<P> Spacecraft operating in the inner Solar System usually rely on the use of photovoltaic solar panels to derive electricity from sunlight . In the outer solar system, where the sunlight is too weak to produce sufficient power, radioisotope thermoelectric generators (RTGs) are used as a power source . </P> <P> The first spacecraft to use solar panels was the Vanguard 1 satellite, launched by the US in 1958 . This was largely because of the influence of Dr. Hans Ziegler, who can be regarded as the father of spacecraft solar power . </P>

Where do satellites in outer space derive their electrical energy from