Crazy Engineering: Astrodynamics

The Cassini Mission has been
exploring the Saturn systemfor nearly 13 years and has
rewritten the textbookson the ringed planet
and its moonsbut the spacecraft is
pretty much out of fuel. Following NASA’s planetary
protection guidelines,the mission will
end with Cassiniplunging into
Saturn’s atmosphere,but before
that happens,scientists and engineers have
planned an exciting Grand Finalethat promises some of the most
amazing science and imagesof the whole mission. So, how are they going
to pull this off?Well, it really is going
to take a special kindof crazy engineering. I am here
with Morgan,she’s a scientist on
the Cassini Project. The Grand Finale, it’s
going to be 22 orbits,about six months, what
do we hope to accomplishin that amount of time?We hope to accomplish a
lot of incredible science,things that we have
never been able to do beforewith the Cassini Mission. We’re going to go screaming
over the top of Saturn. We’ll be able to study the
hexagon at Saturn’s north polein greater detail
than ever before. We’re going to go shooting
between Saturn and its rings,threading the needle,which means we’ll be able to
taste the ring particles,be able to understand more about
what those are made of. We’ll also be able to taste the
atmosphere of Saturn. We’re also going to get a better
idea of the interior structurebecause we’ll be getting closer
to Saturn than we’ve ever been. And then, this will all
culminate in Cassini’sfinal plunge into
Saturn’s atmosphere,taking data for
as long as possibleand transmitting
that back to Earth. To be able to do
this engineering,to thread that needle between
Saturn and its rings,is really challenging. That requires something
called astrodynamics. Okay, so what is
astrodynamics?It’s a form of
engineering. But when we think about
engineering, typically,we think about people who are
using physics and technologyto build stuff. Astrodynamicists are
building flight pathsthat will take our spacecraft
to get where they need to go. Let’s go talk to one of
the engineers who’s pivotalin the design of the flight path
of the Cassini spacecraft. Okay, this is Brent. He’s our astrodynamicist
at JPL. Brent, what makes
the Grand Finaleparticularly difficult
and challenging?The Grand Finale
is a series of 22 orbitswhere the periapsis, or the
closest point of the orbit,is actually in this gap between
the upper atmosphere of Saturnand the innermost part
of the main rings. What we’ve done iswe’ve designed this
trajectory such thatutilizing one
last Titan gravity assist,we can jump the entire
ring system and placethe spacecraft orbit inside
the very, very small gapthat’s only 2,000
kilometers wide. This concept of
gravity assist,I think a lot of people
have heard of itbut maybe not completely
understand it. What it essentially means
is you’re harnessingthe gravity of a body that’s
orbiting another body. For Cassini, Titan, a
very massive moon,is orbiting Saturn. If Cassini is also
orbiting Saturn,I can fly very
close to Titan,depending if I fly in front of
or behind or above or below,I can use that gravity
to bend my trajectory. We harness that power. It’s our engine. It’s
our tour design engine. As soon as we do that
last Titan flyby,Cassini’s fate is sealed. It is going to impact
Saturn no matter what. So, some really
amazing sciencebefore we take the
final plunge into Saturn. And let’s remember
why we’re doing that:Why are we flying
the spacecraft into the planet?It’s to protect the
moons of Saturn. For example, Enceladus,this great moon that has an
ocean underneath the surface. It might just be a cozy little
place for microbes to live. Now, if you look at
our spacecraft,we try to keep
it as clean as possible,but there’s a real
chance we’re bringingmicrobes from
Earth with us. There’s no way
to avoid it. We want the moon as
pristine as possiblefor future missions to
go and exploring. So, for everyone
out there,follow the Grand
Finale of Cassiniand check back here for more
Crazy Engineering.

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