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Changzheng 3A
The Changzheng 3A (CZ-3A, or " Long March 3A") was introduced in the 1990s as a successor to the Changzheng 3 for geostationary orbit launches, capable of delivering up to 2,600kg payload to the GTO. The rocket was developed to target the domestic and international 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.
Although the CZ-3A inherited the first- and second-stage of the Changzheng 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 LOX/LH2 liquid engine, a helium-pressurised propellant tank, a new 4-axis inertial platform-computer guidance, and a digital flight control. The rocket was capable of both single-satellite and twin-satellite launches, and could 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 rocket with increased payload capacity to launch the new Dongfanghong 3 communications satellite (Project 862). In 1985, CALT proposed to improve the existing Changzheng 3 in two stages. The first step 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 2~4 strap-on liquid boosters for increased payload capacity.
The Dongfanghong 3 satellite and CZ-3A launch vehicle development 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 Changzheng 2E development. The CZ-3A was not ready for the first flight until 1994.
On 8 February 1994, a CZ-3A taking off from the Xichang Satellite Launch Centre successfully sent its payloads, a dummy Dongfanghong 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 rocket successfully placed the first Dongfanghong 3 satellite into the GTO (apogee: 36,197km; perigee: 200km).
The CZ-3A has been serving with the Chinese space programme since 1994, with a launch successful rate of 100%. On 24 October 2007, it sent China's first lunar orbiting probe into the orbit.
Design
The CZ-3A retained the first- and second-stage of the Changzheng 3, but featured a redesigned third-stage, which was powered by an YF-75 liquid engine developed by CALT. 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 introduced a fuel management system, which used 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 200kg, and also allowed the engine to be switched on and off freely during the flight to give better adaptability to different launch missions.
CZ-3A
Specifications
| Stages | 3 |
| Boosters | 0 |
| Overall length | 52.52 m |
| Core stage diameter | 3.35 m |
| Take-off mass | 241 t |
| Take-off thrust | 2,961.6 kN |
| Thrust-weight ratio | 1.25 |
| Payload capacity | 2,600 kg to GTO |
| First flight | 1994 |
| Launch site | Xichang |
| Status | Operational |
Stages
| First-stage | Second-stage | Third-stage | |
| Length | 26.972 m | 11.276 m | 12.375 m |
| Diameter | 3.35 m | 3.35 m | 3.00 m |
| Gross mass | 183.28 t | 34.116 t | 20.935 t |
| Empty mass | 11.23 t | 3.56 1t | 3.062 t |
| Propellant mass | 172.05 t | 30.555 t | 18.242 t |
| Engine | DAFY6-2 | (Main) DaFY21-1 (Swivelling) 4 X YF-23B |
YF-75 |
| Propellant | N2O4/UDMH | N2O4/UDMH | LOX/LH2 |
| Thrust* | 2,961.6 kN | (Main) 742 kN (Swivelling) 4X 47 kN |
156.9 kN |
| Isp* | 2,556.2 N.s/kg | (Main) 2,922.4 N.s/kg (Swivelling) 2,834N.s/kg |
4,334.5 N.s/kg |
| Burn time | 146 s | (Main) 114 s (Swivelling) 119 s |
478 s |
* Sea-level values for the first-stage, and vacuum values for the second- and third-stage
Payload Fairing
| Length | 8.887 m |
| Diameter | 3.35 m |
| Mass | 500 kg |
Last updated: 23 February 2012