I’m at the Jet Propulsion Laboratory in Pasadena,
and I’m here to see the first drone
that’s gonna fly on another planet.
It’s the Mars helicopter. Come on!
So this is our baby.
That thing right there is the actual machine
that is going to take off and land on Mars.
It’s going with the Mars 2020 mission.
That is the Mars helicopter.
This will be the first powered flight in another planet.
– How awesome is that? – I mean this is…
Now it’s necessary to say first powered flight,
because in 1985, the Soviet Vega missions
deployed two helium balloons on Venus.
They transmitted data for over forty six hours
while floating at an altitude of 54 kilometers in Venus’s dense atmosphere,
which at the surface has a pressure of over 90 Earth atmospheres.
In contrast, Mars has very little atmosphere, only around 1 % of Earth’s.
相反 火星气压非常稀薄 大约只有地球大气压的1％
Flying this kind of helicopter is equivalent to flying a similar helicopter
on Earth at a hundred thousand feet.
So you don’t know,
you don’t hear about many helicopters at a hundred thousand.
I think forty thousand feet is probably the record.
Forty thousand feet is the record altitude reached by helicopters on Earth.
85,000 feet is the highest a plane has ever flown.
On Mars, the air is even thinner than that.
Right. In terms of density is 1 % of what you have in this room.
对 火星的空气密度是 你所处这个空间空气的1%
So in this room,
a cubic meter of air is about a kilogram.
– Yeah. – The same cubic meter on Mars will be
about 15 grams to 18 grams.
– So that much – So you have to push a lot of air down.
Yes. You gotta get a lot of air flowing.
And so the obvious trick, if you will,
is to spin the blades faster.
It can spin between 2300 rpm and 2900 rpm.
That is fast.
That is fast. Yes.
Here I’m trying to work out exactly how fast that is.
So I looked it up,
and on Earth helicopters typically spin their rotors at around 500 rpm.
So the Mars helicopter will have to
spin its blades five times faster.
But there are some limits you know,
you really don’t want to get the tips of
the blades breaking the speed of sound,
Cause then you have shockwaves and all sorts of
and you get all kinds of funky aerodynamics and
you know the transonic flows and things like that,
so you don’t want to go there.
So we, in our designs,
keep the tip Mach numbers down to below about 0.7.
So 70% the speed sound actually did
Yeah. It was very conservative.
One advantage of flying on Mars is that gravity is
only 38 % of what it is on Earth.
Even so, making the craft lightweight was essential.
Keeping the mass of this vehicle contained during the entire design process
has been the major challenge.
Every single part had to be considered.
The entire vehicle is less than 1.8 kilograms
So, less than four pounds.
That’s about the same as this laptop.
The blades are a foam core with carbon fiber layup.
Each of them is about 35 grams.
Yes, it’s quite light. Yes.
对 它很轻 没错
35 grams is the mass of six quarters.
Think about that: two 35 gram blades lifting an 1800 gram helicopter
by spinning 40 times per second in just 1% of Earth’s atmosphere.
How long can it fly for?
It’s designed to fly up to 90 seconds.
A minute and a half of flight.
To me that sounds like forever,
when you’re talking about another planet, flying autonomously by itself
in 1/100 earth atmosphere, I mean, come on!
Like, that’s a long time!
That is. Yeah.
One of the questions I had was,
why didn’t they use a quadcopter design?
Well, because on Mars, the blades have to be so long
that the whole craft would barely fit on the rover.
Two counter-rotating propellers provide the simplest design.
They also generate lift more efficiently
when stacked on top of each other.
The bottom rotor sees the sort of the more compactified flow.
The top one pulls it,
the bottom one sees sort of a more concentrated flow.
So the bottom rotor actually can do better
than if they were separated apart.
But how do you test a helicopter designed
for conditions on Mars or on Earth?
What would happen if you just took your Mars helicopter
and you tried to take off on Earth?
It would just make a lot of noise.
And it probably wouldn’t get the full head speed either.
because of how much atmosphere we’ve got.
Exactly, it’s like trying to swim in a thick soup.
We have a really amazing chamber here on lab
called the 25-foot space simulator.
And in that chamber you could
simulate any kind of atmosphere you want.
You can go to Martian pressures,
you can stay at Earth pressures, whatever you want.
But that only took care of half of the problem,
that was the aerodynamics aspect of it.
There’s the other part which is the gravity.
We needed a way to fake Mars’ gravity here on Earth,
and the best way that we could figure out
to do that was a gravity offload.
Gravity offload just means pulling up on the helicopter,
so it only has to support about 38 % of its weight
just like it will have to do on Mars.
And effectively it was a high-tech fishing reel,
so taking a brushed DC motor,
a reaction torque sensor, and a pulley,
mounting that a couple stories in the air
and then attaching a fishing string
to the top of the helicopter
that would tug the necessary force required
to offload the differences in gravity.
