Re: Decay alert : 29058 Object B

From: Fco. Javier Iruretagoyena (Webmail) (javiru@able.es)
Date: Thu Apr 27 2006 - 03:20:43 EDT

• Next message: Russell Eberst: "2006APR26-27.OBS"

```Does anyone know if object 29058 has decayed already?

Javi
Zaragoza, Spain

---- "BjÃ¶rn Gimle" <b.gimle@chello.se> escribiÃ³:

=============

> Current Space-Track elements seem to show this bottoming out at 138 km
> altitude  at about 15Â°N, 108Â°W at 23:43 UT this evening, shortly before
> making a southerly pass at my 20 (Toronto, 43Â°N 79Â°W).
>
> Is a perigee of 138 km terminally low?
>
That depends more on the area/mass ratio of the object (roughly proportional
to B* (col.55-61 of line1) and excentricity of the orbit (col.27-33 of
line2).
For a Molniya type orbit (high excentricity) a perigee of  75 km is not
immediately fatal (it will be glowing red after perigee, and lose its solar
panels).
For a circular orbit and "normal" density I consider a mean motion of 16.55
as fatal - this corresponds to perigee=apogee=125 km.
But for any near-circular orbit I use the ndot2 value (col.35-43 of line1)
as a rule-of-thumb: divide 0.06 by ndot2 to get remaining days. I have one
elset with ndot2 ~0.20 at ~06116.86 which would mean decay ~06117.19
An even better way is to plot 1/ndot2 for several recent elsets.
ndot2 tripled between 06116.50 and 06116.86, which would make ndot2 infinite
after about half that interval, at 06117.04

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