The Long March 2 (Chang Zheng 2, or CZ-2) is the longest-serving space launch vehicle family in China, responsible for sending the country’s first recoverable satellite and the first human spaceflight mission to orbit.
The Long March 2 is a two-stage, liquid-propellant rocket derived from the Dong Feng-5 (DF-5, CSS-4) intercontinental ballistic missile (ICBM). Five main variants of the launch vehicle have been introduced: 2, 2C, 2D, 2E, and 2F, each consisting of several sub-variants with minor modifications. Only the 2C, 2D, and 2F variants are still in service today.
The Long March 2 family has been developed by China Academy of Launch Vehicle Technology (CALT, or 1st Academy), with the exemption of the Long March 2D, which was developed by Shanghai Academy of Spaceflight Technology (SAST, or 8th Academy).
In 1965, the Chinese military proposed the concept of the 10,000 km-range DF-5 ICBM. The development of the missile was assigned to the 1st Academy of the Seventh Ministry of Machinery Industry (Ministry of Astronautics). Two U.S.-trained rocket engineers, Tu Shou’e and Ren Xinmin, were put in charge of the missile’s overall design and liquid engine respectively.
In 1967, the 1st Academy was asked to develop the DF-5 into a space launch vehicle for the recoverable remote-sensing satellite (FSW). So instead of boosting a 3,000 kg thermal nuclear warhead into a ballistic suborbital trajectory, the rocket needed to place an 1,800 kg mass satellite into a 180 km low Earth orbit, which would require a higher specific impulse (Isp), i.e. lower thrust that sustains for longer periods of time.
To achieve this objective, the design team proposed two options: to give the DF-5 a new second-stage powered by a 55 t-thrust YF-25 engine, or to optimise the second-stage’s flight profile. As delays in the YF-25 development may threaten meeting the target date of 1974 for the first FSW mission, the second option of optimising the existing rocket design was adopted.
Initially the design team proposed to delay the engine ignition time after staging, so that the rocket’s second-stage would fly powerlessly for some time before its engine ignites. However, this would require a separate jettison mechanism for the vehicle’s first-stage, thus increasing its structural weight, with only marginal benefit (100 kg) in the increase of the rocket’s payload capacity to orbit.
Later a more creative approach was adopted whereby the vernier thrusters on the second-stage kept burning for a further 190 seconds after the main engine cut-off. This would increase the rocket’s payload capacity by 500 to 800 kg, at the expense of a longer flight distance to reach the orbit.
The DF-5 made its maiden flight on 10 September 1971, but the test was only partially successful. The second test launch on 8 April 1973 ended up with the missile exploding in the mid-air 43 seconds into the flight. Chinese Premier Zhou Enlai ordered the DF-5 development to be suspended, and the 4 remaining test missiles in the same batch to be converted into space launch vehicles under the designation Long March 2.
On 5 November 1974, a Long March 2 vehicle carrying the first FSW satellite was launched from Pad 138 of Jiuquan Satellite Launch Centre. The launch vehicle lost control 6 seconds after lift-off and was self-destructed at T+20 seconds. Subsequent investigation identified the cause for the failure being a disconnected cable for the pitch rate gyro signal in the vehicle’s guidance system.
On 26 November 1975, a second attempt was made, with the Long March 2 launcher successfully placing the satellite into its intended 185 km orbit. Two more successful missions followed in December 1976 and January 1978 respectively.
1967 September: Long March 2 development began
The 1st Academy was tasked with the development of a space launch vehicle based on its DF-5 ICBM design to support the launch of the FSW satellite.
1969 June 14: YF-21 liquid engine first successful ground test
1973: Long March 2 production began
The 1st Academy began to convert DF-5 missiles into space launch vehicles.
1974 November 5: The first FSW mission failed
The first FSW satellite was completed in June 1974 and delivered to Jiuquan Satellite Launch Centre on 8 September, followed by the CZ-2 launch vehicle four days later. The vehicle underwent the initial checkout, before being moved to Pad 138 at Launch Complex 3 (North Launch Site) where it was assembled. After the final checkout of the launch vehicle had completed, it was mated with the payload and fuelled with the propellants.
The launch was originally scheduled for 13:00 local time on 5 November 1974, but the launch countdown was halted at T minus 13 seconds as the satellite suddenly lost power. After some investigation, the issue was rectified and the launch finally took place at 17:40. However, the launch vehicle began to swerve off course only 6 seconds into the flight. The self-destruction system onboard the launch vehicle was trigged at T+20 seconds, destroying both the launch vehicle and its payload.
Later investigation concluded that the accident was caused by a disconnected cable for the vehicle’s pitch rate gyro signal.
1975 November 26: FSW-0-1 mission, the first successful CZ-2 flight
The CZ-2 resumed flight almost exactly one year after the initial failure, successfully placing the 1,790 kg FSW satellite into orbit. The satellite was recovered after a three-day mission.
1976 December 7: FSW-0-2 mission
Second FSW-0 mission, placing an 1,812 kg satellite into orbit.
1978 January 26: FSW-0-3 mission
Third FSW-0 mission and the last CZ-2 flight, before it was replaced by the CZ-2C.