Jilin Constellation

Jilin Commercial EO Satellite Constellation of China

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Jilin-1 GXA (Guangxe-A — Optical-A) is a Chinese commercial remote sensing satellite mission, also referred to as JL-1, designed and owned by the Chang Guang Satellite Technology Co. Ltd (CGSTL) of Bejing. The development of the JL-1 constellitation began in 2015, and the first 4 satellites were launched on 7 October 2015. In 2021, there are 30 satellites in the constellation and the constellation will be expanded to 138 satellites to offer high resolution imagery and a high revisit commercial service. ¹⁾

While the new generation of a VHR (very high resolution) microsatellite constellation is being developed by CGSTL (Chang Guang Satellite Technology Ltd.) of China, the data products are being commercialized by the HEAD Aerospace Group, a privately-owned space company with its headquarter in Beijing. Founded in 2007, HEAD has an extended presence globally including subsidiaries in Hong Kong, France, and the Netherlands.

On 15 September 2020, China successfully launched nine Jilin-1 GF-03 satellites on a Long March 11 vehicle from the China Sea, which will further increase the Earth Observation satellite portfolio commercialized by HEAD Aerospace. Jilin-1 GF-03 is part of the Jilin-1 constellation operated and developed by Chang Guang Satellite Technology Co., who is the strategic partner of HEAD Aerospace. ²⁾

The successful launch of the nine satellites of Jilin-1-GF-03 is part of the constellation of 54 sub-meter satellites enabling imaging anywhere on Earth every 10 minutes with observations from 10 to 16 hours. By the end of 2021, the Jilin-1 constellation expects to be composed of 60 satellites in orbit. By the end of 2025, the full constellation of 138 satellites will be in orbit, resulting in round-the-clock, all-weather, full-spectrum data acquisition, capable of providing geospatial information products and services of the highest temporal and spatial resolution globally.

The first small satellite <50 kg named JL1-GF03A satellite, was built and launched in 2019 to verify the design and performance of higher resolution imagery with a smaller satellite. Based on the good in-orbit performance, JL1-GF03B\C came to being, including 3 JL1-GF03C satellites using a frame sensor to output the video and night vision images and 6 JL1-GF03B satellites, using the linear pushbroom sensor technology, offering wide-swath imagery at 17 km instead of market standard at 5 to 6 km. The 9 satellites are so light to be launched with a single launch CZ-11 in 2020 from an offshore launch platform.

On July 3 2011, 3 JL1-GF03D satellites were improved to 0.75 m resolution imagery and launched with JL1-KF01B which are all under in-orbit test and will start service soon. The imagery of the JL1-GF03B spacecraft have been used by different customers and researchers.

Spacecraft

JL1-GF03 series microsatellites are designed based on the rules: higher resolution, lighter, lower cost. This makes a large scale constellation come true, because the higher resolution can meet the need of a global customer base, lighter makes 9 satellites can be launched by one rocket and reduces the cost of buying more rockets, lower cost allows the company to afford the cost of a larger satellite constellation. The main parameters of the satellites [4,5] are listed in table 1 and the satellite design rendering is shown in Figure 1.

The JL-1 constellation was designed to 535 km altitude, and 138 satellites were planned to be launched to achieve about 10 minutes global revisit. As the need of daily visit become stronger and the success of the JL1-GF03 satellites, the DailyVision orbit was brought out. There are 3 satellites in one plane @535 km is enough to visit the target at the equatorial with 45° off-pointing. The orbit parameters are listed in Table 2 and shown in Figure 2.

Due to the orbit parameters, every 3 satellites will revisit the target at different latitude at least once per day, for latitude 60° the revisit number will be up to twice. The revisit times are listed in Table 3. Due to the table daily revisit can be achieved to offer DailyVision service. And after in-orbit test, JL1-GF03D satellites will be added in the service group to reach at least 3 times revisit for DailyVision.

Another important parameter of the orbit is LTDN (Local Time of Descending Node), shown in Table 1, the earliest LTDN is 9:20 a.m. which is earlier than most of the commercial satellites. It makes the satellite can get earlier images and support earlier information for emergency response. Besides the JL1-GF03 series satellites will be launched to the different orbit planes of which LTDN: 10:00 hours~14:00 hours separated every 40 minutes to reach the important images acquisition window to shorten the task time limit which means to support higher time validity service.

Results

During in-orbit test the 9 satellites including 6 JL-1-GF03Bs and 3 JL-1-GF03Cs were scheduled to revisit one target to verify the imaging effect of different satellites. Before orbit control to reach average phase angle, the 9 satellites were scheduled to visit Abu Dhabi International Airport, UAE, within 10 minutes on 29 September 2020 (Beijing time), the 9 images (partial) are shown in Figure 3.

And after orbit transfer of the 9 satellites to be separated to 60° phase angle for JL1-GF03Bs and 120° phase angle for JL1-GF03Cs the satellites were scheduled to support service and to accumulated images for agricultural applications and so on. Many tests have been planned and executed until now. More than 100 imaging tasks have been scheduled for JL-1-GF03Bs to revisit the farmland in China and United States based on cloud prediction. Two multi-temporal visit examples are shown in Figure 4 and Figure 5.

From the figures at different times, the difference of the farmland and forest can be displayed clearly. It can be used to monitor the growing status especially for large farmlands Which are hard to monitor by farmers.

A more important accumulation work has been going on, more than 90 images have been got for only one target from March 2021 to September, and images from 8 consecutive days of the 90 are shown in Figure 6.

It can be seen from the above test, JL-1-GF03 series can be used to get daily images to support DailyVision service for change monitoring that must be useful to agriculture growth monitoring, economy prediction, city planning and so on.

References

1) Kammy Bruna, Xing Zhong, Feng Li, Chang, Wei Sun, Hubert de Beaufort, "Future EO System: The First VHR CCD Camera Constellation of 138 Microsatellite," Proceedings of the 72nd IAC (International Astronautical Congress), 25-29 October 2021, Dubai, UAE (United Arab Emirates), paper: IAC-21-B1.2.4, URL: https://iafastro.directory/iac/proceedings/IAC-21/IAC-21/B1/2/manuscripts/IAC-21,B1,2,4,x66640.pdf

2) "Nine JL-1-GF03 satellites launched, increasing commercial offering in satellite constellation plan," HEAD, 15 September 2020, URL: https://www.head-aerospace.eu/post/
nine-jl-1-gf03-satellites-launched-increasing-commercial-offering-in-satellite-constellation-plan
 

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (eoportal@symbios.space).

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