Original subtitles

- [Narrator] The Soviet era Luna Three

was the first spacecraft to use gravity

to change course to photograph the dark side of the Moon.

The NASA Mariner 10 mission used the technique

to swing by Venus to target Mercury.

The gravity assist or a sling shot maneuver

has become a standard for navigating the solar system

with our probes reaching further, faster,

and more accurately than ever before.

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The Voyager mission started by chance over 40 years ago

when Michael Minovitch, a mathematical PHD student

decided to tackle celestial mechanics holy grail.

It was known as the three body problem, as it looked at

the Sun, a planet, and a third object traveling in space,

and how gravity from the two objects

affected the trajectory of the third.

Minovitch was eager to take advantage

of IBM's latest computer, the 7090.

This computer was a second generation

transistorized version of the IBM 709.

A vacuum tube mainframe which had a processing speed

of around 100 kiloflops per second.

Unthinkably slow by today's standards.

The laws of physics and the conservation of momentum

demand that the probe approaching

the gravitational influence of the planet

and accelerating will then decelerate upon leaving

that gravitational field with a net speed increase of zero.

However, the probe's speed and direction

will change in reference to the Sun.

His solution has become known

as gravity assist or sling shot.

While undertaking an internship at NASA's JPL,

he convinced them to test his model using their data.

The results confirmed his predictions that if it flew

close enough to a planet, a spacecraft could utilize

that planet's motion to accelerate itself away from the Sun.

When Cal Tech graduate Gary Flandro was tasked to see

if gravity assist could aid deep space missions

to the outer planets, he discovered there was to be

an alliance of Jupiter, Saturn, Uranus, and Neptune,

an even that occurred only once over 176 years.

An opportunity not to be missed.

So it was decided to launch a mission in 1977.

Two spacecraft would be launched

which would sling shot past all four of them.

A grand tour of the solar system's

outer planets in a 12 year time frame.

This was to become known as the Voyager missions,

and the rest is history.

- Ultimately we're able to put together a picture

of where we are in the galaxy and how that environment

then influences our environment right here at home.

In particular, the radiation environment

which has implications for all sorts of things,

including human exploration of space.

- [Narrator] Today, those two spacecraft have continued on

beyond the influence of our Sun into interstellar space.

The farthest traveled by a manmade object.

This field of influence found the basis

for all future missions, allowing man to set

his sights on getting into deep space economically.

The Rosetta mission had different challenges

to catch up with and orbit a comet,

67P Churyumov-Gerasimenko.

It had a large elliptical orbit around the Sun stretching

from the orbit of Jupiter to within the orbit of Mars.

Launched in 2004, a year later the probe

passed by Earth for the first gravity assist

that flung it towards the orbit of Mars.

Two years later, Rosetta grazed Mars building up momentum,

then swung by Earth for a second time,

launching it deeper into space.

The following year, Rosetta passed by asteroid Steins

before swinging back for a third gravity assist from Earth.

And in 2010, Rosetta passed by asteroid Lutetia.

Going into hibernation, Rosetta continued its parabolic

trajectory towards its final destination.

Four years later, Rosetta emerged from

its cold sleep as it crossed paths with the comet.

A fortuitous flight indeed.

The spacecraft then embarked on a series of maneuvers

that took it on two successive triangular paths.

It's trajectory was fine tuned with thruster burns until

it closed in to within about 30 kilometers of the comet,

where the spacecraft entered actual orbit around it.

Rosetta remained with the comet, delivering it cargo,

then conducting science observations as it swung

about the Sun, then concluded with a gentle impact

on the comet's surface in 2015.

- We're gonna refine our ideas of what the comet is,

where the comet came from, and encapsulate that

within our ideas of how the solar system formed.

And the complexity of the data set that we have also

allows us to be more complex in our ideas and our theories.

And that is the beauty of Rosetta,

and we're starting to see that happening now.

We're really able to hone down our ideas

of how the comet formed, how that fits in the evolution

of the solar system, and that's going to continue.

The Ulysseys spacecraft had to leave the ecliptic plane

of the solar system to study the polar regions of the Sun.

Accordingly, it needed to change its orbital inclination.

This required a large change in heliocentric velocity.

So a gravity assist maneuver around Jupiter was chosen.

The giant planet's gravity bent the spacecraft's

flight path southward, putting it into a an orbit

over and under the Sun's north and south poles.

The ion powered Dawn spacecraft

took maneuvering a step further.

