Chang Zheng-3

Name: Chang Zheng-3 (CZ-3), or Long March 3 (LM-3)
Type: Liquid-propellant orbital launch vehicle
Contractor: China Academy of Launch Vehicle Technology (CALT, 1st Academy); Shanghai Academy of Spaceflight Technology (SAST, 8th Academy)
First Launch: 29 January 1984
Launch site: Xichang
Status: Retired (CZ-3); Operational (CZ-3A/B/C)

The Long March 3 (Chang Zheng-3, or CZ-3) is a family of space launch vehicles designed for Geostationary Earth Orbit (GEO) and translunar orbit missions. The launch vehicle was based on the first- and second-stage of the CZ-2, and was added with a cryogenic third-stage. The early variant CZ-3 has now retired and been replaced by the improved CZ-3A/B/C series, which continues to support China’s satellite and lunar exploration programme until the introduction of the new-generation launch vehicles.

Development History

China began the development of its first geostationary communications satellite (Project 331) in 1975. The Ministry of Astronautics decided in 1977 that the satellite would be launched by a three-stage, liquid propellant rocket based on the CZ-2. The 1st Academy (CALT) was tasked with the overall design of the launch vehicle and also the development of its third-stage, while the 8th Academy (SAST) was responsible for the first- and second-stage. Base 067 (now the 6th Academy) was responsible for building the liquid rocket engines.

CALT and SAST submitted two design proposals for the new launcher. Both designs were based on the CZ-2, but with different third-stages. The SAST proposal featured a third-stage burning the hypergolic N2O4/UDMH propellant. The technology was relatively mature and would require less time to develop. A second proposal by CALT featured a more advanced third-stage burning the cryogenic LOX/LH2 propellant. The cryogenic rocket engine was more challenging in technology but offered greater payload improvement. Not able to reach a consensus on the selection of the two proposals, the Ministry of Astronautics decided to run two development programmes in parallel. The design with the hypergolic third-stage was designated CZ-2A. The design with the cryogenic third-stage was designated CZ-2B.

CALT developed the cryogenic YF-73 engine for the third-stage, while SAST introduced the YF-44 engine. The Ministry of Astronautics and military were originally in favour of the cryogenic design. However, an explosion during a ground test of the YF-73 engine in January 1978, followed by a fire incident in March of the same year, shifted the decision-makers towards the safer hypergolic option. The cryogenic design was only saved after Ren Xinmin, one of the founding fathers of China’s missile and rocket programme and later Director of CALT, intervened personally and persuaded the military to continue its funding for the development.

The CZ-3 was to be launched from the newly constructed Xichang Satellite Launch Centre located in the central province of Sichuan. The first-stage would cut off and jettisoned at T+126 seconds. The payload fairing would be jettisoned at T+259 seconds. The second-stage engine would cut off at T+255 seconds and the second-stage jettisoned at T+263 seconds.

The third-stage would send the satellite into an initial parking orbit (apogee: 450 km; perigee: 170 km; inclination: 27°) before cutting off its engine. The satellite, still attached to the third-stage, would fly powerlessly until it reached the equator plane. The third-stage engine would then reignite to loft the satellite to GTO (apogee: 36,000 km; perigee: 400 km), where the satellite then uses its own apogee kick stage to move to the intended location on GEO. The entire flight would last 1,245.34 seconds, flying over Sichuan, Hunan, Guangxi, Guangdong, Fujian, and then over the southern tip of Taiwan to fly above the Pacific. The satellite would then be inserted into the orbit at 160.33°E above the Equator.

CZ-3

Engineering development of the CZ-2B, later re-designated CZ-3, began in March 1978. Development of the cryogenic YF-73 engine began in 1978 and the engine passed initial ground testing (800 sec + 700 sec) in 1980. A dummy rocket was produced in 1983 and was delivered to the Xichang Satellite Launch Centre for ground launch exercise.

The first flying CZ-3 launch vehicle (serial No.: Y1) was delivered to the launch centre on the New Year’s day of 1984. The first launch was scheduled in the evening of 26 January. However, the final examination of the rocket on the launch pad identified a fault with the rocket’s inertial guidance platform. The satellite had to be disintegrated from the launch vehicle and the payload fairing removed in order to replace the faulty platform. The issue set back the launch by three days.

At 20:24 local time on 29 January 1984, the CZ-3 (Y1) carrying a DFH-2 communications satellite blasted off from Launch Complex 3 in the Xichang Satellite Launch Centre. The first- and second-stage of the launch vehicle worked normally. The third-stage ignited and shut down as scheduled, but failed to re-ignite after entering the 400 km initial parking orbit. As a result, the satellite was placed into an elliptical orbit (apogee: 64,800 km; perigee: 400 km) instead of the GEO. Despite the failure, the ground control was able to test the positioning and data transmission with the satellite on the wrong orbit.

