Encounters of C.1833 R and C.2227 R

Bjorn Gimle (bjorn.gimle@online.dextel.se)
27 Sep 1995 09:03:55 GMT

The following two orbits are almost co-planar, and with inclinations 
and mean motions that match closely. Thus, they can be seen travelling 
side by side at times, and can be interesting to watch. 
The chance of a true collision should also be investigated.

COSMOS 2227 R   2.0 10.4 3.9 0.0
1 22285U 92093B   95269.09050276 +.00000252 +00000-0 +15801-3 0 05388
2 22285 071.0142 285.7303 0004820 307.2275 052.8403 14.13896789140423
COSMOS 1833 R   2.0 10.4 3.9 0.0
1 17590U 87027B   95269.09009909 +.00000246 +00000-0 +14988-3 0 04667
2 17590 070.9977 288.1911 0004813 181.8964 178.2171 14.15690616440583

Their difference in mean motion, 0.017939, means that, 
when they are close, their separation changes by 57 km/orbit.
The close appulses will occur every 55 days, approximately.
I watched them yesterday, one day after 950925 encounter, which
according to the day's elsets was no better than 18.1 km, at 15:33:47.1.
(I also watched Resurs 1 Rk, KH 11-8, and SeeSat pass less than 
one degree from a common point in Andromeda within a 100 second 
time frame, and travel northbound together around 18:25 UT) 

The next encounter of C.1833 Rk and C.2227 Rk will be Nov.20

Their orbital heights, 836-843 km (C.1833 r) and 842-849 km (C.2227 r)
mean that there is a chance of collision when their perigees are
nearly 180 degrees apart (and common heights fall close to one of 
the orbit intersections), but since the eccentricity is so small,
the shapes of the orbits, and positions of perigees, do not vary
close to linearly, as for other orbits.

Their difference in RAAN, 2.48 degrees on Sep.25, decreases by 0.5
degrees per 55 days, so until the encounters near June 29,1996, and
Aug.26,1996, when the orbits will be nearly co-planar, the chances 
of a collision will increase. In June, the maximum cross-track 
separation will be around 18 km, so even if they overtake near
equator, they will be closer at higher (or lower) latitudes.

Before that, they will intersect near the northern and southern 
apex, at a larger angle than when they are coplanar. At one such 
intersection, every eight weeks, they should be within 29 km 
along-track, and 6 km vertically. (At the apex, their separation 
is 1.6 km cross-track because of inclination difference).

== bjorn.gimle@online.dextel.se ;  59.22371 N, 18.22857 E ==
==(bjorn.gimle@duesenberg.se)      +46-8-7428086          ==

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