The duration limit of current satellites is almost unique. In fact, the current material and technology endures more than the fuel of satellites and rockets. One of the solutions is filling tanks, but it would be very expensive.
Therefore, you have to think something more. But what? Use some parts of the satellites for your fuel. To do this, different thermoplastic composite materials have already been tested, which will provide both the structural strength required at the time of launch and the validity for fuel (by transformation or combustion).
The current tanks are aluminum or graphite and once emptied they are not reusable. From now on, if they are manufactured with another material, once emptied they would serve for fuel.