ROCKET ENGINES

Sergei Korolev, Russia’s great chief designer, once remarked that at the heart of a successful space program lay a sound rocket engine. Russian rocket engines were designated RD – (raketa dgvatel), or “rocket engine”, from -1 onward and China has followed a similar system, using the designator YF-, or yeti fadong (“liquid-type engine”). Data on Chinese rocket engines are much less satisfactory than the Russian data. China has developed a very small number of rocket engine types, but with many variants. In essence, there are four types: the YF-1 to YF-3 series used at the very beginning; the YF-20 to YF-24 series used for the CZ-2 and CZ-3; the YF-40 series used for the CZ-4; and the YF-73 and YF-75 series used for the CZ-3 upper stage (incoming engines related to the Long March 5 are discussed in Chapter 10). These rocket engines have been adapted and modified to serve the entire range of the Long March families. In addition, China has developed a small number of solid – rocket motors and minor engines.

The YF-20 engine, which dates to 1965, with its variants, has been used for the Long March 2, 3, and 4 rockets, being introduced on the Long March 2C in 1975. The YF-20 has a thrust of 70 tonnes and uses UDMH with nitrogen tetroxide as oxidizer. For the Long March 2, the Chinese clustered four YF-20s together to provide a lift-off thrust of 280 tonnes (this configuration was called the YF-21 or 20A). An improved version, the YF-20B, with 7% more thrust, was developed for the Long March ЗА, 3B, and 4 (when clustered, they may also be called the YF-21B). The YF-20B was introduced on the Long March 2D in 1992 and a single YF-20B engine is used on each strap-on booster for the Long March 3B. These are big engines, weighing nearly 3 tonnes (2,850 kg).

For the second stage, the YF-22 engine is used: it is a modification of the YF-20 and is designed to light at altitude. It was introduced as far back as 1975 on the Long

March 2C second stage. Later versions were called the YF-23 and YF-24 series, several with A and В sub-designators. Note that, in directories of Chinese rockets, YF-20, 21, 22, 23, and 24 designators are often seen, but they belong to the same family, the differences between them being small.

The YF-40 is the third-stage engine used on the Long March 4 rocket introduced in 1988. Third-stage engines are relatively small in size and thrust compared to the first and second stages, but they have longer burn times, in the order of 320 sec. These are small engines, 166 kg in weight, 1.2 m long, and 65 cm in diameter.

When the Long March 3 flew in 1984, China became the third country in the world to tame liquid hydrogen-fuelled upper stages after the United States (Centaur) and Europe (Ariane). Not only are hydrogen fuels difficult to master, but a complication is that the third stage must be restartable – firing once to enter Earth

orbit, a second time about 50 min later for the transfer to geosynchronous orbit. Design of a third stage, restartable hydrogen-fuelled engine, the YF-73, began in 1965, but testing of the new designs was not completed until 1979 and, even then, the first flight test failed in January 1984. This problem must have been promptly identified and remedied, for the next mission, four months later, went perfectly. The thrust of the YF-73 liquid-hydrogen third stage was 4.5 tonnes, with a burn time of 13.3 min. An improved version, the YF-75, was introduced with the Long March ЗА in 1994 and was since used by the 3B. The YF-75 weighs 550 kg, is 2.8 m tall, and 3 m in diameter, and has a thrust of 8 tonnes. Restarting problems have, disappointingly, recurred from time to time (though such problems are not entirely absent from the other space programs, especially Russia’s).

China has developed two families of solid-rocket motor engines: the GF series and the PKM (Perigee Kick Motor). With the beginning of flights to 24-hr orbit in 1984, a new generation of solid-fuel rockets was required to carry out the maneuvers necessary to ensure that communications satellites accurately reached their final orbital destinations. The PKM was developed to complete the transfer of comsats to geostationary orbit. Built by the Haxi Chemical and Machinery Company, it is 1.7 m

in diameter, 2.5 m long, and weighs 5,978 kg (5,444 kg is propellant). The GF series was used as a final stage to get the Feng Yun 2 series into 24-hr orbit (the 729-kg GF-36) and the smaller GF-14, 23, and 23A solid-rocket engines have been used as retrorockets for the FSW 0, 1, and 2 series, respectively. The GF-15 solid-rocket motor (500 kg) was developed as the apogee motor for the Dong Fang Hong 2 comsats and the 15B for the Dong Fang Hong 2A.

Overall, Chinese rocket-engine development has been conservative, rather like in Europe, leaving cutting-edge development to the original masters of rocket-engine design: Russia. Evidence of an interest in innovation came at the Asian Joint Conference on Propulsion and Power, held in Xian in March 2012, when reports came out of Chinese interest in developing a methane engine. Exotic engines had been developed in Russia, first by Valentin Glushko’s Gas Dynamics Laboratory (the RD-301), later resumed in the Franco-Russian Ural engine development program. China began its work on electric propulsion in the 1960s, but did not progress until a pulsed plasma thruster, the MDT-2A, was first run in the 1980s and an arcjet in the 1990s.