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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.

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.

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.

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.

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.

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.

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.

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.

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.

And eventually,
into its atmosphere.

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.

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.

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.

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.

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.