Chang Zheng 4C lifts Gaofen-5-02 satellite to orbit

by Adrian Beil

On Tuesday, September 7 China launched the second Gaofen-5 remote imagery satellite into a 705 km sun-synchronous orbit (SSO). The launch took place at 03:01 UTC on a Chang Zheng 4C and was conducted from Launch Complex 9 at the Taiyuan Satellite Launch Center in China.

The first launch attempt on Monday was scrubbed due to an unknown reason.

Gaofen-5’s purpose is hyperspectral observation of Earth’s environments to track environmental impacts, water quality, and atmospheric changes.

The satellite bus is the SAST3000 and carries seven instruments that can observe the spectrum from infrared to ultraviolet and can measure atmospheric data in 15 different channels.

The Gaofen-5 satellites, which first launched in May 2018, are part of the overall Gaofen family of satellites that are themselves part of the CHEOS program. The program was proposed in 2006 and approved and initiated by the Chinese government in 2010, which led to the creation of the Earth Observation System and Data Center of the China National Space Administration (EOSDC-CNSA).

The goal of the program is to improve the capabilities of Chinese Earth imagery systems in sectors like ocean monitoring, disaster studies, environmental monitoring, and forecasting.

The first Gaofen (Gao fen = high resolution) launch was conducted in April 2013 on a Chang Zheng 2D. Since then, 21 more Gaofen launches have taken place, with the last one being the Gaofen 12 launch in March 2021.

The Chang Zheng 4C rocket that launched Tuesday’s mission stood 45.8 meters tall with a diameter of 3.35 meters. Its liftoff mass was approximately 250,000 kg across three stages.

The Chang Zheng 4C (CZ-4C, or Long March 4C as it is known internationally) is mainly used for low Earth orbit (LEO) and SSO missions.

The first stage of the rocket is 27.91 meters long and has a mass of 182,000 kg, more than two-thirds of the liftoff mass. It is powered by four YF-21C engines which run on dinitrogen tetroxide and unsymmetrical dimethylhydrazine.

The hypergolic mixture produces a liftoff thrust of 2.971 kN with a specific impulse at sea level of 259 seconds.

On top of the first stage sits the second stage, which runs on the same hypergolic fuels as the first stage. It has a length of 10.9 meters with thrust produced by a single YF-24C engine — which contains a YF-22C main engine and four YF-23C vernier engines for steering.

Gaofen 5 02 during pre-launch testing. (Credit: China National Space Administration)

The main engine produces a thrust of 742 kN and a specific impulse of 299 seconds. The four vernier engines have a thrust of 47 kN.

The last stage also uses the same fuel mixture as the previous stages and is 14.79 meters in length with a diameter of 2.9 meters. It is powered by the YF-40 engine, which is a gas generator cycle upper stage engine originally built for the Chang Zheng 1D second stage.

The engine was later repurposed as the third stage for the Chang Zheng 4C. The engine can run up to 412 seconds and produces 100 kN of thrust. It has a specific impulse of 303 seconds in vacuum and allows the stage to place its payloads into the intended orbit(s).

Overall, the Chang Zheng 4C has a success rate of 94% and is capable of launching up to 4,200 kg into LEO and 2,800 kg into SSO. The last failure occurred in May 2019 during the Weixing-33 mission.

After a nominal performance of the first and second stages, the third stage had an unknown failure and the payload did not reach orbit. A replacement satellite was launched only one year later.

Tuesday’s flight lifted off from the Taiyuan Satellite Launch Center in Shanxi Province in northern China. It was founded in 1966 and is used to launch many vehicles of the Chang Zheng family, including the Chang Zheng 1, 4, and 6.

A portion of the Taiyuan Satellite Launch Center (Credit: Digital Globe / GoogleEarth)

Officially, the site is used to launch meteorological and scientific payloads into polar orbits and as a test area for intercontinental ballistic missiles (ICBM).

Taiyuan hosts a technical area for the integration of rockets and payloads as well as communication, infrastructure, and launch complex support.

This was the 10th mission of the Chang Zheng 4 this year, the 32nd orbital launch for China in 2021, and the 36th mission of Chang Zheng 4C.

(Lead image: Engine ignition on the CZ-4C just prior to liftoff with Fengyun 3E.)

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