Power in Space—The
Special Requirements
Scientific instruments and electronic, photographic,
and communication equipment are the heart of exploratory
missions because they collect the data and
transmit it back to Earth. Without the technology to
reliably power these instruments in space, our knowledge
of the solar system would be only a fraction of
what it is today. RTG technology was developed to
provide that electric power.
Requirements for power in space are highly specialized.
The weight and volume of hardware launched
into space are carefully considered, including power
sources. The generator must meet mission power
requirements, as well as weight and space limitations.
Safety is also a prime consideration because of hazards
associated with launch, re-entry, and other mission
activities.
How Does an RTG Work?
An RTG has no moving parts. It produces electric
energy through the interaction of its two main
components: the radioactive heat source (fuel and
containment) and the thermoelectric generator.
Radioactive material can be used for fuel because it is
unstable and decays, or spontaneously disintegrates
into a different atomic form. As the material naturally
decays, it produces heat. The other main component
of the RTG, the thermoelectric generator, converts this
heat into electricity.
This heat-to-electricity conversion occurs through the
thermoelectric principle discovered early in the last
century. This principle is a way of producing electric
current without using a device that has moving parts.
It involves two plates, each made of a different metal
that conducts electricity. Joining these two plates to
form a closed electrical circuit and keeping the two
junctions at different temperatures produces an
electric current. These pairs of junctions are called
thermocouples. In an RTG, the radioisotopic fuel heats
one of these junctions while the other junction remains
unheated and is cooled by space.
RTGs are reliable because they produce electricity
without moving parts that can fail or wear out. This
high degree of reliability is especially important in
space applications, where the investment is great, and
repair or replacement of equipment is not feasible.
|
