Re: CYGNUS OA-6 track: Heavens Above or N2YO better?

From: Marco Langbroek via Seesat-l <>
Date: Thu, 24 Mar 2016 17:00:08 +0100
Op 24-3-2016 om 16:33 schreef Bob King via Seesat-l:
> Hi everyone,
> I'd like to see Cygnus OA-6 as it makes its way to the ISS. I'm
> getting different elevations and times from N2YO vs. Heavens Above and
> wonder which might be closer to correct. Also, based on previous
> observations, about how bright do you think the cargo ship will be?
> Thanks for your help!
> Bob

Hi Bob,

N2YO appears to use more recent orbital elements for its prediction at this 
moment (as checked at 24 March 15:40 UT) and hence should be more accurate:

- N2YO uses an orbit with epoch:  16084.45472256  (= 24 Mar 10:54;48 UT);
- Heavens-Above with epoch:       16084.20186872  (= 24 Mar 04:50:42 UT).

There is a 0.25 day difference in orbit epoch and that is why the predictions 
between both sites differ (they are based on different orbits, with HA using an 
older orbit). N2YO uses the most recent Space-Track orbit, HA the previously 
released orbit (at this moment).

HOWEVER: note that these are all predictions based on orbits from 5 or more 
hours ago. And Cygnus AO-6 is actively manoeuvering to get to the ISS.

This means that coming night, the orbit might already be different due to 
manoeuvres, and hence the pass time different compared to the predictions now 
made. Take that into account.

My experience with the Cygnus cargo ships is that they are usually quite faint 
(often non-visible by the naked eye), but with brief bright episodes up to mag 
+2, strongly depending on the phase angle and likley also spacecraft 
orientation. Briefly after shadow egress or before shadow ingress, it is likely 
to be brightest.

See also:

...for an idea on what to expect.

- Marco

Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.

Cospar 4353 (Leiden):   52.15412 N, 4.49081 E (WGS84), +0 m ASL
Cospar 4355 (Cronesteyn): 52.13878 N, 4.49937 E (WGS84), -2 m ASL
Station (b)log:
Twitter: _at_Marco_Langbroek
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Received on Thu Mar 24 2016 - 11:00:34 UTC

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