Overview
The Long March 5B (Chang Zheng 5B / CZ-5B) is a Chinese heavy-lift launch vehicle operated by the China Aerospace Science and Technology Corporation (CASC). It is a single-core variant of the Long March 5, optimised for delivering large payloads directly to low Earth orbit. The CZ-5B was purpose-built for assembling the Tiangong space station — China's permanently crewed modular orbital laboratory.
The CZ-5B is notable not only for its role in China's space station programme, but also for the international controversy generated by its uncontrolled core stage re-entries. Unlike most modern orbital-class rockets, the CZ-5B's entire core stage reaches orbital velocity and has no capability for a controlled deorbit burn, meaning its ~21-tonne core body tumbles back to Earth unpredictably over the following days — the largest objects to make uncontrolled re-entries since Skylab in 1979 and Salyut-7 in 1991.
Specifications
| Parameter | Value |
|---|---|
| Height | ~53.7 m (176 ft) |
| Core diameter | 5 m (16.4 ft) |
| Liftoff mass | ~837,500 kg |
| Core stage engines | 2 × YF-77 (LOX/LH2) |
| Boosters | 4 × 3.35 m strap-ons, each with 2 × YF-100 (LOX/kerosene) |
| Total liftoff thrust | ~10,565 kN |
| Payload to LEO | 25,000 kg (55,100 lb) |
| Stages | 1.5 (core + 4 strap-on boosters, no upper stage) |
| Propellant (core) | LOX / Liquid Hydrogen |
| Propellant (boosters) | LOX / Kerosene (RP-1) |
The Re-entry Controversy
The CZ-5B's 1.5-stage design means the core stage itself — approximately 33 metres long and ~21 tonnes dry mass — enters low Earth orbit alongside the payload. Unlike most rockets, which either deorbit their spent stages over oceans or use upper stages that fall back quickly from suborbital trajectories, the CZ-5B core stage orbits Earth for 5–12 days before atmospheric drag brings it down in an uncontrolled re-entry.
The re-entry footprint is unpredictable until the final hours, and the object's orbit is inclined at 41.5°, meaning it can re-enter anywhere between 41.5° north and south latitude — an area covering most of the world's populated land surface. While the majority of debris is expected to burn up during re-entry, analyses suggest that 20–40% of the core stage mass (4–9 tonnes) could survive to reach the surface as fragments.
CZ-5B Re-entry Events
| Flight | Launch Date | Payload | Re-entry Date | Re-entry Location |
|---|---|---|---|---|
| Y1 | 5 May 2020 | Test capsule | 11 May 2020 | Atlantic Ocean, off Côte d'Ivoire coast. Debris reportedly found on land in Côte d'Ivoire. |
| Y2 | 29 Apr 2021 | Tianhe core module | 9 May 2021 | Indian Ocean, near the Maldives |
| Y3 | 24 Jul 2022 | Wentian lab module | 31 Jul 2022 | Sulu Sea, Philippines region. Some debris reached Borneo (Malaysia/Indonesia). |
| Y4 | 31 Oct 2022 | Mengtian lab module | 4 Nov 2022 | South-central Pacific Ocean |
NASA, ESA and other agencies criticised the uncontrolled re-entries, with NASA Administrator Bill Nelson stating after the Y2 re-entry that spacefaring nations must minimise the risks from space debris. China's space agency maintained that the risk was acceptable and that the re-entries were managed with appropriate monitoring. As of 2026, with the Tiangong station assembly complete, no further CZ-5B flights have been scheduled, though the vehicle could be used for future heavy LEO missions.
Long March 5B vs. Long March 5
The CZ-5B should not be confused with the standard Long March 5 (CZ-5), which is a two-stage vehicle with an upper stage and is used for missions to GTO, the Moon, and Mars. The CZ-5 was used to launch the Tianwen-1 Mars mission (2020) and the Chang'e-5 lunar sample return mission (2020). Because it has an upper stage that separates at much lower velocity, the CZ-5 does not produce the same uncontrolled core stage re-entry problem.