Chinese Gaofen-13 satellite (GEO optical surveillance)

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totoro

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A few days ago China launched Gaofen-13.
spacenews.com

China launches Gaofen-13 observation satellite towards geostationary orbit

China launches Gaofen-13 observation satellite towards geostationary orbit
spacenews.com spacenews.com

https://twitter.com/x/status/1315453621241180160
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.
 
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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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...
 
space.skyrocket.de

Gaofen 13 (GF 13)

Gaofen 13 (GF 13) is a geostationary earth observation satellite in the Gaofen series of Chinese civilian remote sensing satellites.
space.skyrocket.de space.skyrocket.de
 
TomcatViP said:
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...
Click to expand...

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

GEO optical surveillance​

Click to expand...

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.
 
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.
 
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.
 
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...
 
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.
 
Josh_TN said:
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.
Click to expand...
Don’t the NRO’s NOSS satellites partly carry out this function allegedly.
 
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.
 
totoro said:
A few days ago China launched Gaofen-13.
spacenews.com

China launches Gaofen-13 observation satellite towards geostationary orbit

China launches Gaofen-13 observation satellite towards geostationary orbit
spacenews.com spacenews.com

https://twitter.com/x/status/1315453621241180160
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.
Click to expand...
GF-13 (2)
F9wvtkEWAAAX3dG.jpg
spacenews.com

China launches second classified Gaofen-13 remote sensing satellite

China launches second classified Gaofen-13 remote sensing satellite
spacenews.com spacenews.com
 
Archibald said:
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...
Click to expand...
Primary because of SOSUS. Offer bad wether, night time capability and target classification including submarines. :)
 
Archibald said:
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...
Click to expand...

The USN probably has never had much difficulty finding ship targets previously. It arguably still doesn't now. There are land based ISR assets (some navy, some USAF) and fighter based assets on the CVs. There are still the NOSS satellites for radiating targets. There probably is also no shortage of acoustic sensors in the WestPac, both in shallow and deep water, including fixed arrays, semi-persistent deployed sensors, and SSNs.

That said, the fact that the PRC can maintain a staring view of the region in SAR and EO clearly challenges the USNs ability to deny them target data.
 
Yaogan-41 GEO optical launched, with probably a 4m diameter SiC aspheric mirror, which is the largest reported worldwide. Rayleigh criterion (1,22λh/D) give a resolution of 6m at 36000km
Capture.PNG
DlL-3XgXgAAMd58.jpg
https://twitter.com/x/status/1735678970434388022
View: https://twitter.com/CNSpaceflight/status/1735678970434388022

www.nature.com

Challenges and strategies in high-accuracy manufacturing of the world’s largest SiC aspheric mirror - Light: Science & Applications

CIOMP report their progress in high-accuracy manufacturing of the world’s largest SiC aspheric mirror. The final surface figure error is 15.2 nm RMS and aerial density is less than 120 kg/m2.
www.nature.com www.nature.com
 
An old interview of Li Guo (chief designer of Gaofen-4) talking about high-res optical imaging technology from GEO:
1st stage Gaofen-4 with 50m resolution
2nd stage 15m resolution, Gaofen-13
3rd stage 3-5m res with 3-4m mirror, probably Yaogan-41
4th stage 1-2m res using "Open system imaging", "quantum imaging system", "thin film radiographic imagin system" etc
1.jpg
 
Those resolutions are adequate for recognition and precise identification of surfaced submarine. Probably enough to recognize carriers too. Technical works however requires more.
. ReqRes.png
 
At 350 m long (or close) they are certainly quite visible from GEO, even with 1-m mirrors.
 
spacenews.com

Why Space Force is growing more alarmed by China’s eyes in the sky

As China expands its presence in orbit, the U.S. Space Force continues to express concern about Beijing’s advancing satellite capabilities. The latest cause for alarm is China’s deployment of imaging satellites in geostationary orbit.
spacenews.com spacenews.com

"One that has caught the Space Force’s attention is an advanced optical imaging satellite launched in December, Yaogan-41. With an estimated resolution of 2.5 meters, it brings a significant improvement over previous GEO optical satellites capped at 15-meter resolution. This level of visual fidelity would allow China to spot vehicles, aircraft, and vessels across wide regions."

"While most remote sensing satellites operate in low Earth orbit for cheaper access and better resolution, it’s notable that China chooses to invest in far more expensive geostationary spacecraft stationed 22,000 miles above Earth, Swope said. It would be difficult to precisely identify small objects from that high orbit, but if there’s a particular item of interest, they would task lower-flying satellites to take a closer look."

"Potentially problematic for the U.S. military is that an optical sensor like Yaogan-41, in certain conditions, could spot stealth aircraft designed to be undetected by radar. “If there are no clouds, you could see an aircraft with an optical capability,” Swope said."
 
The chances of finding stealth aircraft in the satellites narrow field of view and actually being able to do anything about it is fleetingly small. The much greater danger is of such a satellite persistently tracking a naval formation. There would be almost no way of evading it, and it would provide target grade tracks and IDs for everything in its field of view.
 
So, how can a ground resolution be calculated for that 2.5 m mirror peering from 35780 km high - GEO ?
Elements of answers right here.
slate.com

Moon hoax: why not use telescopes to look at the landers?

