Why do rockets have to be launched in autumn?

The launch times of Shenzhou V, Shenzhou VI and Chang 'e I are all in the middle and late June of 10, and the launch of Shenzhou VII will be advanced to the end of this month. According to experts, there are many suitable launch windows in September and 10. However, since Shenzhou VII will carry out the spacewalk mission, the angle of the sun when taking off at the end of September is more suitable for astronauts' extravehicular activities, which can make the spacecraft see the sun in the shortest time and ensure that the astronauts have sunshine when they leave the cabin.

The best meteorological conditions for launching manned space flight mainly include: no precipitation, ground wind speed less than 8 meters per second and horizontal visibility more than 20 kilometers; From 8 hours before launch to 1 hour after launch, there is no lightning activity within 30 km to 40 km of the site; The maximum wind speed in the airspace 3 km to 18 km from the launch site of the ship and arrow is less than 70 meters per second, and there should be no lightning for 9 hours before and after launch.