Issue 116

SJ-23 Changes Course

28 Feb 2025: It appears SJ-23 (55131) reached the easternmost limit of its GEO wandering and has increased its SMA to initiate a westward drift. I took the opportunity to compare SJ-23's pattern of life with China's other two GEO wanderers, Shiyan 12-01 and 12-02 (50321 & 50322). -On 28 Feb SJ-23 increased its average…

28 Feb 2025: It appears SJ-23 (55131) reached the easternmost limit of its GEO wandering and has increased its SMA to initiate a westward drift. I took the opportunity to compare SJ-23’s pattern of life with China’s other two GEO wanderers, Shiyan 12-01 and 12-02 (50321 & 50322). -On 28 Feb SJ-23 increased its average altitude 96.1km. At the time its position was 174°E longitude.
  • Previously it had been orbiting 44km below the GEO belt resulting in an eastward drift of .575° per day.
  • After the raising its average altitude, SJ-23 is now orbiting 51.3km above the GEO belt causing a westward drift of .648° per day.
  • The Joint Commercial Operations Cell (JCO) estimates the maneuver required delta v (fuel) expenditure of 1.92 m/s.8
  • – Prior to increasing its average altitude, SJ-23 had a close approach with satellite EUTE-172A (28924) on 27 Feb at ~ 06:49:04z. At this time SJ-23 was <55km from EUTE-172A and the solar phase angle was optimal (134°) for SJ-23 to image EUTE-172A. After maneuvering and heading west, SJ-23 did not have a close approach (<100km) with EUTE-172A.
  • – Comparison with Shiyan 12-01 and 12-02
    • After launching on 8 Jan 2023, SJ-23 spent its first 11 months traveling from 144.9°E (Jan 2023) to 19.9°E (Apr 2023) and then to 173.4°E (Oct 2023).
    • Having completed its first “lap” SJ-23 has settled into a more regular pattern. It reversed course at 171.3°E in Dec 2023 and continued West for 223 days.
    • At 22.4°E it decreased its average altitude to initiate an eastward drift on 13 Jul 2024. 230 days later it conducted the maneuver described above to begin heading west again.
    • SY-12 01 and SY-12 02 travel further east before maneuvering, both have reversed course at ~178-179°E (compared with SJ-23 174.4°E).
    • SY-12 01 and SY-12 02 also appear to have a further western boundary as both have executed maneuvers at 16-18°E (compared with SJ-23 22.4°E).

SJ-23 increased its average altitude by 96.1 km to reverse course and begin drifting west (celestrak.org).

SJ-23 orbital history from Jan 2023 to Feb 2025, showing its repeated east-west patrol pattern (celestrak.org).

SJ-23 close approach with EUTE-172A on 27 Feb 2025, at a range of less than 55 km and favorable imaging geometry (saberastro.com).

Patrol-area comparison: Shiyan 12-01/02 operated from approximately 16.2°E to 178°E, while SJ-23 operated from approximately 22.4°E to 174.4°E (nasaspaceflight.com).

Patrol-area comparison numbers for Shiyan 12-01, Shiyan 12-02 and SJ-23 (celestrak.org).