What Physicists Do – September 18, 2017 – Scott Manley
What Physicists Do – September 18, 2017 – Scott Manley

[ Music ]>>Okay. If I could have
your attention please, we shall get started today. So in our last talk
we were very happy to welcome someone whose
job title I was envious of. But today we’re welcoming
someone who I’m envious of because they have
an even better job. A scientific communicator
with a great following and making great content. So I’m very pleased to introduce
our speaker Scott Manley. He’s in the [inaudible] series because he attained his
undergraduate in physics and astronomy followed by a
computational physics masters from University of
Glasgow in Scotland. He did this in five years
languishing the academic quagmire at the Anor Observatory
before making that sort of transition into more
private sector work with his work at Apple today. But also the thing that we’re
putting most important is actually his videos on YouTube
and his video productions that really appeal to people. I’ve used many of his
videos in my introductory to astronomy class because they
give a way for me to connect when they are often very
difficult and ethereal ideas to something that
people can really engage with in the material. So let’s welcome
our speaker today. [ Applause ]>>Oh. Everybody
knew that was coming. I’ve got to just say, our MOBS
outfit, it’s not a quagmire. I was making it a
quagmire of my own making. Let’s be clear. Great place. So yeah, you probably know
me from this YouTube thing where I post videos to the
internet and people watch it. I’ve got like 600-something
thousand subscribers. And I split my time between
you now video games and science and somehow make
them work together. But my first big success on
the internet was this video that came from my PhD work,
which never completed. [Inaudible]. So I was studying small
solar system bodies, right? And so this is a map
of the solar system. You can see here this is 1999. So this is basically
showing where asteroids were when they were discovered. And this video actually
starts in the 1970’s and it goes forward and it shows
all these discovery patterns. For example, most of the asteroids were
discovered opposite the earth because you can’t point a
telescope towards the sun. You can see that
it pulses, right? Roughly 12 times a year. And that’s because when
the moon is bright, when you’ve got a full moon,
it’s harder to see things. The discovery rate drops. There’s also a dark
area down here that corresponds
to June and July. And that’s actually because
that’s when it gets cloudy in Arizona and a lot of
telescopes are down there. The other things to see here are
the red asteroids are the ones that cross the earth’s orbit. The yellow ones can come close to earth’s orbit
but don’t cross it. Out here you can see
barely that there is a mass. That is the Trojan asteroids. Those are locked
gravitationally to Jupiter. These ones I’m trying
to figure out. Are these the trailing
over here? No, there’s Jupiter there. So these are leading Jupiter. Oh, and this radial — you
saw that discovery pattern. That came and went. That was a spacecraft
called WISE. That was a White-fueled
Infrared Survey Explorer. And it added so much to our
discovery, to our knowledge. Because it was looking
in the infrared. So yeah, a day on YouTube for me is half the time
I’m doing silly videos like how General Mills helped
the Soviet Space Program image the far side of the moon. You know, can you power the
Death Star with Twinkies? The TV show, the Expanse, I
did a whole thing where I tried to figure out how
amazing the engines were on those spacecraft
and things like that. This video has been
surprisingly popular because people see the
thumbnail and they think, “He’s standing next to
a giant Gatlin gun.” But that is actually a rocket which is launching
out in New Zealand. But yeah, I also play
spaceship video games. There’s Elite: Dangerous,
No Man’s Sky, Star Citizen, Eve Online, more No Man’s
Sky and I don’t know. Some other spaceship game. But the main topic
of my talk is, can a video game really
teach rocket science? And of course the video
game that I am talking about is Kerbal Space Program. Now many of you wonder,
what is Kerbal, because you know what
a space program is. Well Kerbal is a
little green man. That’s these three here. We’ve got Bill, Jed and Bob. And varying abilities. We’re not sure how they got into
this space program, but yeah, they ask, “How hard can
rocket science be anyway?” So Kerbal Space Program. I didn’t develop it. Many people think I had
something to do with it. No, I just started playing it. I was developed by a guy
called Philippe who I was at a Mexican company
that was working in PR. And he really wanted to make
a video game, so they let him. And it became much bigger
than the rest of the company. It was released in June 2001 as
an early access title for free. And the amazing thing about
it was it was almost perfect to start with. Because what you could
do was build a rocket, fly the rocket, crash
the rocket. It had all the important
parts of the game. But it was developed all
the way up to April 2015 when it reached its 1.0 version. And there’s been a few
more updates since then. We’ve got a 1.3.1
release coming. It sold at least 2 million
copies, although they’re kind of quiet about how many exactly. It’s on every major platform. You know, PC, Mac, Linux,
Playstation 4, Xbox One, and it’s in five
different languages. And they were acquired
by Take 2 interactive. But yeah, the way the game
works is you bolt parts together to build a rocket. And then once you’ve got that
rocket, you can unleash the laws of physics on this thing
and attempt to fly it. You have a whole start
system to explore, and optionally you
can play it as a game where you unlock better
parts by exploring. And I think the core part
of this ultimately is that failure is always an
option and can be the best part. So roughly this is
how the play goes. You know, I’ve got a
bunch of parts here, and this is obviously being
played in accelerated time. I get a catch-all, I’m
putting fuel tanks on, putting on an engine. We’ve got a decoupler here
to split the rocket apart. And then I attach some solid
rocket boosters to the side, maybe add some aerodynamics. And we’re ready to launch. And the thing of
course flies away. This is all following
the laws of physics. Every single part of this
rocket is being modelled. You see me ditching
the side boosters. And that’s as far
as that video goes. Yeah, I truncate these things
to fit into a typical talk. So yeah, with Kerbal
Space Program, people love to copy real things. And yes, people build
full-scale Saturn V’s. They replicate the
Apollo-Soyuz mission which of course requires
not just a Saturn V, but a Soyuz rocket. Everybody loves to
build space shuttles and they are the
hardest things to fly. I mean, you know, looking
back at the space shuttle, it’s like a first car. It has all these problems
but you love it nevertheless. It has weird electrical
issues and whatever. And people build aircraft because of course it
models atmospheric physics. There’s the Mere Space Station,
the International Space Station and something even bigger. And hey, you know, you can
also steal ideas from movies. That is a version of the
Aries from The Martian. Obviously heading to Dunum,
which is the equivalent of Mars in the Kerbal Space
Program universe. And people keep building
crazy things. But actually people
do build crazy things. Spaceship, yeah. This is a real spaceship. But going beyond that — yeah. And I’m going to be clear:
this is not just animated. This is actually following
the laws of physics. Somebody built actual
flapping dragon mechanics. It follows all that. You know, Game of
Thrones recently — I had people on Reddit contact
