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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?

GAD3R
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3 Answers3

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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

uhoh
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  • Hey downvoter: the question asks "Is it possible theoretically to know where and when the Long March 5B will be landed approximately?" and this is a reasonable answer to that question. Did you stop at the title and forget to read two whole more sentences to take in the body of the question as well? – uhoh May 08 '21 at 02:13
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    This seems a fine answer to me. Why the downvote? –  May 08 '21 at 02:28
  • @user39728_i_said_user_39728_i_ Because it was a stub when originally posted. – Alex Hajnal May 08 '21 at 02:45
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    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. –  May 08 '21 at 02:53
  • @AlexHajnal I'm not sure that's true. I didn't see the down vote appear until this was pretty much finished, but I was not watching particularly closely so perhaps I missed it. – uhoh May 08 '21 at 02:56
  • @user39728_i_said_user_39728_i_ I did, checking the edit history you can see I didn't remove it until edit #3. I think the down vote is related to the four close votes just as much as my posting a stub is related to the question being so close to answers-blocked status. For more on those four votes see Is this particular close vote's reason absurd and the timing damaging to the site? Does this make us look silly? – uhoh May 08 '21 at 02:59
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    We shouldn't be using downvotes as retribution to others who downvoted us. –  May 08 '21 at 03:07
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    @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. – uhoh May 08 '21 at 03:15
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    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) – Alex Hajnal May 08 '21 at 03:16
  • Do you have a full-earth plot of the orbits? e.g. Mercator projection? The page you linked to is pretty low-res. – Alex Hajnal May 08 '21 at 03:58
  • @AlexHajnal I did not include them in this answer currently because their endpoint predictions keep changing and they can give a false impression of certainty since they have those locations marked even though the uncertainty covers many orbits. If you click on either link (1, 2) you can see the most recent maps, but they change regularly. – uhoh May 08 '21 at 04:01
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    Gotcha. Asking 'cause with the map on that site it's hard to tell where the track lies. Quite a few highly populated areas under the track (and a few truly desolate ones). – Alex Hajnal May 08 '21 at 04:06
  • "Yes!" seems like a huge stretch. It's now 12 hours to go, and the window is still 8 hours long... – asdfex May 08 '21 at 15:12
  • The aerospace.org link redirects to a Twitter account ("AerospaceCorp"). – Peter Mortensen May 08 '21 at 21:00
  • Update at 2021-05-08T211600Z+0 (now +/- 2 hours). – Peter Mortensen May 08 '21 at 21:20
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    Given that the uncertainty originates largely from the fact that the core is a non-uniform shape and tumbling, so its time of re-entry cannot be predicted with any accuracy, I am left wondering about lateral deviation in trajectory, again due to non-uniform shape and time-varying aspect. While in negligible atmosphere, its ground track was determined and plotted forward, but could it end up "steered sideways" by its interaction with the atmosphere and ultimately come down along a different path than predicted, or do such effects "null out" leaving a pure deceleration drag? – Anthony X May 08 '21 at 21:29
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    Update at 2021-05-08T223900Z+0 (still at +/- 2 hours) – Peter Mortensen May 08 '21 at 22:53
  • @AnthonyX that's a good question and probably a good Stack Exchange question, something along the lines of "Can an uncontrolled reentry ever have a significant net non-zero cross-track drag that causes it to veer left or right?" Probably needs better wording. – uhoh May 08 '21 at 23:20
  • @PeterMortensen I recently saw and rejected a proposed edit with a large number of capitalization of things that weren't even sentences and other trivial edits (extreme example: [![enter image description here][1]][1] to [![Enter image description here][1]][1]) but no meaningful improvements I could spot. I don't recall recognizing the user that had made it, but I don't think it was from you. I do have a known and very hard-wired inability to use apostrophes correctly. Its 8:20 AM Sudnay mroning hear, as soon as my coffee kicks in Ill take a look at the mipselligns etc Thansk! :-) – uhoh May 09 '21 at 00:25
  • @PeterMortensen I'd run out of space; that last sentence is my 8:20 AM Sunday morning pre-coffee attempt at levity. – uhoh May 09 '21 at 00:29
  • @PeterMortensen I think I've got them all now. – uhoh May 09 '21 at 02:27
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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.

geoffc
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    Here's a prediction, but it's currently +/- 21 hours. It will get refined as time gets closer https://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 – uhoh May 06 '21 at 00:43
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    @uhoh Upvoting just to counteract your downvote. You should have voted to close the question. – David Hammen May 06 '21 at 05:19
  • @DavidHammen I always vote the correct way, by definition! :-) – uhoh May 06 '21 at 06:41
  • 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. –  May 08 '21 at 02:25
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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.

Ilmari Karonen
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