Chang Zheng 4 (Long March 4)
The Chang Zheng 4A (CZ-4A, or “Long March 4A”) is the three-stage version of the CZ-2, added with a liquid propellant third-stage. The rocket was originally developed as a backup to the CZ-3 for the launch of the geostationary satellite, but was later adopted for the launch of Earth observation remote-sensing satellites into Sun Synchronous Orbit (SSO). The early variant has now been replaced by the improved CZ-4B and 4C.
When the geostationary communication satellite programme (Project 331) was created in the early 1970s, the Ministry of Aeronautics proposed two designs for the launch vehicle. The Shanghai-based 8th Academy (SAST) proposed to add the two-stage CZ-2 with a third-stage burning the same N2O4/UDMH liquid bi-propellant also used by the launch vehicle’s first- and second-stage. The Beijing-based 1st Academy (CALT) proposed a more advanced third-stage burning the low temperature LOX/LH2 bi-propellant.
With CALT’s CZ-2B (later renamed CZ-3) becoming successful in 1984, the CZ-2A (later renamed CZ-4) design proposed by SAST became redundant. However, the design was not abandoned. Instead, SAST developed the rocket into the CZ-4A as the launcher for the polar orbit meteorological satellite Fengyun 1 (Project 771).
The CZ-4A was similar to the CZ-2 in design. By stretching the first-stage by 4 m, it could carry an additional 40 t of propellants. The first-stage also featured an improved YF-21B liquid motor engine, which gave a maximum thrust of 2,942 kN. The newly-developed third-stage was powered by an YF-40 liquid motor engine, which consisted of two fully swivelling chamber motors and carried a total of 11.3 t of N2O4/UDMH bi-propellant. Other improvements included a computerised guidance system, and an onboard propellant management system.
The development of the CZ-4A began in 1985 and the launch vehicle made its first launch successfully on 7 September 1988, placing Fengyun 1A into orbit. Two years later, on 3 September 1990, the CZ-4A made its second flight, putting the Fengyun 1B satellite and two Daqi 1 balloon satellites into their intended orbits. The was also the last flight of the CZ-4A.
On 4 October 1990, the third-stage of the CZ-4A launch vehicle launched a month earlier to loft Fengyun 1B, exploded in the 895 km orbit, creating more than 80 pieces of trackable space debris. This incident later led to a redesign of the subsequent launch vehicles of the same family.
The CZ-4B was introduced in the late 1990s for the launch of the Ziyuan 1 (CBERS 1) remote-sensing satellite. The CZ-4B was generally similar to the CZ-4A in design. The most significant modification was adopting a newly-designed payload fairing 8.48 m in length and 3.35m in diameter in order to house the large remote-sensing satellite. Other improvements included:
Increased payload capacity;
- Replacing the original mechanical-electrical flight control with a digital electronic control;
- Improved telemetry, tracking & control system and self-destruction mechanism, with smaller size and reduced weight;
- A revised nuzzle design in the second-stage for better high-altitude performance;
- A propellant management system on the second-stage of the rocket to reduce the spare propellant requirement, thus increasing the vehicle’s payload capability;
The CZ-4B made its maiden flight successfully on 10 May 1999, placing Fengyun 1C and Shijian 5 into their intended orbits.
In 1993, Chinese rocket engineers confirmed that the third-stage of the new CZ-4B launch vehicle had been redesigned to include a residual propellant venting system. However, the system was not included on the early variant of the CZ-4 rocket, as the satellite designer was concerned that this may damage the satellite. Then another third-stage explosion occurred on a CZ-4B on 11 May 2000, after it had lofted CBERS-1 on 14 October 1999, producing over 300 pieces of trackable space debris in a 735 km orbit. The residual propellant venting system was then swiftly installed on all subsequent CZ-4B flights. No further explosion had occurred since then.
On 9 December 2013, a CZ-4B launch vehicle failed to place its payload CBERS-3 into orbit. During powered flight of the third-stage, one of its two engines shut down prematurely and the satellite failed to reach orbit. The cause was traced to foreign debris that blocked the fuel intake of the rocket engine.
The further improved variant CZ-4C was introduced in 2006 for the launch of the Yaogan 1 reconnaissance satellite. The CZ-4C featured an improved third-stage with multiple re-start capability. While the CZ-4B remained as the primary launch vehicle for SSO satellites, the CZ-4C was used for the launch of heavier satellites and multiple satellites on a single vehicle.
Improvements on the CZ-4C included:
- An improved third-stage powered by an YF-40A engine with multiple restart capability;
- A propellant management system on the third-stage;
- A remotely-operated automated launch control system that integrated various functions previously carried out separately, including launch control, system testing, data transmission, telemetry, and power supply;
- A new flight computer with better calculation performance and a smaller size power supply;
- A new guidance system with GPS input;
The CZ-4C had adopted a different launch checkout procedure to its predecessors. Instead of being tested in a horizontal position before being erected on the launch pad, the vehicle could be assembled and tested vertically on the launch pad at the same time, reducing the launch preparation time by a third.
The CZ-4C made its debut flight on 26 April 2006, lofting the Yaogan 1 reconnaissance satellite into orbit. On 5 March 2010, a CZ-4C carrying the Yaogan 9 reconnaissance satellite atop was launched from Pad 603 of the Jiuquan Satellite Launch Centre. This was the first ever flight of the CZ-4 series from a launch site other than Taiyuan.