Watch the ever-changing Earth from afar: How are meteorological satellites launched?

The launch vehicle gives the artificial satellite enough power to accelerate and rise, and pass through the thick atmosphere to reach the predetermined orbit in space. After the launch vehicle is ignited, the oxidant and reductant inside it burn violently, and the high-temperature and high-pressure gas generated is quickly ejected from the tail nozzle, and the launch vehicle is continuously accelerated. The launch vehicle flies vertically to a certain height, quickly passes through the high-density atmosphere, and then begins to turn according to the set program, and finally adjusts to fly horizontally. After the satellite reaches the predetermined height, the driving force of most launch vehicles will be used to increase the flight speed. When the satellite's flight speed reaches a certain value (the first cosmic speed of 7.9km/s), the satellite will continue to fly in a circle around the earth, and the artificial satellite will not fall to the ground.

The entire satellite flight process is roughly divided into five stages: pre-launch preparation, active launch phase, status establishment, in-orbit testing, and in-orbit operation.

① Pre-launch preparation: from 5 hours before launch to the ignition of the carrier rocket.

② Active launch phase: from the ignition and takeoff of the launch vehicle to the separation of the rocket and satellite. In the active launch phase, the satellite does not receive remote control commands, but only sends status telemetry information to the ground. The ground tracking system monitors the satellite status through telemetry data.

③ Status establishment: It takes about a month from the separation of the rocket and the satellite to the establishment of normal working mode of the satellite. The main tasks of this stage are to deploy the solar panels, establish the normal attitude of the satellite, adjust the initial orbit, ensure the normal operation of various systems of the satellite platform, and start up the payload according to the steps.

④ In-orbit testing: According to the predetermined process and working mode, the satellite is switched under different working conditions and performance tested.

⑤ In-orbit operation: from the completion of the satellite in-orbit test and delivery to the end of the satellite's life. What is the sign of a successful meteorological satellite launch? After a few tens of seconds after ignition, the carrier rocket begins to slowly turn in the predetermined direction according to the predetermined procedure. After more than 100 seconds, at an altitude of about 70km, the first-stage rocket engine shuts down and separates; the second-stage rocket engine ignites immediately afterwards and continues to accelerate the flight; when the carrier rocket flies out of the dense atmosphere (usually above 100km above sea level), the satellite's fairing is thrown away according to the procedure. When the carrier rocket reaches the predetermined speed and altitude, the second-stage rocket engine shuts down and separates, and the accelerated flight phase ends. Subsequently, the carrier rocket relies on the energy it has obtained and, under the action of the earth's gravity, begins the inertial flight phase and flies to a position tangent to the predetermined orbit. At this time, the third-stage rocket engine ignites and begins the final acceleration phase of flight. When it accelerates to the predetermined speed, the third-stage rocket engine shuts down, the satellite and the rocket separate, and the carrier rocket's mission to launch the satellite is completed. When the satellite's solar panels are unfolded, the satellite obtains energy and operates autonomously in orbit. At this time, the launch command center can announce that "the launch mission was a complete success."

Polar orbiting meteorological satellites have a relatively low orbital altitude, so the launch vehicle can directly send the satellite to the predetermined orbital position, and the satellite itself does not need to carry excess fuel for changing orbits.

Geostationary meteorological satellites have high orbital altitudes and launch vehicles are limited in their carrying capacity and cannot be sent directly to a fixed location. Therefore, the satellite needs to carry fuel and make multiple orbit changes before maneuvering to the predetermined working position. The fuel carried by geostationary meteorological satellites accounts for two-fifths of the satellite launch mass. After the satellite separates from the rocket, it first changes its orbit to an elliptical orbit, then changes its orbit to a circular orbit 36,000 km above the ground, and finally the satellite drifts to a predetermined fixed location. After the separation of the satellite and rocket, my country's second-generation geostationary meteorological satellite, Fengyun-4, used the fuel it carried to make five orbit changes before being fixed to a certain longitude position above the equator.

--Excerpt from "Stars Shining in China: Our Fengyun Meteorological Satellite"