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The upper stage of the Falcon 9 rocket that launched the DSCOVR spacecraft is expected to accidentally crash into the moon soon.

How did it get into this position? I found answers here that say it was, or was planned to be, put into a heliocentric orbit. Was there a trajectory error? A malfunction? A change in plan?

Fred Larson
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    Lots of things in heliocentric orbits go splat. When they do so on Earth they're called meteors. – Oscar Lanzi Feb 02 '22 at 19:32
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    Maybe it's a story similar to the Apollo 12 S-IVB stage. – Fred Larson Feb 02 '22 at 19:55
  • This is an excellent question! With n-body problems there is really no hard line between a purely heliocentric orbit and something more complicated. Maybe it mostly orbited the Sun for years then got recaptured in cis-lunar space like a minimoon or maybe it never really left the Earth-Moon system. With both radar and optical tracking complementing each other, it's possible the recorded trajectory can go pretty far out. What is the current record for the farthest detection of a "dead" spacecraft? – uhoh Feb 02 '22 at 20:04
  • also When was the last time that Starman/Roadster was seen? (it was pretty far!) and at ~1.4 million km JWST is now a popular target for ground based telescopes, though it is of course much bigger and potentially much more shiny at times than the F9 2nd stage. – uhoh Feb 02 '22 at 20:11
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    Keep in mind that there's a difference between predicting that it's likely to end up in solar orbit, and that being any sort of intention or goal. There's nothing of value for it to be a realistic threat to, and as long as DSCOVR gets put where it's supposed to be, it doesn't really matter what happens to the upper stage. – Christopher James Huff Feb 02 '22 at 20:37
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    The three answers to which you linked are apparently wrong. People have been tracking the upper stage that placed DSCOVR into its pseudo orbit about the Sun-Earth L1 point, and that upper stage never made it out of the Earth's Hill sphere (which isn't really a sphere). When an object's velocity is just enough to get the object close to the Hill sphere boundary, the object will not cross and will instead stay within the Hill sphere unless it happens to pass through one of two keyholes near L1 and L2. The upper stage in question didn't have enough energy to punch through the barrier. – David Hammen Feb 03 '22 at 12:53

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I suspect @Christoper James Huff's comment is right in that it doesn't really matter where the upper stage goes for this kind of high energy launch. The lyrics of Tom Lehrer come to mind here:

"Once the rockets are up,

Who cares where they come down?

That's not my department,"

Says Wernher von Braun

Additionally, looking at one of the referenced answers, there is the possibility that the Falcon 9 (v1.1 at the time) did not have enough "excess performance" to do a disposal burn. Using HORIZONS you can compute the launch C3 of TESS and DSCOVR (and DART for good measure):

Spacecraft (Launcher) C3 (km^2/s^2): Mass (kg):
TESS (F9 B.4) -2.8 362
DSCOVR (F9 v1.1) -0.6 570
DART (F9 B.5) 6.5 610

(all three missions performed a drone ship landing*, TESS did a disposal burn, DART did not have to: C3>0)

Noting that the jump from v1.1 to B.4 increased performance by ~33% (according to Wikipedia), it's plausible that the DSCOVR 2nd stage just didn't have anymore juice to perform a burn (and thus did not).

*SpaceX used the DSCOVR launch to test first stage recovery doing a soft ocean landing down range (no drone ship).

Bill Gray of Project Pluto has been tracking this object:

What was the timeline on figuring this out?

DSCOVR (and this rocket stage with it) passed close by the moon on 2015 February 13, not long after launch. About a month later, one of the asteroid surveys found this object and posted it to 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.

In this case, a small observatory in California got more data, followed by enough data over subsequent days that I could show that WE0913A had made a close flyby of the moon on 2015 February 13. Further checking confirmed that the flyby matched the one the DSCOVR second stage would have made, and we abandoned the hope that it might be a rock. (Asteroid people want to find asteroids; junk is a bitter disappointment.)

The object's cis-lunar chaotic orbit is shown here since the start of 2022:

orbit 2022

(Project Pluto)

With animations here and here.

BrendanLuke15
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    That's a nice plot for explaining the complexity of predicting its orbit. Look at that kink in the trajectory around the Jan 7 mark, where it got close to the moon and had its trajectory significantly changed. That's the kind of thing where a tiny difference in radiation pressure on the tumbling booster on the way in could cause big changes in the trajectory it ends up in after passing the moon. – Christopher James Huff Feb 03 '22 at 23:27
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    It also helps reinforce that its short term behavior is always pretty predictable. Some people get the wrong idea about what "chaos" means. – Christopher James Huff Feb 03 '22 at 23:29