Two months later, on 8 April at 19:20 local time, the CZ-3 (Y2) launch vehicle lifted off from Xichang, successfully placing DFH-2-02 into GTO. Six days later, the satellite was moved to its intended location on GEO at 125°E, making China the fifth country in the world capable of developing and launching a geostationary communications satellite.

On 7 April 1990, a CZ-3 rocket launched from Xichang successfully lofted the Asia 1 telecommunications satellite into orbit—China’s first commercial launch mission for a foreign-made satellite.

CZ-3A

The CZ-3A was introduced in the 1990s as a successor to the basic variant CZ-3. Capable of delivering up to 2,600 kg payload to GTO, the launch vehicle was intended specifically to target the commercial space launch market, featuring better economy, flexibility and adaptability. By adopting a modular design approach, the rocket was also expanded into a family of commercial launch vehicles to meet different mission requirements.

The CZ-3A development programme was initiated in the mid-1980s for the launch of the new DFH-3 communications satellite (Project 862). In 1985, CALT proposed to improve the existing CZ-3 in two stages. In the first stage, a new third-stage featuring the 157 kN YF-75 liquid engine was introduced. Then in the second stage, the improved core vehicle would be added with 2 or 4 strap-on boosters to further increase its payload capacity.

Although the CZ-3A inherited the first- and second-stage of the CZ-3, the rest of the rocket was completely redesigned, with 70% of its onboard the technologies being new. Major improvements included a redesigned third-stage powered by a new YF-75 cryogenic engine, a helium-pressurised propellant tank, a new 4-axis inertial platform-computer guidance system, and a digital flight control. The launch vehicle was capable of both single-satellite and twin-satellite launches, and could deliver the payload to either GTO or Super GTO.

The YF-75 engine consists of two 78.5 kN-thrust chamber motors with fully swinging nozzles (4° on each direction), and had the re-ignition capability to allow it to be switched on and off during the flight in order to achieve maximum payload efficiency. The vacuum thrust of the YF-75 was 78% higher than that of the old YF-73.

The fuel management system on the CZ-3A uses low-temperature helium gas carried inside the 7 onboard bottles to keep the liquid oxygen and liquid hydrogen tanks pressurised. This measure increased the payload capacity by 200 kg, and also allowed the engine to be switched on and off freely during the flight to give better adaptability to different launch missions.

The DFH-3 satellite and CZ-3A launch vehicle development programmes were officially approved by the State Council in February 1986, with the first flight scheduled for 1992. However, the development of the CZ-3A was delayed due to CALT having to give higher priority to the CZ-2E programme. As a result, the CZ-3A was not ready for flight until 1994.

On 8 February 1994, a CZ-3A taking off from the Xichang Satellite Launch Centre successfully sent its payloads, a dummy DFH-3 satellite named Kuafu 1, and a scientific research satellite designated Shijian 4, into their intended orbits. Nine months later, on 30 November, a CZ-3A successfully placed the first DFH-3 satellite into GTO (apogee: 36,197 km; perigee: 200 km).

Since then, the CZ-3A has been serving with the Chinese space programme with a launch successful rate of 100%. On 24 October 2007, it placed China’s first lunar probe into orbit.

CZ-3B

The CZ-3B is a derivation of the CZ-3A, using the same core vehicle but added with four strap-on boosters to achieve greater payload capacity. The launcher is capable of delivering 5,200 kg (5,500 kg on later variants) to GTO, or 11,200 kg payload to a 200 km LEO, making the rocket the most powerful launch vehicle in service with China, and (at the time of introduction) the second most capable operational launch vehicle in the world, only after the Russian Proton.

The CZ-3B was developed as the second phase of the CZ-3 upgrade programme. The focus of the development was to adding the CZ-3A-based core vehicle with four strap-on boosters, each powered by a single DAFY5-1 liquid engine burning the N2O4/UDMH propellant. Other onboard systems were largely unchanged. The development of the launch vehicle began in July 1989, with the first flight taking place 1996.

The maiden flight of the CZ-3B on 15 February 1996 ended up in the worst disaster in the history of the Chinese space programme. Only few seconds after lift-off, the launch vehicle carrying the Intelsat 708 telecommunication satellite began to veer off course, and then hit a hill 1,200 m away from the launch pad at T+22 seconds, destroying the US$125 million satellite onboard. The impact and violent explosion of the rocket killed six people and injured another 57, and also destroyed over 80 buildings in a nearby village.

