Perseverance, NASA’s latest Mars rover, is a one-ton, $2 billion marvel. The plan was for it to enter the Mars atmosphere going 12,000 miles an hour. The problem: How do you slow it down enough to set it down gently on the surface? You can’t use retro rockets, because they’d stir up so much dust, the rover’s cameras and instruments would be ruined. You can’t deliver Perseverance inside a larger spaceship, because the rover wouldn’t be able to drive out of the landing crater. You can’t even control the descent from Earth, because it takes so long for our signals to reach Mars; by the time the rover received a course-correction instruction, there’d be nothing left of it but a smoking wreck. Yet NASA pulled it off—with a nutty, Rube Goldberg-y, multi-stage, seven-minute-long, completely automated system involving a parachute, an airborne launch platform, and a cable.

Guest: Alan Chen, NASA Entry, Descent, and Landing Lead for the Mars 2020 mission.

Episode transcript

Intro

Seven months after liftoff, the Perseverance rover approached Mars going 12,000 miles an hour. 

The problem for NASA: How to slow it down to a gentle touchdown? You can’t use rockets, because their thrust would make a crater that would trap the rover. 

And you can’t control any of it from earth. It takes too long for a signal to reach Mars.

Allen Everybody’s dying a little bit on the inside, right? That you can’t do anything. 

But NASA pulled it off—with a seven-minute-long chain of tricks involving a parachute, a jetpack, and a rope. 

I’m David Pogue—and this is “Unsung Science.”

BREAK

Story

Season 1, Episode 5: 7 minutes of terror. How to land a 2 billion dollar Mars Rover when all you can do is watch

[music]

Late one night when I was six years old, my parents rushed into my bedroom and shook me awake. “Dave! Dave! Wake up! Come downstairs. Hurry up!” my mom said.

I remember distinctly climbing onto the couch with my older brother and sister. And the whole family watched, on the TV, the first human being step onto the moon.

NEIL: I’m at the foot of the ladder.   I’m gonna step off the LEM now.   That’s one small step for man, one giant leap for mankind.   

By the way—for decades, I never understood what Neil Armstrong was getting at. “One small step for man?” Doesn’t “man” mean “mankind?” That’s like saying, “one small step for mankind, one giant leap for mankind.” Doesn’t make any sense! 

Years later, we learned that Armstrong meant to say “one small step for a man, one giant leap for mankind.” Let’s play it slower:

NEIL: That’s one small step for man, one giant leap for mankind.  

Well, I don’t know. Maybe he intended to say “a man,” but he swallowed it or something. But anyway, “one small step for a man” makes it a much better quote. Now it’s contrasting one individual with all of humanity.

Anyway. That moment, in 1969, is when I became …a space nerd. I mean, if my parents rustled me out of bed so I could experience that moment—space must be really important. That’s probably the instant when I got bit by the science bug, too. I distinctly remember saying, “Mommy? Daddy? This will make a great introduction for a podcast someday.”

Anyway. Fast-forward 50 years. 

[music]

I’m standing at NASA’s Jet Propulsion Laboratory—JPL—in Pasadena, California, looking through a glass partition at a huge, dust-proof clean room. Inside, workers in white clean-room suits were assembling the latest Mars rover. I was doing a story for “CBS Sunday Morning,” and my guide was Adam Steltzner, chief engineer for the Mars 2020 mission. 

ADAM: at the far left here, you’re seeing the rover.  

POGUE: That’s– that’s the actual thing? That’s going to Mars–

ADAM: Yeah,   those guys working on that thing, the thing they’re working on will go to the planet Mars.

POGUE: Wow.

ADAM: Hopefully. (LAUGH) 

Yeah I don’t know if you caught that last word – hopefully. Because landing on Mars is really hard. Over the decades, various countries have tried to land on Mars 18 times—and half of them ended in disaster—usually crashy-and-burny disaster. The Soviet Union is oh for 6; the European Union is oh for 2. China tried and succeeded once. But the U.S. has landed successfully on Mars 8 out of 9 times.

Five of our landings have been rovers—wheeled robots that can move around. In 1997, NASA’s Sojourner, about the size of a microwave oven, proved that we could build a remote-controlled Mars rover. In 2004, Spirit and Opportunity discovered evidence that there used to be water on Mars. In 2012, the Curiosity rover discovered that the warm, wet environment of ancient Mars could have supported life. Not, you know, movie Martians with, like, three eye stalks. We’re talking microbes here—but still.

And now, here I was, admiring Curiosity’s successor, the cornerstone of the Mars 2020 mission. 

POGUE: And what are we calling this rover?

