Desert sky and launch windows
The Jiuquan Satellite Launch Site sits at an altitude of about 1,000 meters on the edge of the Badain Jaran Desert in northwest China. Its location in the Gobi Desert provides one of the most important factors for spaceflight: predictable weather. The site experiences a continental arid desert climate, resulting in over 300 days of clear skies each year. This high number of launch-ready days was a main reason for its selection when it was established in 1958.
The climate is defined by extremes. The average annual temperature is a mild 8.5°C, but this figure masks significant seasonal and daily fluctuations. The region receives very little precipitation, with some parts of the surrounding Badain Jaran Desert getting less than 40 mm annually. Relative humidity is also consistently low, typically ranging between 35-55%. While the lack of rain and clouds is beneficial, the desert environment presents its own meteorological challenges. Strong winds and sandstorms, particularly in the spring, are a major operational concern. These events can reduce visibility and pose a physical threat to the rocket and ground equipment.
Micrometeorology for a perfect launch
Launching a multi-story rocket requires a precise understanding of the atmosphere it will immediately travel through. At Jiuquan, a network of advanced micrometeorological stations provides a high-resolution, three-dimensional model of the lower atmosphere. This is more detailed than a weather forecast. These systems are designed to measure a phenomenon called wind shear—an abrupt change in wind speed or direction over a short distance. During the first few hundred meters of ascent, a rocket is at its heaviest and moving relatively slowly, making it susceptible to strong, sudden gusts that can push it off its trajectory or exert dangerous structural stress.
To create a complete atmospheric profile, technicians use a combination of ground-based sensors, weather balloons (radiosondes), and remote sensing systems like sodar and lidar. These instruments gather real-time data on temperature, humidity, pressure, and, most importantly, wind vectors at various altitudes. This data is fed into launch computers that model the rocket's path through the measured conditions. A launch window, the specific period during which a launch can occur, depends on this information. If wind shear or ground-level winds exceed established safety limits, the launch is scrubbed. Forecasters at the center provide hourly updates for 72 hours leading up to a launch, ensuring decision-makers have the most accurate data to approve the final countdown.