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I have read some articles about the uncontrolled space rocket the Long March 5B including some space tracker websites but none of them give any useful information about the rocket landing.

Is it possible theoretically to know where and when the Long March 5B will be landed approximately?

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    $\begingroup$ "We don't know yet" should not be the accepted answer to this question. There are predictions, and they will increase in accuracy as time gets closer. Related: Tiangong-1 reentry impact place probabilities $\endgroup$
    – uhoh
    May 6 at 0:41
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    $\begingroup$ @uhoh "We don't know yet" is exactly the correct answer, for now, and probably until Friday (or later). $\endgroup$ May 6 at 3:19
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    $\begingroup$ I’m voting to close this question because it was asked prematurely. The correct answer for now is we don't know. The current answer is essentially we don't know. That answer will no longer be correct a day or two or three from now because there will be a predicted reentry point that will be fairly accurate by then. $\endgroup$ May 6 at 5:17
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    $\begingroup$ Probably in the ocean as ocean covers the majority of the planet $\endgroup$
    – Slarty
    May 6 at 7:27
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    $\begingroup$ If the user were to post a duplicate of the question later, would that really change the answer to "Is it possible to know...?" The booster has landed, now we can close the question because it was asked too late. $\endgroup$
    – Greg
    May 9 at 10:34
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Is it possible theoretically to know where and when the Long March 5B will be landed approximately?

Yes!

Take it from Jonathan McDowell @planet4589's tweet:

The EU SST prediction is narrow enough that we can start to talk about location now!

In particular, none of the orbits within the predicted window cross the northwestern US or the mid Atlantic seaboard.

enter image description here


More generally:

At the time of asking, No, but as we get closer the answer increasingly becomes Yes.

We can see from https://aerospace.org/reentries/cz-5b-rocket-body-id-48275 that the uncertainty in the time of reentry is currently1 +/- 8 hours. About 2.1 days ago it was +/- 21 hours.

1actually about 7 hours ago 07 May 2021 18:55:50.470 UTC the latest updated prediction posted on the site as of the time of writing.

Orbit Epoch                  07 May 2021 18:55:50.470 UTC
Predicted Reentry Time       09 May 2021 04:19        UTC ± 8 hours

Contributors to uncertainty include variations in the density of the Earth's atmosphere primarily around 150 km and below (where the spacecraft does most of its velocity loss) and the aerodynamic drag of a rocket body of unknown orientation (probably tumbling).

Past performance is not indicative of future results

From CNN's Rocket debris expected to crash into Earth soon

CNN’s Kate Bolduan: It seems even the smartest people aren’t able to calculate where this is going to land, yet. Why can’t they?

Ret. US Astronaut2 Scott Kelley: Well it’s because the satellite is spinning, and when something is spinning like that it doesn’t have a stable trajectory; it’s hard… and so the drag is always changing.

Scott Kelley on CNN

2 cmdr STS-118, EXP-26, EXP-45, EXP-46


From https://www.eusst.eu/newsroom/eu-sst-monitors-reentry-cz5brb/

enter image description here enter image description here

click for larger

left: "Doppler variations with a period of 4.5 seconds detected by radar MFDR-LR during the pass, which help infer the rotation of the object" right: "Signal-to-Noise Ratio (SNR): the ratio of the signal power to the noise power detected by radar BIRALES during one pass, with periodicity of the peaks visible about every 2.5 seconds"

The orbital period is about 88 minutes now, so an uncertainty of 8 hours means that currently one can only narrow down the location to a large swath of the Earth (roughly half of the Earth's surface) where it will happen.

As we get close, this will be come narrowed down first in terms of what part of the Earth the orbits cover (each orbit moves by about 22 degrees in longitude).

So when the uncertainty narrows to +/- 1.5 hours you'll know it will reenter +/- 22 degrees in longitude from the next-to-lat orbit and +/- 41.5 degrees in latitude, since that's the inclination of the orbit and it can't go (much) farther north or south than that.

Further: if you want to consider probabilities, those orbits spend most of their times far from the equator, so the most likely areas are concentrated between say 30 and 41.5 degrees both sides of the equator.

