spacecraft’s
scientific
instruments, including the
Ultraviolet
Spectrometer,
the Cosmic Ray experiment,
the Plasma experiment, the
Photopolarimeter, and the
Low-Energy Charged Particle
experiment.
A
second,
longer
boom carried a series of
magnetometers and two
whip antennae for the plasma
radio experiment.
Furthermore, all of Voyager
1’s experiments were designed to be compact,
lightweight, and draw as little
power as possible. During
periods
of
interplanetary
cruise
and
high-science
data accumulation, data
not immediately transmitted Voyager before launch in the
back to Earth was designed
to be stored on a digital tape
recorder with about 536 megabits capacity (about 67
megabytes), enough to hold roughly 100 images.
But the truly remarkable aspect of Voyager 1, and
the main element that enables the probe’s continued
mission today, is its power source: three Radioisotope
Thermoelectric Generators (RTGs) located on the third
deployable boom.
An impressive feat of engineering at the time, each
of the three cylindrical RTGs on Voyager 1 were built
with six layers of four 2-inch diameter plutonium (238)
oxide encapsulated in a thin shell of iridium. These shells
of iridium were in turn wrapped in graphite yarn and
stacked in graphite cylinders.
Each ball produced about 100 watts of thermal
energy at launch, for 2,400 watts of thermal power
from each RTG.
However, like all spacecraft, the power source
underwent changes and modifications in the
development process.
In fact, during development, it was recognized that
the thermocouples (designed to convert the contrast
in temperature between the hot plutonium and cool
space environment into electricity) were degrading far
too quickly in the very warm RTG cylinders
This led to the suggestion that the thermocouple legs
be coated with silicon nitride to prevent sublimation
of thermocouple material that was causing electrical
shorts, which reduced power output.
This careful engineering resulted in robust RTGs on
Voyager 1 that have been in continuous operation for
over 36 years, though they are only producing about
60% of their original output as of today due to the
radiation- and temperature-induced degradation of
the thermocouples.
But even with the robust power source, none of
12
12
Voyager 1’s instruments would
have been able to return any
data without the complex
control of the probe’s six
interlinked computers.
Voyager 1’s Computer
Command System (CCS)
was designed by engineers
to control the sequences
of activities to be carried
out by the spacecraft; the
Flight Data Subsystem (FDS)
was designed to control the
acquisition and downlink of
data; and the Attitude and
Articulation Control System
(AACS) was designed to
control the attitude of the
spacecraft and orientation of
the science scan platform.
Additionally, the electronics
of Voyager 1 had to be
SAEF II at KSC. Image: NASA
radiation-hardened to survive
the probe’s planned encounter
with Jupiter.
With all of this forethought and complex engineering,
the Voyager 1 spacecraft has been essentially remade
since its launch as various systems issues forced mission
controllers to improvise and the probe completed its
primary mission in 1980.
Upgrades to the indispensible Deep Space Network
have also enabled continued communication and
tracking with Voyager 1 at greater distances than were
possible when the spacecraft was first launched.
Trek through the solar system
Voyager 1’s mission began on 5 September 1977 with
its launch aboard a Titan III-C rocket from the Cape
Canaveral Air Force Station in Florida.
Artist rendering showing the Voyager spacecraft on their grand
Image: NASA/JPL-Caltech
tour through the solar system.
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