  Energy harvesting is the fundamental activity in almost all forms of space
exploration known to humans. So far, in most cases, it is not feasible to
bring, along with probe, spacecraft or rover suitable supply of fuel to cover
all mission's energy needs. Some concepts of mining or other form of
manufacturing of fuel on exploration site have been made, but they still base
either on some facility that needs one mean of energy to generate fuel, perhaps
of better quality, or needs some initial energy to be harvested to start a self
sustaining cycle. Following paper summarizes key factors that determine
satellite energy needs, and explains some either most widespread or most
interesting examples of energy harvesting devices, present in Earth orbit as
well as exploring Solar System and, very recently, beyond. Some of presented
energy harvester are suitable for very large (in terms of size and
functionality) probes, other fit and scale easily on satellites ranging from
dozens of tons to few grams.
