Voyager 1 Fires Up Thrusters After 37 Years

If you tried to
start a car that’s been sitting in a garage
for decades, you might not expect
the engine to respond. But a
set of thrusters aboard the Voyager 1 spacecraft
successfully
fired up Wednesday after 37 years without use.

Voyager 1,
NASA’s farthest and fastest spacecraft, is the only
human-made object in
interstellar space, the environment
between the stars. The spacecraft, which
has been flying for
40 years, relies on small devices called thrusters to
orient
itself so it can communicate with Earth. These thrusters fire
in tiny pulses,
or “puffs,” lasting mere milliseconds, to
subtly rotate the
spacecraft so that its antenna points at our
planet. Now, the Voyager team is
able to use a set of four
backup thrusters, dormant since 1980.

“With
these thrusters that are still functional after 37 years
without use, we will
be able to extend the life of the Voyager
1 spacecraft by two to three
years,” said Suzanne Dodd,
project manager for Voyager at NASA’s Jet Propulsion
Laboratory,
Pasadena, California.

Since 2014,
engineers have noticed that the thrusters Voyager
1 has been using to orient
the spacecraft, called “attitude
control thrusters,” have been
degrading. Over time, the
thrusters require more puffs to give off the same
amount of
energy. At 13 billion miles from Earth, there’s no mechanic
shop
nearby to get a tune-up.

The Voyager
team assembled a group of propulsion experts at
NASA’s Jet Propulsion
Laboratory, Pasadena, California, to
study the problem. Chris Jones, Robert Shotwell, Carl Guernsey
and
Todd Barber analyzed options and predicted how the
spacecraft would respond in
different scenarios. They agreed
on an unusual solution: Try giving the job of orientation to a
set of thrusters
that had been asleep for 37 years.

“The Voyager flight team dug up decades-old data
and examined
the software that was coded in an outdated assembler language,
to
make sure we could safely test the thrusters,” said Jones,
chief engineer at JPL.

In the early
days of the mission, Voyager 1 flew by Jupiter,
Saturn, and important moons of
each. To accurately fly by and
point the spacecraft’s instruments at a
smorgasbord of
targets, engineers used “trajectory correction maneuver,”
or
TCM, thrusters that are identical in size and functionality to
the attitude
control thrusters, and are located on the back
side of the spacecraft. But
because Voyager 1’s last planetary
encounter was Saturn, the Voyager team
hadn’t needed to use
the TCM thrusters since November 8, 1980. Back then, the TCM
thrusters were used in a
more continuous firing mode; they had
never
been used in the brief bursts necessary to orient the
spacecraft.

All of Voyager’s thrusters were
developed by Aerojet
Rocketdyne.
The same kind of thruster, called the MR-103, flew
on other NASA spacecraft as
well, such as Cassini and Dawn.

On Tuesday, Nov.
28, 2017, Voyager engineers fired up the four
TCM thrusters for the first time
in 37 years and tested their
ability to orient the spacecraft using
10-millisecond pulses.
The
team waited eagerly as the test results traveled through
space, taking 19 hours
and 35 minutes to reach an antenna in
Goldstone, California, that is part of
NASA’s Deep Space
Network.

Lo and behold, on Wednesday, Nov. 29, they learned the TCM
thrusters
worked perfectly — and just as well as the attitude
control thrusters.

“The Voyager team got more
excited each time with each
milestone in the thruster test. The mood was one of
relief,
joy and incredulity after witnessing these well-rested
thrusters pick
up the baton as if no time had passed at all,”
said Barber, a JPL propulsion engineer.

The plan going
forward is to switch to the TCM thrusters in
January. To make the change,
Voyager has to turn on one heater
per thruster, which requires power — a
limited resource for
the aging mission. When there is no longer enough power to
operate the heaters, the
team will switch back to the attitude
control thrusters.

The thruster
test went so well, the team will likely do a
similar test on the TCM thrusters
for Voyager 2, the twin
spacecraft of Voyager 1. The attitude control thrusters
currently used for Voyager 2 are
not yet as degraded as
Voyager 1’s, however.

Voyager 2 is
also on course to enter interstellar space,
likely within the next few years.

The Voyager spacecraft were built by JPL,
which continues to
operate both. JPL is a division of Caltech in Pasadena. The
Voyager missions are a part of the NASA Heliophysics System
Observatory,
sponsored by the Heliophysics Division of the
Science Mission Directorate in
Washington. For more
information about the Voyager spacecraft, visit:

https://www.nasa.gov/voyager

https://voyager.jpl.nasa.gov

News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov

2017-310

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