China Launches First Geosynchronous Orbit Radar Satellite (spacenews.com) 38
China launched what is thought to be the world's first geosynchronous orbit synthetic aperture radar satellite on Saturday. SpaceNews reports: A Long March 3B rocket lifted off from Xichang Satellite Launch Center in southwest China at 1:36 p.m. Eastern (1736 UTC) Aug. 12. The Land Exploration-4 01 (Ludi Tance-4 (01)) satellite successfully entered geosynchronous transfer orbit, the China Aerospace Science and Technology Corp., (CASC) announced within an hour of liftoff. Few details of the satellite were provided by CASC. However the group's "blue book" outlining plans for 2023 released in January noted the launch of a "high-orbit 20-meter [resolution] SAR satellite."
The L-band synthetic aperture radar (SAR) satellite will provide all-day, all-weather observation of China and surrounding areas, boosting the country's disaster prevention, reduction, and relief capabilities. The land observation satellite series and "high-orbit SAR technology" are listed in the country's Medium and Long Term Development Plan for Civilian Space Infrastructure (2015-2025). The plan includes establishing high and medium resolution optical and synthetic aperture radar constellations for a range of land, marine and atmospheric monitoring. The series is separate from the China High-resolution Earth Observation System (CHEOS), which consists of Gaofen ("high resolution") satellites. China's Gaofen-4 satellite is a GEO optical satellite. SAR at GEO, while providing much lower resolution than satellites in low Earth orbit, can provide constant coverage and imagery despite cloud cover.
It is not yet known what orbital scheme the Land Exploration-4 (01) satellite will enter. An inclined GEO orbit would produce a "figure eight" ground track over the area of intended coverage. Chinese academics from the Beijing Institute of Technology have produced a study of various schemes, while others have published research into modified signal models for GEO SAR. The (01) designation suggests China could launch other SAR satellites into geosynchronous orbits. The satellite was developed by the China Academy of Spacecraft Technology (CAST.)
The L-band synthetic aperture radar (SAR) satellite will provide all-day, all-weather observation of China and surrounding areas, boosting the country's disaster prevention, reduction, and relief capabilities. The land observation satellite series and "high-orbit SAR technology" are listed in the country's Medium and Long Term Development Plan for Civilian Space Infrastructure (2015-2025). The plan includes establishing high and medium resolution optical and synthetic aperture radar constellations for a range of land, marine and atmospheric monitoring. The series is separate from the China High-resolution Earth Observation System (CHEOS), which consists of Gaofen ("high resolution") satellites. China's Gaofen-4 satellite is a GEO optical satellite. SAR at GEO, while providing much lower resolution than satellites in low Earth orbit, can provide constant coverage and imagery despite cloud cover.
It is not yet known what orbital scheme the Land Exploration-4 (01) satellite will enter. An inclined GEO orbit would produce a "figure eight" ground track over the area of intended coverage. Chinese academics from the Beijing Institute of Technology have produced a study of various schemes, while others have published research into modified signal models for GEO SAR. The (01) designation suggests China could launch other SAR satellites into geosynchronous orbits. The satellite was developed by the China Academy of Spacecraft Technology (CAST.)
resolution (Score:2)
20 meter resolution is terrible.
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More seriously, are they that far behind? I assumed China already had many geosynchronous orbit synthetic aperture radar satellites! Oh OK, maybe somebody else launched those for them, that's true /s
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The very first line of the summary points out that this is thought to be the WORLD'S first satellite of this type. Nobody else has them, as far as we know.
As for the resolution, it appears to be a trade off to get better coverage with enough resolution for the purpose the satellite is designed for. China is very big.
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The question is, what's the benefit? They can afford to put up more satellites, and closer, where the resolution would be better. The only thing this satelitte can do that their others can't is see satellites in LEO. Is that its purpose?
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Another possibility is that th
Re: resolution (Score:3)
It could just be a matter of "sensor integration/fusion" -- having a second, different perspective on weather conditions from a different vantage point to act like a reference point for OTHER satellites and/or terrestrial radar.
