RE: Mir Orbit Looks Synchronous Again?

Ted Molczan (
Sun, 29 Sep 1996 16:25:04 -0400

Bjoern Gimle wrote:

>>James E. Byrd wrote:
>>Mir ... repeat it's ground track every 7 days 20 hrs 52 minutes.
>Ted Molczan wrote:
>>I find the following groundtrack repetition frequencies:
>>Epoch   46 revs       123 revs
>>96185  2d 23h 57m    8d 00h 24m
>>96270  2d 23h 48m    8d 00h 01m
>I don't quite see what you mean with a ground track repetition 
>period of a near integer number of days. 
>To me, that is something that only occurs for sun-synchronous 
>and almost geostationary satellites (and periods larger than 
>about 40 days for low-inclination orbits, that have moved their
>ascending node once around the Earth-Sun line).

I was in error. I should have expressed it like this:

           3 day resonance        8 day resonance
Epoch     revs      period       revs      period
96185   46.0303   2d 22h 49m   122.7474  7d 20h 51m
96270   46.1203   2d 22h 48m   122.9875  7d 20h 50m

The orbit is exactly resonant when it makes an integer number
of revolutions in the specified time. The 3 day resonance is
referring to an integer number of days, but the period of
2d 22h 49m is the exact time separating the start of the 
repeating track.

My conclusion remains the same: The three day repetition has 
deteriorated slightly; the 8 day repetition has improved 

Ted Molczan