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GPHS

GPHS stands for General Purpose Heat Source. It is a nuclear heat source used to power radioisotope thermoelectric generators (RTGs) on spacecraft, providing reliable electricity for long-duration missions in environments where solar power is impractical. The heat is produced by the alpha decay of plutonium-238, and the thermoelectric conversion of that heat into electricity powers instruments and systems aboard distant spacecraft.

A GPHS module contains ceramic plutonium-238 oxide fuel pellets encapsulated within robust graphite structures. The design

RTGs built with GPHS modules have powered a range of space missions, particularly those venturing far from

Plutonium-238 has a half-life of 87.7 years, which allows GPHS-powered RTGs to provide usable power over many

See also: Radioisotope thermoelectric generator, Pu-238, space nuclear power.

employs
multiple
containment
layers,
including
a
graphite
impact
shell
and
additional
safeguards,
to
prevent
release
of
radioactive
material
in
accidents
such
as
launch
mishaps
or
reentry
events.
The
modules
are
designed
to
withstand
extreme
conditions
and
to
minimize
the
risk
of
dispersal
of
plutonium.
the
Sun
where
solar
panels
are
ineffective.
Notable
missions
include
Galileo,
Ulysses,
Cassini–Huygens,
and
New
Horizons,
among
others.
The
system’s
long-lived
heat
source
and
relatively
simple,
maintenance-free
operation
make
it
suitable
for
multi-year
or
multi-decade
missions.
years
as
the
heat
output
gradually
declines.
The
GPHS
program
represents
a
collaboration
among
NASA,
the
U.S.
Department
of
Energy,
and
national
laboratories,
focused
on
safe
production,
testing,
and
deployment
of
these
heat
sources
for
space
exploration.