Chang Zheng-4

Name: Chang Zheng-4 (CZ-4), or Long March 4 (LM-4)
Type: Liquid-propellant orbital launch vehicle
Contractor: Shanghai Academy of Spaceflight Technology (SAST, 8th Academy)
First Launch: 7 September 1988
Launch site: Taiyuan, Jiuquan
Status: Retired (CZ-4A); Operational (CZ-4B/C)

The Long March 4 (Chang Zheng-4, or CZ-4) is a family of three-stage, liquid-propellant orbital launch vehicles introduced in the 1980s for Sun-Synchronous Orbit (SSO) launch missions. It was based on the two-stage CZ-2, but added with a hypergolic third-stage in order to reach higher orbit. The early variant CZ-4A has retired and been succeeded by the improved B and C variants.

Development History

When the geostationary telecommunication satellite programme (Project 331) was launched in the early 1970s, the Ministry of Aeronautics proposed two designs for the launch vehicle. The first proposal by the 8th Academy (SAST) was to add the two-stage CZ-2 with a hypergolic third-stage burning the N2O4/UDMH bipropellant. A second proposal by the 1st Academy (CALT) featured a more advanced cryogenic third-stage burning the LOX/LH2 bipropellant.

While the Ministry of Astronautics and the military were both in favour of the CALT proposal, the SAST proposal was also kept as a backup. The two development programmes were run in parallel until 1984, when the development of the CZ-3 with the LOX/LH2 third-stage finally succeeded. However, the SAST design was not abandoned. Instead, it was developed into the CZ-4A for China’s first polar orbit meteorology satellite Fengyun 1 (Project 771).

CZ-4A

The development of the CZ-4A began in 1985 and the launcher made its first flight successfully on 7 September 1988 from the Taiyuan Satellite Launch Centre, placing Fengyun 1A into orbit. Two years later, on 3 September 1990, the CZ-4A made its second flight from the same launch centre, placing Fengyun 1B and two Daqi 1 balloon satellites into their intended orbits. This was also the last flight of the CZ-4A.

The CZ-4A was similar to the CZ-2 in design. By stretching the vehicle’s first-stage by 4 m, it could carry additional 40 t of propellants. The first-stage of the vehicle also featured the improved YF-21B liquid engine, which gave a maximum thrust of 2,942 kN. The third-stage was powered by the YF-40 liquid engine, which consisted of two fully swivelling chamber motors and carried 11.3 t of the N2O4/UDMH propellant. Other improvements included a computerised guidance system and an onboard propellant management system.

CZ-4B

The CZ-4B was developed in the late 1990s for the launch of the Ziyuan 1 (China Brazil Earth Resource Satellite, or CBERS) remote-sensing satellite. The development of the satellite began in 1989 and the launch vehicle launched its first mission in May 1999 from the Taiyuan Satellite Launch Centre, placing Ziyuan 1-01 (CBERS 1) into orbit.

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 3.35 m 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;

On 4 October 1990, the third-stage of a CZ-4A, which had just placed the Fengyun 1B meteorology satellite into orbit, exploded in a 895 km Earth orbit, producing more than 80 trackable space debris pieces. In 1993, Chinese space engineers revealed that the third-stage of the new CZ-4B launch vehicle had been redesigned with a residual propellant venting system. However, the system was not included on the CZ-4A, as the designer of the satellite was concerned about possible damage the satellite during the mission.

Another third-stage of a CZ-4B launch vehicle exploded on 11 May 2000 after it had placed Ziyuan 1-01 (CBERS-1) into orbit seven month before, producing over 300 trackable space debris pieces on a 735km Earth orbit. The residual propellant venting system was then swiftly installed on all subsequent CZ-4B flights. No further explosion had occurred since then.

CZ-4C

Originally designated CZ-4B Batch-02, the CZ-4C was an improved variant of the CZ-4B, introduced in 2006 for the launch of the Yaogan 1 reconnaissance satellite. The CZ-4C features an improved third-stage with the re-ignition capability. While the CZ-4B remains operational for launching medium-sized payload to SSO, the CZ-4C has been used to launch heavier satellites and multiple payloads using a single launch vehicle.

Improvements on the CZ-4C included:

– An improved third-stage powered by an YF-40A engine with 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 that of its predecessors. Instead of being tested in a horizontal position before being erected on the launch pad, the C variant could be assembled and tested at the same time while remaining in a vertical position on the launch pad, reducing the launch preparation time by a third.

The CZ-4C made its maiden flight in April 2006 from the Taiyuan Satellite Launch Centre, placing a reconnaissance satellite Yaogan 1 on orbit. From 2010, the CZ-4C operations have also been expanded to the Jiuquan Satellite Launch Centre.

Specifications
General                   CZ-4B          CZ-4C
----------------------------------------------------
Stages:...................3              3
Strap-on boosters:........0              0
Overall length (m):.......45.576         47.977
Take-off mass (t):........248.47         249
Take-off thrust (kN):.....2,971          2,971
Thrust-weight ratio:......1.21           1.21
700 km SSO payload (kg):..2,295          2,944
900 km SSO payload (kg):..1,473          2,647

Stages                    1st-stage      2nd-stage      3rd-Stage
---------------------------------------------------------------------
Length (m):...............24.65          10.4           4.93
Diameter (m):.............3.35           3.35           2.90
Gross mass (t):...........193.33         38.326         14.56
Empty mass (t):...........9.998          2.932          1.727
Propellant mass (t):......183.34         35.374         12.814
Engine, main:.............YF-21B         YF-22B         YF-40 (CZ-4B)
                                                        YF-40A (CZ-4C)
Engine, vernier:..........No             4x YF-23B      No
Propellant:...............N2O4/UDMH      N2O4/UDMH      N2O4/UDMH
Thrust, main (kN):........2,971          742            100.85
Thrust, vernier (kN):.....               4x 47.1
Isp, main (N.s/kg ):......2,550          2,922.4        2,971.4
Isp, vernier (N.s/kg):....               2,834
Burn time, main (sec):....N/A            126.8          N/A
Burn time, vernier (sec):.               136.8

Payload fairing           Type A      Type B     Type C     Type C Short
--------------------------------------------------------------------------
Length (m):...............5.907       8.483      10.684     9.656
Diameter (m):.............2.90        3.35       3.80       3.80
Weight (kg):..............            1,350
Gallery
CZ-4B
CZ-4C
References
  • 李成智 [Li Cheng-zhi], 2003. 中国航天技术发展史稿(中)[“A Draft History of Space Technology in China (Part 2 of 3)”]. 山东教育出版社 [Shandong Education Press].
  • 邸乃庸, 朱维增, 吴瑞华 [Di Naiyong, Zhu Weizeng, Wu Ruihua], 1998. 长征系列运载火箭介绍:长征四号系列 [“Introduction to the Long March 4 Series Launch Vehicles”]. 中国航天, 1998年第12期至1999年第4期 [China Spaceflight, 1998 Issue 12—1999 Issue 4]

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