Yunyao Aerospace Constellation

Quick facts

Overview

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Summary

Mission Capabilities

The YunYao-1 series represents the first phase of the YunYao Aerospace Constellation. Each satellite in the series is equipped with a GNSS-R and GNSS-RO instrument, combined into a single unit called YunYao Receiver.

YunYao Receiver collects temperature data from the stratosphere and upper troposphere, humidity data from the lower troposphere, and also performs ionospheric sounding and surface parameter measurements. It can simultaneously receive radio signals from the Global Positioning System (GPS), the BeiDou Navigation Satellite (BDS), the Global Navigation Satellite System (GLONASS), and Galileo. The instrument is highly accurate with high vertical resolution. The data it collects is used in numerical weather prediction (NWP) centers, and has helped improve the accuracy of global weather forecasts.

Performance Specifications

The GNSS-R payloads use a 4x5 antenna array, while the GNSS-RO payloads use a 3x1 antenna array. To expand Doppler search ranges, the YunYao program incorporates raw intermediate frequency (IF) data.

All of the satellites of the YunYao-1 series operate across 12 sun-synchronous orbits at an orbit altitude of approximately 500 km and an orbit inclination of 50 degrees.

Overview

The YunYao Aerospace Constellation is a commercial network of LEO satellites designed to collect highly-accurate meteorological data on the Earth's atmosphere and ionosphere through the use of YunYao GNSS-R and GNSS-RO instruments. The development of the constellation began following a successful launch of five experimental satellites in 2020, which carried YunYao payloads, including China’s first commercially deployed GNSS-RO instruments. The nano-satellites were developed and manufactured by Chang Guang Satellite Technology, which also produced the J1-01B satellite, which carried YunYao’s first commercial GNSS-R instrument into orbit. 1) 2) 4) 5) 13)

Launch

The majority of YunYao-1 satellite have launched from the Jiuquan Launch Center in Gansu Province, China. YunYao-1 satellites have also launched from the Yellow Sea aboard the Dong Fang Hang Tian Gang heavy load carrier, as well as aboard Long March-6 rockets from the Taiyuan Space Center in Shanxi Province, China. YunYao-1 15 to 17 were relaunched following a Hyperbola-1 rocket failure on July 10, 2024. Additionally, YunYao-1 x1 through x6 failed to reach orbit after a Lijian-1 rocket lost altitude three seconds after ignition on December 27, 2024, due to a faulty battery. 7) 8) 9) 10) 11) 12)

Mission Status

• December 27, 2024: The YunYao x1 through x6 satellites failed to reach orbit due to a malfunction of the Lijian-1 rocket, operated by CAS Space. The rocket lifted off from the Dongfeng Commercial Space Innovation Test Area of the Jiuquan Satellite Launch Center at 20:00 local time. An internal investigation concluded that a faulty battery powering a third-stage servo caused the failure. CAS Space released a statement, which noted that “We can confirm that the first two stages were nominal. Stage 3 lost attitude three seconds after ignition and the self-destructing mechanism was activated.”. 14)
• July 10, 2024: YunYao-1 15 to 17 failed to reach orbit following a Hyperbola-1 rocket failure, marking iSpace’s fourth launch failure in seven attempts. The launch took place at the Jiuquan Launch Center in the Gobi Desert. "The first, second and third stages of the rocket flew normally, but the fourth stage worked abnormally, and the launch mission failed," iSpace stated in an update following the unsuccessful launch. 14)
• July 26, 2022: The GNSS-RO data collected by YunYao’s satellites has been evaluated by the China Meteorological Administration as being at an international advanced level. 14)
• December 7, 2021: The first satellite of the YunYao-1 series has been launched, marking the beginning of the YunYao Aerospace Constellation program. 14)

Sensor Complement

Global Navigation Satellite System Reflectometry (GNSS-R)

The GNSS-R instrument aboard YunYao-1 series satellites is a passive sensor designed to collect atmospheric and surface data by utilizing reflected signals from Global Navigation Satellite Systems (GNSS), including Global Positioning System (GPS, operated by the USA), BeiDou Navigation Satellite System (BDS, operated by China), Globalnaya Navigazionnaya Sputnikovaya Sistema (GLONASS, operated by Russia), and Galileo (operated by Europe). The instrument observes characteristics such as signal delay and Doppler shift and the receiver constructs Delay Doppler Maps (DDMs), which show the distribution and shape of reflected signal energy. DDMs are influenced by the dielectric properties and roughness of the reflecting surface, allowing for the collection of geophysical data, such as sea state, ocean altimetry, soil moisture, or wind speed. 1) 15)

GNSS-R functions as a bi-static radar system with significant spatial separation between signal transmitters and the receiver. The technology supports multi-static observations, allowing YunYao-1 satellites to receive signals from multiple GNSS satellites simultaneously, improving coverage and temporal resolution. The integration of BDS has significantly enhanced detection capabilities over East Asia and Oceania. The increase in supported GNSS sources also demands receivers with higher channel capacity to handle simultaneous reflections. 1) 15)

To expand Doppler search ranges, the YunYao program incorporates raw intermediate frequency (IF) data. This approach enables more efficient processing and higher-resolution DDM generation. The system uses GPU-based DDM generation methods, which allow real-time processing and adjustable resolution suited to specific applications. 1) 15)

