ChangZheng 3 (CZ-3, or Long March 3 in its translation) is a family of space launch vehicles (SLV) developed by the Beijing-based China Academy of Launch Vehicle Technology (CALT), a subsidiary of the China Aerospace Science & Technology Corporation (CASC). The CZ-3 series SLV have been providing the geostationary earth orbit (GEO) mission capability in the PRC since the mid-1980s. The CZ-3A and CZ-3B are in active use, with the CZ-3C expected to be launched for the first time in April 2008.
CZ-3
CZ-3 launch vehicle (Chinese Internet)
In 1978, CALT was appointed the main contractor to develop a new SLV to send the PRC’s first communications satellite to the GEO. CALT was responsible for the general design of the launch vehicle as well as the development of the third-stage, while Shanghai Academy of Space Flight Technology (SAST) carried out the development of the first and second stage. The CZ-3 was based on the two-stage CZ-2 (DF-5 ICBM), added with a newly developed liquid oxygen/liquid hydrogen (LOX/LH2) third-stage. It can deliver 1,400kg payload to the geostationary transfer orbit (GTO), where the satellite then uses its own apogee kick stage to manoeuvre to its intended position on GEO. A new satellite launch centre was also being built at Xichang, Sichuan Province dedicated for the GEO launches using the CZ-3.
Development of the cryogenic third stage engine was a major technical achievement for the Chinese at the time. This advanced in technology engine was superior in performance (vacuum specific impulse 50% more than that of a conventional propellant engine). Its combustion products were safe and non-toxic. But the boiling points of liquid hydrogen and liquid oxygen are low (-253 deg C and –183 deg C respectively) and they are inflammable and explosive. Many problems in low temperature technology and multiple restarting of the engine in high vacuum and zero gravity had to be solved. During development longitudinal coupling vibration was a key problem that took some time to cure.
The first launch of the CZ-3 vehicle from the Xichang Satellite Launch Centre (XSLC) took place on 29 January 1984, but the third-stage of the launch vehicle failed to restart to move from Low Earth Orbit (LEO) parking orbit to GTO. As a result, the PRC’s first experimental communications satellite DFH-2 carried onboard the launch vehicle was placed into an elliptical orbit, making the satellite unusable. Despite the failure, most tests on the satellite and the launch vehicle were carried out as planned. A rigorous analysis was made for the launch vehicle telemetry data and the cause of the malfunction was identified as being an abnormal mixture ratio in the gas generator for the third-stage.
After some modifications on the third-stage, the CZ-3 restored its flight three months later and carried out six successful missions between April 1984 and April 1990, including PRC’s first commercial launch for a foreign customer (AsiaSat 1). On 28 December 1991, a CZ-3 launch vehicle carrying the domestic ChinaSat 4 (ZhongXing 4) communications satellite failed, again due to third-stage malfunction, leaving the payload with an apogee of only 2,450 km instead of nearly 36,000 km as required.
The CZ-3 returned to flight in July 1994, carrying out another five GEO missions successfully between 21 July 1994 and 25 June 2000, before it was finally retired and replaced by the improved CZ-3A.
CZ-3A
CZ-3A launch vehicle (Chinese Internet)
The CZ-3A is an improved variant of the CZ-3. The diameter of the third stage has been increased from 2.25m to 3m, and the propellant capacity has been increased from 8,200kg to 17,600~18,200kg. As a result, the GTO payload capability of the CZ-3A has been increased from 1,400kg to 2,600kg. An improved control system also allows greater flexibility for altitude control and better adaptability to a variety of launch missions.
Development of the CZ-3A was carried out between 1986 and 1994. The first launch took place on 8 February 1994 at XSLC, with a CZ-3A successfully sending a LEO satellite and a GEO satellite into the orbits. On 30 November 1994, a second CZ-3A successfully placed the first DFH-3 communication satellite into the GTO, but the satellite could not reach its intended orbit because its apogee kick stage malfunctioned. A further 13 flight missions have been carried out since then, with a success rate of 100%.
The latest flight mission of the CZ-3A took place on 24 October 2007, when a modified CZ-3A carrying the PRC’s first lunar orbiting probe Chang’e 1 was launched from XSLC at 18:05 local time (10:05 GMT). The launch vehicle placed the spacecraft into the lunar transfer orbit 20 minutes 49 seconds after the take-off as scheduled.
The first and second stage of the CZ-3A carry the UDMH/N2O4 (nitrogen tetroxide) storable liquid propellant, and the third stage uses the liquid oxygen/liquid hydrogen (LOX/LH2) propellant.
The first stage of the launch vehicle is powered by a YF6-2 rocket engine consisting of four YF-20 chambers motors with swinging nozzles, each producing 75,500kg thrust. The second stage of the core vehicle has a rocket engine consisting of one 75,600kg (742kN)-thrust YF20-1 main motor with fixed nozzles and a YF21-1 swivelling venire motor with four chambers motors (4,800kg/47kN-thrust in total). There are four stabilising fins located at the lower end of the first stage.
The third stage employs a YF-75 engine that produces 16,000kg (157kN) thrust. The restarting ability the of third-stage engine allows heavier payload to be delivered to the GTO.
The payload fairing is 8.887m in length and 3.35m in diameter. The nose cone of the fairing is made of glass fibre materials and the rest part made of alloy materials. There are windows on the fairing for pre-launch examination and receiving radio signals. The vehicle can carry two satellites in a single launch.
