspect a pattern.)

"Proper disposition", by the way, may mean different things for different objects. For some, it could mean the Pacific Ocean; others might be best left to hit the moon, or put into solar orbit. The answer may not be the same for every bit of junk. But simply ignoring the issue, as has been (mostly) the policy to date, shouldn't be an option. It's an especially bad idea for objects for objects such as this, with orbits that bring them close to the moon. You get chaotic orbits in that case, where you really don't know where they'll eventually end up.

What about the new US Space Force plans to start tracking cislunar objects?

This is a newly announced US Space Force scheme to track objects around the moon, using a 'Cislunar Highway Patrol System' (CHPS) satellite.

The YouTube video from USSF describing their plan is very light on details. They describe a satellite "272000 miles from Earth", which sounds as if they plan to put it at the earth-moon L2 point, hovering over the far side of the moon. That would place it nicely to detect objects in close orbit around the moon, which is a blind spot for us right now. I rely on telescopic observations, and you can only get just so close to the moon before the sky background is too bright to see faint junk.

The military interest here is quite sensible. If I were going to hide a satellite, putting it near the moon would be a good place to do so. (Earth-Sun L1 might be even better; less fuel required, and it's easier to drop out of that orbit and come back toward Earth unobserved if you're so inclined.) Any debris near the moon would otherwise go unobserved. There's speculation, for example, that the Apollo 11 ascent stage may be orbiting the moon. If so, this spacecraft could possibly find it, and the various radars and ground-based telescopes couldn't.

A satellite of this sort, though, will do nothing for the debris that is in high orbits but doesn't spend much time close to the moon. (For example, this object, which occasionally came close to the moon, but spent about 99% of its time nowhere near the moon.) So I don't think CHPS will get me off the hook for tracking high-altitude debris any time soon.

I think the timing of this announcement (a day after the 5-T1 stage hit the far side of the moon) is coincidental; there's enough stuff going near the moon to prod them into thinking about this problem.

So if this isn't the SpaceX booster you thought it was, where is the SpaceX booster?

That's a good question. I wish I had a good answer. But I strongly suspect that nobody does. (Update: I've received orbital data which seems to support my 'guess' below. Still investigating.)

I don't think SpaceX knows. If they did, they could have raised their hand in the last couple of weeks and said, "That's not our rocket stage hitting the moon." This is not proof -- SpaceX is, I gather, notably uncommunicative -- but given how much grief they were getting, you'd think they would have pointed this out. (For that matter, I don't know how well China tracks its leftover rockets.)

My guess (and guesses are mostly what we have now) is that it went along with DSCOVR itself out to the Earth-Sun L1 point, a spot about a million miles closer to the sun than we are. DSCOVR stayed there (and is still there, returning images of the earth regularly). The booster, I think, kept going and escaped into an orbit around the sun. (You can't just go to the L1 point and stay there without maneuvering; orbits there are unstable. DSCOVR has to make small adjustments to its orbit every few months, much as the James Webb Space Telescope will in order to stay at the L2 point on the opposite side of the earth. It's very much like keeping a ruler balanced on the end of your finger.)

While this is a guess, I think it's a pretty good one. We often track upper stages by looking for the spacecraft and seeing the stage nearby in the sky; that is how, for example, we tracked the upper stage for the James Webb Space Telescope, the booster for China's Tianwen-1 mission to Mars, and the EMM-Hope booster on its way to Mars.

The alternative would be that the DSCOVR second stage went out along with DSCOVR, but didn't have quite enough energy to escape into orbit around the sun. But in that case, the odds are good we would have eventually seen an unexplained object orbiting the earth that had been near the earth-sun L1 point. We haven't. So I'd lean to the "escaped into orbit around the sun" scenario.


* As I understand it, early rockets would be left in orbit with leftover fuel in them, and the fuel would eventually heat up and cause the rocket to explode, creating more junk. So a 'pressure relief valve' was added : pressure builds up, a valve opens, and the leftover fuel leaks out. Home water tanks usually have a similar valve in case pressure gets beyond what the system could probably handle : better to have water released safely than sprayed all over your house.