me asking, “Could you figure out the aerodynamics of dragons? Because we have a few questions of whether Denaerys
can hold on.” Again, you know, popular culture
is everywhere in this game. Obviously Mad Max. We don’t have flamethrowers
in the game, but we do have rocket engines which are a pretty
good substitute. Anime robots, yeah. Again, this is fully
physically modelled. This isn’t just animated. Somebody built a
transforming robot with a sword and they flew that. It blows my mind. So yeah, the truth is though
that when it comes to space, space is awesome and
reality isn’t far away from the crazy ideas that
people put into this game. And so a common idea is the
rocket-powered lawn chair. And basically you know,
you’ve heard with the guy with the lawn chair
and the balloons? Well you know, you’ve
got rockets. Let’s attach some rockets
and fly around like that. But it turns out that NASA,
or you know, people associated with the Apollo project were
actually investigating something like this for moving
around the moon. Obviously the rover
was the better choice because it could travel further
and it required less fuel. But this was a real thing. It was called — well, I
can tell you about it later. We have the Man Out
in Space Easy, which I’m wearing the T
shirt of today actually. This was a concept that if
your spacecraft was in space and it suffered some
sort of terrible failure and could not return to earth, you would have a
suitcase you could open up and it would contain
enough materials to make a foam heat shield. You would have handheld
rocket thrusters. So you would more or less
maneuver your heat shield to the right orientation
and guess and just fire your thrusters,
try to keep yourself straight. And then you would parachute
back after performing reentry on basically a giant
marshmallow. Like astronauts were expected
to be awesome back then. And truthfully, astronauts
are still awesome today. We have the rotary rocket. This was another legit
concept which was developed. They flew a prototype
of this out at Mojave. It was all the worst
parts of the helicopter and the rocket combined
into one. Brian Benny I believe was
one of the test pilots and he considered it to be the
hardest thing he’d ever flown. And he was a guy that
flew Spaceship One. And yeah, this was —
somebody get a patent on the rocket catcher. The idea is that a rocket coming
back would fly up horizontally and be captured by
a giant pneumatic — I don’t know what
they were thinking. They clearly didn’t
do their math. But yeah. Coming
back to crazy ideas, coming back to the
lunar escape system. So the lunar escape system — remember that rocket-powered
lawn chair? The idea behind that was that
as the Apollo program was going to be spending more and more
time on the surface of the moon, there would be more and more
things that could go wrong with the ascent module
and the spacecraft. And so they wanted to
have a backup plan. And so this was the backup
plan they came up with. They would be able to
fly this back to orbit. And you see a few
different versions here. We’ve got one guy standing
up and one guy reclining with some instruments. The fuel tanks would
be flexible. They would take fuel
from the lunar module and then just actually
inflate the tanks. They would have a spare engine and they could fly
that to space. The thing is, since it would
be an emergency system that had to be carried to the surface
of the moon, they had to cut down as much unnecessary
weight as possible. For example, they couldn’t have
the Apollo guidance computer because that was huge and
it needed lots of power. So the ascent profile
was literally, they would have a table of
times and they would fly upwards for three seconds and then it
would pitch forward 45 degrees, fly that profile for a
certain amount of time. And then there would
be another stopwatch where they would have
to level out exactly. So that was possible. But then somebody had the bright
idea of saying, “You know what? We could actually get rid of
the reaction control thrusters that steer this thing and
just have the guy kind of leaning left and
right, just like a Segway and fly a rocket like that.” So they actually tested this. This is a simulator. This guy is standing on essentially a load cell here
you know with four transfusers in the corners and it’s
needing a computer. And they flew that into
orbit, and this was 1970. NASA basically invented
the Wii balance board. And yeah, you know, of
course you can link this up to Kerbal Space Program. I did this for fun. This is my son Orion and he’s
trying to fly this aircraft in rather dramatic
style I guess. It turns out that flying
aircraft using a balance board isn’t the easiest
thing possible. But it’s fun nevertheless. So yeah, Kerbal Space Program
lets you do all these things. It lets you simulate
all the physics. And it turns out
that is actually used by rocket scientists. And I say used. It’s played with. There’s some quotes
here and there. “We are SpaceX software
engineers. Do you play Kerbal
Space Program? Are you kidding? That’s how we design
our rockets.” [ Laughter ] Here’s someone, a NASA sim
labs engineer who has talked about you know playing
with Kerbal Space Program. He’s helping out. Here’s Twitter. Here’s Tory Bruno who’s head
of the Knight Launch Alliance, the Launch Atlas
and Delta Rockets. And of course Elon Musk also
loves Kerbal Space Program. And yeah, Elon Musk
— I don’t know if you’ve watched
the recent videos. They had a great blooper
reel showing all their failed landings and one
magnificent conversation. This is one of my favorites. This is from Vandenburg. It was a little mistake
and their gear froze up. The thing was, when that was
shown, the Kerbal players came up with a plan to help
Elon Musk with this, because they knew he was a fan. So again, simulating this
thing entirely in physics. There are no like — there’s no
cheap animation going on here. Yeah, somebody thought, maybe
we could build a giant robot and just grab the rocket. Again, this blows my mind. Because that’s every single
joint there is simulated according to the
laws of physics. They’re a little
squishy, but yeah. So let’s talk about the
physics in the game. Because of course we are
physics and astronomy. So the game is based
on the Unity engine. And Unity comes with
a physics engine which lets you model solid
bodies with colliders and models that are inertia. And the rockets are
actually made up of a bunch of
individual parts. Now when you see the rocket, you might think that’s
one single entity. It’s actually many
different parts all flying in extremely close formation. So for each part, you’re modelling the
motion and the rotation. You’re modelling the forces of
gravity, thrust, aerodynamics. You’re modelling the joint
strength between these things. You’re modelling the impacts
between that and other objects. You’re also modelling the fuel
transfer between parts, right? Which can be very important
for aerodynamic stability. The joints can break
of course as well. That’s another thing. You’ve got these parts
that can be broken apart or they can explode. And one other thing I should
mention is that once you get out to really large scales, we switch over from this very
detailed physics simulation to a kind of global
Kepler’s laws so you can model the orbital
mechanics a lot easier than would be available with
the Unity physics engine. So an example of all this
working together is this video of — this was supposed
to be an SR-71. And what’s going to happen
is this engine is going to shut down. We’re traveling at about Mach 3. And all the physics is
going to kick in and yeah, aerodynamic forces
shear it apart. Because you have an asymmetric
thrust, it turns yaws. The aerodynamics tear it apart. The joint forces get exceeded. And yeah, the whole
thing falls apart. This actually happened to an
SR-71 Blackbird in testing. They had — I don’t
