Original subtitles

- [Stuart] Brute force at work.

A European Ariane 5 rocket lifts off from Kourou.

For BepiColombo, Europe's first mission to Mercury,

the real journey has begun.

Its 7.5 year flight is a major challenge

in orbital mechanics, and will see it reach

the smallest and innermost planet

in our solar system in 2025.

There, it's discovery mission will really begin.

(intense music)

(dramatic music)

A joint program with the Japanese space agency, JAXA,

BepiColombo is one of the most complex

scientific missions ever launched.

It carries two orbiters designed

to unravel many of Mercury's mysteries.

These include an unusual magnetic field,

strange surface features called hollows,

and ancient ice hidden in polar craters.

- One spacecraft is provided by ESA,

which is an MPO, we call it MPO,

Mercury Planetary Orbiter, and this spacecraft

has to focus more on the planet.

We want to observe the planet through remote sensing,

characterize the surface around the craters,,

wanting to know about the composition of the surface,

the interior of the planet.

And in addition, we have a second spacecraft,

and this spacecraft is called the Mercury Magnetospherical

Orbiter, more focused on the environment.

And this spacecraft is provided

by the Japanese space agency.

- And we know the Mercury's very hot,

and we have to make the satellite

that can survive in that harsh environment.

And we know, well, it is very difficult,

and we started, when we started,

we already some development,

and we think that we can do it.

But actually, the hot is much harder

than we expected, and takes a long time.

But now, you see, this is the flight model.

- [Stuart] BepiColombo's road, design, research,

and development phase, construction assembly

and testing phase has bene long and hard, culminating

in the launch from the European space port in French Guiana.

- 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 spacecraft, special materials to be developed,

for the antenna, for the solar panels,

and yeah, that was a very big challenge

for the mission in itself.

- Now, of course, we do the health checks

to verify the system is healthy,

and we do the alignment, mechanical checks,

electrical checks all over.

We check the propulsion subsystems,

to see if the propulsion elements are still leak tight

in preparation for the fueling.

- [Stuart] Hardware apart, training of the scientists

and technicians back on earth was extensive,

requiring years of preparation.

(dramatic music)

- Okay, so I have no questions.

- The simulations campaign is the first time

that all the experts involved in the BepiColombo spacecraft,

design, integration, testing, and operations,

worked together as a single team.

The campaign is essential for this group

to learn to work as a single team,

to train the decision making process.

The campaign ins also very important for us

to fine-tune our plans and procedures.

It's the first time that we exercise the flight plans

and procedures in a realistic context,

taking into account communication constraints,

ground station and timing.

- In preparing for a mission like this,

we have to carefully train all the aspects.

What we actually do in the rehearsal,

we do in preparation of a launch.

We train the teams to work together.

We train the teams to work with the flight procedures,

and also we train the teams

as much as we can in flight conditions.

So normally when we test before,

we test with many work arounds.

What we try to simulate here is actually to replicate,

as much as possible, flight condition.

And we typically do between 20 and 30

of these rehearsal before a flight.

- [Stuart] With a nail biting launch sequence complete,

for many it's time to sit back, and wait.

- The cruise will be about seven years.

We will fly by once the Earth, two times Venus,

and six times Mercury itself,

before we come into the orbit, which allows us

to capture, with the small gravity

of planet Mercury against the big sun.

That means when we fly, we constantly brake against the sun,

because we fly into the inner side

of our solar system, yeah?

And then when you fly towards the most heaviest

element there, you constantly accelerate.

We don't want that.

That's why we decelerate.

(dramatic music)

- Because this planet is so close to the sun,

you need to have a lot of energy to go there.

It's even easier to send a spacecraft

to Pluto than to Mercury.

You have to brake into the gravity of the sun,

and you need a lot of energy.

And for that reason, our mission takes quite a long time,

because we also need the help of planetary flybys

in order to bring our spacecraft in.

Then, we want to send two spacecraft in an orbit

around Mercury, and that, in itself,

is also a problem, because on the other hand,

you need to brake against the sun,

but, on the other hand, you also need to accelerate

your spacecraft to bring it in the same speed

as Mercury goes around the sun,

and then to finally drop it into an orbit of the planet.

I'm working now 14 years on this mission,

so it's really like a baby growing up,

and leaving the house finally.

So for me, it's a special moment.

- BepiColombo's main component parts

are two orbiters and one transfer module.

These took four weeks to disassemble and pack,

and required 70 shipping containers

and four cargo planes to ensure safe delivery

to the European space port at Kourou.

