Chang Zheng 3B lifts Shijian 21 to orbit

by Adrian Beil

Without any prior announcements, China launched another Chang Zheng 3B/E rocket with the Shijian 21 payload to Geostationary Transfer Orbit (GTO). The rocket took off at 01:27 UTC on October 24 from the Xichang Satellite Launch Center’s LC-2.

The launch was called a success two hours later and it was confirmed that the payload, Shijian 21, will be used to mainly test and verify space debris mitigation technologies. The serial number of the satellite is Y83, and the weight, final orbit, and further details on the satellite’s function are unknown at this point.

The name “Shijian” translates to “Practice” and is a series of missions that are used to verify and practice new technologies for later missions. The first Shijian satellite that was launched was only the second Chinese satellite ever. It used a Chang Zheng 1 in March 1971, which was the last of two flights for this line of rockets.

The most recent Shijian prior to Shijian 21 launched on a Chang Zheng 5 in December 2019 and was used to perform the maiden flight of the DFH-5 ultra-high-performance satellite, which uses an ion propulsion system. At that time it was a very critical launch, as it came after two launch failures in a row of the Chang Zheng 5, which was scheduled for very important missions later, such as the first test flight of the next-generation crewed spacecraft in 2020.

The Chang Zheng 3B/E at LC-2 prior to launching Shijian 21

Chang Zheng 3B/E, also known as the 3B/G2, is an upgraded version of the previously flown 3B variant. It features an upgrade to all of the four liquid rocket boosters and the center stage and increases the payload capacity of 11,500 kg to Low Earth Orbit (LEO) and 5,500 kg to GTO.

The 3B/E is mainly used to bring communications, telecommunications, and experimental satellites to GTO or directly to Geostationary Orbit (GEO), with a few uses for Medium Earth Orbit (MEO) as well. So far it has launched 68 times, including this launch, of which 66 were a success. This makes it the most flown rocket configuration of the Chinese space program.

In the past, it was also used for the historic launch of the Chang´e 3 mission, which was China’s first lunar lander. It was launched in December 2013 and successfully soft-landed on the moon. Together with the lander, it launched a 140 kg lunar rover. It also launched the follow-up mission of Chang´e 4, which landed on the far side of the moon, making China the first nation to perform a landing there.

Its last failure was the Palapa-N1 launch in April 2020, in which the third stage of the rocket failed to ignite, which resulted in a complete loss of the mission, making it the only complete failure of the 3B/E.

Before that, the launcher had an issue with one of its Reaction Control System (RCS) during the Chinasat-9A mission. The satellite was able to use its onboard propellant to reach the target orbit with the rocket underperforming, making the flight only a partial failure.

One of the four side boosters is transported to LC-2 for stacking

The rocket, built by the China Academy of Launch Vehicle Technology, stands 56 meters tall with a liftoff mass of 458,970 kg. It can feature up to four stages, depending on what the needs for the launches are.

The first stage of the rocket is using a cluster of four YF-21C engines which provide a liftoff thrust of 2961.6 kN and a specific impulse of 260.69 seconds. It has a height of 24.76 meters and a diameter of 3.35 meters. 

Attached to the main stage are the four side boosters, which run on liquid propellants as well. They use the same engine, based on the YF-20C, called YF-25. They are 16.1 meters tall with a diameter of 2.25 meters each, and together they provide the same thrust as the center core, which brings the liftoff thrust of the vehicle up to 5923.2 kN.

On top of the first stage sits the second stage, which is ignited roughly two and a half minutes into the flight. It has a height of 12.92 meters with a diameter of 3.35 meters and uses a single YF-22E engine to boost the payload into orbit. The engine provides 742 kN of thrust and is assisted by four YF-23F vernier engines that steer the rocket during this phase of the flight.

The center stage and four booster ignite to lift Chang Zheng 3B/E and Shijian 21 off the pad

All engines on the first and second stage, as well as the optional fourth stage, use a combination of dinitrogen tetroxide (N2O4) and dimethylhydrazine (UDMH). This hypergolic combination burns as soon as it contacts each other and is highly poisonous for humans. It also results in the rocket creating a characteristic red smoke during liftoff.

After the second stage finishes its job, the 12.37-meter long third stage ignites its two YF-75 engines. They provide 78.45 kN of thrust each at an impressive specific impulse of 438 seconds. It also has shutdown and restart capabilities which helps for complicated orbital insertions which require multiple burns. It runs on liquid hydrogen and liquid oxygen.

There is a possibility to add a fourth optional Yuanzheng-1 upper stage, which can be used as a kick stage to boost satellites that are lacking the capabilities to climb to their desired orbit on their own. It uses a single YF-50D engine with a thrust of 6.5 kN. It is used on rare occasions and has not been used since December 2019.

Like all Chang Zheng 3B launches, the complex used for this mission was the Xichang Satellite Launch Center in southern China. It flew from LC-2, which is used for the CZ 2E, CZ-3A, CZ-3B, and CZ-3C. It is one of the three launch complexes in Xichang with two of them being active now that LC-1 is being used as a viewing area. The rocket and payload were transported by railway to the launch center and integrated earlier this month.

Related Articles