Long March 3B/E launching APStar-9

Tianhui-2-02 | Long March 4B

Lift Off Time
February 05, 2021 – 22:32 UTC | 06:32 BJT
Mission Name
Tianhui-2-02, a set of Tianhui-2 Earth observation satellite
Launch Provider
(What rocket company launched it?)
China National Space Administration (CSNA)
(Who paid for this?)
Chinese Ministry of Defense
Long March 4B
Launch Location
LC-9, Taiyuan Satellite Launch Center, China
Payload mass
Unknown, up to 2,800 kg (6,200 lb) to Sun-synchronous orbit
Where did the satellite go?
490 x 505 km sun-synchronous orbit
Did they attempt to recover the first stage?
No, the boosters of the rocket are not recoverable
Where did the first stage land?
It will crash back over land in North-West China
Did they attempt to recover the fairings?
No, the fairings are not recoverable
Was the fairings new?
This was the:
– 43rd flight of a Long March 4B
– 78th orbital launch attempt of 2021
Where to watch
There is no replay available

How did it go?

The China National Space Administration successfully launched the Tianhui-2-02 satellites atop a Long March 4B. It is an Earth observation satellite that was deployed into a 490 km by 505 km sun-synchronous orbit.

Tianhui Satellites

The Tianhui (or “sky drawing”) constellation of satellites are Earth observation satellites built by Dong Feng Hong and operated by the People’s Liberation Army, which is part of the Chinese ministry of defense. The Tianhui-2-02 satellites will monitor the ground in both the visible and infrared spectrum, with two cameras. With these cameras the satellite has a resolution of under 5 meters and a field of view of roughly 25°. The satellite will also survey human activities.

Due to the nature of the payload, very little is known about the actual satellite. However, it is known that the satellite is equipped with two solar arrays and the two aforementioned cameras.

What is the Long March 4B?

The Long March 4B is a 3-stage, medium-lift, liquid-fueled rocket, which has been in service since 1999. It uses hypergolic fuels in all three stages. Long March 4B is an expendable launch vehicle, meaning that none of the stages are recovered.

Long March 4B haiyang 2D
Long March 4B (Credit: Wang Jiangbo/Xinhua)

Stage 1

The Long March 4B’s first stage is 27.91 m long, with a diameter of 3.35 m. It uses unsymmetrical dimethyl hydrazine (UDMH) for fuel and nitrogen tetroxide (N204) for an oxidizer. It has four engines designated YF-21C that use the Gas Generator combustion cycle. For more information on different types of engines, check out Everyday Astronaut’s video and article, “Is SpaceX’s Raptor engine the king of rocket engines?”

The YF-21 is a designation that refers to a cluster of four YF-20 engines mounted together. The stage as a whole has a thrust of around 2,960 kN (666,000 lbf). Taking all the engines together, they have a combined specific impulse of 2,550 m/s (8,400 ft/s).

Stage 2

The second stage has a length of 10.9 m and a diameter of 3.35 m (same as the first stage). It also uses UDMH and N2O4 as fuel and oxidiser, respectively. The stage uses a single YF-24C engine. YF-24C is a designation that refers to a module of a YF-22C main engine and a set of YF-23C Vernier thrusters for attitude control. The YF-22 is the high altitude version of the underlying YF-20 engine used on the first stage. The thrust of the second stage is 742 kN (166,800 lbf). The specific impulse for the stage is 2,942 m/s (9,650 ft/s) for the main propulsion elements and 2,834 m/s (9,300 ft/s) for the Vernier thrusters.

Stage 3

The third stage is 4.79 m tall, and has a diameter of 2.9 m. This stage again uses UDMH and N2O4 as for the two previous stages. The stage uses a pair of YF-40 engines. Each of these engines is a dual combustion chamber, in which each combustion chamber can gimbal for control authority. The YF-40 has a thrust of 103 kN (23,000 lbf) and a specific impulse of 303 seconds.

Rocket section by Andy Law

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