When we watch our rocket launch, observant friends may notice that during the time the rocket is in the sky, many small "debris" will fall from above.

    Source: Aerospace Eighth Academy

    In fact, the "debris" that falls from the rocket is the insulation layer that covers the rocket fairing before launch.As is well known, inside the fairing of a rocket, there are usually satellites or manned spacecraft. Whether it is a satellite or a manned spacecraft, there are many precious equipment that need to be stored at room temperature, usually including some propellants. The environment required for the equipment requires that the fairing should not be too hot, let alone too cold.Supplementary reading:The temperature of a typical satellite should be controlled within the range of tens to twenty degrees, while the temperature of a manned spacecraft should be controlled within a smaller range.From a geographical perspective, the commonly used Jiuquan Satellite Launch Center and Taiyuan Satellite Launch Center in China are located in mid to high latitudes with low temperatures, while the Jiuquan Satellite Launch Center in the desert also faces a significant temperature difference between day and night.Friends who understand the rocket launch process know that the temperature control equipment on the launch tower needs to be set up one hour before the launch. At this time, the thin fairing is difficult to withstand the cold winds of the desert and valleys. More importantly, the temperature control equipment of the satellite and manned spacecraft itself can only work after successful orbit insertion and deployment of the solar panels.Therefore, in order to prevent satellites and manned spacecraft from catching a cold and causing equipment and instruments to malfunction within this hour, the designers added an insulation layer to the fairing. The material is closed cell foam plate, which is cheap and effective, and can easily lock the heat in the fairing.Because the foam plate itself is extremely light, the rocket takes off slowly, and will not hurt the rocket if it falls down. Sometimes the foam plate may stick firmly, but it will also gradually ablate as the rocket accelerates and the friction with the atmosphere intensifies. By the time the fairing is separated, most of the foam plates have fallen off. Even if there are still several pieces of foam on them, they will fall into the atmosphere with the separated fairing.Source: Technological equipment

    Because the foam plate itself is extremely light, the rocket takes off slowly, and will not hurt the rocket if it falls down. Sometimes the foam plate may stick firmly, but it will also gradually ablate as the rocket accelerates and the friction with the atmosphere intensifies. By the time the fairing is separated, most of the foam plates have fallen off. Even if there are still several pieces of foam on them, they will fall into the atmosphere with the separated fairing.