(dramatic music)

Spacecraft have got up close and personal with Mercury

twice before, thanks to NASA's Mariner 10 probe,

and some 40 years later, the Messenger mission.

Messenger mapped the surface, and identified strong evidence

for water ice in shaded craters,

but its mission also raised new questions

about this mysterious planet.

This latest probe has a sophisticated suite of sensors

and instruments that will come into play

when it reaches orbit around Mercury.

- So, the big step forward for BepiColombo

is the fact that we have two spacecraft,

the European Space Agency spacecraft,

which is looking directly, designed to look

at the surface of the planet,

and to study the planet in detail,

and the orbiter's designed such

that you maximize the objectives

that you can do relating to the surface.

And the second spacecraft is designed

to look at the environment, and so,

having two spacecraft will enable us

to do a great deal of new science

compared to the previous missions.

- With BepiColombo, with the two satellite approach,

we have one satellite, the MMO, sitting in the solar wind,

and the other one is inside the magnetosphere,

so we can see what is coming towards the magnetosphere,

and what is driving changes within this magnetosphere.

- We have 11 instruments on board the spacecraft.

And when we are at Mercury, these instruments

are gathering data, and then they will store it in,

effectively, a large hard drive,

which we have on board the spacecraft.

That data is then collected over a number of hours,

and when we have a visibility with the spacecraft

in Mercury, typically it's every 16 hours

we can talk to the spacecraft at Mercury.

The data is then down linked using

a very large high gain antenna.

It's a very powerful antenna in order to have

a data rate of about 340 kilobits per second.

If you compare it to your home internet, this is nothing.

It's a very slow data rate, but it's very fast

considering we are very close to the sun,

and we might get some interference

from the energy from the sun.

So it's as powerful as we can have

with the resources we have on board the spacecraft.

- [Stuart] With the assistance of gravity flybys,

the spacecraft will rely on its solar

electric propulsion system.

It consists of four TX ion thrusters,

fueled with xenon gas that is ionized

and electrically propelled out,

providing thrust for months at a time.

The thrusters will rely on the spacecraft's

solar arrays for power.

The T6 thrusters can accelerate

BepiColombo 15 times more efficiently

than a conventional chemical thruster.

- So at Earth, the solar flux is 1.4,

more or less, 1.4 kilowatts per square meter.

As we approach Mercury, which is the most,

innermost plant of the solar system,

that solar flux has risen 10 times.

So now we have 14 kilowatts per square meter.

Now you might think that's a good thing,

in the sense that it gives you more energy

to turn into electricity, to be able to run your thrusters,

but it turns out that that immense flux

that we're getting from the sun

also drives the temperature of the spacecraft very high,

and in particular, our solar arrays, which are sensitive

to high temperature, need to be protected.

Now, we do that in a number of different ways.

We keep as much of the open surface covered

in little mirrors that we call OSRs,

optical surface reflectors, or with specially developed

white coatings, which help to reject the heat from the sun.

But perhaps the biggest mechanism that we use

to keep the solar array cool is to off point.

Rather than pointing the solar arrays directly to the sun,

we point them at a very shallow angle.

And what that does, is it means it keeps

the thermal energies under control,

while still giving us the necessary energy

to turn into electric power for the thrusters.

Now, the reason why the solar arrays are big

is because we're off pointing by so much,

that in order to get sufficient cross section

of the solar array, the solar array needs to be big.

(dramatic music)

(gentle music)

- [Stuart] Protected by multilayered insulation,

hand stitched thermal blankets, and a radiator

to dissipate heat, ESA's Mercury Planetary Orbiter

will have to cope with extreme environments.

- If a unit is getting too hot, if one of the payloads

is getting too hot, in order to stop that payload

from being damaged, we'll switch it off,

we'll send an emergency message back to the Earth,

reporting that there's an issue.

We need ESA to take action, to investigate

why items are getting to hot,

and then to recover the unit and the spacecraft.

- [Stuart] Once they reach Mercury in late 2025,

the orbiters will separate from the transfer module

to begin their comprehensive scientific mission in 2026.

(upbeat music)

- In principle, all the planets have the same

chemical elements, because the whole solar system

has the same chemical composition,

but it's distributed differently

in different planets, and different environments,

so it is vital to understand what is the ratio,

or the abundances of different elements to understand

the structure of the surface of Mercury.

- [Stuart] One of the advanced censors aboard BepiColombo

is a sensitive imaging x-ray spectrometer called MIXS,

which produces a global map of Mercury's surface,

atomic composition, at high spatial resolution.

