Issue 114

Special Relationship: A Look at Yaogan-31 & Yaogan-34

31 Jan: I took some time over the past couple of weeks to analyze the relationship between the Yaogan-31 (YG-31) and Yaogan-34 (YG-34) satellites. I was surprised to find that all were orbiting at almost the identical altitude of 1,089.3km. The satellites are not co-planar (except for 2 of the 3 YG-31 in each…

31 Jan: I took some time over the past couple of weeks to analyze the relationship between the Yaogan-31 (YG-31) and Yaogan-34 (YG-34) satellites. I was surprised to find that all were orbiting at almost the identical altitude of 1,089.3km. The satellites are not co-planar (except for 2 of the 3 YG-31 in each formation) but they do have identical inclinations (63.4°) and the 4 YG-34 satellites have an east RAAN offset of 3-5° from a YG-31 triplet. YG-34s are also all trailing YG-31 triplets between 9-16 minutes. Based on only circumstantial evidence, China may be using YG-31 to “listen” for radio frequencies of interest and then using a set of “eyes” (YG-34) following 10-15 min behind to better identify the signal source.

Western defense analysis suggests that Yaogan (“remote sensing”) satellites are military reconnaissance satellites and part of intelligence, surveillance and reconnaissance systems for the People’s Liberation Army.

– YG-31 satellites orbit in triplet formation where they form a nearly equilateral triangle, typical for satellites designed to collect and geolocate radio signals.

– They may be seen as analogous to U.S. Department of Defense Naval Ocean Surveillance System (NOSS) satellite triplets. Such satellites locate and track vessels by detecting and triangulating radio transmissions.

-YG-31s are the latest variant of Chinese satellites to fly in these formations. YG-9, YG-16, YG-17, YG-20 and YG-25 are similarly deployed. However, the YG-31 orbits are ~200km lower than those of their predecessors.

– YG-34s operate as a single satellite and are reported to be a “government optical remote sensing satellites, likely also used as a military reconnaissance satellites.” Open sources report it has a “ground image resolution of a few meters.”

– Other known Chinese imagery satellites operate at much lower altitudes. For example, China’s 5 Gaofen-11 series of satellites operate between 400-500km. Imagery resolution improves with proximity to the intended target.

– Here are the pairings (I only listed one YG-31 for brevity):

  • YG-31 01 (43276) (2018) & YG-34 04 (56157) (2023)
  • YG-31 02 (47533) (2021) & YG-34 01 (48340) (2021)
  • YG-31 03 (47691) (2021) & YG-34 02 (52084) (2022)
  • YG-31 04 (47857) (2021) & YG-34 03 (54249) (2022)

– The most recent pairing between YG-31 01 and YG-34 04 is the biggest outlier in terms of RAAN offset (5.15°) and Trail time (15min 58sec). These values may trend toward the other three pairings over time.

China has established at least 4 pairings of differing ISR capabilities (in this case ELINT and Imagery). It appears China has made a trade-off between its optimal ELINT collection altitude and optimal imagery collection altitude in order to leverage ELINT to cue imagery collection.