Issue 116

China Declassified Ludi-Tance 4 01 GEO SAR Imager

22 Feb 2025: Many will recall that on 12 Aug 2023 China launched the world's first GEO based Synthetic Aperture Radar (SAR) imaging satellite, Ludi Tance-4 01 (57624) on a Long March 3B rocket from Xichang. Watch mission rendition Video . On 27 Feb 2025 Chinese scientists officially disclosed some of the technology…

22 Feb 2025: Many will recall that on 12 Aug 2023 China launched the world’s first GEO based Synthetic Aperture Radar (SAR) imaging satellite, Ludi Tance-4 01 (57624) on a Long March 3B rocket from Xichang. Watch mission rendition Video. On 27 Feb 2025 Chinese scientists officially disclosed some of the technology behind this satellite. Excerpts below are from

Sujita Sinha’s article in Interesting Engineering.

– The satellite’s beam synthesis technology integrates phased-array emitters across a 65-foot deployable antenna for enhanced radar precision.

– Ludi operates at an altitude of 22,370 miles (36,000 km), granting China persistent surveillance over one-third of the Earth’s surface. This high-altitude system significantly surpasses US radar satellites, which remain confined to low Earth orbit.

– Ludi employs a novel “space power combination” system that synthesizes multiple microwave beams mid-space between two objects, thereby enhancing radar signal strength and stability.

– Given its capabilities, the system could be integrated with other Chinese reconnaissance satellites to enhance real-time tracking and targeting.

– Ludi Tance 4 employs an advanced stability control mechanism that relies on ultra-precision gyroscopes, as well as positioning signals from both China’s Beidou and the US GPS network, allowing it to maintain exact antenna alignment despite gravitational perturbations.

– A key innovation is Ludi’s back-projection algorithm, which corrects for orbital curvature distortions that traditionally degrade SAR image quality. “It mathematically compensates for orbital curvature that would blur conventional SAR images beyond recognition,” the research team explained. This computational enhancement ensures high-resolution imaging even under dynamic orbital conditions.

– China is already working on next-generation geosynchronous SAR satellites designed to meet higher performance benchmarks.