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Scott Tilley 🇺🇦 Profile picture
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Mar 5 • 15 tweets • 6 min read
Some details on what is known about the MERIDIAN 990MHz transponder system. This transponder seems to be a legacy of the older Soviet MOLNIYA system as evidenced by this excerpt from a report to the US congress in the 1980s.
THREAD
When the last of the MOLNIYA's were still operational amateurs noted transponder activity from them while the spacecraft were on the Russian/European apogee. But by 2011 MOLNIYA went silent and was replaced by MERIDIAN and during the gap no one looked...
Amateurs lost track of the 990MHz transponder and it wasn't until the Breakthrough Listen Candidate 1 signal was reported on 982MHz that I began searching the band in an effort to determine if there was satellite activity that we noted there actually was.
After working with amateurs with larger aperture instruments and lashing up my own we were able to confirm the emissions coming from Molniya orbit was from MERIDIAN 4, 7 and 8 (and later 9).
Prolonged monitoring of the transponder revealed little intentional traffic while the spacecraft are at the North American apogees. However, plenty of unintentional traffic was noticed. Cellular emissions, Turkmen TV and RADAR...
The RADAR detections where of particular interest and studied by members of our community. A possible source of the emissions could be Ukraine as they manufacture hardware for this band and have a gap in cellular service within this range.
Meanwhile in Europe, colleagues there reported intentional transponder usage. Research conducted on the purpose of the transponder points in the direction that it is part of a strategic air communications system.
Intentional transponder activity while over North America has been seen on limited occasions. Perhaps indicating Russia was operating a strategic air asset over the western hemisphere at the time.
The transponder appears to range from ~980-1001MHz with the lower end of the transponder heavily attenuated to prevent unintentional cellular traffic from interfering with it. But weak signals have been detected there.
Based on historical research the uplink for this transponder is ~169.2MHz below the downlink range, non-inverting and non-regenerative. As can be seen in this plot strong RADAR emissions de-sense the transponder every 10s. This suggests the transponder is vulnerable to jamming.
This legacy of the Soviet union is still operational over us. The MERIDIAN constellation is suppose to have 4 operational satellites. 2 at apogee and operating and the other 2 moving to replace them.
But the reality is the constellation presently has holes in it as follows:
MERIDIAN 4 [37398, 2011-018A], appears to either have been decommissioned or failed.
MERIDIAN 7 [40296, 2014-069A] is active on 278, 484, C-band and X-band but unlike other MERIDIANs emits nothing on 990MHz. Perhaps indicative of a failure of this hardware.
MERIDIAN 8 [44453, 2019-046A] and,
MERIDIAN 9 [45254, 2020-015A] are both apparently fully operational as they emit on all know bands used by MERIDIAN.
Finally, the true purpose of the 990MHz transponder is unknown, whatever it is the transponder is vulnerable to unintentional emissions and is only partly operational due to failed spacecraft and malfunctions perhaps limiting Russia's war fighting capability.

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More from @coastal8049

Scott Tilley 🇺🇦 Profile picture
Mar 6
Here's how to understand the RADAR data I'm sharing.

The Russian MERIDIAN satellites are in High Earth Orbit and have their apogees fixed above the Northern hemisphere over Russia and North America. This allows the spacecraft to see both places at once.

THREAD
1. Image
Being in a highly elliptical orbit the MERIDIAN satellite is actually visible to observers on the opposite side of the world at a very low elevation in their sky. Here's an example plot of simulation of MERIDIAN 8 at the North American apogee visible from Ukraine.
2. Image
Examining geometry you can easily see that the satellite is visible to both stations in North America and Europe/Asia. The geometry below is when MERIDIAN 8 is setting over Ukraine. Satellite footprint is the yellow circle on the Earth. Anything within that can see satellite.
3. Image
Read 8 tweets
Scott Tilley 🇺🇦 Profile picture
Mar 4
It's March 4th.

Today a piece of humanity's cast off technology will impact the Moon in a event that would have gone unnoticed had it not been for the work of a few folks looking up in unpaid and normally unnoticed toil... (1/4)
In order to explore the Moon and for all of humanity to share in the potential positive aspects of that exploration and utilization we need to be able to monitor activity around the Moon in a more transparent and accessible way.

(2/4)
We shouldn't need to rely on the reports of amateurs, astronomers focused on other research and defence systems focused on other priorities. We need a focused cislunar space situational awareness asset to enable humanities growth in this realm.

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Read 4 tweets
Scott Tilley 🇺🇦 Profile picture
Feb 27
Based on research here's the layout of Russian military satellite communications at this time from Ukraine. 1st image is a sky view as you would see it from ground looking at the GEO satellites, 2nd a chart view of all assets visible and 3rd a map view. (1/n) ImageImageImage
Understanding where command and control assets would need to view these satellites limits their tactical options to hide and helps one hunt them. (2/n)
More skyview perspectives showing all assets with elevations and azimuth grid on. ImageImage
Read 5 tweets
Scott Tilley 🇺🇦 Profile picture
Feb 27
A primer on the Russian military's MERIDIAN satellite constellation.

MERIDIAN is an High Earth Orbit (HEO) Russian military satellite designed to provide communications to northern latitudes (I.e. Russia et. al.). It is a modern version of the MOLNIYA constellation. Image
The MERIDIAN constellation is primarily designed to offer communications to high northern latitudes where access to GEO satellites could be difficult or impossible.
MERIDIAN satellites are known to operate on the following bands:
~279MHz, 484MHz, 990MHz (non-regenerative)
TT&C ~3410MHz
3400-3900MHz and 7500MHZ (+/- 80MHz) regenerative transponders.
Russian Geostationary assets are known to mirror these transponders to some extent.
Read 4 tweets
Scott Tilley 🇺🇦 Profile picture
Feb 26
This could be very well be a beacon of hope, the sound of resistance that can be heard around the world.

Russian military satellite MERIDIAN 8 reveals radar emissions that most are coming from Ukrainian forces defending themselves. After days of onslaught Ukraine stands.
Multiple RADAR signals are being heard.
Read 4 tweets
Scott Tilley 🇺🇦 Profile picture
Feb 26
This is the P-441 communication complex that the Russian military uses for MERIDIAN, RADUGA and maybe transponders on other assets. It uses C and X-band. On these bands a clear view of the satellite is needed. Many variants of this system exist. (1/n)
Tactically, you'd likely want to hid this thing as it's a critical asset and part of your command and control which limits your options to deploy it. MERIDIAN could give you the ability to hid it and use those satellites high elevation to advantage. From the operating manual...
So if your a commander in a tactically active environment not having a MERIDIAN for 8 hours could be a reason you need to take higher risk and expose the system for a view of a GEO satellite.
Read 6 tweets

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