Satellites orbiting the earth have a finite life and sometimes debris of satellites fall to the earth. This is because                                          [NCERT Exemplar]

As the total energy of the earth satellite bounded system is negative $\left(\frac{-GM}{2a}\right)$ , where a is radius of the satellite and M is mass of the earth. Due to the viscous force acting on satellite, energy decreases continuously and radius of the orbit or height decreases gradually.