Long March 4B

Shiyan-6-03 | Long March 4B

Lift Off Time/Launch Window
(Subject to change)
April 8, 2021 – 23:01 UTC
April 9, 2021 – 07:01 BJT
Mission Name
Launch Provider
(What rocket company is launching it?)
China National Space Administration (CNSA)
(Who’s paying for this?)
China Aerospace Science and Industry Corporation (CASIC)
Long March 4B
Launch Location
Launch Complex 9, Satellite Launch Center, Xinzhou, China
Payload mass
Unknown, up to 2,800 kg (6,200 lbs) to SSO
Where is/are the satellite(s) going?
Sun-Synchronous Orbit (SSO) at ~1,450 km, with a 101.65° inclination
Will they be attempting to recover the first stage?
No, the Long March family does not support booster recovery
Where will the first stage land?
It will crash land over North East China
Will they be attempting to recover the fairings?
No, the Long March family does not support fairing recovery
Are these fairings new?
How’s the weather looking?
Winds are predicted to be 6.5 km/hr (4 mph).
Temperature is expected to be 5.5 °C (42 ° F)
The cloud cover is expected to be only 12%.
This will be the:
– 4th launch of a Long March 4 (any variant) in 2021
– 1st launch of a Long March 4B in 2021
– 41st launch of a Long March 4B ever
– 29th orbital launch attempt in 2021
Where to watch
Livestream (if available)

What does all this mean?

China National Space Administration (CNSA) is launching a payload known as Shiyan-6-03 to a Sun-Synchronous Orbit (SSO). The payload will orbit with an inclination of 101.56°, at an approximate altitude of 1,450 km. The launch is from the Taiyuan Satellite Launch Center in Xinzhou, North East China.

Shiyan-6-03 payload?

We know nothing at all about what Shiyan-6-03 actually is. There is no public information available as the Shiyan-6 satellites are classified.

We do know that its predecessor, Shiyan-6-02, was launched on a Long March 2D rocket into a different orbit (484 km perigee, 36,000 km apogee) than the one planned for this mission. This suggests that the Shiyan-6 series may be a technology program rather than a set of identical satellites.

What is the Long March 4B?

The Long March 4B is a 3-stage liquid-fueled rocket which has been in service since 1999. It uses hypergolic fuels in all three stages.

Long March 4B and Shiyan-6-03
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) as oxidizer.

It has four engines designated YF-21C. These engines use the Gas Generator combustion cycle. The YF-21 is a designation that refers to a cluster of four YF-20 engines mounted together.

The stage as a whole has 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 (the 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 control. The YF-22 is the high altitude version of the underlying YF-20 engine mentioned for 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.

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