Why was Changmo-1 launched in Xichang?
Among China's three space launch sites, only the Xichang Satellite Launch Center has the capability to launch Long March 3A and other high-thrust rockets. Therefore, Xichang Satellite Launch Center has no choice but to shoulder this important task.
In addition to astronomical considerations, meteorological conditions are also important factors. Guo Xuewen, senior engineer at the Meteorological Office of Xichang Satellite Launch Center, pointed out that October is the "golden season" for satellite launches in Xichang.
The Xichang area has high altitude, low latitude and sparse population in the landing area. It is an ideal geographical location for launching satellites. However, the meteorological conditions are the most complex among several satellite launch centers in China. It is located at the eastern foot of the Qinghai-Tibet Plateau, and in the undulating area where the Yunnan-Guizhou Plateau transitions to the Sichuan Basin. To the southwest is the Bay of Bengal, and the meteorological systems that affect the weather in the area are complex. Not only that, the site is also on the edge of the southwest minefield, one of the three major thunderstorm areas in China. There are many thunderstorms and convective weather, which has a great impact on the launch mission.
"Launching rockets and satellites has strict requirements on meteorological conditions." Guo Xuewen, who has been engaged in meteorological forecasting for space launches for more than 20 years, listed in detail several meteorological conditions that must be met for "Chang'e" to fly into space: During the entire launch During this period, that is, within 4-8 hours, there cannot be precipitation exceeding 1 mm, that is, more than light rain; during the period from fuel refueling to rocket launch, there cannot be any lightning activity within 30 kilometers around the site; the surface wind cannot be greater than 14 meters/second, which means it must be lower than level 5.
Guo Xuewen said, "After October, the unfavorable factors affecting the meteorology of the launch site area gradually decreased, and the meteorological conditions tended to be stable."
Xichang Satellite Launch Center Meteorological Office's analysis of 1974 Meteorological data up to 2006 were collected, and special studies on precipitation, thunderstorms and lightning, and high-altitude winds were carried out. The results showed that the average precipitation in October was 70.8 mm, and the average number of precipitation days was 17.9, accounting for 57.8% of the total days; the average number of thunderstorm days was 3.1 days, accounting for 10.1% of the total days; The average wind speed is 0.8 m/s, the maximum is 1.4 m/s, and the minimum is 0.3 m/s; the average high-altitude wind speed is 32 m/s, the maximum is 42 m/s, and the minimum is 23 m/s. Second.
"These meteorological characteristics create favorable conditions for the successful launch of satellites, and are also the reasons why Xichang launches most satellites during this period." Guo Xuewen said.
In addition, the Xichang Satellite Launch Center has established China's first relatively complete lightning warning system, which can increase the accuracy of short-term rainy season forecasts and comprehensive lightning forecasts in the launch site area to more than 95%.