The Problem
Unlike most modern launch vehicles, the Long March 5B (CZ-5B) uses its core stage to reach orbit alongside its payload. The ~21-tonne core stage then remains in a low, uncontrolled orbit that decays over days to weeks. Because it lacks a restart capability for a controlled deorbit burn, the re-entry location cannot be predicted until the final hours before atmospheric entry — and even then only to within thousands of kilometres.
At ~21 tonnes, the CZ-5B core stage is the largest object to make uncontrolled re-entries since the 77-tonne Skylab station in 1979 and the 40-tonne Salyut-7/Cosmos-1686 complex in 1991.
Timeline of Re-entries
| Launch | Mission | Re-entry Date | Re-entry Location | Notes |
|---|---|---|---|---|
| 5 May 2020 | Cabin test (uncrewed) | 11 May 2020 | Atlantic Ocean / Côte d'Ivoire | Debris found on ground in Côte d'Ivoire — 12 m pipe landed near village |
| 29 Apr 2021 | Tianhe (CSS core module) | 9 May 2021 | Indian Ocean (near Maldives) | Largest uncontrolled re-entry since 1991 |
| 24 Jul 2022 | Wentian (CSS lab module) | 31 Jul 2022 | Indian Ocean (Sulu Sea) | Debris reportedly found in Borneo, Philippines |
| 31 Oct 2022 | Mengtian (CSS lab module) | 4 Nov 2022 | South Pacific Ocean | Landed in open ocean |
What Survives Re-entry?
A 21-tonne rocket stage does not burn up completely during re-entry. Estimates from the Aerospace Corporation and ESA suggest 20–40% of the mass (approximately 5–9 tonnes) may survive to reach the ground, creating a debris footprint potentially hundreds of kilometres long. Dense components like engine parts, propellant tanks, and structural joints are most likely to survive. In the May 2020 event, a 12-metre-long pipe was found on the ground in Côte d'Ivoire, near an inhabited village.
International Criticism
NASA Administrator Bill Nelson stated that China was "not meeting responsible standards regarding their space debris." ESA, the European Space Agency, and numerous national space agencies have criticised the uncontrolled re-entries. By comparison, all other major launch providers — including SpaceX (Falcon 9), ULA (Vulcan/Atlas V), and Arianespace (Ariane 6) — perform controlled deorbit burns to target re-entry over uninhabited ocean areas.
Future Missions
China has largely completed the assembly of its Tiangong space station, so no further CZ-5B launches for station modules are expected in the near term. However, the CZ-5B may be used for future large payload missions, potentially repeating the uncontrolled re-entry scenario unless China modifies the vehicle to include a controlled deorbit capability.