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China's eye in the sky: An Analysis of China's satellite surveillance

China is investing heavily on spy satellites, dozens of which are whizzing high above Earth at this very moment. Indeed, China's 2015 Defense White Paper described space as a military domain, and China currently has 75+ military satellites operated by the Strategic Support Force of the People's Liberation Army (PLA).

When the USA dispatched aircraft carriers in the 1995-96 Taiwan Strait Crisis to deter China in the international spat, Beijing leaders promised themselves they would develop systems and weapons to both detect and then attack such powerful US military assets. However, a US Navy carrier can travel 800km per day, so China desperately needed to find ways to keep eyes on potentially hostile platforms in a perpetual game of hide and seek.

China uses a multitude of sensors - such as satellites soaring above, over-the-horizon radars, surface warships and submarines, maritime patrol aircraft and underwater sensors - to keep track of adversaries sailing in places like the South China Sea, Taiwan Strait and East China Sea. Not only that, but China's interests are creeping farther into the Western Pacific and the Indian Ocean.

Professor David Stupples, director of electronic warfare systems research at City University of London, explained that "tensions in the South China Sea have demanded a significant Chinese military presence supported by unprecedented levels of signals intelligence (SIGINT) activity...driven by China's need for economic growth, security and to become the dominant world power."

Thus, China is constantly adding to an integrated maritime SIGINT system combining data collected from acoustic sensing buoys, surface SIGINT vessels, satellites and underwater gliders to strategically placed intelligence centers. A large PLA SIGINT facility on Hainan Island helps monitor US naval activity in the South China Sea. Many analysts expect Woody Island in the Spratly Islands to become a major SIGINT facility to give Beijing an unprecedented reconnaissance overview of that area.

It is also reported that China is monitoring US naval activity near Guam through acoustic sensors it planted in the Mariana Trench and near the island of Yap. Such work is routinely done under the heading of "scientific research", but it has a much more nefarious purpose.

Stupples assessed that China's military SIGINT human resources are around 200,000 personnel and with an estimated budget of USD10-15 billion per annum. Thus, if the upper range of this figure is accepted, China could be spending about 10 per cent of its defense budget on SIGINT. The English professor stated, "China maintains, by far, the most extensive SIGINT capability of any nation in the Asia-Pacific region."

Just like the USA and Russia, China relies heavily on the space domain, with constellations of space-borne electronic intelligence (ELINT) and communications intelligence (COMINT) systems plus photo-reconnaissance, imaging and communications satellites. To monitor maritime territory like the South China Sea, surveillance comprises the two separate tasks of detecting and identifying all ships in a wide area and then tracking specific ships overtime after they have been identified as objects of interest.

In terms of coverage of the world's oceans, China's Yaogan series of high-resolution optical and radar reconnaissance (i.e. tactical imaging and ELINT) satellites is critical. The most recent satellite in this series, the fifth batch of Yaogan-30, was successfully launched by a Long March-2C rocket from Xichang on 26 July 2019. State media euphemistically reported that the high-revisit satellite triplet would be used mainly for "electromagnetic detection and related technological tests". In more explicit terms, these satellites hunt in groups of three by gathering information derived from ship/aircraft radar and electromagnetic signatures.

This particular Yaogan-30 Group-05 launch was the 308th mission for the Long March rocket series, and it placed the satellites in a 35° orbit 600km above Earth. The Yaogan-30 series built by the Chinese Academy of Science operates in threes in relatively close proximity so they can accurately pinpoint signal emissions. A sixth triplet of the Yaogan-30 series was expected to be launched by the end of October 2019.

The first Yaogan-30 triplet was lofted into space on 29 September 2017. The addition of successive triplets to the same orbital plane improves the family's revisit rate, with an eventual constellation of 18 satellites to be created. This will allow the PLA to pass over an area 19 times per day in vertical-imaging mode, or 54 times a day in off-vertical SIGINT mode. Indeed, Stupples suggested, "There will be almost continuous coverage of key areas of the globe."

Yaogan-30 is just one ELINT part of the extensive Yaogan network that includes SAR and optical-imaging satellites. An analytical report that first appeared on the French-language East Pendulum website provides more detail on this family and China's efforts to conduct maritime surveillance from space. This report was also published in English by its author "Gosnold" on an online blog called SatelliteObservation.net.

Gosnold lists other ELINT satellites (Yaogan-9, -16, -17, -20 and -25 triplets) in the JianBing-8 constellation that are orbiting at an inclined 63° plane, though the first two are likely already replaced. As well as being ELINT devices, they might carry an optical and SAR too. They can hunt for radio and radar emissions from warships but, if targets are under radio silence, they will naturally not be so effective.

Whilst on the topic of ELINT satellites, Tongxin Jishu Shiyan-1 is one too, having a geostationary orbit at 155° after being launched in 2015. China described Tongxin Jishu Shiyan-4, launched on 17 October 2019, as an "experimental communication satellite", but this family remains very mysterious and military applications are implied by such secrecy.

