After nearly 50 years in space, the two Voyager spacecraft
are very low on nuclear power. Voyager 1 just shut off another instrument to
save the mission.
After nearly half a century in space, the Voyager 1
spacecraft just shut down one of its last remaining science instruments in a
desperate attempt to preserve power. NASA's decision to turn off the instrument
comes just ahead of a last-ditch "Big Bang" moment that mission
managers hope will give the two Voyager probes an extra boost of life later
this summer.
On Friday (April 17), Voyager 1 was commanded to shut down
the Low-Energy Charged Particle (LECP) experiment, an instrument that has
looked at ions, electrons and cosmic rays surrounding the spacecraft for the
past 49 years.
But now, Voyager 1 is running critically low on nuclear
power, especially after a planned roll maneuver on Feb. 27 created an
unexpected power drop.
The spacecraft launched in 1977, initially to survey Jupiter
and Saturn, before its mission was extended again and again. In 2012, Voyager 1
officially crossed into interstellar space, becoming the first spacecraft to
send data from outside the solar system. It remains the most distant spacecraft
in history.
The twin probe Voyager 2, which surveyed all of the outer
planets from Jupiter to Neptune, entered interstellar space about six years
later, and the two spacecraft are still transmitting from the black.
But their time is running short. Both spacecraft rely on a
radioisotope thermoelectric generator, which converts decaying plutonium into
power. The spacecraft lose roughly 4 watts of power a year.
"Power margins have grown razor thin, requiring the
team to conserve energy by shutting off heaters and instruments while making
sure the spacecraft don't get so cold that their fuel lines freeze,"
representatives from NASA's Jet Propulsion Laboratory (JPL), which manages the
Voyager program, wrote in an April 17 blog post.
After the latest shutoff, only two of Voyager 1's 10 science
instruments remain powered, while three instruments are currently running on
Voyager 2. These instruments have helped scientists characterize the conditions
of space beyond the solar system, as well as the physical properties of the
heliopause, the boundary where the solar wind clashes with the interstellar
medium.
A "Big Bang"
This latest Voyager 1 instrument shutoff will grant the
spacecraft only about one year of life, as things stand, but there's a plan to
get more out of the spacecraft: JPL will use a "Big Bang" procedure
to try extending the dwindling power reserves of not only Voyager 1 but also
Voyager 2.
"The idea is to swap out a group of powered devices all
at once — hence the nickname — turning some things off, and replacing them with
lower-power alternatives, to keep the spacecraft warm enough to continue
gathering science data," JPL representatives wrote in the blog post.
For now, two instruments on Voyager 1 are examining magnetic
fields and waves of plasma (superheated gas). But if all goes according to
plan, the team hopes to gain back enough power from the Big Bang to turn the
LECP back on. In fact, engineers decided to keep a small, half-watt motor for
LECP running for now, just in case the instrument can be used again.
In May and June, JPL will run some Big Bang tests on Voyager
2, which has more power supplies available and is slightly closer to Earth.
Assuming all goes well, the riskier Voyager 1 Big Bang moment would happen no
earlier than July.
Sending any commands to Voyager 1 takes 23 hours because it
is so far from Earth — 15 billion miles (25 billion kilometers) away. After
JPL relayed its commands, the LECP shutdown process took a little more than
three hours. Starting it up again, especially given the cold and distance,
could be a bit trickier.