Featured image credit: Ren Hui / Xinhua
Lift Off Time | September 20, 2022 – 23:15 UTC September 21, 2022 – 07:15 BJT |
|---|---|
Mission Name | Yunhai-1 03, a Chinese weather satellite |
Launch Provider | China Aerospace Science and Technology Corporation (CASC) |
Customer | Unknown, probably the Chinese Government |
Rocket | Long March 2D |
Launch Location | Site 9401 (SLS-2), Jiuquan Satellite Launch Center, China |
Payload mass | Unknown, a maximum of 1,300 kg (2,900 lbs) based on orbital parameters |
Where did the satellites go? | ~765 km circular Sun-synchronous orbit (SSO) at 98.5º |
Did they attempt to recover the first stage? | No, first stage recovery is not a capability of the Long March 2D |
Where did the first stage land? | It crashed on land in central China |
Did they attempt to recover the fairings? | No, fairing recovery is not a capability of the Long March 2D |
Were the fairings new? | Yes |
This was the: | – 65th launch of a Long March 2D – 119th orbital launch attempt of 2022 (115th successful) |
Where to watch | Unofficial Replay |
How Did It Go?
The Yunhai-1 03 weather satellite was successfully launched atop a Long March 2D rocket serial numbered Y76 by the China Aerospace Science and Technology Corporation. The launch vehicle lifted-off from the Jiuquan Satellite Launch Center, in China, and was injected into a ~765 km Sun-synchronous orbit at 98.5 degrees of inclination, joining another two Yunhai-1 spacecraft.
What Is The Yunhai-1 Satellite?
Because of how little public information is available about the Yunhai-1 satellite, it leaves some room to read between the lines, and assume the spacecraft is used for military application. Nevertheless, official sources (e.g., see here and here) have stated its purpose is to take environmental measurements related to the atmosphere, the oceans, and space, as well as disaster prevention and mitigation, and other scientific tasks.
Probing With Yunhai-1
Conversely, in other cases this spacecraft is classified as a global navigation satellite system radio occultation (GNSS-RO) weather satellite. Such a detection technique profits from these systems, from which the most popular is probably GPS. However, there are other very important ones like the Russian GLONASS, the Chinese BeiDou, and the European Galileo. Each of them works by having a constellation where every satellite emits a signal, which is received on the surface. Typically, this is translated into information such as positioning, navigation, or timing.
GNSSs place their satellites in what is called a medium-Earth orbit (MEO), at about 20,000 km in altitude, although the characteristics of the used orbits change from system to system. On the other hand, a Yunhai-1 satellite — or any other GNSS-RO one — is stationed closer to the planet. These are equipped with sensors that await the signal coming from the navigation system. In order for this electromagnetic wave to carry information about the atmosphere, it must have traveled through it, becoming influenced in the process.
Adequately selected instruments are then capable of reading the outcome from the signal-atmosphere interaction. As a result, a 3D map with very accurate measurements of parameters such as temperature, pressure, humidity, and so on, can be created. In this way, it enables the study of weather forecasting and climate monitoring, as well as ionospheric processes, or space weather. Adding to these capabilities, GNSS-RO also provides coverage where ground stations or balloons cannot.
Hardware On Yunhai-1
Developed by the Shanghai Academy of Spaceflight Technology (SAST), a subsidiary of CASC, the Yunhai-1 is believed to be outfitted with two deployable solar arrays and batteries for storage of the generated electricity. In terms of its instruments, the Shanghai Institute of Technical Physics (SITP), part of the Chinese Academy of Sciences, developed two of them:
- Infrared Earth horizon sensor: spacecraft usually need to have a precise idea of their orientation. Only by knowing this, their instruments can be pointed to where it is useful. This sensor helps in that task by finding where the horizon of our planet is. Other sensors need the light of the Sun to do this, which means they cannot work in eclipse, and weakness the infrared ones do not share.
- Infrared scanning radiometer: when meteorology is involved, the measurement of temperatures becomes a very important task. Heat emission in infrared form happens when something has a temperature – basically always. A sensor detecting this spectrum can consequently be used to that end. Sometimes, however, the presence of clouds could lead to contamination in the values obtained, and microvawes can then be used instead – except when the effect of the clouds is of interest.
Bus Controversy
The Yunhai-1 weather satellite is reported to be built based on the CAST2000 bus. According to China Great Wall Industry Corporation (CGWIC), this platform could mass up to 600 kg, allowing up to another 400 kg of payload (instruments) mass. Even with these specifications matching the Long March 2D’s capabilities for a SSO launch, a minor detail does not seem to add up. In an animation broadcasted by CCTV during the Yunhai-1 02 deployment, the represented spacecraft looked different when compared to the one portrayed in CGWIC’s site.
