The Long March 2 (Chang Zheng-2, or CZ-2) family of space launch vehicles was developed from China’s Dong Feng-5 (DF-5, CSS-4) ICBM introduced in the 1970s. The launch vehicle also formed the basis on which the Long March 3 and 4 families were developed. All three launch vehicle families share the same airframe and engine design, with different upper stages and onboard systems.
The core stage of the Long March 2 consists of two stages connected by an inter-stage structure, all 3.35 m in diameter. Each stage has two propellant tanks: an oxidiser tank at the front and a fuel tank at the rear, connected by an inter-tank ring section. Oxidiser is pumped to the engines via a pipe penetrating through the centre of the rear fuel tank. The two propellant tanks and the inter-tank ring section form part of the vehicle’s thrust and weight bearing load structure and are constructed from high-strength aluminium-alloy LD10.
The first-stage comprises (from front to rear): oxidiser tank, inter-tank ring section, fuel tank, engine frame, and tail section. The front end of the forward oxidiser tank is protected by a fibreglass heat insulation layer to prevent damage from the high pressure and hot stream of engine exhaust from the second-stage engine during stage separation. The four main engine motors are mounted on the engine frame secured to the rear of the fuel tank. The frame transfers the thrust of the engines to the rocket’s thrust and weight bearing load structure.
The stage is powered by the YF-21 engine, which consists of a cluster of four parallel YF-20 single-chamber motors arranged symmetrically at an angle of 2°50’ to the axis of the core vehicle. Each motor has a swinging nozzle that can be pivoted up to +/-10° at radial direction to provide directional thrust and steering.
The tail section is a two-piece shroud 3.5 m in diameter and 2.4 m in length. It protects the main engines from aerodynamic forces and also houses engine components and linkages. On some variants the tail section is also incorporated with four fixed stabilising fins. A honeycombed fibreglass heat shield situated between the engine nozzles and the rear structure safeguards engine components and the fuel tank from the flames and heats of engine exhaust during launch. Four pressure relief valves regulate the pressure inside the shroud during flight. The erected vehicle is supported by four weight bearing points on the tail section, secured to the launch pad’s base unit with explosive bolts, which are detonated less than a second before the vehicle lifts off.
The four strap-on boosters used by the E and F models are 2.25 m in diameter and have a similar structure to the first-stage. Each booster is powered by a single YF-20 motor with fixed nozzle, and is mounted on the engine frame of the first-stage of the core-stage.
The launch vehicle uses a ‘hot separation’ method, where the two stages are separated by the impingement of the hot exhaust gas jet from the second-stage engines. The engines ignite while the two stages are still connected, thus eliminating the need for jettisoning devices to provide the separation impulse and avoiding unpowered flight during the separation.
The inter-stage structure comprises an inter-stage shroud and a grid structure. The inter-stage shroud, 3.35 m diameter and 3.2 m in length, houses second-stage engines to protect them from aerodynamic forces, and is connected to the rear of the second-stage’s fuel tank with explosive bolts.
The grid structure, which consists of thirty-two 60 mm diameter metal bars, was designed to let exhaust gas from the engines on the second stage to escape.
On the 2E and 2F variants, the grid structure was replaced by a ring-shaped structure with exhaust venting windows.
The second-stage maintains the overall diameter of the first-stage at 3.35 m and comprises (from front to rear): instrument compartment, oxidiser tank, inter-tank ring section, and fuel tank. The engines are directly mounted on the rear of the fuel tank. The instrument compartment at the front houses the flight control system, navigation platform, and gas canisters.
The stage is powered by an YF-22 main engine with fixed nozzle, and a swivelling vernier engine consisting of four YF-23 chamber motors. The swivelling vernier engine is designed for steering and sustaining propulsion for a further 190 seconds after the main engine cut-off. The stage also has four small solid fuel rocket motors, which are fired for only half a second after the second-stage engine cut-off. This reduces the velocity of the rocket stage to allow the payload to be separated from the stage.
A secondary payload can be placed at the front end of the second-stage between the instrument compartment and the prime payload fairing. The payload is mounted on a two-piece payload adaptor 2.2 m in diameter, with the upper part of the adaptor providing electric and mechanical interfaces for the prime payload, and the lower part secured to the instrument compartment of the second stage. The two parts are connected by four explosive bolts. After the prime payload is separated from the rocket stage, the booster can adjust its flight trajectory and then detonate the explosive bolts to release the secondary payload into its planned orbit.
A two-piece payload fairing protects the satellite from aerodynamic forces during flight. The fairing is connected together by 12 explosive bolts and secured to the second-stage by 8 explosive bolts, and is jettisoned at an altitude of about 120 km.