know if you know, the Blackbird had very
complicated engines for the time. And a big part of it was the
intake had to have the cone in the correct position. If it moved too far forward, then the shockwave would get
lost and if it’s too far in, the shockwave would be
putting too much energy. And it had a complicated analog
computer to control this. And sometimes that went wrong. And that did actually
happen to an aircraft. One of the pilots survived. Like he literally got
torn out of the aircraft and the pressure
suit protected him. The other one, sadly, didn’t. So one of the themes I think of
Kerbal Space Program really sets up as a learning
tool is the fact that everybody makes mistakes. And smart people
learn from them. And Kerbal Space Program gives
you an opportunity to learn from mistakes you
could only ever make with multibillion-dollar
spacecraft. And one of my favorite examples of a rocket scientist making
a mistake is this guy. Does anyone know who he is? Goddard, right. Robert Goddard. He was one of the first people
to build liquid fueled rockets. He was a real innovator
and this is the 1920’s. Now the thing about
his rocket is that he put the exhaust
nozzle, right, the actual rocket engine
is sitting at the top. And the fuel is down here. Now he made the mistake
that many, many amateurs do. What he thought was that this
would behave like a pendulum where because it was being
suspended from the top, if it deviated it would
swing back, right? And that’s a very
tempting thing to think. However, the problem is that
once you start going up, if you start to deviate over, well your thrust vector is
deviating with your vehicle. So it doesn’t act as
a restoring force. And his rocket went up and
crashed exactly like that. It doesn’t matter where
you put the rocket exhaust. The vehicle is equally stable. So it doesn’t lose stability. It just doesn’t get you
any magic stability. Another favorite example of
people getting things wrong and learning from the
mistakes is Gemini IV. Gemini IV was most famous
because it was a Gemini mission where they performed the first
spacewalk in the US, right? But part of that mission was
also a kind of opportunity that was added at
the last minute. They said, “Hey, we figured out
that you’re now going to be able to fly your Gemini spacecraft. Could you try turning it around and flying back towards
the upper stage booster and practice rendezvousing
with it?” Now it would only
be like a mile away when they started doing this. So they turned the
spacecraft around and they thrust towards it. And of course, they
didn’t want to hit it. They did this rather slowly. And they’re estimating
the distance. And what happened of course
is they spent the next hour and a half just flying
in circles, unable to get close to it. They were flying
Gemini like an aircraft. They were test pilots. When you have two spacecraft
or two objects in space, I’m going to use this
pointer here, you’re traveling around the earth like
this in a circle. And when this one
accelerated towards the booster that was behind it, it
slowed its orbital velocity, which meant that it
began to drop down. And as it began to drop down, it picked up the
converted potential energy into kinetic energy. And so it began to go faster. And this is one of the things
that gets people all the time. If you slow down in space, you
actually end up going faster. Right? This gets
people all the time. So they were unable to do it. They didn’t have
the gear to do it. In later Gemini missions
they would perform rendezvous with the Agena. They would learn it all. Many people made the excuse
these guys didn’t have the proper gear to do it. But I’m going to point out
that this guy, Buzz Aldrin — you might have heard of him. His PhD thesis was on
orbital rendezvous. And on Gemini XII he
was on, they were going to perform a rendezvous. And the radar equipment that
the previous Gemini had used broke down. Of course, he was Buzz Aldrin. He brought out his
sighting gear, some slide rules, did the math. Yeah, he calculated
the rendezvous by hand. So yeah, you know, he
was pretty awesome. There was also Jim
Lovell in there. So yeah. How well I
understand orbital mechanics. I mentioned [inaudible]. I mean, this is so true. I get this all the time, right? There was somebody, Planet
Labs I was talking to. They launched these little
Cube Sats into earth orbit for earth observation. They’re basically
doing Google earth but they’re refreshing it
every single day with new data. So he was explaining to me
how they launch everything, all these Cube Sats
in one bunch. But they want to spread
them out through the orbit. So they take the Cube Sats and they turn their
solar panels edge-on into the air to increase
the drag. And he was halfway through
explaining this, how the ones that you know increase the
air resistance slow down and go back along the orbit. And then it’s like, “No, wait. This is orbital mechanics. The ones that slow down
go forwards in the orbit.” So you know, it’s very
hard to get through this until you’ve played
with it a lot. And that’s one of
my themes of this. Kerbal Space Program gives
you the chance to mess around with all these things. So how does Kerbal Space
Program actually help? What can it really teach you? So I’m going to start out, yes, it teaches you Newton’s
laws of mechanics. And I’m not saying that it
teaches you Newton’s one, two and three. It doesn’t teach you
that force is equal to mass times acceleration. What it gives you is the
sense for how these laws work. Right? It gives you the idea that a bigger thruster will
accelerate you faster, right? That if you don’t apply any
thrust, you’ll kind of float in the same direction. That if you bounce into
things, you will bounce off. It teaches you Tsiolkovsky’s
rocket equation. Kepler’s equations
for orbital mechanics. The Oberth effect, which
you may not have heard of. It teaches you things like
how aircraft stability works. And of course it gives you
plenty of opportunities. It gives you the
inspiration to go out and read about real-world rocket science. So let’s go into something that
plays a part of the science of Kerbal Space Program:
delta v. Delta v is of course the change
in velocity, right? This is what the normal
engineer would tell you. Of course a rocket engineer
will say, “Oh, [inaudible].” Right? This is from SMBC. But yeah, delta v is essentially
how much velocity change you have either required
for a set of maneuvers, or how much delta
v your rocket has. And these two things
go hand-in-hand. Now I don’t know if you
guys have done this, but you can derive delta v of
a rocket using Newton’s laws. What you have of
course is a rocket, and then it expels
a slug of fuel. That’s exactly how a
rocket works, right? So v plus delta v —
you can do calculus. You end up with Tsiolkovsky’s
rocket equation. I’m not going to go into
the derivation of this. But you understand
conservation of momentum, right? You have a small increase
over a small amount of time. And as you spit out more
of these chunks of fuel, your mass goes down so you have
to integrate over it and you end up with this logarithm
here of your starting mass, which is the mass of the
rocket plus the fuel. And the final mass
which is the mass of the rocket without the fuel. And you multiply this by the
exhaust velocity of the fuel. So this is just — it’s
an integrated version of your conservation
of momentum. This was derived by a guy
called Konstantin Tsiolkovsky in the 18th century
actually, 19th century. He was a real inspiration. Back like — he was the
first guy to suggest that hydrogen would make
an awesome rocket fuel. And they had barely shown that liquid hydrogen
could exist back then. He also designed a spacecraft. And it’s amazing because he
has these reaction wheels which would be you