Other Yunhai-1 Launches
As indicated by the “03” numeral after the name of the spacecraft, Yunhai-1, this is the third satellite of the same type placed in orbit. In the following table all of them are listed. “Jiuquan” stands as a short form for Jiuquan Satellite Launch Center.
| Satellite | Launch Site | Launch Vehicle | Present Orbit |
| Yunhai-1 01 | Site 9401 (SLS-2), Jiuquan | November 11, 2016, 23:14 UTC | SSO, ~784 km x 98.6° |
| Yunhai-1 02 | Site 9401 (SLS-2), Jiuquan | September 25, 2019, 00:54 UTC | SSO, ~790 km x 98.5° |
| Yunhai-1 03 | Site 9401 (SLS-2), Jiuquan | September 20, 2022, 23:15 UTC | SSO, ~765 km x 98.5° |
Yunhai-1 02 Break-Up
On March 18, 2021 at 7:41 UTC, two objects cataloged in low-Earth orbit (LEO) were going to pass really close to one another — 1 km apart or less. On the one hand, there was a smaller piece that came off of the second stage of the Zenit-2 rocket that launched the Tselina-2 satellite in September, 1996. Even when the stage was left in a higher LEO, this object’s orbit decayed, lowering its altitude year after year. On the other hand, the Yunhai-1 02, launched not two years prior to this event.
After the mentioned date and time, several new objects were detected originating from the intersection of these two orbits. It followed, that they had collided and the Yunhai-1 had broken up. Despite being a small part of the Zenit-2, because of the velocity these bodies have in space, any one hitting another one assuredly leads to a catastrophic end.
Against all odds, this Yunhai-1 satellite did not meet its demise. What is more, not long after the break-up, the spacecraft was reported maneuvering and transmitting radio signals. As previously shown, to this day it is still circling the Earth, most probably carrying on with its intended task.
What Is The Long March 2D?
Developed and manufactured by SAST — based on the Long March 4A — the two-stage Long March 2D purpose was to serve the SSO and LEO market segments in the lower range of the medium-lift launch vehicles. It is possible to find it mentioned in its short form “LM-2D,” or by its Chinese name “Chang Zheng 2D,” or abbreviated “CZ-2D.”
| Characteristic | Value |
| Stage quantity | 2 (3, optional) |
| Length [m] | 41.06 |
| Lift-off mass [t] | 250 |
| Mass to LEO [kg] | 3,700 |
| Mass to SSO [kg] | 1,300 |
| Fuel | UDMH (all stages) |
| Oxidizer | N2O4 (all stages) |
Originally provided with the type-A fairing — 2.90 m in diameter — a larger new one was later offered to customers — type-B, 3.35 m in diameter. Further developments included a second stage’s attitude control motors, and a passivation and deorbiting system for this same stage.
In spite of lifting off mainly from the launch center in Jiuquan, there have been Long March 2D rockets launching from the Taiyuan and the Xichang ones. Derived from the flight-proven technology of the Dong Feng 5 ICBMs, it only suffered a partial failure on December 28, 2016, otherwise keeping a flawless record since its maiden flight on August 9, 1992.
Deorbiting The Second Stage
Recent in-flight tests of a sail for increasing the orbital decay of the second stage of the Long March 2D have been reported for Yaogan 35 launches. That is, at least, apparently valid for Groups 02, 03,and 04. Such a device is a Chinese effort in reducing space debris generation.
First Stage
Four YF-20 engines power this first stage, working under a gas generator cycle, and using hypergolic propellants (as already mentioned) with an ISP of 260 s at sea level. This group is identified as the YF-21 engine, its C version being the one installed in this stage. Further information can be seen in the comparative table.
Second Stage
When adapted to a vacuum environment, where the second stage operates, the YF-20 engines are designated as YF-22. These feature a thrust of ~742 kN and an ISP of 300 s. Vernier engines give a stage attitude control capabilities when the main engine does not gimbal. One such vernier is the YF-23, generating ~47 kN of thrust and with an ISP of 289 s. These two engines are part of what is called the YF-24 engine, which is solely fed the hypergolic propellants listed before.
| Stage Number | Length [m] | Diameter [m] | Propellant Mass [t] | Engine Name | Thrust [kN] |
| 1 | 27.91 | 3.35 | 182.0 | YF-21C | 2,961.6 |
| 2 | 10.90 | 3.35 | 52.7 | YF-24C | ~789.1 |
Third Stage — Optional
The China Academy of Launch Vehicle Technology (CALT) is responsible for having developed the Yuanzheng (YZ) upper stage. Adapted to ride atop the Long March 2D — its third version, YZ-3 — it adds restarting capabilities, allowing for higher energy final orbits, or circularization maneuvers. These are achieved with burns of 6.5 kN in thrust, burning the same two hypergolic propellants already indicated in this text.
Yuanzheng 3 flew only once: on December 29, 2018, stacked onto the Long March 2 Y35, and launching Yunhai-2 satellites and Hongyan-1.
