In the year 2070, the primary source of energy for travel within the Solar System is the EmDrive, which gets its power from electromagnetic energy. Of course, the electromagnetic energy has to have a source and be continuously replenished, and this energy is supplied in the form of heat by the Cold Fusion unit. The heat from Cold Fusion is converted to electromagnetic energy by a passive, solid state, piezoelectric device that is extremely efficient. However, the energy losses due to inefficiencies, small though they may be, must be removed from the energy generation system or the heat will melt it. This it does through radiation, and the EmDrive system does get warm during sustained operation.
Cold Fusion is a loosely applied term. In Robot Dawn, it applies to both or either the fusion of two particles and/or a matter particle and an antimatter particle. In the early decades of the 21st century, antimatter was in short supply. However, a series of (fictional) discoveries remedied this situation and paved the way for Cold Fusion energy generation for EmDrive propulsion.
What is “distributed Cold Fusion”? Not only was Cold Fusion made practical because of abundance, the methods used to produce it were easily miniaturized almost to the point of invisibility. This enabled it to be distributed through the body of a robot so that once the robot was created, it was powered almost indefinitely. Although no one knew for sure at the time, the projected life of a robot was three to four hundred years.