know turned by hand to orient the spacecraft. So yeah, in rockets we use
the rocket equation to figure out how much performance
we get, how much delta v. But in real rocket
math we actually tend to use something
called specific impulse. And this is an interesting
thing if you’ve done physics. Because specific impulse
is essentially measuring exhaust velocity. But it’s expressing seconds. Which doesn’t really
gel for many physicists because of course you’re
thinking in terms of newtons. But rockets of course, the original development
was done by engineers. And they were more concerned
with thrust to mass ratios. So instead of using newtons
to calculate their force, they would use kilograms
and multiply that by the force of gravity. So what they were
really calculating here for their specific
impulse was the amount of impulse you could get for a
given mass of fuel over time. And yeah, I’ve got a table here of some rough numbers
with fuel types. This is like a solid
rocket like you would have on a space shuttle on the side. This is a hyperbolic
fuel, for example they use in storable propellants. Because hyperbolic is
where you mix the two fuels and they just explode without
having to set fire to them. That’s what North Korea is
using right now incidentally. Locks RP-1. RP-1 is basically kerosene. So that’s what’s being
used by the Atlas and the Merlin —
sorry, the Vulcan IX. And liquid hydrogen,
liquid oxygen is of course what the
space shuttle used. So you’ll notice that
this is way better. So this is the effect of
the exhaust velocity, right? I mean, you’ll notice that
the space shuttle gets higher exhaust velocity. So you get more delta v for these fuel types
compared to other ones. That’s just what I’m
trying to get at. You can choose fuels based
upon your requirements. And now that you’ve got
your rocket engines, you figure out how much
delta v you can get from it. You can then figure
out how far you can go. And this is actually a page from
a study of the Apollo missions that figures out
how much delta v in feet per second
unfortunately. So do the conversions
in your head. But it shows you there’s
many parts to the mission. You’ve got launch to earth
orbit, your lunar coast — sorry, you get your launch. You’ve got your boost
to the moon. You get transient
coast with corrections. Landing, all that stuff. They had to add all of
this up and make sure that the different stages all
added up to the correct amount of delta v. Otherwise it
would be stranded in space. So we’re going to actually
do a bit of math here, because we know physics, right? So if you have Kepler’s laws, this is how you calculate
the velocity in an orbit. So if you’re in low earth
orbit, the radius — so this is the radius of your
orbit, the constant of gravity, the mass of the gravitating
body. So yeah, radius is about
6.8 or 600-800 kilometers. That’s 400-plus kilometer orbit. The mass of the earth is
about 6 to the 24 kilograms. And that turns out 7.8
kilometers per second or about. Geostation orbit, you’re going
about 3 kilometers per second. If you’re out to the moon, you’re only moving
at about 1.04. Now if you switch the central
body to that of the sun, the earth moves around
the sun at 29.8. And if you look at
low lunar orbit, if you’re orbiting
the moon, than 1.65. Now if you convert that, if
you then enhance the equation, you go for an elliptical orbit, then you’ve got two
different numbers. You’ve got what’s called the
semi-major axis which is, if you imagine an orbit is
egg-shaped, then the long axis, that’s your major axis. So half of that is
your semi-major axis. Easy enough. That’s constant. But your radius from the
center of the planet changes. So you can calculate
the velocity at any point using
this equation. And that lets us actually
calculate the transfer to the moon. So we’re going to start from low
earth orbit, perform a burn here to get up to the moon and then
we’re going to make another burn to put us into the same
circular orbit as the moon. So we can do some quick
math to calculate this. I’m not going to show
you the gory details, but the initial radius is
6.8 or 600-800 kilometers. The final radius is 38,400. That means the semi-major axis
is the average of these two. So you can plug that into
the equation minutes showing that to be on this orbit
you need to be at 10.93. So that’s up from 7.8. So you subtract 7.8 and that
means your first burn has to be 3.13. The upper G velocity,
well so you know that — you figure out again using that
equation in the previous slide and it says, “Yeah,
you are now moving at .2 kilometers per second
when you get up there.” So you want to move at the
same speed as the moon now. So that means you
need to add in .84. So that comes out to like 3.97. So that’s about 4
kilometers per second. But I missed the fact
that the moon has gravity. And you’re actually
starved so you have to fall into the moon’s gravity and it will accelerate
you and cool you down. So if you fall in from
zero velocity from infinity or falling in at
essentially same velocity — so at 1,800 kilometer orbit,
which puts you, you know, pretty close to the surface. Puts you like in the
6.3 kilometer orbit, you would be moving at 2.33. You need to get down to 1.65, so you need an extra .68
kilometers per second. So add that onto the 4. But wait, we can combine
those last two maneuvers. We don’t need to slow down
to get into the moon’s orbit and then let us catch it. We can actually just go
straight into the moon and then stop when we’re there. And then we get a weird thing
called the Oberth effect kicking in. So you probably know if you’ve
done basic physics, right, that energy is force
times distance. And this has really interesting
connotation for rockets, because rockets apply
the same force regardless of how fast they’re moving. And that means that
rockets produce more energy when they’re firing their
engines if they’re going faster. And you can exploit this to
get bigger and bigger changes. So capturing into orbit around the moon is all
about losing energy. So yeah, if you’ve
fallen from this — if you’re going 200 meters per
second and the moon comes up and catches you and
you’re moving at .84 kilometers per
second relative to the moon. So you actually square these
two numbers and add them because of course these
are kinetic energies. And that means that when you
get down to low moon orbit, you’re actually moving at 2.47. And that means your
counter burn is .827. which by the way is less
than circularization burn. So by using the gravity
of the moon and the fact that you’re moving faster
near the surface of the moon, you’ve actually saved fuel of
over simply getting it to orbit. Another weird thing about orbital mechanics
is biologic transfer. If you consider, “Hey, let’s
throw something into the sun.” We’ve heard that before, right? It’s actually incredibly hard
to throw something into the sun. You have to give
up a huge amount of orbital velocity
from the earth. The earth is moving at nearly
30 kilometers per second. That’s a lot, and this
spacecraft goes that fast. Now normally if you want to
drop something into the sun, you can go out to Jupiter and have its gravity you
know, flip you around. But using another trick
you can actually go up to escape velocity and
travel a really long way until you’re just barely moving. And because you’re
barely moving, the proportional changes
are hugely enhanced. So essentially with this
practically zero velocity change you can get to any
other location. So it turns out the minimum
amount of energy needed to get anywhere — an element of
delta v needed to draw something into the sun is actually
12 kilometers per second. So yeah, I never
finished that slide. You can also do other
things like hey, you can actually switch
these into reverse orbits and other tricks like that. And I’m actually skipping ahead because I think I’m