The cause of failure was traced to the launch vehicle’s guidance and control system. A gold-aluminium solder joint in the output of one of the gyro servo loops failed, cutting electrical current output from the power module and causing the inertial reference platform of the vehicle’s guidance and control system to slope. This caused computers to send the vehicle veering off the planned trajectory shortly after lift-off. The failed module was the only one of six similar modules that lacked conductive adhesive to reinforce the solder joint.

Despite the initial failure, the CZ-3B made a successful second launch on 20 August 1997, sending the Philippine Agila 2 MABUHAY satellite into GTO. This was followed by another 8 consecutive successful flights by 2008. The early basic variant CZ-3B has subsequently been replaced by the improved CZ-3B/G1 variant, which remains in service today.

The enhanced variant CZ-3B/E was first introduced in May 2007 for the launch of NIGCOMSAT 1. In order to carry additional propellant, the first-stage of the launch vehicle was stretched by 1.5 m, and four strap-on boosters were stretched by 0.8 m, which has increased the launcher’s GTO payload capacity by 300 kg. It now includes 4 variants: CZ-3B/G2, CZ-3B/G3, CZ-3B/YZ-1, and CZ-3B/G5.

CZ-3B/G5

The latest variant of the CZ-3B series, designated CZ-3B/G5, is said to have been derived from the CZ-3B/YZ-1 that made its debut in July 2015 to place a pair of Beidou-III experimental navigation satellites into a 21,500 km Medium Earth Orbit (MEO). The launch vehicle consists of a three-stage core vehicle, four strap-on boosters, and a Yuan Zheng-1 (YZ-1) upper stage, all burning the hypergolic UDMH/N2O4 bi-propellant.

The main improvement on the CZ-3B/G5 over its predecessor is its payload fairing, which has been stretched by 0.9 m to accommodate larger payload. CALT also highlighted the improved flexibility of the CZ-3B/G5, which is said to be capable of supporting not only GEO and Translunar Orbit launch missions, but also Sun-Synchronous Orbit (SSO) missions from the Xichang Satellite Launch Centre.

CZ-3C

The CZ-3C is the third variant in the CZ-3A family, developed in the late 1990s to fill the payload capacity gap between the 3A and 3B models. Capable of delivering 3,700 kg payload to GTO, the CZ-3C is almost identical to the CZ-3B in design, apart from being fitted with two strap-on boosters instead of four. A minor difference was that the 3C model didn’t have the stabilising fins found at the bottom of the boosters on the CZ-3B.

Development of the CZ-3C began in March 1995, and the launch vehicle was almost ready by early 1996. However, following the CZ-3B incident on 15 February 1996, the CZ-3C programme was suspended so that CALT could focus on improving the CZ-3B. The two satellites originally scheduled to be launched by the CZ-3C were launched on the CZ-3B instead. As a result, the 3C variant didn’t make its maiden flight until 12 years later in 2008.

Specifications
General                   CZ-3A          CZ-3B          CZ-3C
----------------------------------------------------------------
Stages:...................3              3              3
Strap-on boosters:........0              4              2
Overall length (m):.......52.52          54.838 (3B)    54.838
                                         56.326 (3B/E)
Take-off mass (t):........241            426 (3B)       345
                                         458.397 (3B/E)
Take-off thrust (kN):.....2,961.6        5,923.2        4,442.4
Thrust-weight ratio:......1.25           1.42           1.31
GTO capacity (kg):........2,600          5,200 (3B)     3,700
                                         5,500 (3B/E)

Stages                    1st-stage      2nd-stage      3rd-Stage    Booster
------------------------------------------------------------------------------
Length (m):...............23.272         9.943          12.375       15.326
Diameter (m):.............3.35           3.35           3.00         2.25
Gross mass (t):...........183.9          49.6           21.304       40.75
Empty mass (t):...........12.12          3.848          2.742        3.00
Propellant mass (t):......171.8          45.752         18.193       37.75
Engine, main:.............DAFY6-2        DaFY21-1       YF-75        DAFY5-1
Engine, vernier:..........No             4x YF-23F      No           No
Propellant:...............N2O4/UDMH      N2O4/UDMH      LOX/LH2      N2O4/UDMH
Thrust, main (kN):........2,961.6        742            156.9        740.4
Thrust, vernier (kN):.....               4x 47.07
Isp, main (N.s/kg ):......2,556.2        2,922.4        4,334.5      2556.2
Isp, vernier (N.s/kg):....               2,843
Burn time, main (sec):....146            178            469          125
Burn time, vernier (sec):.               184

Payload fairing
-----------------------------------------------------
Length (m):...............9.561
Diameter (m):.............4 or 4.20
Weight (kg):..............1,500 kg
Gallery
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:长征三号系列 [“Introduction to the Long March 3 Series Launch Vehicles”]. 中国航天, 1998年第3—9期 [China Spaceflight, 1998 Issue 3—9]

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