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Over the past days, Paul Camilleri in Australia and me in the Netherlands have been
tracking an object in
GTO with a
Mean Motion of 1.5 revolutions per day. It produces brief bright (mag +8) flashes each ~5 minutes. We are certain this is
MUOS 5 (2016-041A) launched June 24 (see
my earlier post here, about Paul's orbit insertion and Centaur fuel vent imagery).
The image below was shot by me from Leiden, the Netherlands, during the night of 4-5 July 2016. The object was at an elevation of only 16 degrees above the horizon:
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Paul first imaged it from Australia on
June July 3, when it passed a few degrees from the position where we expect MUOS 5 to be placed in GEO. I next imaged it from the Netherlands during the night of
June July 4-5, low at my southeast horizon not far from Mentor 6. A few hours later, Paul observed it again from Australia. All these observations can be fitted to yield this GTO orbit:
MUOS 5 15242 x 35703 km
1 41622U 16041A 16186.93646397 0.00000000 00000-0 00000+0 0 08
2 41622 9.8319 324.4682 3211964 178.4686 182.8307 1.52727671 09
rms 0.003 from 14 observations Jul 3.46 - Jul 5.57 (arc 2.1 days)
Comparing this orbit to the
initial GTO insertion orbit from June 24-25 provides a clear link. The RAAN values of both orbits agree to within a few degrees, and the apogee direction is also very similar, as can be see in the plot below:
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In the plot above, the red orbit is the June 24 initial
GTO insertion
orbit. Somewhere after June 25, the satellite manoeuvered (multiple times probably) to increase its perigee from 3900 km to 15240 km. The white orbit is the resulting "current" GTO orbit from the July 3-5 observations.
[
UPDATE 7 Jul 2016 17:25 UT:
I have since done an analysis that suggests that a perigee-raising manoevre from the initial 3903 km to 15242 km could have happened on July 3, near 14:33 UT, in apogee. I suspect however that it was in reality a series of smaller manoeuvres [update July 8: series of manoeuvres confirmed
here]]
The grey orbit is the eventual
geosynchronous orbit in which MUOS 5 will be inserted a few days from now (probably with a position near longitude 172 W). It will probably make more manoeuvres for that purpose the coming days. [
update: there is a possibility it actually did so only a few hours after our last observation on July 5]
UPDATE July 8 17:00 UT: News has come in that something went wrong and
MUOS 5 is snagged in GTO for now. More on the
Spaceflight.com website and a brief follow-up post
here].
The plot below shows how during this manoeuvering, the orbital inclination has been lowered, from 19.0 degrees
initially, to 9.8 degrees currently. It will be further lowered to ~5.0 degrees upon GEO insertion:
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The object shows a
clear brightness variation, from mag +8 to invisible, with a peak-to-peak period of ~5.0 minutes, indicating the satellite is spin-stabilized. [update:
Ted Molczan has noted that this 5-minute periodicity seems to be typical for the Lockheed A-2100 bus in GTO].The bright peaks are of short, specular and somewhat variable duration: lasting ~0.5 to 1 minute. During the lows, the object was not visible for my equipment.
The image sequence below, from my
June July 4-5 imagery, shows a part of the described brightness behaviour:
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As I have written
earlier, MUOS 5 will likely be placed in a geosynchronous, 5-degree inclined orbit near longitude 172 W,
probably within a few days from now or perhaps even on July 5th already [see the update already mentioned above: MUOS 5 has
got stuck in GTO! See also the brief
follow-up post here]. This is an initial check-out position. It will stay there for 4 to 6 months, and then be moved to longitude 72 E where it will be placed as an on-orbit spare. In 2015, we observed this with MUOS 4 (see previous posts
here and
here).
(
this post was thriple updated, on 7 Jul 17:25 UT and 8 Jul 8:30 UT and 17:00 UT)
