Chang Zheng 3 (Long March 3)
The Chang Zheng 3 (CZ-3, or Long March 3) is the three-stage version of the Chang Zheng 2 (CZ-2), specifically for the launch of geostationary satellites from the Xichang Satellite Launch Centre (XSLC) in Sichuan Province in central China. First introduced in 1984, the launch vehicle was designed to send the payload into a highly elliptical Geostationary Transfer Orbit (GTO), where the satellite then uses its own apogee kick stage to move to its intended location on Geostationary Earth Orbit (GEO). The launch vehicles of the family in current use were all based on the improved CZ-3A introduced in 1994.
China began the development of its first geostationary communications satellite (Project 331) in 1975. The Ministry of Astronautics decided in 1977 that the satellite was to be launched by a three-stage, liquid propellant rocket based on the CZ-2. The 1st Academy (CALT) was tasked with the launch vehicle’s overall design as well as its third-stage. The 8th Academy (SAST) was responsible for the development of the launcher’s first- and second-stage. Base 067 (AALPT) was responsible for the liquid rocket engines.
Two design proposals were submitted for the three-stage launch vehicle, both based on the CZ-2 but with different third-stages. The proposal by the 8th Academy featured a third-stage that burns the N2O4/UDMH bi-propellant. The technology was relatively mature and would require less time to develop, as the expense of lower payload capacity. The 1st Academy proposed a more advanced design burning the LOX/LH2 bi-propellant. The boiling points of liquid oxygen and liquid hydrogen were low and the propellant was highly inflammable and explosive, making the engine much more challenging to develop but offering bonus in payload capacity.
Not able to gain a consensus view on the selection of the third-stage design, the Ministry of Astronautics decided to run two projects in parallel – the CZ-2A with a N2O4/UDMH third-stage, and the CZ-2B with a LOX/LH2 third-stage. The Ministry of Astronautics and military were originally in favour of the more advanced LOX/LH2 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, led to serious doubt about the design. The development was only saved after Ren Xinmin, Director of the 1st Academy and a founding member of China’s missile and space programme, persuaded the military to continue their funding for the project.
Finally, the YF-73 LOX/LH2 liquid engine successfully passed 800 seconds ground testing in 1980, paving the way for the engineering development of the CZ-2B launch vehicle, now renamed CZ-3. A ground test vehicle of the CZ-3 was delivered to the Xichang Satellite Launch Centre for a launch rehearsal in 1983.
The first flying CZ-3 vehicle was delivered to Xichang on the new year’s day of 1984. The launch was originally scheduled in the evening of 26 January. However, the final examination of the launch vehicle on the pad identified a fault with the its inertial guidance platform. The satellite and payload fairing had to be removed from the launch vehicle in order to allow the faulty platform to be replaced. This delayed the launch by three days.
At 20:24 CST on 29 January 1984, the CZ-3-Y1 launch vehicle carrying the DFH-2-01 communications satellite blasted off from Launch Complex 3 of the Xichang Satellite Launch Centre. The first- and second-stage of the rocket 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 CST, the second CZ-3 launch vehicle was launched from Xichang. 13 minutes into the flight, its payload, the DFH-2-02 communications satellite, was successfully placed into the GTO. Six days later, the satellite was moved to its intended location in the GEO at 125°E. China became the fifth country in the world capable of developing and launching the geostationary communications satellite.
In 1985, the Chinese Ministry of Astronautics announced its intension to provide commercial launch service for foreign customers using its Chang Zheng series of launch vehicle. On 7 April 1990, a CZ-3 rocket launched from Xichang successfully placed the U.S.-built Asia 1 satellite into orbit. This was China’s first commercial satellite launch.
Flight Sequence and Trajectory
The CZ-3 was launched from the Xichang Satellite Launch Centre located in Sichuan Province in central China. The first-stage was shut down and jettisoned at T+126 seconds. The payload fairing was jettisoned at T+259 seconds. The main engine of the second-stage was shut down at T+255 seconds. The second-stage was jettisoned at T+263 seconds.
The third-stage sent the satellite into an initial parking orbit (apogee: 450 km; perigee: 170 km; inclination: 27°) before shutting down its engine. The satellite, still attached to the rocket, flew powerlessly until it reached the equator plane. The third-stage engine then re-ignited to push the satellite into a GTO (apogee: 36,000 km; perigee: 400 km), where the satellite then used its own apogee kick stage to move to the intended location on GEO.