running a little behind. So yeah, this is just a
graph to show that yes, you can actually go up and down. And that’s sometimes
more efficient than a traditional
Hogman transfer orbit. So we’re going to be coming
back to pretty pictures, you’ll all be happy to know. For the Kerban system,
obviously no player of the game does all this math
unless they’re crazy like me. The Kerban system is of course where Kerbal Space
Program takes place. We have these wonderful maps
that people have made up. And these are much
easier to use. You know, you start in Kerban and say you need 3,500 meters
per second to get into orbit. Now from there it tells you you
need 860 to get to the moon. And then you need
about 210 to get past. And then you need
maybe another 640. So you can map out you
know your trajectories to all these things just
by adding up a few numbers. Of course if you’re — [ Inaudible ] These are planets in the game. So these are all planets in
the game, I should clarify. Like Duna is a Mars analog
and Eve is a Venus analog. And Jewel is the Jupiter analog. So of course players of
the game really go to town. They actually have taken
you know planning tools that are used by actual
spacecraft designers and they do pork chop plots. Because of course you
can export the data. I’ve also seen a NASA project for open mission management
software which they use Kerbal as their kind of demo for
schools and everything. But of course the
thing that really works about Kerbal Space
Program is trying and failing experimenting. And for that we have
maneuver modes. And this is the way
it is in the game. It doesn’t have all these tools. The game by default,
it comes with this map. And on the map you
can say, “What happens if I make a maneuver here?” And it will figure out, will
project your trajectory forward if you make a burn at that time. So you can drag your
maneuvers around and figure out what orbit you
actually need to do. So this is just going to demonstrate what’s
going on here. This is a spacecraft in low Kerban orbit being
flown by Jebidi Kerban. And we go out to the map. Here we’re in low orbit. So what I’m going to do
is I can show that we’re in orbit around Kerban. These beautiful orbits and
everything, it all works. You can see that our Apple apps
and Perry apps there are shown on the maps, which
shows the orbit where we’re going to be, right? Now I can click on anywhere in
this orbit and add a maneuver. And this creates like a little
thing with six controls. You can drag and adjust. And these correspond to six
different thrust vectors, or three thrust vectors
in two directions. So for example, I can
change the inclination of the orbit by firing
that there. Or I can drag it down. Now what’s important here is
if you look at this number, it’s telling me how much
delta v it will require to perform this maneuver. So this isn’t like
mission planning you get for real spacecraft. This is the kind of
thing you would give to somebody who’s
wanting to learn. It lets you play around with it. So that’s me doing that. Hold on. And then that’s
me doing radial burns. You can see a radial burn
is actually very inefficient for deorbiting. So you wouldn’t do that. The main way you would perform
a deorbit is by doing a burn in a prograde or retrograde. So look, we have all the tools. We can build whatever
mission we like using these. And again, it’s not really
teaching you the math of rocket science. What it’s doing is
giving you an impression. It’s giving you a hands-on
way of experimenting with it. You know, you probably
learned to drive, right? Learning to drive, you
don’t learn the physics of how rubber meets the
road and all of that. You don’t learn the physics of
internal combustion engines. You get this kind of handle
for how your vehicle moves and maneuvers just by doing. And that’s what Kerbal
Space Program is doing. Now another thing I want to talk
about again is the aerodynamics. The aerodynamics is
pretty fun in the game. You may know this diagram. It shows the four forces of
aircraft design, you know, lift, weight, thrust, drag. Or if you’re a pilot,
this is more appropriate. As an aside, most people
get taught the wrong — they get taught that
this is how wings work, when in fact it’s a
combination of all three. And also if you’re
seeing reentry heating — what do people say? That’s friction? It’s actually more to do with ram pressure compressing
the air in front of it. So a simple example of aerodynamic stability
comes from rockets. So this is a diagram. And if you imagine this
rocket is going up, this is the wind blowing into it
and its heating these tail fins. Now if the rocket perhaps
deviates from the direction of motion, the air
coming down hits these and it pushes them back. Because the center
of mass is here, it revolves around
that center of mass and straightens out again. But if your fins are at
the front and you deviate, then the force is
again applied here. But because the central mass
is there, it rotates that way. And so the design is unstable. That’s why rockets have fins at
the back rather than the front. And on top of that, you know, you can add control
surfaces to your aircraft. And then of course it’s a
whole giant rabbit hole full of aircraft design. This is like a 20-page
long document I’ve — you get a handle on all of this,
you can read all this stuff. Sure. But you can actually
just build the aircraft and then you find this
all out very quickly. You know you have a plane and
it’s taking off on the runway and it runs off the end of the
runway and you’re like, “Okay. I’m clearly going fast enough.” So you move the wings forward
and you go and then you flip that because you’re
now unstable. And then you get them
in just the right spot and then you realize
you can’t pitch up because your control surfaces
are pushing down on your wheels. So you have to move
your wheels forward. It’s a continual
learning process. So let’s talk realism
in the game. It’s a game. So gameplay wins at all times. For example, ion engines
in the game do exist. They’re incredibly powerful
because people don’t want to wait five months for
their orbit to change. They have nuclear engines. To balance out the game
the engines are very heavy because the Kerbal
system is smaller. We don’t have any problems with engines lighting
or not lighting. They always throttle
between 0 and 100%. And there’s no engine on
the planet that does that. You don’t have to worry about your fuel evaporating
or freezing. You can have pipes that carry an
amazing amount of fuel around, because it just makes
for a better game. They also shrink down the Kerban
system to make it manageable. So this is the rear
earth, this is the moon and this is Kerban
and this is the moon. So a factor of 10 in size. So that means that rendezvous
for example are easier. Your orbits are only
about half an hour. It makes the game
go a lot better and helps with attention span. But gamers love to
play in hard mode. And yes, people have
taken the game and they’ve made it
work for full-scale. So there’s a realism overhaul
which lets you build actual — this is an Apollo application. It was a suggestion of how to go to Mars using the
Apollo spacecraft. So yeah, gamers are
problem solvers. I think we’ve talked about the
games require participation and attention. Actually, games turn out to be in many cases optimizing
— optimization issues. For example, with
Starcraft, right? And many game players
treat problems as solvable, which is a really
interesting attitude. They get all these ideas
for how to do things. They love to build out — so these are just some mods
that people add to the game. And you don’t just have
current technologies. You have future technologies. For example, people
have suggested that you could build a
rocket engine on the moon by electoryzing the alumini
in the surface into aluminum and oxygen and then