An actual fishing line?
Yeah, real fishing line.
But isn’t that stretchy,
like don’t you want something that’s perfectly rigid so as soon
as you apply the torque it gets applied to the craft?
Right right, and we did a lot of testing with different vendors
to find out which fishing line had the best spring constant for us.
What does the helicopter sound like?
I imagined that in 1 % of Earth’s atmosphere,
the helicopter would be pretty quiet.
Yeah you’re still at 1%, but it’s still, real loud.
是的 你仍处于1%的地球大气压 但持续下去真的很吵
Yeah, we have audio recordings of it too.
But it’s it’s, I would characterize its
more like a ‘baaaaah’, something sound like that.
When gravity offload systems working and the chamber was pumped down,
the helicopter thought it was on Mars.
It felt like it was on Mars.
How do you actually steer this thing around and drive it?
So the way helicopters work is they have
something called collective and cyclic.
So what collectives do is they change the pitch on the blades uniformly.
So throughout the entire revolution you will move the collective,
因此 通过整个循环 你将推动集合体
the blades will change,
you can change your angle of attack, you’ll get more lift
so that’s basically what you would provides you height control.
You pitch more you go up,
pitch less you come down.
But then, there’s something called a cyclic on helicopters,
which basically what it does is
it modulates the pitch
as it goes around,
so it can pitch it a little bit more here, less here,
所以 它可以在这边更倾斜一点 这边更平缓一点
so it kind of like modulates.
So what that does is it provides an asymmetric torque, right?
When you pitched it up there you get that additional torque.
Now you get it,
depending upon the stiffness system you actually get it,
with that a gyroscopic lag that can happen afterwards.
So once you get an asymmetric torque,
the vehicle wants to start pitching or rolling. Right?
So once it pitches and rolls,
you’re doing it stably.
You are now pointed in a direction
and your thrust vector now has a component
that’s horizontal in the direction that you pitched. Right?
So then you start translating in that direction.
I’ve heard that
initially someone tried to fly it with a joystick?
– Yes. – Was it an early prototype?
If you were sitting right there on Mars
and you were trying to joystick it,
what is it like?
And it’s almost unflyable.
And the reason for that is the
aerodynamics of when you want to command a roll to the left
because you see yourself starting to move to the right
and you start commanding a roll to the left.
There’s a delay aspect.
So that that delay effect makes it very very difficult
for a human to try and pilot it.
You can’t fly this from Earth.
Because of the twenty-minute kind of time delay,
so you have to resend sequences.
So essentially you’re gonna push a button,
and like 20 minutes later it’ll take off and do its thing
and then you will find out.
The way this flies autonomously,
it has onboard gyros, onboard accelerometers and onboard camera,
an altimeter and an inclinometer;
and so using that sensor suite, real-time measurement,
you know against terrain
and of course the gyros and the accelerometers sensing onboard
the real-time estimation of the state of the vehicle
is made continuously again at hundreds of Hertz
and then that’s fed into the closed-loop control algorithm,
that takes the estimated state
and then generates the correction that’s needed at the blade level,
and then the blades are continuously being controlled.
So when you see video tapes of our ‘successful flights’, see, right？
所以 当你看到我们“飞行成功”的录像带 对吧？
And the vehicle looks dead calm, it’s coming up,
and hovering, and going laterally, coming back;
盘旋 侧向行驶 返回
you know the machines are working very very fast and
very very hard it just looks very calm,
but yes, so that the blades are being continuously controlled.
That is amazing.
How will it handle a gentle breeze?
– A lot of the movies depict – Dust storms?
The big dust storms as being very aggressive on Mars.
The truth of the matter is that with 1 % Earth’s atmosphere,
there is very little matter actually hitting you.
You mean, you’re using that to lift yourself.
Exactly, so there’s enough to lift, right?
没错 那种环境的风力足够把人举起来 对吧？
But we also need to spend at 2200 rpms to
be in the ballpark of lifting ourselves.
We built our own wind tunnel
that we put inside this 25 foot chamber.
How many fans was it, Teddy?
960 computer fans.
So, but it does sound like a like a jet engine taking off.
So we built a fan wall array,
it’s called an open cross-section wind tunnel,
where you don’t need the walls,
just the fact of having an array of fans
we are very confident of being able
to go at 11 meters per second,
in this vehicle.
if I had known that
somewhere along the way I’d be building a wind tunnel to do this,
I would have probably not taken the job on, right?
How long does it take to recharge?
We recharge the whole day.
So, the whole day at Mars.
Right. But does that mean that
you could do one flight a day kind of thing?
In theory, yes, by design it can.
What is the size of the battery?
Between 35 and 40 watt hours total.
That’s equivalent to just three smartphone batteries.
And get this-most of that energy isn’t even used for flying.
It has to survive temperatures as low
as about minus 80 to minus hundred degrees C at night.