- [Marc] Dawn's the only spacecraft ever

in more than 58 years of space exploration

to orbit two extraterrestrial destinations.

The last uncharted worlds in the inner solar system.

And it not only allows us to get to these distant bodies,

but once we're in orbit, we can maneuver

extensively in order to get the best possible

science that we can from them.

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- [Narrator] NASA's latest mission is under way.

Osirus Rex is the agency's first attempt

at intercepting and touching down on an asteroid.

No ordinary asteroid, either.

Bennu is its name.

Orbiting the Sun very close to Earth's orbit,

it has been deemed a possible

impact threat in the coming centuries.

NASA intends to take a sample of the asteroid

and return it to Earth for further study,

and possibly help form plans to redirect Bennu.

To match the orbit, Osiris Rex made a very close

swing by the Earth a year after launch.

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It passed by the south pole to change its orbital

inclinations several degrees to match that of Bennu.

Once matching orbits, Osiris Rex must perform

a series of braking maneuvers to match the velocity

and enter an orbit around the asteroid.

After mapping and studying the body,

Osiris Rex will drop down to the surface

and collect a sample of material.

With some clever robotics,

the sample return capsule will be delivered back to Earth.

- Well the thing that is so intriguing to me

about asteroids is that they really are time capsules.

They actually are samples of what the solar system

was like billions of years ago.

Asteroids are small bodies that never

got made into something big like a planet.

So anything that got made into a planet got melted down,

got changed, there were lots of things that went on.

Asteroids are pristine.

Nothing really altered them for billions of years.

So when you go out and you take a sample of an asteroid,

you have in your hands a real sample of

what the solar system was like billions of years ago.

What were the conditions, what was the chemistry like?

What can you learn about the formation of our own planet

and ourselves by looking at what the solar system

was like billions of years ago?

And this sample is incredibly scientifically important.

I think that people will be studying it

for generations to come.

- [Narrator] The Juno space vehicle

was launched in August 2011.

In 2012 at Perihelion, the craft performed

some maneuvers out beyond Mars orbit and arched back

towards Earth for a kick in speed and direction.

In October 2013, it flew by Earth

a mere 500 kilometers from the surface.

This sling shot sent it on a three year journey

directly towards an intersection with Jupiter.

- Jupiter orbit insertion is probably one

of the most important things in the entire mission,

and it's because that changes us from being in orbit

around the Sun to being captured in orbit around Jupiter.

And if you're not in orbit around Jupiter,

you can't do the science we want to do.

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And what we're learning now is, even in other solar systems,

they don't always all have a monster like Jupiter.

And many people think,

boy you almost need a Jupiter to have an Earth maybe.

Jupiter played a big important role.

But its environment, everything about it is extreme.

It's the planet on steroids, right?

It is the most extreme in every way it can be.

So it has the strongest magnetic field,

the strongest gravity field, it has the most

harsh radiation, it's spinning super fast.

I mean it's, everything about it is extreme environment.

- The Juno mission is unique because it's the first time

that we've ever gone in a polo of it,

which goes from pole to pole.

Over the north pole, through periapsis,

and under the south pole.

All the other missions we've done and all the observations

we've made from Earth were made from the equator.

And you don't see the poles very well

if you're sitting on the equator.

So this is the first time we got the first clear,

unobstructed view of what the aurora looks like

and what the polar phenomenon looks like.

And at the same time we're flying through the magnetosphere

right above the aurora so we can sample

the charged particles that are precipitating down

magnetic field lines, the guys that are exciting

the emissions that we see.

This is the first time we've ever been able to do that.

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- [Narrator] The 6.7 year, five billion kilometer

transit journey of the Cassini probe

was slightly longer than the direct home and transfer.

The mass of the Cassini spacecraft was such

that even with a Titan Four launch vehicle,

Cassini needed added help to reach Saturn.

So to gain momentum, the Cassini mission

included several gravitational sling shot maneuvers.

Two flyby passes of Venus, one of the Earth,

and then one from the mighty planet Jupiter.

The Cassini orbiter then spent several years orbiting

and maneuvering around the planet and its moons.

Finally diving through the inner rings of the planet.

- When we go into the proximal orbits between the rings

and the planet, we've never been there before

and we'll be a little bit more concerned.

Here we've actually been closer to these rings,

the Janus/Epimetheus Ring and the F Ring,

when we went into orbit around Saturn.

So this is not unexplored territory at this point.

The nice thing about this though is that

we've got a much better viewing angle of the rings

because of the Sun this time around.

- [Narrator] And eventually, into its atmosphere.

