[Prev][Next][Index][Thread]

(meteorobs) Iridium satellites WRT re-entry



The Iridium satellites are cylinders with length of four meters,
diameter of 1.3 meter, and a mass of 689 kg:

http://www.friends-partners.org/~mwade/craft/lm700.htm

The mass includes of course the three "main mission antennas" 
that produce the famous flares, and two solar arrays.  I don't 
know how much of the mass is propellant that would be spent 
before re-entry.  (One of the main reasons for deorbiting them
would be to reduce the risk of in-orbit propellant explosion, so 
I would assume that almost all of it would be either burned or 
vented.)

Given those data and the re-entry velocity of about 8 km/sec at a 
very shallow angle, I wonder how much, if any, of the satellites 
will survive to reach the surface.  I wonder what mass object of 
solar system origin would enter the atmosphere with similar 
energy?  (I don't know the equations for calculating that sort of 
thing.)  

Presumably the main mission antennas and solar panels (and other
fragments) will be shed along the re-entry path and might make 
for an even more interesting display.  

From what I've heard so far, it could be as long as two years 
before the last ones leave orbit.

The re-entry of Compton Gamma-Ray Observatory (length, 9.1 m;
diameter, 4.6 m; mass 15,620 kg [including 1,900 kg propellant])
would be a truly spectacular show, but my guess is that they 
will try to keep observers well clear of the predicted re-entry 
field. 

Different topic:  Regarding flashing geosynchronous satellites 
-- some flash brightly (up to at least +2 if not brighter) as 
infrequently as once per two or three or more minutes, and 
during each minute the field of background stars moves about 
.25 degree to the west.  For probably most of them as observed 
from any given location, there's an episode of bright flashes 
each night that may last only a few minutes.  Probably most of 
the ones that flash like this are actually not quite 
geosynchronous and drift a few degrees from night to night.  
Many also have a few degrees of north-south motion every 24 
hours.  Rapidly flashing satellites are obvious, but the ones 
with infrequent bright flashes could be deceptive.  For one 
thing, their flashes are slow -- as long as 0.5 second, if not 
longer, due to the slow rotation of the satellite.  From 
reading this list for a while now, I get the sense that true 
point meteors must be fairly rare.  I saw a couple that were 
pretty close to points during the 1998 Leonids, but they 
weren't perfect.

There are any number of other satellites that can flash 
infrequently.  One example that comes to mind was a solitary 
flash someone reported that proved to match perfectly in time 
and position by Midas 9, an old "early warning" satellite 
orbiting in a high, circular, nearly polar orbit.

Ed Cannon - ecannon@mail.utexasdot edu - Austin, Texas, USA
http://wwwvms.utexasdot edu/~ecannon/meteorlinks.html

To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html