Issue 114

A Look Back: US LDPE-3A & SJ-23 Interaction Nov 2024

28 Jan: I was collaborating with Robin Planell from LSAS again and we (Robin really) noticed an unusual interaction between two GEO satellites, the US test satellite LDPE-3A (55264) and the Chinese test satellite SJ-23 (55131), between Oct-Nov 2024. Specifically, LDPE-3A conducted a series of maneuvers which resulted…

28 Jan: I was collaborating with Robin Planell from LSAS again and we (Robin really) noticed an unusual interaction between two GEO satellites, the US test satellite LDPE-3A (55264) and the Chinese test satellite SJ-23 (55131), between Oct-Nov 2024. Specifically, LDPE-3A conducted a series of maneuvers which resulted in a close approach (<25km) with SJ-23 with favorable lighting conditions for LDPE-3A to view SJ-23. SJ-23 did not maneuver during this time period. These interactions were reported in open source. Below is a more detailed analysis. See Video.

– The Timeline:

  • Mid-September-28 October 2024: LDPE-3A was further east than SJ-23. On 28 October LDPE-3A was located over 111.2°E and SJ-23 was at 98.5°E (a difference of 12.7°)
  • 29 Oct: LDPE-3A increased its SMA ~229km, reversing its 1.0° per day eastward drift and initiating a westward drift of ~1.9° per day.
  • 30 Oct – 3 Nov: SJ-23 (which continued its 0.7° eastward drift) passed LDPE-3A moving east.
  • 4 Nov: LDPE-3A decreased its altitude 192.2km and reversed its westward drift and initiated a 0.5° per day eastward drift.
  • 4-5 Nov: LDPE-3A has two point of closest approach (POCA) with SJ-23.
    • The first POCA was on 4 Nov at ~1945Z at <90km with optimal lighting conditions for LDPE-3A to observe SJ-23.
    • The second POCA occurred 12 hours later at ~0745Z on 5 Nov. Range was <25km and again lighting conditions were favorable for LDPE-3A to observe SJ-23.
  • 6-9 Nov: LDPE-3A falls further behind SJ-23 as SJ-23 is drifting 0.2° further east per day.
  • 9 Nov: LDPE-3A reduces its SMA 15.4km and matches SJ-23’s 0.7° per day eastward drift. With this change LDPE-3A maintains its position ~ 0.7° behind SJ-23.
  • 10 Nov-Present: SJ-23 remains 0.7° further east of LDPE-3A.

LDPE-3A conducted at least 2 significant maneuvers 29 Oct – 3 Nov: the first closed its distance with SJ-23 and put it to the west of SJ-23. The second placed LDPE-3A into a trail position with favorable lighting conditions to support observation for 24 hours. During that first 24 hour period the POCA between LDPE-3A and SJ-23 was <25km. On 9 Nov LDPE-3A again adjusted its orbit to match SJ-23’s 0.7° per day eastward drift and maintain a consistent relative position.

– Background:

  • Per Gunter’s Space Page: LDPE (Long Duration Propulsive EELV Secondary Payload Adapter (ESPA)) are experimental satellites built for the U.S. Air Force Space and Missiles Center (AFSMC) to carry small payloads and deploy small satellites.
  • LDPE-3A was launched from Cape Canaveral, Florida on 15 Jan 2023 on a Falcon Heavy. It hosts five payloads, which remain attached…one of them, Catcher, is a prototype sensor designed to provide local space domain awareness insights. WASSAT…is a prototype wide-area sensor with four cameras that searches for and tracks other spacecraft and space debris in geosynchronous orbit. LDPE 3A also carries payloads from the military’s Space Rapid Capabilities Office, two of which are operational prototypes for space situational awareness missions.
  • China launched Shijian-23 from Wenchang using a LM-7A on 9 Jan 2023. It was the first Shijian satellite to be launched on a LM-7A Space Launch Vehicle (SLV). Initially, analysts believed SJ-23 was a communications test satellite and a follow-on to theSJ-13. However, on 19 Jan 2023 SJ-23 released a small object. The release of a sub-payload is more indicative of SJ-17, TJS-3, and SJ-21. In its 2+ years on orbit SJ-23 has drifted between 19.8°E to 174.4°E and its most recent large maneuver was on 14 July 2024 when it decreased its SMA (altitude) to reverse its westward drift and begin drifting east at ~0.7° per day.