Radioisotope Thermoelectric Generator (RTG)
Nuclear technology has been
used in the U.S. space program over the past 25 years to provide power for more
than 20 NASA spacecraft. The power source has been an ingenious device called a
radioisotope thermoelectric generator, or RTG. RTGs use the natural decay of
plutonium-238 to produce heat, which is directly transformed into electricity
through a thermocouple device. A typical RTG produces about 230 watts of
electricity and will operate unattended for years. It is ideal for
interplanetary travel, not only because of its long power-generating life span,
but also its compactness. A typical RTG measures 45 inches in height, 18 inches
in diameter, and weighs only about 123 pounds.
Because RTGs contain plutonium-238, the transport of these devices are strictly
controlled under the rules and regulations of the Nuclear Regulatory Commission
(NRC). Q-Metrics was a key team member in the development of a complete RTG
Transportation System which met the safety requirements of the NRC and the
thermal performance imposed by NASA to ensure the thermal integrity of the RTG
and prevent thermally induced creep damage.
The
first application was to deliver three RTG power generators to NASA Kennedy
Space Center for the launch of the Cassini spacecraft on October 15, 1997. The
mission of the Cassini spacecraft, one of the largest, heaviest, and most
complex interplanetary spacecraft ever built, consists of delivering a probe
(called Huygens) to Titan, a moon of Saturn. The spacecraft then remains in
orbit around Saturn for detailed studies of the planet and its rings and
satellites. 
The fact that the RTGs are the
only power source for the spacecraft meant that the reliability was paramount to
the success of the mission. Reliability of the RTGs, in turn, required that the
devices be maintained within strict temperature limits and low thermal
gradients. The critical nature of the thermal analysis provided for this
project meant that a series of thermal tests had to be conducted to ensure the
accuracy of the thermal analysis provided by Q-Metrics.
These tests, conducted under
the Dept. of Energy and NASA control, demonstrated that all RTGs thermal
criteria were not only successfully attained, but actually beaten in many
cases. In fact, the test results were within 3% of the temperature levels
predicted by the Q-Metrics’ analysis. Subsequent
monitoring of four RTGs transported to the Kennedy Space Center also showed that
all system thermal criteria were beaten.