burning that as rocket fuel. There’s crazy things
like nuclear cores where the actual
fission core is gatious. Fusion engines, yeah. Tritium, and yeah, this
is a whole set of stuff for the interstellar mod. Which isn’t just some
guy making up numbers. I mean, they actually
calculated all these things and all the fuel flows for
their charge particles, their thermal flows,
their electricity. And yeah, this is specific
impulse and everything computed for all these theoretical
propulsion systems. And all the resource flows as
well, if you’re perhaps doing in situ resource utilization. So people actually, they try to do [inaudible] Mars
direct in the game. And yeah, people love
to go get more detail. That means it’s more fun, right? More things to optimize. Well, yeah. There’s a game that
has gone even deeper into the physics game hole, and
that’s Children of a Dead Earth, which is basically the most
realistic spaceship game ever, basically. And you can tell it’s realistic because all the spaceships
have giant radiators that are always red hot
because in space that’s one of your big problems,
is getting rid of heat. They are for example
modelling the interior of their spacecraft, trying
to get rid of their heat. Notice that you have two sets
of radiators because you have to get rid of heat for
the people living there or working there. They model like their
armor penetration and everything using
the weapons. It’s a war game. But even further than that
they have this really cool tool where you can start
messing around trying to build rocket engines. You know, for example build your
chamber our of aluminum nitrite and running a fluid
methane fuel mix. You know, I don’t
want to be near that. You can build nuclear reactors and it will model again your
heat exchanger cycle and figure out how much power
you get out of it. Or hey, nuclear weapons. Yeah, these are all the
boosted fission devices, so they’re pretty low tech. They’re not at thermonuclear. So yeah, Kerbal Space Program,
what has the game taught me? As a physicist, what
have I learned? Well I’ve learned actually that
flying a spacecraft is possible. In fact, it’s easy. You know, I can now land on
the moon using an exact model in terms of delta v of
the lunar module, right? I can do that after
a six pack of beer. It’s kind of easy. What really matters is
the instrumentation, which is way better than what
the Apollo team had obviously. I’ve learned that crazy
spacecraft actually exist in reality or were designed. And I’ve also learned
that every mistake that players have made
has real-world analogs. I’ve also learned
boy, kids are amazing. They come up with the
craziest stuff that works. And more importantly I found that those kids have
learned stuff and they’ve taken it
back to school with them. So yeah, I get messages
like this all the time. This is the part
of being you know, promoting science on YouTube. “Thanks for all these
things that you’ve done. Thanks for inspiring me. Thanks for the things
I’ve learned.” This one really kind
of is embarrassing because this guy is taking
flying lessons because of me, and I’ve never taken a
flying lesson in my life. Yeah. You also get
people using it in school. This guy actually,
he’s a physics teacher and he contacted me because
he noticed a couple years ago that there were kids coming into
his class that were knowing more than they should have
at the end of the class. And he asked them —
he couldn’t figure out, had they taken summer
classes or something? Eventually he figured out
they were all playing Kerbal Space Program. Now they weren’t
learning the equations, but they understood
Newton’s laws. That was kind of this
innate understanding. So why does Kerbal Space Program
succeed as a teaching tool? Well, I’m going to
say it’s designed to be a game first
and foremost, right? The education qualities of
the game emerge naturally just by putting people
in this sandbox with all these toys
to play around with. And the consequences
can be hilarious. When you’re rocket explodes
it’s like, “Oh, it exploded. That was so awesome. Let’s try it again.” Right? And the truth is it’s not that Kerbal Space Program
is a particularly successful educational environment. The truth is that most education
games are just terrible games. So they don’t stick. And yeah, I’ve seen like Moon
Base Alpha was an education thing by NASA. People ended up just playing
the speech synthesizer rather than trying to learn
about the moon base. There was the A mission which
was a mobile app that played like a freemium mobile
game, which was awful. So yeah, you can teach
anything through games. But you’ve got to try and
make them games first. So with that in mind there’s a
few other game/science links I want to talk about. Yes, SpaceX actually
recruits game devs. And you’ll occasionally
actually see things like this in their slides. Yeah, this is the Apollo
international space station, image credit Kerbal
Space Program. Video games have made graphics
processor cards incredibly cheap and powerful. And SpaceX actually uses
this to model their Raptor. This is a simulation of
their combustion cycle in a Raptor engine. This is a startup basically. And this has been modelled on essentially end
user video cards. Can you actually
participate in science? Well Eve Online, which
is a game that I love and will never play again because it takes
too much time — they have something
called Project Discovery. And one of the things
they’re doing in it is looking for transits in coral data. Coral data is already being
analyzed by scientists. Now they’re letting thousands
and thousands of players mess with it as part of the game. They get in-game rewards. Because there’s a lot of
downtime in Eve Online as you’re waiting for
your enemy to jump through the gates so
you can kill them. They did a thing last year
related to cell classification. They’ve got more classifications
that the project had had in its entire life, and
they’ve started to work with the data on that. Another great example
I think of games and science is something
called Folded. You might have heard
of folding at home. That’s basically where it’s
a distributed protein folding application that uses the
processing power of lots of people’s computers to try and
figure out how proteins fold. So people would watch
the screen saver on that and they would launch it
and they would see it kind of sitting in a loop
stuck on something that they could see
was so obvious. And so some people
basically created a game where the players could
actually help the computer. They could take it and say, “I can see this is your
minimum energy route. Just trust me on this.” And then the program
would follow through and they could try and figure out if they can minimize
the energy of their complexly folded
protein or whatever. And yeah, this paper
was credited to the players of
the game, right? Crystal Structure or whatever. There’s a bunch of proteins
that had resisted folding by various other methods,
computational methods. And then Folded managed
to solve it. So yeah, they were
credited as coauthors. If you want to play
games about space, I’ve got a few other
recommendations. Orbiter 2016 is an
accurate simulator and it’s completely free. If you really want to get down
to all the details, it’s there. There is a version of
the Apollo missions which includes a fully working
Apollo guidance computer. I am not meaning an
emulation, like a simulation. It actually runs a simulation of the core running the
actual code inside the game. There is Universe
Sandbox which is like an end body modeling
application for fun. It takes all the boring stuff
you have about asteroid orbits and says, “Let’s just
smash planets together or smash galaxies together.” There’s no game in here. It’s just let’s see
how the universe works. If you’re cheap, you