So we keep the batteries warm
and we surround the batteries with our electronic boards
so the electronic boards also stay warm.
We take approximately two-thirds of energy
just keeping things warm and warming things up to operate.
Only one-third of the energy is available for flight.
Do you have insulation on there to keep it warm?
Yes. When you look at that helicopter, right,
you have the solar panel on top with antenna,
and then next is the rotor system,
and then bottom what you see this cube,
is what we call the fuselage,
you are seeing it now actually uncovered
because you’re seeing the last day of final.
We’re recovering for delivery to be integrated onto the rover.
Okay, so usually you won’t be seeing that.
So the center of the cube is the ring of batteries, okay.
There is space between the battery
and the circuit boards that you are seeing.
And then there will be a shell
that we put on called the fuselage shell,
and that will close like CO2, the gas, around.
And so the enclosure itself,
we’re using the CO2 gas as the insulation material.
Oh wow! No aerogel?
We did consider it.
It was in the game,
it was in the consideration in the beginning,
and it turns out that just the CO2 as insulator itself
was sufficient for us to close our thermal model.
And so guess why we wouldn’t want to
use aerogel if we have a choice.
Yep, there you go. Welcome to our team.
对 太聪明了 欢迎加入我们团队
Now before the helicopter can experience the frigid conditions on Mars,
first it has to get there.
And that’s a reminder that not only this is an aircraft,
it’s also a spacecraft.
It has to survive launch.
It has to survive launch loads which,
easily exceed about 80G
You know, because of the vibration. Vibrational loads are 80G.
Then it has to survive the seven-month trip,
complete with radiation.
And finally after pulling nine Gs on entry into the Martian atmosphere
the helicopter needs to be deployed.
This is gonna be on the rover,
before you take off, does the rover like
pick you up and put you down somewhere?
We’re gonna be stowed underneath the rover
on the belly pan on our side.
And there’s gonna be several sequences of
firings of explosive devices to actually
rotate us right side up and then drop us on the surface.
For example the very last thing the rover does
is this got us by this bolt,
it’s holding us about this high,
and then it goes has to drop us, right?
– Yeah. – So how do you undo a bolt on a spacecraft?
You blow it up.
You blow it up.
Basically its materials, you know, undergoes a phase transition
which suddenly increases the stress in the metal part of the thing and
makes the bolt break. It’s gonna frangible.
Then once we’re on the surface,
the rover drives over us,
it gets about 100 meters away,
and then we have about a two-hour counter internally,
where we’ll wake up after 2 hours,
wait to hear some RF transmissions,
and if we do get that link with the rover then great.
Our base station on the rover would issue the ‘fly now’ command.
First flight will probably be a mutual selfie, you would think.
This is after all the selfie age.
I like that as the goal of the first flight.
Yes, it is.
In fact, it is good to know the best time to fly.
This is at 11 o’clock in the morning local time on Mars,
and that the reason for that is,
we would have come out of the night,
where we would have
spent a lot of battery power trying to, you know, stay warm.
By 11 o’clock, the state of the charge
would have gotten to the point where you could fly without
risking a brownout on the battery and then, you know,
dropping the whole craft to the ground.
Also 11 o’clock is where the sun would have warmed up things,
so we don’t quite have to heat up as much.
And also it’s not late afternoon, where because of the warmth,
the density has begun to drop.
Okay？ and the winds have begun to pick up.
Now, what we will investigate is
after we get the first couple of flights under our belt,
I’m sure we will try to fly in the afternoon
and you know do more exploratory things.
But the most conservative thing we can do
is to sort of pick a mid-morning flight.
So, what is the purpose of this mission?
The Mars helicopter is first and foremost a technology demonstration
to prove that we can fly on another planet.
The helicopter can take color photos and videos,
but its purpose is not to make scientific discoveries.
Instead it is to help engineers figure out
how to design and build aircraft for future missions.
You can imagine something that’s about 30 kilograms
carrying you know a 2 kilogram science payload,
doing exploration, acting like a scout, like a small vehicle,
在做探索 像侦察员一样行动 像个小交通工具
like this, scouting ahead for some future rover;
or it could be a
gadget that goes and picks up some kind of samples
and brings it back to a central lander for more sophisticated analysis;
or it could be a completely standalone craft,
and maybe more than one
that are exploring places where
humans and rovers can’t get to easily:
polar ice caps, you know
sides of cliffs and so forth.
So the real emphasis here is to try
to get back all the engineering data
so that it can inform that future design.
Flying on other planets will provide a new dimension in space exploration.
An aircraft is faster and capable of
covering more ground than a rover
and it can provide higher resolution imagery than an orbiting spacecraft.
So maybe one day,
aircrafts will be the companions of future rovers
or even astronauts exploring other worlds.
I’m at the Jet Propulsion Laboratory in Pasadena,