Free research sample · Sources checked 15 September 2026 · Historical case study
Shijian-21: assessing GEO servicing capability
OrbitRabbit assessment: SJ-21 is best assessed as a GEO orbital-servicing technology demonstrator. The reported BeiDou-G2 relocation provides the stronger capability evidence; subsequent SJ-25 proximity reports support a servicing interpretation, while propellant transfer remains unconfirmed in the sources reviewed here.
For an analyst comparing servicing capabilities, relocation belongs in the evidence-based baseline. Refuelling belongs in a conditional scenario until stronger evidence is available. The announced debris-mitigation purpose and servicing capability are compatible.
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1. Announced purpose · 24 October 2021
Xinhua reported Shijian-21's launch from Xichang and described its principal purpose as testing and validating space-debris mitigation technologies. This establishes the public description given at launch. The complete mission portfolio and later operational tasking require additional evidence.
2. Reported operation · January 2022
Lin reports SJ-21's January 2022 relocation of BeiDou-G2. His study analyses 2010–2019 photometry to predict the target's rotation for docking preparation. It combines PMO observations with additional Graz measurements and reports one-year prediction errors below 3° for the rotational axis and 0.11°/s for rotational speed. These are the study's model results. SJ-21's navigation accuracy requires spacecraft-specific measurement data.
The useful analytical connection is between target-state knowledge and servicing preparation. Optical observation support is relevant to that assessment. Identifying a controlling ground station requires assignment-specific evidence. Our review covers the published model results and reported operation.
S2 · arXiv:2204.09258v2, 25 April 2022 — especially pp. 1–2 and 5
3. Observer report · 2 July 2025
COMSPOC's published description says Shijian-21 and Shijian-25 became optically inseparable on 2 July. It retains two explanations: docking or very tight formation flying. Our review covers the provider's published description. Optical inseparability alone is insufficient here to label docking or refuelling as confirmed.
S3 · COMSPOC, published 29 July 2025 — published description reviewed