Hydrogen-Oxygen Fuel Cell
It produces electrical power through an electrochemical reaction, which involves the oxidation of hydrogen. During the oxidation reaction, hydrogen atoms react with the oxygen atoms to form water, and it is in the course of the reaction that electrons are freed. The electrons flow via an external circuit, hence, generating current. Since the power produced by a single cell has a low voltage, the cells have to be assembled in a stack to attain the power required to drive specific unmanned vehicles (National Aeronautics and Space Administration, 2015). Furthermore, it does not require recharging as hydrogen and oxygen can both be supplied from outside.
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Photovoltaic Cell Arrays
They are often used in unmanned aerial vehicles (National Aeronautics and Space Administration, 2015). The photovoltaic cells contain a semiconductor layer that is particularly treated such that it has both a positive and negative end required to create an electric field. Therefore, when light incidences on the cell, the release of electrons from the semiconductor is triggered. If the system forms a closed circuit in that the positive and negative ends are connected, the electrons move freely in the circuit system; hence, generating electricity. The electricity generated then powers the unmanned vehicle.
Radioisotope Thermal Generators (RTGs)
RTGs operate on the principle that radioactive matter, especially plutonium-238, produce heat as they decay into non-radioactive particles (Radioisotope Power Systems, 2019). The thermocouple then converts heat generated into electricity to power the unmanned vehicles. It is often used as a power source for unmanned aerial vehicles. The thermocouple consists of two metals connected in a closed-loop. Therefore, if when they are at different temperatures, an electric potential is generated between them. This brings about the flow of electrons and, consequently, current.
National Aeronautics and Space Administration. (2015). NASA technology roadmaps TA 3: Space power and energy storage. Web.
Radioisotope Power Systems. (2019). Power systems. Web.