Consider a balancing robot. If you only give it an accelerometer, it can't tell the difference between "acceleration due to gravity" and "acceleration due to motion"... so within a matter of seconds, a slight wobble (and naive PID compensations for it) turns into violent thrashing u
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Firstly, it's for weather observation and disaster relief use, not to keep track of ################ like the US' classified ################ Program does. 20m is way more than enough for that.
Secondly, it's SAR, not optical, for which a 20m resolution is pretty decent.
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>> 20 meter resolution is terrible
Not at all, you can monitor giant floods in the 10 to 20 meter height, so very useful for CN.
Besides that, try developing a GEO SAR radar with better resolution, instead of writing silly comments.
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20 meters from a geostationary orbit, which means 35000+ kilometers above LEOs.
That orbit means one satellite is enough to cover China with neighborhood.
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That's mostly a consequence of geosynchronous orbit being a considerably larger distance from the surface, compared to the lower orbits normally used by this type of satellite. The other downside is, the orbit is geosynchronous, so ipso facto the satellite can only ever see the part of the globe that it can see. The only upside I can think of, is that it would be able to see a larger amount of the surface at once.
The usual selling point of geosynchronous orbits is not
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For weather forecasting?
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For radar it is not so bad, though!
better solution (Score:2)
Equip a satellite constellation like Starlink with cheap optical cameras.
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It's a radar satellite, not optical. Optical can't see through clouds or in the dark.
Adding radar to Starlink satellites would greatly increase their size. Well, so would optical.
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Interesting idea.
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>> I don't think it'd hard to change firmware in the Starlink sats to make their phased array antennas act like Ku-band SAR though...
Wrong. probably impossible without fundamental HW redesign.
Link budget of one way comm VS fine pitch SAR is worlds appart.
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As a point of comparison: it's widely known that the US' KH-11 spy satellites can do ~0.1-m resolution. (One way that we know is because the dumbass Orange One fucking tweeted an unredacted image [npr.org].) A KH-11 looks an awful lot like a Hubble space telescope, except pointing down at the Earth inste
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Geosynchronous is on the equator (Score:3)
If it can real-time track movements across all of China, presumably including Tibet, then it can do the same to the same latitudes south. That covers all of SE Asia, India, Philippines, Australia, New Zealand.
And probably more ocean than all the land combined. There's a lot of reflective ships on those there waters. Which probably means the coverage extends over Japan too.
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There are already a lot of satellites that monitor the movement of traffic globally. Ships, aircraft, and even larger road vehicles.
What's novel about this one is that it's the first to be placed in geosynchronous orbit. Synthetic aperture radar (SAR) systems use the fact that they are orbiting around the Earth to scan over its surface. The area underneath them keeps changing as they orbit, like how a document scanner has a fixed 1 dimensional scanning head and moves the paper past it to create a 2D image.
G
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And I'm guessing that it is probably intended to keep an eye on the ocean where there might be the US fleet...
How can a SAR be stationary? (Score:5, Interesting)
Re:How can a SAR be stationary? (Score:5, Informative)
I guess that's why the article says it's latitude will be inclined to move through a "figure eight" over the land.
What incline do you think would be needed? Bearing in mind that a larger incline will create greater temporal coverage holes.
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You can read all about the possibilites in one of the papers linked to from the fine article: Research progress on geosynchronous synthetic aperture radar [sciencedirect.com]
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It has a geosynchronous orbit [wikipedia.org], which is a superset of geostationary orbits. Geosynchronous orbits includes inclined orbits that trace out analemma shapes on the ground. In fact, geostationary orbits are unstable and require occasional station-keeping maneuvers to reduce their orbital inclination.
An interesting extreme IGSO is Tundra orbit [wikipedia.org]. That's probably not what this satellite will use, because as you point out, SAR requires relative motion so apogee dwell is counterproductive for it, but it has intere
Aluminum Foil Hat Provides Some Protection : ) (Score:2)
Do you know what this means boy????? (Score:2)
Firefly (Score:2)
Firefly.
https://www.imdb.com/title/tt0... [imdb.com]