Gaofen-11-03 | Long March 4B

Lift Off Time
(Subject to change)
November 19, 2021 – 01:50 UTC | 09:50 BJT
Mission Name
Gaofen-11-03, a Chinese remote sensing satellite
Launch Provider
(What rocket company is launching it?)
China Aerospace Science Corporation (CASC)
(Who is paying for this?)
China National Space Administration as part of the China High-resolution Earth Observation System
Long March 4B
Launch Location
LC-9, Taiyuan Satellite Launch Center, China
Payload mass
Likely around ~1,100 kg, but a maximum of 2,800 kg (6,100 lbs) based on orbital parameters
Where is the satellite going?
Unknown sun-synchronous orbit, likely ~400 km circular
Will they be attempting to recover the first stage?
No, this is not a capability of the CASC
Where will the first stage land?
It will crash on land in North-West China
Will they be attempting to recover the fairings?
No, this is not a capability of CASC
Are the fairings new?
This will be the:
– 44th launch of a Long March 4B
– 115th orbital launch attempt of 2021
Where to watch:
In the unlikely event of a livestream it will be listed here

What does all this mean?

The China Aerospace Science Corporation will launch an Earth observation satellite on their Long March 4B rocket. The Gaofen-11-03 mission will launch from the Taiyuan Satellite launch center, in China, to a Sun-synchronous low-Earth orbit with an unknown altitude. This launch will mark the 31st launch of a Gaofen satellite.

Gaofen Satellites

The Gaofen constellation is a series of Chinese civilian Earth observation satellites. The constellation currently consists of just over 30 satellites, with the Gaofen 02C satellite failing to reach orbit in September of 2020. The Gaofen constellation will provide Chinese civilians with near real time observations for geographical mapping, resource surveying, environmental research, climate change monitoring, and several other observation activities.

While not much is known about the Gaofen satellites, a lot can be learned from the Gaofen 1 satellites, which are similar. Each satellite has a mass of roughly 1,100 kg (2,400 lbs) and is based on the CAST-2000 extended spacecraft bus. The Gaofen-11-03 satellite has a lifespan of roughly 5 to 8 years and contains two sets of cameras. The first set of high resolution cameras have a swath of roughly 69 km (43 miles) and the second set of wide field of view cameras have a swath of 830 km (516 miles).

The Gaofen-11-03 satellite is also equipped with a 3-axis stabilization which ensures that the satellites are always pointed towards the Earth. Due to this, an individual satellite is able to revisit every part of the Earth in under 4 days.

A Gaofen-1 satellite (Credit: CAST)

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). All the engines together 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.

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