USA 186 manoeuvre times (Re: CB Obs September 18, 2014: USA 186 seen!)

From: Marco Langbroek via Seesat-l <seesat-l_at_satobs.org>
Date: Fri, 19 Sep 2014 15:01:40 +0200
Marco Langbroek via Seesat-l schreef op 18-9-2014 23:53:
> C. Bassa via Seesat-l on 18-9-2014 23:00:

>> If the orbit is correct then it suggests a manouvre at apogee around
>> 18:30UT on September 17th, raising the perigee from 260 km to 320 km.

> Marco Langbroek via Seesat-l on 18-9-2014 23:53:

>> This suggest a manoeuvre on 17 Sep 17:46:15 UT in the ascending node over
>> Africa, only 5-6 mins after passing perigee. Result of the manoeuvre is a more
>> circular orbit with raised perigee and lowered apogee.


After a comment by Bjorn and some rethinking, I think it is possible that it was 
a compound (double) manoeuvre.

It appears that both apogee and perigee were changed, and inclination slightly 
adjusted. The latter is best done at one of the nodes, during which either 
apogee or perigee can also be changed in the same boost. Apogee is best changed 
while passing perigee, perigee while passing apogee.

An analysis with COLA shows two close approaches of the pre- end post-manoeuvre 
orbits: nominal times that COLA gives are 17:46:16 and 18:23:23 UT (17 Sep 2014).

The 17:46 UT time almost exactly coincides with the sat being in its ascending 
node, the classic moment to change inclination and change perigee or apogee 
(apogee in this case, as the sat passed perigee only a few minutes earlier) in 
one boost.

The 18:23:23 time coincides with passing through apogee, a good moment to raise 
perigee.

So, as I envision it, the first part of the manoeuvre then would have been at 
the ascending node and just after perigee near 17:46 UT. This lowered apogee and 
slightly adjusted the inclination. This then would be followed by a second 
manoeuvre half an orbit later near 18:23 UT around apogee and just before the 
descending node, raising the perigee. There is no need for the latter to happen 
in one of the nodes. USA 186 was west of California at that time descending 
towards Hawaii.

But perhaps this assessment changes once we have a better established 
post-manoeuvre orbit.

- Marco


-----
Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
e-mail: sattrackcam_at_langbroek.org

Cospar 4353 (Leiden):   52.15412 N, 4.49081 E (WGS84), +0 m ASL
Cospar 4354 (De Wilck): 52.11685 N, 4.56016 E (WGS84), -2 m ASL
Cospar 4355 (Cronesteyn): 52.13878 N, 4.49937 E (WGS84), -2 m ASL
Station (b)log: http://sattrackcam.blogspot.com
Twitter: @Marco_Langbroek
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-----
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Received on Fri Sep 19 2014 - 08:03:11 UTC

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