Retired satellites must return to Earth in 5 years

Satellites are important for the modern world. Satellites are the base of the Global Positioning System (全球定位系統) which helps ships to avoid losing their way when they travel on the sea. The system also helps cars to find ways to their destinations (目的地). Satellites send signals from a central television station that generates  (產生) programming to smaller stations that send the signals locally ...Read More