Why are all the Chang'e series satellites launched from the Xichang Satellite Launch Center?

There is a small city called Xichang in the southwest of our country. The moon view here is particularly famous. Since ancient times, there is a saying that "the moon in Jianchang is beautiful with gentle breeze and rain". Sima Xiangru of the Han Dynasty once left a famous sentence here: "The moon rises from the water of Qiongchi, and the sky is clear and transparent", so it is named "Moon City".

Xichang Daliangshan

Perhaps the ancients would never have thought that this "Moon City" famous for its moon scenery has now become a veritable moon exploration port. As one of my country's four major satellite launch centers, the Xichang Satellite Launch Center is where Chang'e 1, 2, and 3 all started their journeys into space, and the highly anticipated Chang'e 4 will also set sail from here.

Xichang Satellite Launch Center in the depths of Daliang Mountain

Why did the Chang'e family choose to launch from the Xichang Satellite Launch Center? What exactly is it capable of?

Theoretically, the closer the launch site is to the equator and the lower the latitude, the more fully the rocket launch can utilize the centrifugal force of the earth's rotation. In this way, when carrying out the same launch mission, the rocket launched from the launch site at a low latitude can use less propellant and carry more payload.

Compared with Jiuquan Satellite Launch Center and Taiyuan Satellite Launch Center, the biggest advantage of Xichang Satellite Launch Center is its low latitude. Launching geosynchronous orbit satellites under such geographical conditions can save propellant and thus save launch costs, which is more advantageous.

The Xichang Satellite Launch Center is at a lower latitude than the Jiuquan and Taiyuan launch centers.

To give a simple example, the internationally recognized ideal launch site is the Kourou Space Launch Center in Guyana, South America. The launch site is located at 5° north latitude and is managed by the European Space Agency. For a geosynchronous orbit satellite of the same mass, launching from the Kourou Space Launch Center saves 15% of propellant compared to launching from the Kennedy Space Launch Center at 28.5° north latitude. The difference is very obvious. At the same time, the low latitude is also an important competitive advantage of the Kourou Space Launch Center in the international commercial launch market.

Kourou Space Launch Center

Therefore, the Chang'e series of satellites chose to be launched at the Xichang Satellite Launch Center, which is beneficial to increasing the rocket's payload on the one hand and reducing the rocket's launch cost on the other.

Another big advantage of the Xichang Satellite Launch Center is the good weather conditions. Xichang has always been known as the Little Spring City, with an average annual temperature of 18°C, 320 days of sunshine, and almost no fog. The Chang'e series satellites were launched here with fewer meteorological restrictions and a good launch window. In addition, the Xichang Satellite Launch Center is located in a place with a solid geological structure and an ideal communication environment, so it is not surprising that the Chang'e series satellites were launched here.

Although the Xichang Satellite Launch Center has many advantages, it is not the most ideal choice. Due to historical reasons and considerations of concealment and safety, the Xichang Satellite Launch Center was built in Daliang Mountain. This caused trouble for rocket transportation. Rockets can only be transported by rail, and they need to pass through many tunnels during transportation, so the maximum diameter of the rocket components cannot exceed 3.5 meters.

The maximum diameter of the Long March 5 carrier rocket is more than 5 meters, so rail transportation is not an option. The future Chang'e 5 will use the Long March 5 carrier rocket, so Chang'e 5 cannot be launched in Xichang.

Long March 5 carrier rocket

In addition, although the Xichang Satellite Launch Center is located at a lower latitude than the Jiuquan Satellite Launch Center and the Taiyuan Satellite Launch Center - 28.2° north latitude, it is not the best choice for my country to build a launch site on land. Therefore, in 2009, my country built its fourth launch site - the Hainan Wenchang Launch Center.

Hainan Wenchang Launch Center

The Wenchang launch site in Hainan is located at 19°19′N and 109°48′E. It is the lowest latitude on the Chinese land and the closest to the equator. The Long March series rockets can increase the carrying capacity of geosynchronous orbit satellites by 10%-15% and extend the life of satellites by two years when launching geosynchronous orbit satellites from Wenchang compared to launching from Xichang.

At the same time, rockets can be transported by water, and the size of components is not limited. In addition, when launching a rocket from Wenchang, there is a vast ocean within 1,000 kilometers of its launch direction, and falling debris is not likely to cause accidents.

In the future, the Wenchang Launch Center in Hainan will shoulder the important task of lunar exploration. After the successful launch of Chang'e 4, the next Chang'e 5 should be launched here! Let's wait and see!

References/Destination Moon, The Story of Moon Exploration, CCTV.com, Xinhuanet