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The New Horizons spacecraft had further to go than Cassini,

but being far less massive a probe it was able

to be launched directly towards Jupiter.

The spacecraft was launched in 2006

and made its way to Jupiter.

Its closest approach happened only a year after

its departure at a distance of 2.5 million kilometers.

The flyby provided a gravity assist

that increased the probes speed.

It also allowed for a general test of New Horizon's

scientific capabilities, returning data about

the planet's atmosphere, moons, and magnetosphere.

Most of the post Jupiter voyage was spent

in hibernation mode to preserve onboard systems.

In 2014, New Horizons was brought back

online for the Pluto encounter.

It flew 12,500 kilometers above the surface of Pluto,

making it the first spacecraft to explore the dwarf planet.

And the on into the Kuiper belt towards its next target,

A Kuiper belt object most likely composed of frozen

volatiles or ice, such as methane, ammonia, and water.

A future probe to return to Jupiter's moons

is destined for another multi-year journey.

Juice, to be launched in 2022, will embark upon a seven year

odyssey taking the spacecraft via an Earth swing by,

then to Venus, back to Earth with a sling shot to Mars,

then back to Earth for a final kick direct to Jupiter.

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Heading outward bound is one thing, but launching payloads

inward towards the Sun is another set of problems.

For example, the BepiColombo mission from Mercury launching

this year will require nine gravity assist maneuvers.

After launch, a two year journey using ion propulsion

will bring it back to Earth for a kick towards Venus.

Followed a year later by another flyby of Venus

sending it closer towards the orbit of Mercury.

In the following four years the spacecraft will pass by

Mercury, tightening its heliocentric orbit, until it can

match Mercury's speed, and with the aid of chemical rocket

motors, insert itself into that planet's orbit in 2025.

- So studying Mercury is crucial to better understand

the formation of our solar system.

Our Earth was formed, it evolved,

and where we are coming from.

So Mercury is in a way, the missing piece in the big puzzle

of the formation of the solar system, and a crucial end

member because it's close to the Sun and if you're going to

get the full picture you have to look at the planet

close to the Sun, as we also did in past missions that

we were looking at the comets and planets further out.

- Our main target is the environment around Mercury,

especially the interaction between

the solar wind and magnetosphere.

- Mercury is three times closer to the Sun,

and therefore the radiation or the heat

which we are getting from Mercury is 10 times higher.

So everything which we had to develop had to

withstand the higher temperatures, but also the higher

radiation doses, which we got from the solar wind.

And for that we need special insulation of our space craft,

special materials to be developed for the antenna,

for the solar panels, and that was a very big

challenge for the mission in itself.

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- [Narrator] There are two more missions in the next year

or two that will travel further inward than Mercury.

ESA's solar orbiter, and NASA's Parker solar probe.

Planned for a 2018/19 launch, ESA's solar orbiter will take

several gravity assists from Earth and Venus to enter

an elliptical orbit resonant with Venus so that subsequent

gravity assists will raise the orbital inclination,

resulting in an operational orbit of 25 degrees

and climb to the ecliptic plane,

and increasing to 34 degrees,

making direct viewing of the Sun's polar regions possible.

During the nominal seven year mission, the main scientific

activity will take place during the near Sun encounter

and high latitude parts of each orbit,

with different science goals planned for each orbit.

Together with NASA's Parker solar probe mission,

it's hoped it will revolutionize our understanding

of the Sun, where changing conditions can percolate out

into the solar system affecting Earth and other worlds.

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Launch window is late 2018.

It will use Venus gravity assists during

seven flybys over nearly seven years

to gradually bring its orbit closer to the Sun.

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At closest approach, the Parker solar probe will travel

around the Sun at approximately 700,000 kilometers an hour.

At closest approach to the Sun, some 10 times closer

than Mercury, the front of Parker solar probe's solar shield

faces temperatures approaching 1,377 degrees Celsius.

It will travel through the Sun's atmosphere,

closer to the surface than any space craft before it,

facing brutal heat and radiation conditions,

and ultimately providing humanity

with the closest ever observations of a star.

Flying into the outer most part of the Sun's atmosphere,

known as the corona for the first time, Parker solar probe

will employ a combination of instrumental measurements and

imaging to revolutionize our understanding of the corona,

expand our knowledge of the origin and evolution

of the solar wind, and explore what accelerates

the solar wind as well as solar energetic particles.

It will also make critical contributions to our ability

to forecast changes in our space environment

that effect life and technology on Earth.

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