Long March 5B reentry prediction from https://aerospace.org/reentries/cz-5b-rocket-body-id-48275

above: Source captured at 2021-05-08 02:00 UTC below: Source captured at 2021-05-08 04:00 UTC

Long March 5B reentry prediction from https://www.eusst.eu/newsroom/eu-sst-monitors-reentry-cz5brb/


We can talk latitude probabilities any time!

From this answer to the 2018 question Tiangong-1 reentry impact place probabilities:

From the pros, from the Spaceflight 101 article Tiangong-1 Re-Entry, click for full size:

Spaceflight 101 Tiangong-1 Re-Entry

and

Even more interesting is the time-binned histogram rescaled by $1/ \cos(\lambda)$ for surface area rather than latitude, as recommended by @Litho's comment. If you were looking for debris, or looking to avoid getting hit by debris personally, this would be the plot for you.

enter image description here

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    $\begingroup$ This seems a fine answer to me. Why the downvote? $\endgroup$
    – user39728
    May 8 at 2:28
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    $\begingroup$ Ah, OK. Good answers often start as stubs, though. Maybe we should mark them as stubs when we write them so others know "work in progress"? Wouldn't want to discourage any answer simply because the poster happened to not have the time to finish just yet (or the references to throw in, or all thoughts firmly collected). You know how it goes---if you postpone it now waiting for the right time to write it, you might never come back around to writing it. $\endgroup$
    – user39728
    May 8 at 2:53
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    $\begingroup$ We shouldn't be using downvotes as retribution to others who downvoted us. $\endgroup$
    – user39728
    May 8 at 3:07
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    $\begingroup$ @user39728_i_said_user_39728_i_ those are four close votes (not down votes) and the effect of five is to prevent anybody in the community from posting an answer until five reopen votes are then collected, and that can take days or a week or more sometimes, and other times it may never happen. $\endgroup$
    – uhoh
    May 8 at 3:15
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    $\begingroup$ Yea, it was at -1 when it was just a stub. (IIRC) @user39728_i_said_user_39728_i_ It was marked as a stub when originally posted. (For the record: not a down or close voter) $\endgroup$ May 8 at 3:16
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You need to rephrase your question... Give a time frame?

From right after launch, can we predict where it will re-enter? No. Too many variables. (Height and density of earth's atmosphere).

Right the second before it hits the Earth? Yes.

In between? It depends, and it gets more accurate the closer to re-entry it gets.

Side note: Not landing, that is what SpaceX does with Falcon and Starship. This is uncontrolled re-entry.

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    $\begingroup$ -1 "You need to rephrase your question" and " It depends" are wishy-washy comments and do not a proper Stack Exchange answer make. Now this has become the accepted answer @@ Don't post comments as answers! $\endgroup$
    – uhoh
    May 6 at 0:26
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    $\begingroup$ Here's a prediction, but it's currently +/- 21 hours. It will get refined as time gets closer aerospace.org/reentries/cz-5b-rocket-body-id-48275 You know the drill: "authoritative yet unsupported answers get -1, edit adding links/supporting sources get +1 $\endgroup$
    – uhoh
    May 6 at 0:43
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    $\begingroup$ @uhoh Upvoting just to counteract your downvote. You should have voted to close the question. $\endgroup$ May 6 at 5:19
  • $\begingroup$ @DavidHammen I always vote the correct way, by definition! :-) $\endgroup$
    – uhoh
    May 6 at 6:41
  • $\begingroup$ But I think you can run a monte carlo simulation with a good drag model and wind model along with estimates of state vector data... and get a range of places where the debris is likely to fall... You wouldn't get a precise location with great certainty, but you could get an approximate location with a statistical degree of confidence---and that's not too bad. $\endgroup$
    – user39728
    May 8 at 2:25
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Yes, it is now.

The rocket has fallen down now and the approximate location where it fell is known.

According to the China Manned Space Agency (as reported on their official website and quoted by multiple news agencies worldwide):

The debris of the last stage of the Long March-5B Y2 carrier rocket reentered the atmosphere at 10:24 a.m. on Sunday (Beijing Time) […] the landing area of the debris is around a sea area with the center at 2.65 degrees north latitude and 72.47 degrees east longitude […].

This location lies in the Indian Ocean, just west of the Maldives islands.

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  • $\begingroup$ Posting this since the accepted answer is now outdated. $\endgroup$ May 10 at 20:02

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