China Declassifies a Top Secret Spacecraft: The Highest-Altitude Radar Satellite Ever Created

China operates the Ludi Tance 4-01 satellite at an altitude of 22,370 miles in geostationary orbit. Launched in August 2023, it’s the first synthetic aperture radar (SAR) deployed at this altitude, providing China with a unique permanent observation capability over one-third of the Earth’s surface.

Recently declassified. Chinese scientists recently disclosed the design and capabilities of the Ludi satellite, which had previously been kept secret. It’s officially intended for weather observation, earthquake monitoring, and natural disaster prevention. However, recently declassified details have raised concerns among rival countries, particularly the U.S.

The Space Force has rejected the Chinese narrative, suggesting that the satellite isn’t solely for civilian use. Instead, U.S. officials believe Ludi is a high-resolution reconnaissance tool designed for intelligence gathering in the Asia-Pacific region. This essentially makes it a powerful spy satellite with both civilian applications and military capabilities.

The satellite’s altitude. Ludi is the first and only SAR to operate in geostationary orbit. Positioned at 22,370 miles, the Chinese satellite remains synchronized with the Earth’s rotation, allowing it to continuously observe the same region. Unlike optical systems, SAR can penetrate clouds and operate at night.

Ludi achieves a resolution of around 65 feet, which is lower than the sub-meter resolution of some low-orbit spy satellites. However, it compensates by being able to monitor about one-third of the Earth’s surface, particularly in the Asia-Pacific region.

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Tech specs. Ludi was launched with its antenna initially folded down. To obtain a useful resolution from such a long distance, the satellite incorporates several phased-array emitters that can be coordinated to work in unison.

This beam synthesis technology allows multiple microwave beams to combine in space, functioning as a single, very powerful radar beam. This makes high-quality imaging possible.

China only. The launch of Ludi in August 2023 marked the beginning of a new type of Earth observation platform. U.S. scientists had pursued the concept of radar surveillance from geostationary orbit since the Cold War. Technical challenges had kept all these plans unimplemented. However, China has been successful. Ludi is just one of the Yaogan satellites that China operates in geostationary orbit.

Images | NASA | China Association for Science and Technology

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