Re: HST close approaches
Bjoern Gimle (b_gimle@algonet.se)
Mon, 24 Mar 1997 07:16:36 +0100
Russell Eberst <eberst@cableinet.co.uk> wrote:
...
>>HST
>>1 20580U 90037B 97080.05727574 +.00000377 +00000-0 +25237-4 0 09658
>>2 20580 028.4675 240.1986 0014574 358.9811 001.0726 14.86427821179933
...
>With the revs/day for Cosmos1666 being very similar to the figure for HST,
>this indicates that if there is one close approach between the two objects
>as calculated for 3/24/97 at 04:42, then there must be other close approaches
>every half-orbit (that's about every 48 minutes). It would be interesting to
>see calculation of the 2 series of close approaches which occur at the two
>orbinodes. (I just invented that word, for the point where two orbits cross)
I used these two elsets:
Cosmos 1666 623 x 596 km
1 15889U 85058A 97079.11427531 .00000278 00000-0 28772-4 0 4669
2 15889 82.5246 290.8691 0019773 314.0859 45.8729 14.86283170632244
Cosmos 1666 623 x 596 km
1 15889U 85058A 97080.12412792 .00000252 00000-0 25809-4 0 4733
2 15889 82.5247 289.9198 0019748 310.7573 49.1928 14.86283453632392
MM differs from HST's by about 0.0014 revs/day, or 9 seconds, but the
inclinations, and hence the progression of the perigees and the ascending
nodes differ much more.
MM is the inverse of the anomalistic(perigee-perigee) period, which has
little to do with the 'orbinodes'. Since HST's perigee advances by
about 9.5 degrees/day, and C*1666's regresses by 3.6 degrees/day,
the nodal periods differ by an additional 3+ minutes, making the total
difference 228.3 seconds/day.
The orbinodes are located near the northern and southern apex of HST's
orbit, and since the ascending nodes regress by 6.5 and 1.0 degrees/day,
this effectively moves the orbinodes 5.5 degrees East each day, or
about 4.5 degrees along HST's orbit, adding another minute to the
separation. These are the reasons you see the minimum separations
increase so quickly :
3/24/1997 11:05:06.9 15889 Cosmos 1666 64.7 +4.35
3/24/1997 11:53:29.6 15889 Cosmos 1666 39.4 +4.38
3/24/1997 12:41:59.1 15889 Cosmos 1666 2.4 +4.41
3/24/1997 13:30:21.7 15889 Cosmos 1666 30.8 +4.45
3/24/1997 14:18:51.2 15889 Cosmos 1666 66.3 +4.48
3/24/1997 15:07:13.8 15889 Cosmos 1666 94.3 +4.52
(from the first elset)
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