[amsat-bb] Tiangong Re-entry (0000 UTC +/- 2.5 hrs)

[Robert Bruninga]

Since this is journalism, I think you and some others are right.  If one
simply looks at latitude as a number, then the latitude near the
inclination will have a higher probability of appearing.  But the best
feedback came from Ralph W0RPK who pointed out this page which is tracking
the orbit with updated predictions:
http://www.aerospace.org/CORDSuploads/TiangongStoryboard.png

And the USA is about as far as you can get from the predicted impact.  The
USA is 12 hours out of cycle with the orbit.

The prediction there is currently showing about 0000 UTC which is 8 PM EDT
plus or minus 2.5 hours. (which is about 3 orbits worth).  And although
those orbits cover a vast Pacific and Atlantic oceans, a good portion of
them cross the middle east through Russia and china.

Bob, WB4APR

On Sun, Apr 1, 2018 at 11:26 AM, Gary Bender, WS5N <ws5n at wildblue.net>
wrote:

>
> I was thinking the favoring of higher latitudes for reentry was because
> the apparent sine wave of the ground track naturally slows down in
> "latitude velocity" as it peaks at 43 degrees and reverses.  Add in the
> rotation of the earth under it and you end up with a bit more dwell time
> above 38 degrees.  It is changing latitude much faster between the
> extremes.  (Or maybe I am over thinking it.)
>  --
>     Gary, WS5N
>
> ----- Original Message -----
> From: "Robert Bruninga" <bruninga at usna.edu>
> To: "amsat bb" <amsat-bb at amsat.org>
> Cc: "TAPR APRS Mailing List" <aprssig at tapr.org>
> Sent: Saturday, March 31, 2018 5:55:17 PM
> Subject: Re: [aprssig] [amsat-bb] Tiangong Re-entry on Heavens bove
>
> > Hi Bob, do you know the object number by chance?
>
> No, but this link shows that the higher probabilities or re-entry are
> between about 38 to 43 degree latitudes north and south.
>
> https://www.theguardian.com/science/2018/mar/30/chinas-tiangong-1-space-st
> ation-will-crash-to-earth-this-weekend
> <https://www.theguardian.com/science/2018/mar/30/chinas-tiangong-1-space-st%0Aation-will-crash-to-earth-this-weekend>
>
> Im not sure why those would be slightly higher.  43 degrees is its maximum
> excursion (matches its inclination)...  Maybe its because as it passes
> over the equatorial bulge, it sees the higher drag and that will start the
> demise which will occur then 20 minutes later?
>
> Bob
> -----Original Message-----
> From: Robert Bruninga
> Sent: Saturday, March 31, 2018 9:16 AM
> Subject: [amsat-bb] Tiangong Re-enetry on Heavens bove
>
> You can see the live track of Taengong to re-enter in the next 24 hours on
> http://www.heavens-above.com/
>
> Just remember, as it suffers increased drag, it will speed up and be ahead
> of classic predictions.
>
> But at least you can see when you are under the orbit as to whether it is
> worth going outside.  I 'd go out several minutes before the prediction
> since we dont know how quickly they are updating the elements as it speeds
> up.
>
> and even if it is daytime, you will see it if it comes in in your area...
>
> Bob
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