# Unidentified subject!

Björn Gimle (b_gimle@algonet.se)
Thu, 26 Nov 1998 22:12:27 +0100

>within 268km/166 statute miles. At the speed they are whizzing
>around at, does this constitute as a near miss or is this  a=20
>regular occurence. Being an absolute novice at this, you may
>all be rolling around on the floor at such a naieve question!

Most of us are happy to see any question that has no easy answer
recently, or in the VSO home pages or their FAQ (see below)

Rob Matson's COLA program answers this from the view of one 'target'
satellite at a time. Running with a large elset, you'll probably find
several per day below 10 km. If the orbits are within 1 km in height =
where
they intersect, and the elsets are inaccurate, or drag is high, a =
combined
prediction error of 20 seconds could make up for over 200 km distance, =
if
the meet almost head-on.

Usually elsets are more accurate for a few days, and if the vertical =
track
distance is more than a few km, there is not a 'Near hit' (sic) =
situation.
-------------------------------------------------------------------------=
--------------------Example:

COLA will search for satellites having altitude ranges
that intersect the range from   309.60 to   400.22 km,
and that come within  40.0 km of the target satellite at
a time within +/-   7.0 days of both satellite epochs.
Satellites in range of Mir Complex     32.7  4.2:   89

Date     UTC Time  Norad           Name          Range (km) NdAng =
EphAge
11/27/1998  7:39:18.1 23690 Mir Debris JM    0.5  0.0    31.9    63.8 =
+2.96
11/29/1998 16:53:09.9 23941 TOMS r           3.0  0.0    19.7    38.9 =
+4.17
11/27/1998 22:36:01.7 25544 ISS              4.5  4.0    35.4   177.2 =
+2.37

--------- and another: ------------------------
Satellites in range of ISS              4.5  4.0:  114=20

Date     UTC Time  Norad           Name           Range (km) NdAng =
EphAge 11/30/1998  8:54:46.9  1844 Cosmos 100 r     3.8  2.6    17.0   =
178.8  4.83
11/30/1998  7:49:37.9  4120 Meteor 1-2 r     3.8  2.6    15.0    80.4  =
4.77
11/30/1998  8:35:48.8  4120 Meteor 1-2 r     3.8  2.6    20.8    24.8  =
4.80
11/29/1998 10:14:09.0  8755 Cosmos 808 r     3.8  2.6    27.9    14.4  =
4.37
11/27/1998  4:30:37.5  9854 Cosmos 895 r     3.8  2.6    35.1   133.8  =
1.96
11/27/1998 22:36:01.7 16609 Mir Complex     32.7  4.2    35.4     2.8  =
2.45
11/30/1998  6:08:40.4 25018 Lacrosse 3 r    10.0  3.5    27.5   150.7  =
4.73
12/ 1/1998  1:16:24.8 25532 Irid 2 Delt r    5.9  2.4    11.7    59.8  =
5.66
--------------
The 177.2 node angle indicates ISS is passing 35 km above Mir.
Near 90 degrees, the risk is much greater.

-- bjorn@tieto.se (office)         b_gimle@algonet.se (home) --
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