After 18 months of eye-in-the-sky secrecy, Chinese scientists have revealed the revolutionary technology behind the world’s first geosynchronous orbit synthetic aperture radar (SAR) satellite, giving China a permanent view of one-third of the Earth’s surface.
Ludi Tance 4-01 – or Ludi – which was launched in August 2023, is the highest flying surveillance satellite ever launched. It continuously monitors the Asia-Pacific region from an altitude of 36,000km (22,370 miles), far above US remote-sensing radar satellites that are positioned in low Earth orbit, according to the project team, led by senior engineer Ni Chong, with the China Academy of Space Technology (CAST).
The satellite is equipped with a “space power combination” system that merges multiple microwave beams in mid-space, between two objects. The feat – reminiscent of the Death Star in the Star Wars films – allows it to achieve high, stable radar emissions that can penetrate cloud cover and darkness while maintaining relatively high resolution, Ni said in an article published in the latest issue of Chinese Space Science and Technology, a peer-reviewed journal run by the academy.
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Beijing has said that Ludi is intended for civilian purposes, such as weather observations and earthquake monitoring, to improve disaster prevention and responses. It can also be used to help researchers in oceanography, meteorology, agriculture and forestry.
However, the United States military remains wary about Beijing’s advancing satellite capabilities.
Ludi can be coordinated with other powerful Chinese surveillance satellites to make a “qualitative leap” in tracking and targeting capabilities, according to Chief Master Sargeant Ronald Lerch, an intelligence specialist at the Space Systems Command under the United States Space Force, who was quoted by US Space News in January last year.
The US military finds it “worrisome” because it enables China to have persistent visual and radar surveillance over strategically important areas such as the Indo-Pacific, he said.
Ni’s team said that the US has wanted such a satellite since the Cold War, and scientists came up with numerous proposals. Due to technical challenges, “they all remain on paper by today”, the team said in the article. “Only China makes it.”
The disclosures by Ni and his team have, for the first time, confirmed numerous breakthroughs on sensitive, electronic warfare-related technology.
For instance, the beam synthesis technology can seamlessly coordinate phased-array emitters across the 20-metre (65 feet) foldable antennas, according to the paper.
A new stability control mechanism based on ultra-precision gyroscopes and both Chinese Beidou, and US GPS positioning signals maintains antenna alignment with unprecedented accuracy despite orbital perturbations.
But the real magic, according to the team, lies in a back-projection algorithm. “It mathematically compensates for orbital curvature that would blur conventional SAR images beyond recognition,” the team wrote.
China is now working on its next generation geosynchronous radar satellites, which will be required to meet much higher performance benchmarks, they added.
There appeared to be some strategic calculus behind the timing of the disclosures, according to a Beijing-based communication technology researcher.
“By declassifying core technologies, China shows the world an upper hand in electronic warfare,” said the researcher, who asked not to be named due to the sensitivity of the matter.
“Like AI company DeepSeek’s open-source models, this will force rivals to play catch-up in areas where China holds structural advantages,” he added.
More from South China Morning Post:
- Latest China satellite Ludi Tance to survey one-third of Earth in high-orbit breakthrough
- China launches high-orbit satellite internet that could challenge SpaceX’s Starlink
- China launches first reusable satellite, with payloads from Thailand and Pakistan
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