decay modelling

Walter Nissen (dk058@cleveland.Freenet.Edu)
Sat, 23 Dec 1995 13:22:02 -0500

I especially thank Bjoern Gimle, Rainer Kracht, Pierre Neirinck, Patrick 
Schmeer, and Jon Marchant for messages about the decay of C* 398.  (If I 
left someone out, please chastise me). 
> Pierre Neirinck wrote: 
> > 1. NORAD ndot/2 before decay are always lower than actual ndot/2. 
Yes, this is certainly likely to be true.  And even ndotdot/6 should be 
insufficient at the end. 
> > 2. Most decays I saw were southbound and shortly after perigee. 
Is this the empirical evidence which obviates my proposal that the decays 
should be distributed about the orbit?  I see this as an important 
question because I can't figure out what need the world has for theories 
which explain things that don't happen. 
> From: (Patrick Schmeer) 
> Later videotext messages mentioned that 
> fragments with masses of up to 200 kg had hit the ocean about 2000 km 
> southeast of Hawaii. 
What is not clear here is whether what was being reported was 
a) the anticipated event?   -or- 
b) an actual observation? 
If the latter, the obvious question is "how was the mass measured?". 
As Jon Marchant has implied(?) in his recent message, this information 
seems more like an anticipation of the decay than an observation. 
Jim Varney writes: 
> A date wasn't given, but I assume it's Dec. 10.  In that case, the orbit 
> was still slightly eccentric (about 25 km difference between semi-major 
> and semi-minor axes) at decay and had not circularized as I had 
> said earlier. 
Maybe so, but your model seems logical to me.  Perhaps it has considerable 
J.M.Marchant writes: 
> We've just got the latest (Dec 18/25) Aviation Week here: it says that 
> Cosmos 398 "was observed entering the atmosphere over the Atlantic Ocean 
> by a U.S. Air Force/TRW Defense Support Program (DSP) missile warning 
> satellite in geosynchronous orbit". It goes on to say that "it fell into 
> the atmosphere and impacted about 200 miles north of the Falkland Islands 
> at 2040 GMT". 
I'm not sure my tools are adequate.  One calculation I did suggests that 
the final perigee was above a point which is approximately lambda = -139 
degrees, phi = +15 degrees.  Is that correct?  Projecting the orbit down 
onto the Earth's surface, i.e., to the curve traced by the sub-satellite 
points, a point 200 miles North of the Falklands would be about 95 degrees 
along the way from (this presumed) perigee to apogee.  That point is 
closer to apogee than perigee. 
(Recall, if you would please, the challenge and response: 
"Did you know that half of all murders occur within a week of full moon?" 
"Did you know that half of the month occurs within a week of full moon?") 
Where do you think the business about "2000 km southeast of Hawaii" came 
from?  That doesn't seem to be the reentry point, so much as the final 
This DSP report sounds pretty credible to me; missile reentries certainly 
must have been an obsession of the US military for decades, so it would be 
logical that they would have effective technolgy for detecting and 
locating them. 
Even it, though, uses the phrase "fell into the atmosphere", which is 
ludicrous on its face, however meaningful it may be.  (If it was out of 
the atmosphere, why did it fall in the first place?) 
I wrote: 
> So the 
> real question is:  How much energy will remain for the final plunge?  This 
> is where I leave the mathematical realm where I am smart and enter the 
> physics realm where I am not.  It seems to me that the amount remaining 
> would be taken from a random distribution over a range beginning at zero 
> and going up to some value sensibly close to enough to get it around one 
> more time.  Not quite that much, because the atmosphere gets denser as you 
> descend, but close.  Evidently, you think otherwise.  In fact, you think 
> the distribution is pretty close to a point at zero. 
> (Mike, and others), are you going to let me twist in the wind? 
No response yet. 
I don't want to panic anyone, but is there evidence that reentries occur 
disproportionately frequently near perigee?  Or is that the only place 
people are looking?  So many "reports" of reentries, such as those quoted 
here in SeeSat-L, seem to be crude anticipations, not from actual 
observations.  If somebody can refute my naive physics, or cite good 
empirical evidence, I'll stop displaying my ignorance, and be grateful for 
the opportunity to do so. 
Walter Nissen              1-216-243-4980 
Did you see the evening star?