Haiyang 2D | Long March 4B

Lift Off Time/Launch Window
(Subject to change)
May 19, 2021 ~ 03:55 UTC | 11:55 BJT
Mission Name
Haiyang 2D
Launch Provider
(What rocket company is launching it?)
Chinese Aerospace Science and Technology Corporation (CASC)
(Who’s paying for this?)
Chinese Academy of Space Technology (CAST)
Long March 4B
Launch Location
Site 9401 (SLS-2), Jiuquan Satellite Launch Center, China
Payload mass
1,575 kg (3,400 lbs)
Where is the satellite going?
1,300 km (800 mi) Sun synchronous orbit (SSO) at a 66° inclination
Will they be attempting to recover the first stage?
No, this is not a capability of the Long March 4B
Where will the first stage land?
It will crash downrange in mainland China.
Will they be attempting to recover the fairings?
No, this is not a capability of the Long March 4B
Are these fairings new?
How’s the weather looking?
No information available
This will be the:
– 4th Haiyang 2 satellite
8th Haiyang satellite
– 400th Chinese orbital launch attempt
– 42nd launch of a Long March 4B rocket
– 45th orbital launch attempt of 2021
Where to watch
If available, an official livestream will be listed here

What’s all this mean?

China will be attempting to launch another Earth observation satellite from Jiuquan Satellite Launch Center, China. Haiyang 2D will be lofted into orbit by a Long March 4B rocket, capable of lifting up to 4,200 kg (9,300 lbs) to low Earth orbit (LEO). Haiyang 2D is built and operated by the Chinese Academy of Space Technology (CAST) and will work alongside previously launched Haiyang satellites to capture valuable data about Earth.

What is Hiayang 2D?

Haiyang 2D is part of the Haiyang (commonly referred to as HY) satellite family, which is a family of Earth observation satellites. Haiyang (meaning “ocean”) satellites are built and operated by the Chinese Aerospace Science and Technology Corporation (CASC). Each of the previous HY satellites have housed various instruments for observing different aspect of the Earth. The main purpose of the HY 2 satellites is to monitor the wind, temperature, and height of the ocean’s surface using microwave sensors.

SatelliteLaunch VehicleOrbitStatusLaunch Date
Haiyang 1ALong March 4BSSONot OperationalMay 15, 2002
Haiyang 1BLong March 2CSSONot OperationalApril 11, 2007
Haiyang 2ALong March 4BSSOOperationalAugust 16, 2011
Haiyang 1CLong March 2CSSOOperationalSeptember 6, 2018
Haiyang 2BLong March 4BSSOOperationalOctober 25, 2018
Haiyang 1DLong March 2CLEOOperationalJune 10, 2020
Haiyang 2CLong March 4BSSOOperationalSeptember 21, 2020
haiyang 2C, haiyang 2D, casc
A render of the Haiyang 2C satellite, which is identical to HY 2D. (Credit: CASC)

What instruments are on Haiyang 2D?

The Haiyang 2D satellite is a slightly refined version of the previous HY 2A and 2B satellites. It does not have the Microwave Radiometer Imager, but has a different microwave imager to perform subtly different functions, which are unknown. Also unlike its predecessors, HY 2A and 2B, Hiayang 2D will feature 2 solar panels instead of one.

Doppler Orbitography and Radiopositioning Integrated by Satellite

The Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) is an instrument designed to aid the satellite in gathering positional data on its precise location in orbit. It does this by measuring the doppler shift of radar waves from various ground tracking stations. When this data is combined with the oceaongraphy data, scientists can pinpoint exact locations and angles of where each measurement is taken. DORIS has a mass of 91 kg (200 lbs) and draws 42 watts of power.

Radar Altimeter

One of the main instruments on the Haiyang 2D satellite is the Radar Altimeter (Alt). This instrument measures the wave height and the wind speed on the surface of the ocean below. It can operate in two frequencies, 13.58 Ghz and 5.25 GHz.


Similar to the radar altimeter, the scaterometer (SCAT) also has the capability to measure the ocean’s surface wind level. However, it measure’s much larger areas of the ocean including anywhere from 25 km to 50 km. SCAT only operates in the Ku band of 13.58 GHz.

Calibration Microwave Radiometer

The Calibration Microwave Radiometer (CMR) is an instrument used for correcting any inaccuracies of the radar altimeter. CMR is not affected by the water vapor in the atmosphere, while the radar altimeter can get occasional inaccurate results. This way, the CMR can correct for any false data points that the radar altimeter receives. The resolution of the CMR is only 25 km and can operate at three different frequencies 18.7, 23.8, and 37 GHz.

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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