Chinese Gaofen-13 satellite (GEO optical surveillance)

totoro

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A few days ago China launched Gaofen-13.

View: https://twitter.com/i/web/status/1315453621241180160


That wouldn't be news worthy if it wasn't for the fact it was launched to a GEO orbit, some 36 km up.
Officially, it's part of the CHEOS program, civilian crop monitoring, land surveying, urban planning, agriculture and disaster relief.
And the visual depiction of the satellite released makes it clear it has a rather huge mirror.

5 Years ago China launched Gaofen-4, a similar but smaller GEO optical satellite. Basically a constantly staring sensor.
But being smaller, its resolution was touted as 50 m. Which is actually nothing to be sneezed at either.

But now, various estimates of the mirror size of this Geofen-13 seem to go from "at least 1.5" to "anywhere between 1.7 and 2 m".

If the 1.7m aperture would be correct, that'd point out to ground resolution of 15 meters or better.

To my knowledge, while other space agencies did talk about GEO high res observation sats, China is the only one which is actually
launching them. And seems to be improving resolution to quite useful levels.

Implications of satellites with such capabilities may be significant.
 

totoro

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Can't find it yet on websites that usually track satellites, probably because launch happened just a few days ago. But Gaofen 4, GEO sat from five years ago, is sitting over the southern enterance to the South China sea, just northeast of the Malacca strait. Off nadir angles of 10 percent would still be almost as useful, though. And from GEO, even such small angles mean the actual coverage is almost the entire earth half sphere surface. Of course, objects closer to the edge of the sphere would be looked at more from the side than from above, which isn't nearly as useful. Roughly outlining the angles and distances on paper, I'd say at least some 3000 km away from nadir point would still yield a perspective that's 30 degrees off a perfect straight angle (and 60 degrees off the plane of the earth's surface) Such off nadir angles are compromised but still useful. (Speaking of Gaofen 4 location, that's basically from its location to Taiwan)
 
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TomcatViP

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Thank you @totoro . I guess they are keeping traces of every maritime movement, civilian and military in the region.

And also probably keeping count of the yet uncaged Uyghurs they have...
 

Flyaway

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Josh_TN

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Thank you @totoro . I guess they are keeping traces of every maritime movement, civilian and military in the region.

And also probably keeping count of the yet uncaged Uyghurs they have...

Is Gaofen 4 still active? It was roughly over Singapore and my understanding was it was for naval monitoring - a persistent EO capability over their primary area of interest, presumably cued to ID targets by other satellites/sensors. I think the PRC has at least a half dozen SAR satellites as well as a similar number of passive ESM constellations (similar to Parcae/White Cloud) for ocean surveillance. There are a number of LEO EO satellites as well, but the advantage of this satellite and its predecessor is the lack of any dwell time limitations over the area it covers.

EDIT: It also would be out of the range of any known ASAT capability.
 

Archibald

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Which is definitively NOT GEO, so the thread title has a big problem.

GEO optical surveillance​


There is no way in hell putting spysats in GEO, 22 000 miles high, and getting a ground resolution similar to the Key Holes 100 to 300 miles high. Earth thick and turbulent atmosphere, plus being 100 times farther = no way.
 

stealthflanker

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Well the one i'm addressing is Jilin-1 Not Gaofen.

The one being sent to GEO orbit was Gaofen-13. and it's been explained up there that it has 15m resolution from Geostationary orbit.
 

Flyaway

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Josh_TN

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The GEO electro optical satellites seem to specifically be used for naval ISR, because 15 meter resolution is sufficient to identify ship type and the dwell time is 24/7 over the coverage area.

The Jilin-1 conversation is a bit of a divergence from the original topic.
 

Archibald

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Many thanks ! Ok, 15 m from GEO is impressive. and plenty enough for ships, indeed, only 300 m long is 20 times more.

Makes one wonder why the NRO never tried that. Perhaps because the soviet Navy wasn't too much of a threat, at least before 1980...
 

Josh_TN

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It seems likely the USN has other means to ID ships, predominantly aircraft. There are a number of oceanic surveillance constellations that geolocate radar/radio emissions that used to come under the project names 'Parcae' or 'White Cloud' in open sources, but these are low altitude ESM satellites that basically work like GPS in reverse, using differential time of arrival amongst the 2-3 satellite in a group (older satellites were triplets; more modern satellites operate in pairs). The Russians used to operate something similar and the Chinese have at least several constellations of the same type (they still use triplets). To the best of my knowledge, only the PRC employs GEO optical satellites - my guess is that they have a uniquely regional need to track USN ships in the WestPAC, specifically CVNs, and that this orbit and resolution is sufficient for that particular target set.
 

Flyaway

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It seems likely the USN has other means to ID ships, predominantly aircraft. There are a number of oceanic surveillance constellations that geolocate radar/radio emissions that used to come under the project names 'Parcae' or 'White Cloud' in open sources, but these are low altitude ESM satellites that basically work like GPS in reverse, using differential time of arrival amongst the 2-3 satellite in a group (older satellites were triplets; more modern satellites operate in pairs). The Russians used to operate something similar and the Chinese have at least several constellations of the same type (they still use triplets). To the best of my knowledge, only the PRC employs GEO optical satellites - my guess is that they have a uniquely regional need to track USN ships in the WestPAC, specifically CVNs, and that this orbit and resolution is sufficient for that particular target set.
Don’t the NRO’s NOSS satellites partly carry out this function allegedly.
 

Josh_TN

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That is what I’m referring to; I’m probably just using very dated Program names for the satellites. I’m not sure what current name is.
 

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