The entire flight lasted 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 is then entered the orbit at 160.33°E above the Equator.
The 3A model was introduced in the 1990s as a successor to the original CZ-3. With an increased GTO payload capacity of 2,600 kg, the CZ-3A was intended as a contender for the international commercial satellite launch market to compete with foreign launch vehicles. By adopting a modular design approach, the rocket was also expanded into a family of launch vehicles with different payload capacities to meet different mission requirements.
Although the CZ-3A inherited the first- and second-stage of the CZ-3, the rest of the launch vehicle 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 LOX/LH2 liquid engine. The engine consisted of two 78.5kN-thrust chamber motors with fully swinging nozzles (4° on each direction), and had the re-ignition capability to allow the rocket engine 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 CZ-3A also features a fuel management system, which 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 launch vehicle is capable of both single- and dual-satellite launches, and can deliver the payload to either the GTO or Super GTO.
The CZ-3A development began in the mid-1980s in response to the demand for a launch vehicle with increased payload capacity to lfot the new-generation DFH-3 communications satellite (Project 862). In 1985, CALT proposed to improve the existing CZ-3 in two phases. The first phase was to introduce a new third-stage featuring the 157kN YF-75 liquid engine. Then in the second phase the redesigned core vehicle would be added with 2 or 4 strap-on liquid boosters for increased payload capacity.
The DFH-3 satellite and CZ-3A launch vehicle proposals were officially approved in February 1986, with the first flight scheduled in 1992. However, the development of the CZ-3A was delayed due to CALT having focused most of its resources on the CZ-2E project. As a result, the CZ-3A was not ready for the first flight until 1994.
On 8 February 1994, a CZ-3A lifting off from the Xichang Satellite Launch Centre successfully sent its payloads, a dummy DFH-3 satellite named Kuafu 1, and a scientific research satellite Shijian 4, into their intended orbits. Nine months later, on 30 November, a second CZ-3A launcher successfully placed the first DFH-3 satellite into the GTO (apogee: 36,197 km; perigee: 200 km).
Since then, the CZ-3A has been serving as a reliable workhorse for China’s geostationary missions, with a success rate of 100%. On 24 October 2007, it lofted China’s first lunar orbiting probe into orbit.
The CZ-3B is the second variant of the CZ-3A series, designed to deliver a single heavy communications satellite or multiple satellites to the GTO. With four strap-on liquid boosters, the launch vehicle’s GTO payload capacity was increased to 5,200 kg (5,500 kg on later variants), making the it the most powerful launch vehicle in China, and (at the time of its 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 adding the CZ-3A core stage with four strap-on boosters, each powered by a single DAFY5-1 liquid engine burning the N2O4/UDMH bi-propellant. Other onboard systems were largely unchanged. The development of the launch vehicle began in July 1989, with the first flight scheduled in 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 two-seconds after the lift-off, the rocket carrying the Intelsat 708 communication satellite began to veer off course, and then hit a hill 1,200m 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 launcher’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.
Despite the initial failure, the CZ-3B made a successful second launch on 20 August 1997, sending the Philippine Agila 2 MABUHAY telecommunications satellite into the GTO.
The enhanced variant CZ-3B/E was introduced for the first time 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. This has resulted in an increase in the launch vehicle’s GTO payload capacity by 300 kg.
The CZ-3C was the third variant in the CZ-3A series, developed in the late 1990s to fill the payload capacity gap between the 3A and 3B model. The launch vehicle is capable of delivering 3,700 kg payload into the GTO. The CZ-3C is almost identical to the CZ-3B in design, but fitted with two strap-on boosters instead of four. A minor modification on the 3C model is the lack of the stabilising fins found at the bottom of the 3A and 3B variants.
Development of the CZ-3C began in March 1995, and the rocket was almost ready by early 1992. However, following the CZ-3B incident in February 1996, the CZ-3C development was suspended so that CALT could focus on the improvement of the CZ-3B. The two satellites originally scheduled to be launched by the CZ-3C were launched on the CZ-3B instead. The 3C variant didn’t make its maiden flight until 12 years later in 2008.