Placeholder Image

Subtitles section Play video

  • [♪ INTRO]

  • For more than forty years, the two Voyager probes

  • have delighted us with information and pictures

  • from across our solar system.

  • But now, they've embarked on a new mission.

  • As of 2018, both probes had left the solar system

  • and begun an interstellar journey

  • a quest to drift between the stars

  • and take measurements wherever they go.

  • But for as beautiful and poetic as that is,

  • we can't expect this mission to go on forever.

  • Both Voyagers' clocks are ticking, and these days,

  • they're running out of juice.

  • Since they launched in 1977, these spacecraft

  • have really earned their names, and so far,

  • each has taken an epic journey of more than 17 billion kilometers.

  • On that journey, Voyager 1 visited Jupiter and Saturn,

  • then crossed into interstellar space in 2012.

  • Meanwhile, Voyager 2 took a more scenic route

  • that also passed Uranus and Neptune,

  • so it only moved beyond the Sun's influence in 2018.

  • Right now, both craft are still transmitting data,

  • and are measuring the interstellar environment

  • with a suite of instruments.

  • They're detecting magnetic fields, cosmic rays,

  • and plasma waves.

  • But this isn't likely to last much longer,

  • as the two sources of fuel the probes launched with

  • are slowly running out.

  • One of those fuels is hydrazine.

  • This simple compound is typically used as

  • a propellant for thrusters, since it's cheap

  • and has a very low freezing point.

  • But in this case, it's not used to push the Voyagers along.

  • They got their speed from their initial launch,

  • plus gravity-assisted slingshots around the planets they visited.

  • So instead, their hydrazine is used

  • for trajectory correction and as an

  • attitude control propellant to control

  • the spacecrafts' orientation.

  • This helps correct for any rolls or tumbles,

  • and keeps the probes pointed toward Earth,

  • so they can beam back results and receive

  • commands from mission control.

  • These kinds of corrections only need to be made every

  • once in a while, so the hydrazine isn't used up very quickly.

  • In fact, NASA estimates they're running at a fuel economy

  • of about 13,000 kilometers per liter, which puts

  • pretty much every other vehicle to shame!

  • But stillit has been 40 years since these things launched.

  • So even though both Voyagers left Earth with

  • 104 kilograms of hydrazine each, supplies are running low.

  • NASA reckons Voyager 1's hydrazine will last until 2040,

  • but Voyager 2's will run out in 2034.

  • That's because it used up more of its supply

  • maneuvering around Uranus and Neptune.

  • After that, the craft will keep speeding through

  • interstellar space, but they might not be pointing

  • in the right direction to send back results.

  • So we'll likely have to say goodbye.

  • 2034 and 2040 might seem like a

  • long time from now, but sadly, the Voyagers

  • will probably go silent before then.

  • Because as well as liquid fuel,

  • the probes have another power source,

  • one that makes electricity for its onboard systems.

  • It's called a radioisotope thermoelectric generator, or RTG.

  • And the ones in the Voyagers are on their last legs.

  • RTGs work by generating heat.

  • And they do this thanks to their

  • four and a half kilograms of plutonium dioxide.

  • Like other radioactive compounds, this stuff is unstable.

  • So over time, the plutonium atoms decay,

  • breaking down into smaller particles

  • and more stable uranium atoms.

  • This decay process gives off heat, which the RTGs

  • are able to convert into electricity.

  • Both Voyagers were fitted with three of these generators,

  • which together provided about 470 watts of power at launch.

  • It doesn't sound like muchyour average toaster

  • uses more than 1000 wattsbut it was enough

  • to power the central computer, communications equipment,

  • and a suite of ten instruments.

  • Unfortunately, at this point, a large portion

  • of the plutonium has decayed away.

  • What's left is only able to provide about 250 watts.

  • So, to conserve that power for the probe's

  • more critical functions, scientists have

  • one by one

  • started shutting down the probes' instruments.

  • For Voyager 1, they started with the cameras and heaters in 1990.

  • Then, 20 more components followed over the years.

  • Voyager 2 has suffered the same fate,

  • although its shutdowns started in 1991.

  • And it's now lost its radio astronomy setup, among other functions.

  • These days, Voyager 1 has just four working instruments,

  • and Voyager 2 has five.

  • That's enough to take good data about things

  • like magnetic fields.

  • But soon, they won't have enough power for that, either.

  • Starting in 2020, engineers will have to likely

  • start shutting down the remaining systems

  • or switch them on and off sequentially

  • to make the most of the remaining power.

  • Either way, as time goes on, the Voyagers

  • will have less and less to say to us, and eventually,

  • they'll fall silent forever as the central computer shuts down.

  • Of course, we should remember that these probes

  • are flying at incredible speeds through

  • totally uncharted territory between stars.

  • They're passing through unknown fields and particles,

  • so they could also encounter an entirely unexpected problem.

  • One that could shut down their power systems

  • or take out instruments ahead of time.

  • So, whether their missions last for days,

  • years, or decades more, they will eventually come to an end.

  • But honestly, even if something happens to them tomorrow,

  • the probes have already achieved great things.

  • They've given us unprecedented insights

  • into the giant planets of the solar system and their moons.

  • And they've taught us about everything

  • from giant storms on Jupiter to active volcanoes on Io

  • to shepherding moons in Saturn's rings.

  • Plus, they've been in space longer, and traveled farther,

  • than any equipment we've ever made.

  • Which by itself, is definitely worth celebrating.

  • Thanks for watching this episode of SciShow Space!

  • Somehow, it's the last episode of 2019, which is kind of amazing!

  • We've talked about so much cool stuff this year,

  • and we couldn't have done it without you.

  • So to everyone who watched the show,

  • left us comments, subscribed, shared a video,

  • became a patron, or anything in-between

  • thanks for being part of the SciShow Space family.

  • We'll see you next year!

  • [♪ OUTRO]

[♪ INTRO]

Subtitles and vocabulary

Click the word to look it up Click the word to find further inforamtion about it