The first GNSS-R payload developed by YunYao was launched as a secondary instrument aboard the Jilin-1 01B satellite (J1-01B) on July 3, 2021, from the Taiyuan Satellite Launch Center. Orbiting at an altitude of approximately 500 km, the payload used a 4x5 antenna array to collect reflected signals and generate DDMs based on the satellite's orbital position. It also supported IF data collection and downlink at 58 Mb/s. During its 90-minute orbital period, the instrument alternated between DDM mode and amplitude-delay (AD) mode, enabling both real-time and raw data acquisition. Over a 9-day observation window, the GNSS-R payload covered extensive sea regions and continental areas, providing important research data, such as DDMs recorded over the South Pacific and West Africa. 1) 15)

Global Navigation Satellite System Radio Occultation (GNSS-RO)

The GNSS-RO instrument aboard YunYao-1 series satellites is a passive limb-sounding sensor used to monitor atmospheric and ionospheric conditions. It measures the excess phase delay of GNSS signals from GPS, BDS, GLONASS, and Galileo as they pass through the Earth’s atmosphere. These delays are detected using both a zenith-facing positioning antenna and a side-facing occultation antenna. As the signals are refracted by atmospheric gradients, the resulting data can be used to derive vertical profiles of refractivity, temperature, pressure, humidity, and electron density with high accuracy and vertical resolution. 1) 6)

GNSS-RO is accurate during both rising and setting occultation events and provides global coverage in all weather conditions. This makes the system useful for numerical weather prediction (NWP), climate trend monitoring, and ionospheric research. In the neutral atmosphere, refractivity is affected by temperature and moisture, while in the ionosphere, it is influenced by electron density. GNSS-RO measures both ranges, with neutral atmospheric profiles extending up to 40 km and ionospheric electron density data reaching from 60 km to LEO altitudes. 1) 6)

The first commercial GNSS-RO payload developed by YunYao was launched from the Taiyuan Satellite Launch Center on January 15, 2020, becoming China's first successful commercial deployment. By August 2021, a total of five experimental GNSS-RO instruments had been launched. One of the instruments flew aboard the MN50-3 satellite, a medium-resolution imaging platform. It carried a 3x1 antenna array and operated for 219 total hours between November 2020 and May 2021. Data collected in December 2020 showed high-density ionospheric occultation coverage, especially across Africa and oceanic regions. 1) 6)

Refractivity Data Quality Assessment

The refractivity data collected by the GNSS-RO instrument aboard the satellites has been assessed as being highly precise and accurate, and suitable for use in weather forecasts and scientific research. The evaluated data shows a standard deviation of less than 3.4%, with variations in accuracy mostly at lower altitudes in the troposphere and stratosphere, where factors such as atmospheric moisture, receiver tracking limitations, and super-refraction can affect measurements. The lowest standard deviation is observed below 4 km altitude, while the values for BDS, GPS, GLONASS, and Galileo remain relatively consistent between 4 km and 30 km. The absolute mean bias remains under 1.5%, with the smallest bias found between 4 km and 40 km when using GLONASS. The radio occlusion bias in the lower troposphere can be caused by various factors, such as super-refraction. 2)

References  

1) ResearchGate, “AN INTRODUCTION OF GNSS REFLECTOMETER REMOTE SENSING MISSION FROM YUNYAO AEROSPACE TECHNOLOGY CO., LTD.”, September, 2021, URL: https://www.researchgate.net/profile/Mapoet-Niphy/publication/356512953_An_Introduction_of_GNSS_Reflectometer_Remote_Sensing_Mission_From_Yunyao_Aerospace_Technology_Co_Ltd/links/6225d005a39db062db86f80e/An-Introduction-of-GNSS-Reflectometer-Remote-Sensing-Mission-From-Yunyao-Aerospace-Technology-Co-Ltd.pdf

2)Copernicus, “Quality Assessment of YUNYAO GNSS-RO Refractivity Data in the Neutral Atmosphere”, URL: https://amt.copernicus.org/preprints/amt-2024-150/amt-2024-150.pdf

3) WMO OSCAR, “YunYao-receiver”, URL:  https://space.oscar.wmo.int/instruments/view/yunyao_receiver

4) WMO OSCAR, “YunYao-1”, URL:  https://space.oscar.wmo.int/satellites/view/yunyao_1

5) WMO OSCAR, “YunYao Aerospace Constellation”, URL: https://space.oscar.wmo.int/satelliteprogrammes/view/yunyao

6) eoPortal, “GNSS Radio Occultation”, November 8, 2024, URL: https://www.eoportal.org/other-space-activities/gnss-ro

7) Gunter’s Space Page, “Yunyao-1 14, ..., 40”, URL: https://space.skyrocket.de/doc_sdat/yunyao-1-18.htm

8) RocketLaunch, “YunYao-1 (15-17)”, URL: https://www.rocketlaunch.live/launch/yunyao-1-15-17

9) Space, “Chinese company iSpace suffers 4th launch failure in 7 tries”, July 13, 2024, URL: https://www.space.com/china-ispace-fourth-launch-failure-hyperbola-1-rocket

10) SpaceNews, “China suffers commercial rocket failure but sets record for annual launches”, December 27, 2024, URL: https://spacenews.com/china-suffers-commercial-rocket-failure-but-sets-record-for-annual-launches/

11) VesselFinder, “DONGFANGHANGTIANGANG”, URL: https://www.vesselfinder.com/vessels/details/9980473

12) Wikipedia, “Jiuquan Satellite Launch Center”, URL: https://en.wikipedia.org/wiki/Jiuquan_Satellite_Launch_Center

13) NewSpace, “Yunyao Yuhang (Yunyao-1)”, URL: https://www.newspace.im/constellations/yunyao-yuhang

14) Tianjin University, URL: https://www.tju.edu.cn/

15) Wikipedia, “GNSS reflectometry”, URL: https://en.wikipedia.org/wiki/GNSS_reflectometry