Circling the Earth in the orbital spaceship I marvelled at the beauty of our planet. In a trip to other planets, many resources need to be reusable.
Energy is necessary to do work.
In space, vehicles can use different sources of energy. The Sun is the main source of energy in space. The main purpose of this method is to reduce the mass of the vehicle by allowing it to receive the power from the outside. In the other hand, other energy sources can be integrated in the vehicle, as the nuclear power plants. For long trips, nuclear power sources are rather used because of their long life.