can run Simple Rockets on a phone or an iPad. And that’s very similar
to Kerbal Space Program, but it’s only in 2D so
it’s kind of easier. The same guy has Simple Planes. So it’s 3D. It doesn’t really
have rockets in it, but it does have all
the issues in terms of aerodynamic stability
and stuff to worry about. Space Engine is fantastic. It’s just fly around the
universe and look at things. It procedurally generates
large parts of the cosmos. So you literally
can go anywhere. And if you’re a traditional
gamer, this is good for kids. It’s not so good for
adults, but this was designed by Dante Lauretta who’s
the principle investigator on the OSIRISREx mission. He’s also got another one
about star classification. And High Frontier is
this legendary board game about exploiting
the high frontier. And again, it has all these
amazing future technologies in it. Which of course urges
you to go out and learn. And so yeah, this is kind of
my point about all of this. It urges you to go
out and learn. And there’s this quote
which somebody sent me and then I found out it wasn’t
actually by Benjamin Franklin. “Tell me and I forget;
teach me and I may remember; involve me and I will learn.” Thank you. [ Applause ]>>Thank you very
much for that talk. We have a few minutes
before 5:00 so let’s take some
questions from the audience. [ Inaudible ]>>Yes, they added — with 1.0
they added Valentina Kerbal, named after Valentina
Tereshkova of course. Yeah, there’s male
and female of course. And I’ll point out that
Valentina is actually better than Jebidi who was
previously the best. She’s pretty awesome.>>Yeah, since we’re
talking about science, is there any recent research that shows video games
have educational benefits?>>Actually there’s
a lot of recent — so there’s a thing
I cut out of this. There was another talk. But yeah, there’s ones
that obviously show that just playing action
games increase your visual attentiveness. It actually makes you a
better driver apparently because you’re more
likely to see things. There was another study
where they compared — was it surgeons that
do keyhole surgery versus gamers doing the same
keyhole surgery in simulation. And it turned out
that the people that were gamers
were vastly better. They were faster
and more accurate.>>Sorry, I wasn’t very clear. But for learning physics.>>For learning physics, well
I think that for a start, there was that quote from
that teacher who claimed that he thought that
this worked for sure. I mean, as I said, I think
it’s like driving a car. You know, you learn
how to drive a car. You don’t learn the
physics behind the car. This teaches you
how to fly rockets. It teaches you orbital
mechanics, and that’s enough of a basis that if you then
needed to go do the math, you would know where you were. You would know that these
weren’t just abstract equations. You would have an understanding. And I think that’s very
important to learning.>>Is there a Kerbal that
translates into North Korean? [ Laughter ]>>I believe that
would be covered under the various
embargoes at this time. Besides, North and South
Korea both speak Korean. I don’t know if there’s a
Korean translation coming. I’ll tell you that. Actually, somebody has simulated
the North Korean rocket because we believe
they’re using — I think it’s an RD-151
derivative, it looks like.>>That rocket simulation
is really very interesting. The thing you showed
about the DSP’s being used for simulations.>>Oh yeah, yeah, that. That’s amazing. The GPU’s, yeah. It’s amazing. And you know, I work
at Apple as well and machine learning
is taking off because of these cheap
GPU’s that are available. They’re making computational
problems solvable that were not available
simply because — it would not be available
on a simple CPU cluster. Because GPU’s are amazing good
at highly paralyzable tasks.>>I was just thinking I’ve
spent far too much time kind of walking around on the earth
with actually no intuition for orbital mechanics, as
you were describing them. But you had one slide which
showed the delta v that you do for [inaudible] towards
the moon.>>Yep.>>Then you captured that. And it looked as
though counterclockwise around the earth, you’d end
up aiming in front of the moon and ending up in
a clockwise orbit. That’s what it looks like.>>Yeah, you can go into
any orbit around the moon. It just depends on how you
pick your capture time.>>Well my question was,
is there any advantage or disadvantage to sort
of aiming behind the moon since you’re already
going too fast I guess.>>So yeah, you’re talking
about gravity assist.>>Yeah.>>So I’ll tell you in the Apollo program they
would deliberately go in front of the moon, and the reason
is because that would then — it would flip their
orbit around and put them on a free return trajectory. So the idea was that they would
launch the Apollo spacecraft and its translunar trajectory, on an orbit that if it then
had a failure in its engines, it would get swung back
around the moon to earth. However, yeah, if you didn’t
have to worry about that, you would want to go into
orbit around the moon in the same direction
as its rotation so that you could minimize
your landing speed. But it doesn’t matter so much because the moon is
moving so slowly. And you know, that’s another
thing you get, is that you know, when you’re launching a
rocket, you almost always want to launch it east because the
earth rotates in that direction. And you also want to
launch closer to the equator because there’s more orbits
that are accessible from there.>>So we’re coming up on 5:00, so just a few things
to let you know. Our speaker [inaudible]
please come up and see me and we’ll introduce
you in our group. Otherwise, those of you who
have extra credit since, it’s coming up to 5:00 you’re
welcome to depart as quickly and quietly as you can. But if you’re taking the course
for credit, please stay behind and ask a few more questions. And meanwhile, let’s
thank our speaker again. [ Applause ] [ Chatter ]>>All right, does anyone have
any questions for our speaker?>>Can you talk a little
bit about your transition from graduate school to
these different jobs?>>I would be delighted to, because I am often asked
about career advice. Because usually kids
in the audience want to be professional
YouTubers and I’m like — yeah, so I went to Arma and I was studying
basically minor bodies in the solar system. I actually kind of started to
go off in weird directions. I really got into collision,
asteroid impacts and stuff like that, because my
advisor was on that. But he actually advised
me to stay away from it because I wouldn’t
be taken serious. But I found it a
lot of fun and most of my research continued
in that direction. But I’d always been
a computer nerd. And so a lot of the
time in my spare time after hours I would be
working on various projects. Animations, I did
a lot of animations like the asteroids
discovery one. I did various spacecraft
and things like that. But one side project was I
brought internet radio software because I wanted to play
music to my friends. And that software ended up getting used and
I got Headhunter. So I came out here. Now I think my advice actually
is that you know, the best thing about being a student is you
have spare time to do things. And it’s always good to have
projects in different fields that you’re interested in. If you’re interested in
computers, I think my big advice for transitioning to
a computer science or computer technology
side of things is that open source
software is amazing. Because you can write
something and put it out there and if it’s good,
people will use it and then people will
know who you are. And that’s really how I ended
up getting into a tech career. And I find a lot of people
who have done computer science in college, they don’t do the
open source side of things. And so they have no body of
