Page 68 - BBC Sky at Night - September 2017 UK

68

Voyager
mission

timeline

On their long travels, the
Voyagers visited four planets
and imaged 48 moons. 20 AUGUST 1977 5 SEPTEMBER 1977 10 DECEMBER 1977
Voyager 2 launches from Cape Voyager 1 launches at 12:56 Voyager 2 enters the
Now they are at the very
Canaveral at 14:29 UT atop a UT from Cape Canaveral also asteroid belt, swiftly
edge of the Solar System Titan IIIE-Centaur launch vehicle atop a Titan IIIE-Centaur followed by Voyager 1

orty years ago, in August and September
1977, NASA launched two spacecraft
on an audacious mission that would
Feventually study all four giant outer
planets and 48 of their moons, and go on to
explore the outer reaches of our Solar System.
Today, Voyager 1 is our most distant spacecraft,
and in 2012 became the first to enter interstellar
space. Voyager 2 isn’t far behind; it’s hoped that
it too will ‘go interstellar’ in the next five years.
The origins of the mission hark back to 1965,
when it was realised that a planetary alignment in
the latter half of the 1970s would enable a spacecraft
to make a complete survey of Jupiter, Saturn, Uranus,
Neptune and Pluto. Such an alignment only occurs
every 175 years – it was an opportunity not to be missed.
To make the most of it, NASA settled on two The two final
identical spacecraft to travel on two separate
NASA/JPL-CALTECH X 8, NASA/JPL-CALTECH/JHUAPL, MARK GARLICK largest moon Titan. Voyager 2, meanwhile, would þ The Voyager LECP that they would be able to complete the extended
trajectories. Both would study Jupiter and Saturn.
Voyager 1 would then go on to fly by Saturn’s
trajectories were
chosen from 10,000; this
is an early one, covering
have the option to go to Uranus and Neptune,
Jupiter, Saturn and Pluto
becoming the first spacecraft to visit either. Each
planetary flyby would alter the spacecraft’s flight
path to deliver it onto the next planet and increase
its velocity, reducing the flight time to Neptune
mission to Uranus and Neptune. They launched
from 30 years to just 12. Pluto was off the table;
with 11 scientific instruments: four on Voyager 1
the choice was between it and Titan, and Titan
continue to send back data about its surroundings,
instrument; like all others
was seen as a more interesting target.
while five remain operational on Voyager 2.
that remain operational,
One of the instruments still active on both is
Budget constraints meant the spacecraft were
it has long surpassed its
the low-energy charged particle detector (LECP)
officially only built to last five years, with the hope
expected working life
instrument, which scans the sky through 360º every
few tens of seconds measuring cosmic rays. That
it continues to function is extraordinary, says its
principal investigator, Dr Stamatios M Krimigis.
“The most remarkable design feature of LECP
was the stepper motor,” he says. “A mechanical
device like this in space was frowned upon because
everyone thought it could get stuck in short order.
We tested the motor for about 500,000 steps,
twice the expected usage and it survived. Now it’s
performed over seven million steps and counting.”
Science data from the instruments is returned
Rotating stepper
platform to Earth in real time via each probe’s high-gain
antenna. The signals are picked up by the Deep
Space Network (DSN), a global spacecraft tracking
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