What Lies Beyond the Edge of Our Solar System?

Every 176 years, the four planets in our outer
solar system present us with a rare opportunity. They’ll align in such a unique way, that
it’s possible to use their gravitational forces to slingshot from one planet to the
next. A PhD student figured this out back in 1965
during his summer job at the Jet Propulsion Laboratory, using just a slide rule and simple
computer programs. This insight became part of an ambitious mission
to send two probes and golden records out into space for a grand tour.

The Voyagers took some of the first detailed
snapshots of planets and moons. And after cruising for over 43 years with
18 billion kilometers traveled, they’re taking humanity into the next great beyond:
interstellar space. The Voyager probes are two obscure looking
robots, weighing about 800 kilograms with giant arms and big ears designed to sense
what’s out there. And it took 1,500 engineers and scientists
to bring these robotic explorers to life. I started working on Voyager right out of
college. It was my very first job as an engineer. Good morning, and welcome to the 5 o'clock edition of
voyager update, I'm your host, Suzanne Dodd. So, Voyagers were really developed in the
early 70's. They were launched in 1977, and the original
goal was just a 4 year mission to explore the Jupiter and Saturn systems. With the possible opportunity to go further
out to Uranus & Neptune, the NASA engineers developed a mission within a mission, outfitting
the probes with 11 different instruments redundant systems and autonomous controls. They each also carried a golden record for
a potential extraterrestrial to decipher.

That's a time capsule of us here on Earth. And if any other being were to find it, they
would know what we on Earth were like in 1977. We have liftoff of the Titan Centaur carrying
the first of two Voyager spacecraft to extend man’s senses farther into the solar system than
ever before. As they hit each planet, the Voyagers beamed
back observations of Jupiter’s turbulent atmosphere, Saturn’s moons, and Titan’s
hazy layers. I really think that the Neptune encounter
was probably the most significant thing in my career. I was involved with all the design on the
closest approach sequence, I really felt like I owned what the spacecraft
was going to execute. And it went flawlessly. We got a big send-off afterwards. The Planetary Society had Chuck Berry come
and play because his Johnny B. Goode song is on the record. I'll always remember that as one of the highlights
of my career. If not, the highlight. As the Voyagers cruised beyond our neighborhood,
Carl Sagan convinced NASA to tell Voyager1 to flip its camera around, and take the first
planetary family portrait.

That’s us, 6 billion kilometers away, the
pale blue dot. And that should have been the end of the mission. But to everyone’s surprise, the Voyagers
kept going, entering a place no one had ever seen before, the final frontier. Since flying past all the planets, we turned
off the instruments basically that were designed to take pictures and repurposed the memory
for this long Voyager Interstellar Mission. The space beyond the planets is very empty,
very dark, very cold. And as you travel further and further, you
see less strength of the Sun. The heliosphere is the bubble of charged particles
around our star, our Sun. They expand out, and then eventually they
stop. And they stop due to the pressure from the
interstellar medium and the wind from the interstellar medium.

The interstellar medium wind is actually created
by exploding stars, supernova, all the other stars and material that are out there are
pushing on our bubble and that is what keeps the shape of it. In 2012, Voyager 1 started detecting changes
in its immediate environment. We started to see dropouts in particles from
the Sun, and increases in particles from the interstellar medium. They dropped down, and then they'd go back
up again. And then on August 25 of 2012, they just dropped
down and stayed down. And similarly, the particles from interstellar
space do the opposite. They bumped up, and they stayed up. The plasma instrument on Voyager 1 wasn’t
working properly, so it was hard to confirm if it really crossed the boundary. There was a lot of debate and by a nice coincidence
there was a solar flare that happened 13 months previously.

Finally reached Voyager 1, and that solar
flare excited the plasma around the spacecraft. That was when the particle instruments said,
"Hey, we're in interstellar space. We see the change in the particles.” Voyager 2 has an active working plasma science
instrument. So we saw the density of the plasma change
almost instantaneously. As they travel through the interstellar medium,
the sheer scale of the universe really comes into perspective. It's studying the interaction of our star,
our Sun, with what's beyond it.

And when you study our Sun, you're studying
the energy that's giving us life here on Earth. Voyager 1 detected unexpected pressure at
the edge of our solar system for the first time, giving scientists clues about the dynamics
we might find in other star & planetary systems. To keep data like this coming in, the Voyager
Flight team has to make careful energy management decisions
We use a nuclear power source that decays at 4 watts per year, and so one of our biggest
concerns now, and what will really limit the lifetime of the mission, is just how much
power the spacecraft has to continue operations.

We also have to pay attention to the temperature
of the spacecraft. We don't want to freeze the propellant lines
that we use to keep the antenna pointed at the Deep Space Network. It's 20 hours to get the signal from Earth
to the spacecraft, and 20 hours for the spacecraft to turn around and acknowledge that they got
that signal. Which really means that the Voyager spacecraft
have to be autonomous. They have to be able to sense for themselves
what's going wrong, put itself in a safe state if it feels like it's under stress. Our day to day engineering activities relate
toward keeping the spacecraft warm enough, making determinations of whether we have to
turn off another instrument heater or not, and then which instrument would you turn off? All of these instruments have been on since
1977. Now these principal investigators who are
in their 80's now, they don't want to see their instrument turn off. The Voyager engineers are still manning this
mission today until the signals eventually stop.

One day we'll come in to the office, and it
won't be there. And that will be the loss of the spacecraft. And that will be a very sad day but also one
where you can reflect on how great the mission was. I think Voyager has touched humanity in many ways. And I think that connects us, as humans, to space exploration..

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