SpaceWeather.com's newsletter states

Sky watchers are reporting two new objects in the night sky: China's new space station and an out-of-control booster rocket that helped launch it. The tumbling booster is flashing brighter than some of the brightest stars in the sky.

My usual star-gazing app does not have the rocket booster in its database (yet), and I did not manage to spot it yet (from cloudy central Europe). Is there an official name for the object? Could somebody help me how to find it in the remaining 2 days while it is still in orbit around Earth? Or maybe somebody could even share a picture or two?

Bonus question: Maybe somebody could also enlighten me in how far any single-use booster-rocket could be in-control after it ejected its payload? Wasn't that the default for many years? Also: Now that we can observe the rocket we know the trajectory and could also forecast when it will crash and where, aren't we?


  • $\begingroup$ I was too fast, my bad: Tianhe-1 is indeed the space station, I should have double-checked. @User123 Thanks for pointing that out. $\endgroup$ – B--rian May 6 at 21:05
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    $\begingroup$ We would love this question on the Space Exploration Stack Exchange! I'm sure you could also get some pretty cool answers there! $\endgroup$ – James Ervin May 7 at 16:17
  • $\begingroup$ I will ask a different flavor of the same question over there tonight... $\endgroup$ – B--rian May 7 at 16:42
  • $\begingroup$ That's awesome to hear! $\endgroup$ – James Ervin May 7 at 20:37
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    $\begingroup$ I just tried to see if I could spot it from Spain. I think I did - some brief flashes, as I would expect from a tumbling object - but not 100% sure. I definitely saw Tianhe, five minutes later, at 0447h GMT+1, and confirmed with Stellarium (the satellites plugin has been updated with CZ-5B and Tianhe since you posted this question) $\endgroup$ – Aaron F May 8 at 3:03

The name of the module is Tianhe (天和), and the name of the rocket is Long March 5B, but it got a special designation of 2021-035B. It is not really official, but I think it is good enough to get some data. I found this website for current position (live on globe). Your userpage says you live in Europe, so the rocket will fly over Greece at 00:30 CEST (22:30 UTC) tomorrow (in 1.5 hour if you have time to be awake for that long). I also calculated the maximum angular speed (on May 6) of around 1.85 °/s (on May 7, it is 2.7 °/s).

There are already some images; I found only that one. The booster's visual magnitude is around –1, so pretty bright to spot.

So, if you have time, try to look to the South and spot the booster at 22:30 UTC today. Maybe you are going to have luck tonight : )

There are some equations I derived with basic trigonometry about the rocket's visibility:

Distance $D$ at which the rocket can be seen right on horizon: $$D = R \ \arccos\left(\frac{R}{R+h}\right)$$ Where the calculator calculates radians, $R$ is Earth's radius and $h$ is the altitude of the booster (you can get that on previously given website; at the moment it is 170 km).

The angular height of the booster which is $D$ kilometers away from us (on Earth) is given by:

$$\alpha = \frac{\pi}{2}-\arcsin \, \left(\frac{(R+h)\sin{\frac{D}{R}}}{\sqrt{2R^2+2Rh+h^2-2R(R+h)\cos{\frac{D}{R}}}}\right)$$ Again, the calculator must be set in radians.

Update: The rocket fell on May 9 at 02:14 UTC into the Indian Ocean, so no one was hurted.

  • $\begingroup$ @B--rian Have you seen it yesterday? $\endgroup$ – User123 May 7 at 6:38
  • $\begingroup$ Nope, was too cloudy. $\endgroup$ – B--rian May 7 at 7:40
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    $\begingroup$ I also included the equations for visibility, and if you live in UK or in Germany, the Greece is too far. Also note that the booster is currently falling. $\endgroup$ – User123 May 7 at 7:43
  • $\begingroup$ +1 yay for equations! $\endgroup$ – uhoh May 8 at 1:07
  • $\begingroup$ "It is not really official..." It really is official for those who track and catalog objects in Earth orbit (governments, militaries, etc.) Just like 2021-035A is the COSPAR International Designator for Tianhe, 2021-035B is the international designator for the LM 5B core stage from that launch. $\endgroup$ – uhoh May 8 at 3:17

I found an openly available CZ-5B Rocket Body (ID 48275) reentry prediction:

Reentry Prediction

Most intersting I found the following graph which shows how slowly error bars of the predicted reentry time decrease over time (as obtained from The Aerospace Corporation Tweet):

error bars of the reentry

Last but not least, I also learned from a Business Insider story called "The US is tracking an uncontrolled Chinese rocket traveling at 18,000 mph that is expected to crash down around May 8" more on why the rocket was called "uncontrolled":

McDowell told Space News that letting debris reenter the atmosphere uncontrolled was "unacceptable." "Since 1990 nothing over 10 tons has been deliberately left in orbit to reenter uncontrolled," he said.

  • $\begingroup$ Yes, the location in Europe is here crucial. If you live in South Europe, you might have a possibility of seeing it. But if you live on greater latitude than 50°, you might not have this possibility. $\endgroup$ – User123 May 7 at 9:59
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    $\begingroup$ I prefer seeing it in transit rather than in my backyard :-) $\endgroup$ – B--rian May 7 at 11:12
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    $\begingroup$ But rocket in backyard would be more unforgettable. $\endgroup$ – User123 May 7 at 11:15
  • $\begingroup$ the aerospace.org link now redirects to their twitter page :-/ $\endgroup$ – Aaron F May 9 at 1:06

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