- The MIXS instrument, the Mercury Imaging

X-ray Spectrometer, looks at the fluorescence

that happens when the sun shines on Mercury in x-rays.

So it's a bit like when you wear a shirt in party lights,

which has been washed in the right sort of washing powder.

The party lights shine on your shirt, and your shirt glows,

and it's exactly the same with the sun and Mercury.

The sun shines on the surface in x-rays,

and the surface of Mercury glows in x-rays,

and if you detect those x-rays,

you can tell what Mercury's made of.

And what it tells you, you're actually

counting the atoms on the surface.

So it tells you, and a very quantitative way,

exactly what the surface layer of Mercury is made of.

- So I would say, one of the most exciting things

about MIXS, is the fact that we will be able

to produce the first images in x-ray wavelengths

of Mercury's surface, and that is going to be able

to give us a great deal of new information,

both on a global scale and on a local scale,

of how the composition of Mercury varies

over its entirety of it's surface.

Another aspect of the MIXS science, which I'm personally

very excited about, is the fact that we can also see

x-rays from the surface, which are being produced

by particles from Mercury's magnetosphere,

actually precipitating on to the surface,

and producing x-rays that we will be able to also measure.

So we can have an extra aspect to the science that we can do

relating to how Mercury's magnetosphere

interacts with the surface.

- [Stuart] Among the mysteries revealed by Messenger

are irregularly shaped depressions,

known as hollows, found in clusters

over a wide range of latitudes and longitudes.

These hollows have bright interiors,

and halos with a fresh appearance

that suggests they are geologically very young.

- I think that there are two mystery,

or two very intriguing objectives of BepiColombo.

The first one, are the hollows.

The hollows are features discovered by Messenger.

These features seems to be quite distributed

all over the south face of Mercury,

and is something related to the volatile,

that come to the south face,

after an impact, after a volcanic event.

(dramatic music)

But, of course, we need BepiColombo

to really characterize it, to understand,

which is the origin of the hollows.

(dramatic music)

- [Stuart] There are also clear traces

of much more recent hollows

where the surface has been eaten away

by some process that removed solid, volatile substances,

such as sulfur, chlorine, sodium, and potassium as vapor.

(somber music)

- And this is because we don't have the composition data.

We have seen, we can measure the dimension,

the size of the hollows.

We can have an idea of the distribution, but no more.

And also, of course, Messenger didn't get so many

high resolution images, and didn't have

the digital terrain mode, the 3D images

at high resolution, as we will provide on SIMBIO-SYS

In other words, I think that the hollows,

the hollows are one of the most interesting

discovery made by Messenger.

- [Stuart] Existing evidence indicates

that if combined and spread out over a city

the size of, say, Washington, the amount of water ice

concealed in Mercury's polar craters

would be over two miles thick.

- The second point is the water,

because even Messenger said that yes,

on the polar region we may have some water ice,

hidden just in the shadow of the craters,

because at the polar region, there are some floor

of the craters, some wall of the craters,

that are not, that are always in shadow,

as occurred on the moon.

But the Messenger didn't have the instruments

to observe if it is, to make a direct measuring of water,

as occurred on the moon.

And BepiColombo and SIMBIO-SYS will be able

to do it with our spectrograph.

(gentle music)

- [Stuart] If confirmed by BepiColombo,

the story of how the inner planets, including Earth,

acquired water, and some of the chemical building blocks

for life becomes much clearer.

It would support the theory that organic compounds,

as well as water, were delivered from the outer

solar system to the inner planets,

and may have led to prebiotic chemical synthesis,

and as a consequence, life on Earth.

- So studying Mercury is crucial to better understand

the formation of our solar system, how Earth is formed

and evolved, and where we are coming from.

So Mercury is, in a way, a 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

want 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 or planets further out.

(dramatic music)

- We all have our individual science objectives

for each of our instruments,

and what we're starting to do now

is to bring all of our ideas together,

which obviously, are complementary to each other,

and we can start to form a broader set of goals

at working group level, so the surface working group

and the environment working group,

and that helps us to, again, maximize the science

that we can get from the mission

by coordinating what it its that we want to do,

potentially looking at specific targets

on the surface, and that kind of thing.

We can work together to get the best

from the mission that we possibly can.

- [Stuart] ESA science and engineering teams

have already been working on BepiColombo

for more than a decade, but with a long journey

ahead, the recent launch marks only the beginning

of the next intriguing stage

of BepiColombo's voyage of discovery.

(upbeat music)