[meteorite-list] Tiangong-1 decay predictions

[Matson, Rob D.]

Hi John,

"Right now: its speed is 4.86mi/s, altitude 87.63 and orbit period is 88mins."

Keep in mind that the altitude is quite variable since the orbit is elliptical and the
earth's radius varies with latitude. Orbital perigee is currently occurring close to
the northern apex of the orbit (on the ascending node); however, minimum
altitude is occurring on the ascending node at much lower (northern) latitudes.

Earth's atmosphere is quiescent right now due to very low solar activity. This
is why the station has stayed longer in orbit than expected. Even over the
last couple days, the predicted time of reentry has shifted later and later; on
Friday it was 7:15 UT +/- 20 hours, and as the hours remaining have dwindled
the predictions evolved to:

10:30 UT +/- 16 hours
14:00 UT +/- 16 hours
16:15 UT +/- 9 hours
23:30 UT +/- 7 hours
4/2 02:00 UT +/- 7 hours
4/2 00:18 UT +/- 2 hours

Decay can really occur at any time; the odds slightly favor the northern hemisphere
because that's where both perigee and minimum altitude are currently occurring.

--Rob