In July 1969, Man first walked on the Moon. Over the course of three more years, we did it five more times.
slate.com slate.com

The ability for a telescope to resolve an object is, as you’d expect, directly related to the size of the mirror or lens. There is a simple relationship between mirror size and resolving power: R = 11.6 / D. What does this mean?


First, R = the angular size of the object in arcseconds. An arcsecond is a measure of angular size (how big an object appears to be – if two objects are the same physical size, the one farther away will appear smaller, and have a smaller angular size). There are 3600 arcseconds to a degree, and to give you an idea of how small a measure this is, the Moon is about 0.5 degrees = 1800 arcseconds across.


D is the diameter of the mirror in centimeters. Hubble’s mirror is 2.4 meters = 240 centimeters across. Plugging that into the formula, we see that Hubble’s resolution is 11.6 / 240 = 0.05 arcseconds. That’s an incredibly small size; a human would have to be nearly 8000 kilometers (4900 miles) away to be 0.05 arcseconds in size!


To be totally accurate, there’s a twist to this. Well, really two. The first is that there’s a wavelength dependence too; for a given telescope size, the shorter the wavelength the more resolution you get (a telescope will resolve blue objects better than red ones, since blue has a shorter wavelength). But this is pretty minor compared to mirror size, and we can ignore it here (plus it’s already compensated for in the constant 11.6 that we used above).


Second, there’s a statistical rule that says that you actually need an object to be twice that theoretical size to be properly resolved (I won’t go into boring details, but you can look up the Nyquist Sampling Theorem if you’re looking for an excuse to slack off at work). So really, Hubble’s working resolution limit is about 0.1 arcseconds. There are tricks you can do to get slightly higher resolution, but that’s getting too picky. Let’s just call it 0.1 arcseconds.
Click to expand...

There is another simple formula you can use to determine the angular size of an object based on its physical size and its distance: (d / D) x 206265 = α. In other words, take the physical size (d) of an object, divide it by the distance (D), multiply that by the constant 206265, and that gives you the angular size (α) in arcseconds (make sure D and d are in the same units!).
So let’s look at our lunar descent stage. It’s 4 meters across, but 400,000,000 meters away. That gives it an angular size of (4/400,000,000) x 206265 = 0.002 arcseconds.
Click to expand...

All right, since that chinese spysat mirror is (roughly) the same 2.4 diameter as Hubble, then : same resolution of 0.1 arcseconds.

But GEO is no lunar orbit: much closer. Let's try tweaking this.

How about 20 meters from GEO ? (20/35,786,000) x 206265 = 0.115 arcseconds

There we are. IF I'm not mistaken: that chinese spysat should be able to see 20 m details (18 m absolute best case).

Plenty enough for Navy warships (100 m to 400 m long) but a bit too short for USAF aircraft. A B-52 could be seen, but forget any fighter.

"Potentially problematic for the U.S. military is that an optical sensor like Yaogan-41, in certain conditions, could spot stealth aircraft designed to be undetected by radar. “If there are no clouds, you could see an aircraft with an optical capability,” Swope said."
Click to expand...

The Wiki tell me B-21 Raider is 40 m in span, so (in theory) could be pinpointed. B-2's 52 m also fit.

en.wikipedia.org

Northrop Grumman B-21 Raider - Wikipedia

en.wikipedia.org en.wikipedia.org
 
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Josh_TN said:
The chances of finding stealth aircraft in the satellites narrow field of view and actually being able to do anything about it is fleetingly small. The much greater danger is of such a satellite persistently tracking a naval formation. There would be almost no way of evading it, and it would provide target grade tracks and IDs for everything in its field of view.
Click to expand...

They can keep a lookout on airbases to check if anything interesting has taken off. Once that has happened it could conceivably track the aircraft for sometime, weather permitting.
 
siegecrossbow said:
They can keep a lookout on airbases to check if anything interesting has taken off. Once that has happened it could conceivably track the aircraft for sometime, weather permitting.
Click to expand...

If the aircraft were based regionally, perhaps, in theory. But using your huge optical satellite to try to track miniscule aircraft that can quickly displace and separate, or easily seek clouds to hide in, seems not only incredibly difficult with very minimal possibility of payout, but also a vast waste of resources that could easily permanent bracket a naval task force in clear weather with none of the problems aircraft tracking would bring. The stealth aircraft most relevant to track - the bombers - would not be based anywhere within the field of view of such satellites and any detection would be happenstance and fleeting as it moved out of the field of view in minutes. I'm sure if the US could convince these satellites to waste their time following stealth bombers, it would assign some specifically to the task.
 
There were some indications yaogan 41 has a nearly 4 m diameter mirror, though. (The fairing on the rocket was a new, enlarged one, measuring over 5min diameter)

Of course, even that would not net 2.5 m resolution from GEO. But probably 10-12m. Give or take.

Of course, being an optical satellite, half the time it won't see much due to night. And half the remaining time there may be cloud cover over area of interest.
 
What spectrum it operates tho.. does it also do Infra Red ? or even Radiometric ? Lower resolution but it works at night too.

I would expect Chinese to also put extra spectrums for those optical Satellites.
 
There were some indications yaogan 41 has a nearly 4 m diameter mirror
Click to expand...
11.6 / 400 = 0.029 arcseconds * 2 = 0.058 arcseconds

(10/35,786,000) x 206265 = 0.0576 arcseconds

A 4 m diameter mirror in GEO could see 10 m details, best case. More probably 11 m.
 

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