work that’s public beyond what they’ve done at school. And so they don’t
really get any callbacks. But the people that have the
websites with the code — even if it’s just a bit of code
that generates some awesome, cool-looking thing, that is a
really great way to get people to understand who you are. So you know, making a presences of what you’re doing is
a very powerful thing. I’m not sure if that’s the
question you’re asking. But you know, so yeah. I ended up there and I came out. I went from one startup to
another and eventually ended up with a startup
later acquired. So that’s how I ended
up with Apple, which is the best way
to end up at Apple. [ Laughter ] Yeah, I’m just going to say
I’m a big fan of plan B’s. I’m always doing more
than one thing at a time. You know, my day job — well
my day job right now is mostly involving computational
linguistics. And that mostly came along because we had an
entirely different problem at the previous company and
I thought it would be fun to write code automatically. It tried to analyze
people’s sentiment based on what they were saying. I kind of did it on a dare and next thing it became the
cornerstone of the product. And now I’m you know working in
machine learning and linguistics because it was on mathematics. And yeah, my open source
work was all fun stuff because I wanted to play
music to my friends. Kerbal Space Program — the Kerbal Space Program
actually happened on YouTube. Because I was so mad
at looking on forums. This game had come out and
people were saying, “Oh, it’s not even possible
to get into orbit. I’ve gone straight up and
I fall straight back down.” I was like, “No, you’ve got
to go up and go sideways.” People had this basic
misunderstanding about how orbits work. And so I of course had
my academic credentials. I knew how this works. I could do it. And I guess I also have a
Scottish accent which helped.>>So with your online videos,
is it more that you think, “I’m going to make
a video about this”? Or do you just play Kerbal Space
Program and find something fun and think, “I’m going to
make a video out of this”?>>So it’s basically
different ones. Obviously the science ones I
plan out beforehand and I write down all my notes and do all
my math and then I’ll speak that into the camera and
then add effects afterwards. Kerbal Space Program, yeah,
I usually have an idea for something that’s crazy
like you know, fly a plane and land a plane
inside another plane and then land that
plane you know. That actually comes from Tuesday
night live streams where it’s like I just go live
on the internet. There’s people watching me and
I say, “Give me a challenge.” And people are like,
“Can you fly from Kerban to the moon in one hour?” And yes, but it’s very
hard and needs a really, really big rocket that
explodes lots of times. Yeah, I mean, so we get
ideas from different sources. Sometimes of course there
will be a space mission that’s in the news. And great, let’s try and fly the
Cassini transfer to Jupiter — or sorry, to Saturn, where it
had to fly past Venus twice and it flew past earth. And then finally flew
past Jupiter and that of course is quite complicated. And that made it fun to try. And I didn’t actually
manage to do it. But I did manage to fly you
know New Horizons trajectory because that was a single
gravity assist past Jupiter. So yeah, I mean just different
ideas from different things.>>Do you have a favorite
real-world space mission?>>Man, I think it would have
to be the Apollo missions. There’s so much to write about. I mean, Apollo 11 was
pretty you know fun and amazing in so many ways. But I like Apollo 14
because of the whole story about how the computer hacker
got phoned up in the middle of the night to save the day and
was having the astronauts type in cheat codes into the
computer so that it would land.>>Which one?>>Apollo 14. The story was that it
got into low moon orbit and they had detached the lunar
module and they were starting to get spurious signals
from the abort switch. So they had to figure out
a way for the computer to ignore the abort switch. So they had to poke
around in the memory and change certain values. The computer thought — what they did was the
convinced the computer as it started the descent
sequence that it was actually in the abort sequence. So that if it got the abort
signal, it wouldn’t abort again. And then they could then
lock out the abort sequence and put the computer back
into the correct mode and complete the landing. And of course they had to do
this in this archaic interface. Yeah. I mean, I have this
weird ambivalent thing with the shuttle. It’s amazing and yet it was
also wrong in many, many ways. Yes?>>In my experience with
math and learning math, especially during high school,
I really hated it to be honest. And I don’t know what it was about Kerbal Space Program
or coding especially. I think it helped me learn — [ Inaudible ]>>I think coding is
absolutely a good way, especially if you’re coding
around mathematical problems. I’ll just say I’m not
very good at calculus and frequently I’ll just
write an iterative solution for the same thing
because it’s faster than looking up everything. No, I think anything
that gets you working with a hands-on experience
is the most important thing for any education. You know? And I see this when
we interview computer scientists all the time. And a lot of them,
they’ve taken a degree and they haven’t done
anything outside of it because they just see the
degree as what they need. They haven’t shown
any real love for it. And the ones that are
good are all the ones that have a side project
that are doing fun things. It might just be a side project
that generates some amazing, psychedelic displays
because they want to use their skills to do that. They might have you know,
messed around with a robot that makes fart sounds. But that’s a great way
to just use your skills. You know, and physics. One of the things I used to do
— I was into roleplaying games as a student — with my physics
I would start doing the math on spacecraft. Okay, so we’re going
to have a fusion drive. Okay, so it’s going to be
deuterium tritium fusion. Okay, wait a second,
too many neutrons. Deuterium helium 3. You start doing all the numbers. And I think it all
just falls together. You try to figure out how hot
is your spaceship going to get and you go off and
start studying it. And hey, suddenly
you’ve learned a lot of physics just by
looking this up.>>Have you built
any actual rockets?>>No, I haven’t. I am terrible at
matchstick toy rockets. I’ve inspired people to
build satellites apparently. I had a 15-year-old kid
who built a satellite and is getting it
thrown in a year or so. But no, I am the worst person because my experience
is entirely self-taught so I wouldn’t qualify
for these things.>>That’s okay. So what about [inaudible]?>>Which one?>>Rockson.>>Oh, Rockson, right?>>They actually use
it in building rockets.>>I know people
who have used that. But I — [ Inaudible ] Yeah, I have seen that. And it’s you know — it obviously goes
into a lot more detail about your grain size
and fuels and that.>>Yeah, but also you can
specify the exact size and shape of all of the different parts
you’re building a rocket out of and calculate the pressure,
calculate the [inaudible]. So you can see if it’s
going to work or not.>>Yeah.>>Cool things like that. But then you can actually
fly the rocket according to the calculations and
see how accurate it was.>>Yeah, yeah. I’d love to spend the
time to do that, for sure. But you know, I’ve
already got two jobs.>>So what I’m hearing is
write open source software, play Kerbal Space Program and
be Scottish are your three tips.>>Be who you are.>>That’s a great
round of questions. Let’s wrap it up at that point. We’ve got to close it out. [ Applause ] [ Music ]

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