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to be controlled by 16 hydrazine
thrusters. However, it would be
too dark beyond the asteroid belt
for solar panels to generate enough
electricity for the spacecraft, and
batteries would not last nearly long
enough. The answer was nuclear
power in the form of radioisotope
thermoelectric generators (RTG),
held out on a boom to isolate
them from sensitive equipment.
Each RTG contained 24 balls of
plutonium that gave out heat,
which was converted into an
electric current by thermocouples.
The power supply was built to
last for nearly 50 years.
Jupiter and its moons
By December 1977, Voyager 1 had
overtaken Voyager 2, which was
taking a more circular trajectory.
It reached the Jupiter system in
January 1978. Most of Voyager 1’s
important discoveries were made
in a frenetic 48-hour period around
March 5, when it made its closest
approach, coming within 217,000
miles (349,000 km) of the planet’s
cloud tops. In addition to sending
back images, Voyager 1 analyzed
the compositions of the clouds and
measured the planet’s immense
magnetic field. It also showed that
Jupiter had a faint ring system. Its
most memorable discoveries came
from the flybys of the Galilean
moons. These were not sparse,
cratered balls but active worlds.
Photographs of Io showed the
largest volcanic eruptions ever
seen, spurting ash clouds into orbit.
Fresh measurements of Ganymede
revealed that it superseded evenTHE TRIUMPH OF TECHNOLOGY
Titan in size, while images of
Europa’s eerily smooth yellowish
disk had astronomers puzzled.
Voyager 2 arrived at Jupiter more
than a year later, and did not
approach as close as Voyager 1, but
it took some of the mission’s most ❯❯The latter half of the next
decade abounds in interesting
multiple planet opportunities.
Of particular interest is the
1978 “grand tour” which would
make possible close-up
observation of all planets of
the outer solar system.
Gary Flandro
Voyager 2’s images of Saturn’s
rings revealed a complex structure
made of small satellites, none of
which were larger than 3–6 miles
(5–9 km) across.