The Changzheng 3B (CZ-3B, or " Long March 3B") was the second variant of the Changzheng 3A (CZ-3A) series designed to launch a single heavy communications satellite or multiple satellites to the GTO. With four strap-on liquid boosters, the rocket's GTO payload capacity was increased to 5,200kg (5,500kg on later variant), 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 Changzheng 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 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. 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 the GTO. This was followed by another 8 consecutive successful flights by October 2008.
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 1.5m, and four strap-on boosters were stretched by 0.8m. This has resulted in an increase in the rocket’s GTO payload capacity by 300kg.
|Overall length||54.838 m (CZ-3B)
56.326 m (CZ-3B/E)
|Core stage diameter||3.35 m|
|Maximum diameter||8.45 m|
|Take-off mass||426.00 t (CZ-3B)
458.397 t (CZ-3B/E)
|Take-off thrust||5,923.2 kN|
|Payload capacity||5,200 kg (CZ-3B) to GTO
5,500 kg (CZ-3B/E) to GTO
|Length||23.272 m (CZ-3B)
24.772 m (CZ-3B/E)
|9.943 m||12.375 m||15.326 m (CZ-3B)
16.126 m (CZ-3B/E)
|Diameter||3.35 m||3.35 m||3.00 m||2.25 m|
|Gross mass||183.90 t||49.6 t||21.304 t||40.75 t (each)|
|Empty mass||12.12 t||3.848 t||2.742 t||3.0 t (each)|
|Propellant mass||171.80 t (CZ-3B)
186.6 t (CZ-3B/E)
|45.752 t||18.193 t|| 37.75 t (CZ-3B)
41.5 t (CZ-3B/E)
(Swivelling) 4 X YF-23F
|Thrust*||2,961.6 kN||(Main) 742 kN
(Swivelling) 4X 47 kN
|156.9 kN||740.4 kN (each)|
|Isp*||2,556.2 N.s/kg||(Main) 2,922.4 N.s/kg
|4,334.5 N.s/kg||2,556.2 N.s/kg|
|Burn time||146 s||(Main) 178 s
(Swivelling) 184 s
|469 s||125 s|
* Sea-level values for the first-stage and boosters, and vacuum values for the second- abd third-stage
|Diameter||4.00m or 4.20 m|
Last updated: 23 February 2012