Re: Zuma and USA 276

From: Marco Langbroek via Seesat-l <>
Date: Fri, 17 Nov 2017 01:46:00 +0100
Op 16-11-2017 om 01:34 schreef Marco Langbroek via Seesat-l:
> if the Zuma launch coming Friday
> happens in the first 15-20 minutes or so of the launch window opening (Area
> Warnings are for a window between 0:55 UT - 3:37 UT, Nov 17), this would mean
> that Zuma would end up very close to USA 276 after orbit insertion.

Now the launch has been postponed again, to the early hours of November 18 UT,
it is clear that this scenario is no longer feasible, at least not in a very
strict sense.

On November 18, the USA 276 orbital plane will pass over Cape Canaveral around
00:48 UT, which is some 12 minutes *before* the launch window opens. If launch
is at 1:00 UT (directly at launch window opening) it would result in a ~3 degree
difference in RAAN between the two spacecraft orbits.

This would nevertheless be still close, and by targetting a (compared to USA
276) slightly different orbit in terms of small differences of inclination and
initial orbital altitude, differential precession of the RAAN of both spacecraft
might still drift them closer towards each other.

Which is just a way of saying that it is not necessary to very strictly launch
into the USA 276 (or ISS) orbital plane in order to engineer close approaches.
Indeed, USA 276 was not launched exactly into the ISS orbital plane in May either.

What is certainly still in the picture as a possibility, is a launch into the
ISS orbital plane. For launch on the 18th, that would be the case if launch
occurs near 2:38 UT, which is inside the launch window (the ISS plane passage
over Cape Canaveral will stay into the launch window for several days to come,
occuring ~24 minutes earlier each successive night).

I have published a short blogpost on it, including a map of the launch Hazard
zones and Falcon 9 upper stage de-orbit hazard zone compared to the plotted
trajectory for a ~50 degree inclined ~400 km orbital altitude orbit. The blog
post is at:

Note that any purported connections between Zuma, USA 276 and the ISS orbital
plane remain pure speculation. Perhaps Zuma has nothing to do with either
spacecraft. Yet, the possibility is interesting enough that we should keep an
eye on them.

- 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
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Received on Thu Nov 16 2017 - 18:46:49 UTC

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