Cassini is reaching the life of a very long a good life.
Soon there will be no fuel left for it to continue to make manoeuvres, and so it has
been decided by the Cassini team at NASA that it will go out with a bang.
It currently is darting in between the rings of Saturn and if it survives that, they will
send it on a collision course with Saturn itself.
This way it will avoid crashing and contaminating any of Saturn’s moons.
Cassini is a remarkable spacecraft.
Were it not for space probes, the best image we would have of Saturn is this.
Instead, we are graced with this, this and this.
Out of all my videos, I enjoyed making my Saturn video most of all and it was thanks
to Cassini and the many “wow” moments it provided.
With it about to take its final bow, I felt it only fitting to do a kind of “Cassini,
this is your life” and share some of these wow moments with you.
I’m Alex McColgan, and you’re watching Astrum and together we will find out everything
there is to know about the Cassini-Huygens probe.
The first probe to reach Saturn was the Pioneer 11 probe in 1979.
It was at this time that scientists confirmed that Saturn’s largest moon, Titan, had an
atmosphere.
They knew they had to go back and visit the moon, but this time with a lander.
Voyager I and II were already en route to Saturn at this point, and so it was naturally
too late to include a lander with those missions.
Thus Cassini-Huygens was born, and in October 1997 was launched into space.
Getting a spacecraft to Saturn is no mean feat, as the whole trip is combatting the
gravity of the Sun, trying to pull Cassini back to the inner solar system.
So to help achieve the speed needed to reach Saturn, Cassini used closer planets as gravitational
assists.
It flew by Venus twice, before returning back to Earth.
Earth’s gravity then slingshotted it towards Jupiter which gave it the final push needed
to reach Saturn.
This alignment of the planets which allowed these gravity assists only occurs once every
600 years so timing in this case was crucial.
Cassini really scrapped past Earth on the second time round too; it was only 1,100 km
above Earth’s surface at its closest approach.
This is made even more interesting when you realise what actually powers Cassini.
It is by three RTGs, or radioisotope thermoelectric generators.
Basically, the power source comes from about 33kgs of radioactive plutonium.
The radioactive decay from the plutonium still produces about 700 watts of power even today.
The issue with the spacecraft carrying this radioactive substance is if the scientists
had got their calculations wrong and Cassini had crashed landed on Earth, everybody on
the planet would have been exposed to the radiation.
Now, 33kgs spread out over the whole Earth is a very small amount, but in the worst case
scenario NASA estimated it would have caused about 5,000 deaths from cancer.
They put this down as an acceptable risk though, as the chances of this happening were only
1 in a million.
Cassini used RTGs because solar panel technology wasn’t good enough at the time for the Sun
to power something so distant.
With RTGs, Cassini would have a very long operational life, and it would still be able
to carry on if it wasn’t for the fact it is about to run out of propellant fuel.
Cassini had numerous objectives, to understand the structure and dynamic behaviour of Saturn’s
rings, explore Saturn’s moons more fully, measure the magnetosphere of Saturn, study
Saturn’s atmosphere, and to study Titan more extensively.
This last part is where the Huygens part of the Cassini-Huygens comes into play.
You see, Huygens was a lander attached to the Cassini spacecraft, designed to see what
is going on under the hazy clouds of Titan.
Now Huygens is the part of the mission built and operated by the ESA.
The probe was only about 1.3 meters wide, and weighed 300kgs.
It detached from the orbiter, and spent 22 days in space before entering Titan’s atmosphere.
The only system aboard that was active at this point was a wake up timer, due to wake
up the probe only 15 minutes before it entered the atmosphere.
And when it woke up, what it saw was amazing.
This video is an actual sped up version of the 2 and a half hour descent.
The main mission of Huygens was actually about this descent, taking readings about the atmospheric
pressure, composition, wind speed etc.
The battery life wasn’t expected to last long beyond the landing.
The scientists thought they could be landing on an ocean or lake and so had designed Huygens
accordingly.
From what you see though, it actually landed on what could be actually the bed of a dried
up lake.
But that is a topic for another video.
The mission for Cassini itself has been remarkably successful.
As well as the scientific data it has picked up over the course of these last 13 years,
it has been able to provide some of the most stunning pictures found of space.
I just want to showcase some of my favourites of Saturn.
And of course Saturn’s moons are beautiful in their own right.
Some very dedicated souls have even taken 1,000,000 photos Cassini has taken to show
us what it would be like to be sitting on the Cassini spacecraft.
These are all real images, only colour corrected and enhanced, there is no CGI.
Simply amazing.
So what is Cassini doing now?
Before is vaporises in Saturn’s atmosphere, it is performing some very close flybys of
the planet and some of its moons, getting closer to Saturn and its rings than it ever
has before.
Beginning on Nov. 30, 2016, Cassini has repeatedly climbed high above Saturn's north pole, then
plunged to a point just outside the narrow F ring (the edge of the main rings), completing
20 orbits.
Then, on April 22, 2017, Cassini will leap over the rings to begin its final series of
daring dives between the planet and the inner edge of the rings.
This is the Cassini "Grand Finale."
After 22 of these orbits, each taking six days to complete, the spacecraft, will plunge
into the upper atmosphere of the gas giant planet, where it will burn up like a meteor,
ending the epic mission to the Saturn system.
NASA’a website states the reason for this final mission.
As it plunges past Saturn during the Grand Finale, Cassini will collect some incredibly
rich and valuable information that the mission’s original planners might never have imagined:
The spacecraft will make detailed maps of Saturn’s gravity and magnetic fields, revealing
how the planet is arranged on the inside, and possibly helping to solve the irksome
mystery of just how fast the interior is rotating.
It will vastly improve our knowledge of how much material is in the rings, bringing us
closer to understanding their origins.
Cassini’s particle detectors will sample icy ring particles being funneled into the
atmosphere by Saturn’s magnetic field.
Its cameras will take amazing, ultra-close images of Saturn’s rings and clouds.
No other mission has ever explored this unique region so close to the planet.
What we learn from these activities will help to improve our understanding of how giant
planets – and families of planets everywhere – form and evolve.
And at the end of its final orbit, as it falls into Saturn’s atmosphere, Cassini completes
its 20-year mission by ensuring the biologically interesting worlds Enceladus and Titan could
never be contaminated by hardy microbes that might have stowed away and survived the journey
intact.
It’s inspiring, adventurous and romantic – a fitting end to this thrilling story
of discovery.
Well thanks for watching!
I will likely do another video on Cassini shortly before it’s mission ends, as it
is already producing some stunning imagery which it wasn’t close enough to get before.
If you liked this video, you will likely enjoy my others too so subscribe for more!
I also now have my fourth patreon!
Thank you to Eli Baum and Tariq Mulla for your support, it means a lot.
So that’s it, see you all next time.