so many years ago my family visited Cape
Canaveral in Florida and we went on some
boring bus tour and then there was an
alligator which was exciting and then at
some point my parents said hey Erica do
you want to go see the decommissioned
Saturn five it looks like this and it
was hot and humid and I wanted to go
back to Disneyworld so I said will it be
air-conditioned and they said yes so I
said okay let's go so we go over there
and the problem with these pictures
everyone has seen these pictures right
the problem with these pictures is they
don't prepare you for the fact that
Rockets are actually really big like
they're actually just enormous and you
can imagine my surprise when this
happens this is 14 year old Erica and
the smallest dimension of the Saturn 5
it is unbelievably large it confused me
I didn't realize this was a real thing
that happened and I think this was the
moment when it occurred to me that maybe
space was big and and and also that
maybe space was interesting and today
I'm gonna talk to you about human space
travel specifically some of the
challenges that human space travel faces
when it comes to fuel so let me sort of
introduce the problem to you now so
suppose we want to have a human mission
to Mars and then we want to bring our
humans back from Mars that's the hard
part so with a Saturn 5 big as it is it
will get you to high Earth orbit and
then at high Earth orbit you need more
fuel ok so let's say we have more fuel
and you get to Mars then at Mars you
need more fuel to come back to Earth but
whatever fuel you're using at Mars you
had to get it there in the first place
and to do that you need more fuel and
you see we have a problem which is that
the farther away from Earth you venture
the more compounding fuel costs you face
as you use fuel to transport fuel and
it's prohibitive and maybe you can think
of some ways around this maybe we could
use solar sails and not need to use fuel
at all maybe we could mine asteroids for
fuel and not have to carry it with us
there's all sorts of really interesting
ideas and one of them was something I
encountered during my high school
science competition days which is called
the interplanetary transit network and
the basic idea here is rather than using
some big rocket to blast our way from
point A to point B instead we're gonna
think really carefully about the path
we're going to take so that the gravity
and movement
all the planets in the solar system will
pull us toward our destination and
that's very abstract so let me give you
a example of the consequences this has
in the in the solar system today here's
a graph of some stuff in our solar
system the horizontal access is distance
from the Sun so Suns on the left then we
have some planets vertical access is
just how elliptical the orbit is and
somewhere in between Mars and Jupiter is
the asteroid belt but we know more about
the asteroid belt than just this we know
the orbits of lots of asteroids in the
asteroid belt and something unbelievably
cool happens when you plot each asteroid
as a dot on this graph look at this
isn't this the coolest graph like what
is going on there there are gaps in the
asteroid distribution there are
particular distances from the Sun where
there are no asteroids what is going on
and and here's what's happening so if we
look at this big gap at two-and-a-half
astronomical units from the Sun if there
was an asteroid there it would go around
the Sun once every four earth years
meanwhile Jupiter orbits the Sun once
every 12 earth years and that means
Jupiter and our asteroid are in sync
every 12 years our asteroid will see
Jupiter off in the same spot then it'll
go around the Sun three times Jupiter
will go around once and it'll see
Jupiter off in the same spot again there
will be a pattern of Jupiter's gravity
pulling and pushing on that asteroid and
over hundreds of thousands of years that
pattern will repeat itself and push that
asteroid off of its orbit so that the
pattern goes away and they're no longer
in sync and each of these gaps are
called Kirkwood gaps is caused by a
resonance between the orbit of an
asteroid and the orbit of a heavy planet
think how many Saturn fives this would
take there are many asteroids that are
just way heavier than anything we're
thinking about sending into space and
they're unprepared yet Jupiter is able
to move them around with its gravity and
this is the effect that the
interplanetary transit network is taking
advantage of the fact that you can use
the gravity of planets to manipulate the
orbits of objects and of course there's
a catch which is that it takes forever
so
in in the top maneuver this is something
it'll save you 20% of your original fuel
cost but it takes over 200 days as
opposed to the original 4 to 5 days and
in another sort of unrelated but also a
fuel saving strategy you can save almost
90% of the original fuel but it takes
years rather than days but the fact that
the numbers in this time required column
are high does not mean that these paths
are useless the fact that we're thinking
about these paths now means we're
considering new types of space missions
that we just never never thought of
before and with our our human space
travel problem we can solve our
compounding fuel issue like this so
remember I said the problem was we're
using fuel to transport fuel so instead
we're gonna use these really slow but
very fuel-efficient paths to transport
our fuel so before we launch our humans
we start launching booster packs
chemical rockets into space and we
slowly pre position them along the path
we're going to take later like bread
crumbs and then 5 years later we launch
our humans they blast right through
picking up all the chemical boosters
enjoying the benefits of fast chemical
rockets without the compounding fuel
costs and I'm gonna close by giving you
an idea of just how much this helps so
if our spacecraft with all the humans
and all the cargo weighs 50 metric tons
this is very conservative by the way
then we would need to launch 3000 tonnes
into low-earth orbit if we're not
pre-play seing our fuel which is a lot
if we do pre place the fuel sort of
using the strategy I I suggested we only
have to launch 600 metric tons into
low-earth orbit and that is an order of
magnitude different that is bringing
space travel human space travel to the
far reaches of our solar system an order
of magnitude closer to reality thank you