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It’s the Mars helicopter. Come on!
- So this is our baby.
- No way!
- 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? They transmitted data for over forty six hours while floating at an altitude of 54 kilometers in Venuss 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 Earths.
- Flying this kind of helicopter is equivalent to flying a similar helicopter on Earth at a hundred thousand feet. I think forty thousand feet is probably the record.
- I checked. 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. 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 got to 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.
- 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.
- 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.
- 35 grams is the mass of six quarters.. How long can it fly for?
- Its 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 quad copter design?. Two counter-rotating propellers provide the simplest design.
- The bottom rotor sees the sort of the more compactified flow.
- Really?
- because of how much atmosphere we’ve got.
- Exactly, it’s like trying to swim in a thick soup.
- 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 - 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, 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?
- Yeah you’re still at 1%, but its still, real loud.
- Really?
- Yeah we have audio recordings of it too. But its, I would characterize it more like a baaaaaaaaah, something 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.
When you’re pitched up there you get that additional torque. 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. 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 unplayable. And the reason for that it’s 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 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 really send 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.
- 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, right! And the vehicle looks dead calm, its coming up, and hovering, and going laterally, coming back; you know the machines are working very fast and very hard it just looks very calm, but yes so the blades are being continuously controlled.
- That is amazing. How will it handle a gentle breeze?
- The truth of the matter is that with 1% Earth’s atmosphere, there is very little matter actually hitting you.
- I mean, you’re using that to lift yourself.
- Exactly, so there’s enough to lift, right?
- 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.
- RightIn theory?
- 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. We take approximately two-thirds of energy just keeping things warm and warming things up to operate.
- 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. so the enclosure itself were using the CO2 gas as the insulation material
- Oh wow! No aerogel?
- No aerogel. We did it 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.
- Right.
- And so guess why we wouldn’t want to use aerogel if we have a choice.
- Weight.
- Yep, there you go. Welcome to our team
- 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 is this an aircraft, it’s also a spacecraft.
- Yeah. 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?
- Were 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 it’s got us by this bolt, its holding us about this high, and then it goes has to drop us, right?
- You blow it up.
- You blow it up. Basically its materials you know undergoes a phase transition which suddenly increases the, the stress in the metal part of the thing and makes the bolt break. It’s called a frangibolt.
- Then once were on the surface, the rover drives over us, it gets about 100 meters away, and then we have about a two-hour counter internally.
- 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, like this.
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