Returning to the Yaogan family, the JianBing-7 constellation (consisting of Yaogan-6, -13, -18 and -23) orbits 520km in space carrying SARs. According to the SatelliteObservation.net report: "SAR satellites are very useful in maritime surveillance, thanks to their wide swath, which can reach several hundred kilometers. This enables them to find ships, given a very rough idea of where they might be, in any weather. However, the wide swath modes of such a system generally have a low resolution, measured in the tens of meters. This makes ship identification difficult. Consequently, a higher-resolution system, or another pass of the same satellite but in high-resolution mode, is needed. Ship motion can severely limit the image quality in high-resolution modes." SARs can be used both in daytime and at night, unlike optical satellites that only function in daylight.

China also operates Yaogan-18 and -23 that operate in pairs so that morning and afternoon passes can occur. These SARs have a maximum resolution of 1m and maximum swath of 650km. The JianBing-5 constellation (Yaogan-10 and -29) flies higher and makes an overhead pass at dusk and dawn with their SARs. They have plenty of electrical power since their solar panels follow the sun's rotation.

As for optical satellites, the JianBing-6 constellation consists of Yaogan-11, -24 and -30 flying in a polar sun-synchronous orbit to give morning and afternoon revisits. They likely carry two cameras to widen coverage and give stereoscopic images. However, their 70km swath is probably too small to detect ships at sea. Even if hunting for previously identified ships, a vessel sailing at 30 knots could escape their visibility in just 40 minutes.

The JianBing-10, a second optical constellation, consists of Yaogan-5, -12 and -21 orbiting at a lower altitude of 500km to provide only morning passes. Their dual-camera system probably gives better resolution but they still face the same limitations as JianBing-6.

The JianBing-11 constellation provides an afternoon supplement to JianBing-10, with Yaogan-14 and -28 optical satellites. Placed on the same orbit as JiangBing-10 is the JianBing-12 (Yaogan-26) optical satellite, but with a single large-diameter telescope that could offer 20-25 cm ground resolution. However, such fine resolution makes it less useful for maritime monitoring.

The JianBing-9 optical constellation features Yaogan-15, -19, -22 and -27 in a polar sun-synchronous orbit 1,200km above Earth. The SatelliteObservation.net report commented: "This constellation is placed on a surprisingly high orbit for optical satellites. Because of this height, the spatial resolution is lowered but the swath is increased. The constellation is made up of a first pair of satellites, which provides morning passes, and a second pair for afternoon passes. This enables same-day revisit of any point around the globe, with a small viewing angle (around 25°). It also makes extremely short revisit times possible: the two satellites of a pair follow each other, with a separation of 10 minutes. Thus, they can successively observe the same region with an acceptable maximum viewing angle (around 45°) and estimate the speed of ships in this region."
This constellation carrying off-axis telescopes is believed to be dedicated to maritime surveillance. They cover a swath 100-1,000km wide and have a resolution somewhere between 4.5m and 80cm. They would have an ability to repoint, which could double their swath. Gosnold speculates these satellites might also possess a thermal infrared sensor so they can spot ships at nighttime. Or instead, they might have a 1,550km-wide-swath camera possessing a 30m resolution. Such performance means they could cover all the world's oceans and detect large vessels like oil tankers and carriers.

Moving on, Gaofen-4 is a one-of-a-kind optical satellite launched in December 2015. It is China's only high-resolution imaging satellite to be placed in geostationary orbit. Its resolution of <50m is sufficient to find the wake of an aircraft carrier. Its uninterrupted coverage of a 7,000km2 area provides instant coverage of military activity, and it can task SIGINT satellites to take a closer look when it sees something of interest.

Gosnold commented on Gaofen-4: "It can revisit a place extremely frequently, and it can even produce video sequences, to make change detection easier. It has a 400km field of view, and it can image any region in East Asia at any time. It also has an infrared sensor with 400m resolution, to take pictures at night. These features enable the satellite to detect and track large ships, and probably to determine their type based on their speed, their heading and their thermal signature. Detecting smaller ships might also be possible."

One other example worth mentioning is the Shijian-16, a new series of low-earth-orbit satellites to provide SIGINT across Asia. Inclined to 75° to the Equator, these satellites can intercept signals from naval formations, and a second satellite in the series was launched in June 2016.

What about the overall performance of China's maritime surveillance network using satellites? The report's author calculated that twelve Chinese satellites per day pass over a given location. However, only four SAR passes per day can be used to track a specific ship. If the target changes course regularly, this would make it difficult for satellites to follow.

Nevertheless, the writer concluded: "Thanks to its satellites, China has optical, radar and electronic capabilities to detect, identify and track ships at sea. Even without taking into account real-time tracking from geostationary orbit, the wide-angle JianBing-9 constellation and the JianBing-5 and JianBing-7 SAR constellations can find contacts in a vast area every day and have a good chance of refreshing the location of the most interesting ships every few hours. Consequently, it seems unlikely a naval group could hide in the ocean for long."

The analyst continued: "However when the weather is very cloudy, only the SAR satellites are able to look through, which severely limits the capabilities of the system. This does not mean China is blind: other means of detection, such as its trans-horizon radars or its long-range patrol aircraft can complement the satellite system and help challenge the defenses of US aircraft carriers. This makes a US intervention in a new Taiwan Strait crisis much more risky, and consequently less likely."
Stupples, for one, is under no illusion that China's SIGINT capabilities are among the best in the world. He believes they trail only those of the USA.