ADAM: Well, you know, we don’t have a name for this rover yet. NASA goes to the students of the nation– the young students of the nation, and sets out a competition and says, “Name our rover.”
  And historically, a young girl somewhere in the middle school era has won that competition.  

POGUE: And why do middle school girls usually get the nod?

ADAM: Well, the boys come up with things like Laser Dreadnought   and Laser Death. And– (LAUGH) and those are great for a Transformer, but maybe not for a rover. The rovers– the– the young ladies come up with   names like Curiosity, and Opportunity and Spirit. (continued)   And so we don’t know what this rover’s name is, but my bet is on a middle– it will be named by a middle school girl. (LAUGH)

Adam actually wound up losing that bet. The 2020 rover was, in fact, named by a boy. 14-year-old Alex Mather from Virginia submitted the winning essay.

MATHER: I named the Mars Rover Perseverance. And I hope that people in the future will look at this rover as a shining example of human perseverance for years to come.

[music]

The Perseverance rover looks a lot like the 2012 Curiosity rover—ten feet long, seven feet high, six aluminum wheels—but it’s bristling with a decade’s worth of new technology. It’s got Moxie, a prototype oxygen-making machine. It’s got a UV laser that searches the soil for chemicals that indicate past life. There’s radar that can see 30 feet underground, maybe even spot water. Plus a weather station, an X-ray spectrometer, a laser micro-imager, 19 cameras, and two microphones.

Oh—and a helicopter. A tiny solar-powered helicopter called Ingenuity that can fly for 90 seconds at a time, looking ahead to scope out a good route for the rover’s next move.

On earth, the Perseverance rover weighs more than a ton and cost 2.7 billion dollars. On Mars, its sensors, drills, and on-board lab will look for ancient signs of life and collect samples of the air and the soil. 

ADAM: What we are going to do with Mars 2020,  is we’re going to take samples for eventual return to Earth.   

POGUE: But– but 2020 is not going to bring the sample back.

ADAM: It’s very hard to bring a sample back from the surface of Mars and it takes more than a single mission. 

That’s right: The Perseverance rover will collect 43 samples. One robo-arm will insert each sample into a sterile, sealed little tube; another arm will tuck the tubes into slots in its belly. The rover will drive them to a designated collection spot…and sort of poop them out. 

And then, in maybe 2026, we’ll send a European fetch rover to Mars. It will pick them up, put ‘em in a little space capsule, and blast it into Mars orbit. Eventually, maybe in 2028, a third rocket will swoop by, catch the capsule, and bring it back to earth, where scientists will use all their big, heavy, sophisticated analysis machines to study those samples—and lose. Their. Minds. 

OK—now you know the master plan for Mars 2020. On July 30, 2020, Perseverance lifted off aboard an Atlas V rocket from Cape Canaveral in Florida. 

NASA: Status check! Go Atlas! Go Centaur! Go Mars 2020.  5, 4, engine ignition, 1, zero. And Liftoff! As the countdown to Mars continues! 

For seven months, the capsule containing the Perseverance rover shot toward Mars at about 48,000 miles an hour—15 times the speed of a bullet.

Finally, on February 18, 2021, it entered the thin atmosphere of Mars. The capsule containing the rover detached from the cruise module that brought it there—

[sound]

—and here’s where our story really begins. 

The rover is the size and weight of a small SUV. It’s inside a capsule going 12,000 miles an hour. The problem NASA had to solve is this: How do you land it gently on the surface of Mars? So gently you don’t smash it? So gently you don’t stir up any dust that might get on the cameras and sensors? It’s the physics problem from hell.

Oh, and before you guess how they did it, get this: The whole thing has to be hands-off. People can’t be involved in this landing. You can’t pilot anything or make any course corrections. You’re 245 million miles away, too far away to send navigation signals. All you can do is sit there in front of a screen, wait for the news from Mars, and have an ulcer.

Allen   for Perseverance, it took about eleven and a half minutes for signals to reach Earth from Mars.   And if we wanted to send the command back, it would take another 11 1 2 minutes. 

This is Allen Chen. He’s worked for NASA at the JPL his entire career. For the Mars 2020 Perseverance mission, he was the EDL lead. That’s Entry, Descent, and Landing. 

Allen (cont’d) You know, everyone’s driven remote control cars before, right? Imagine if you, you know, you saw what the car was doing, you had to wait eleven and a half minutes until you actually could see it. And then you had to wait another eleven and a half minutes to send the command back to that car. That’d be a really difficult way to drive your remote control car, right? 

So, you know, that’s kind of one of the central challenges behind, behind these landings, is that the vehicle has to do it all herself. This is not one of those situations where we have the ability to, to steer things based on what we’re seeing.  

The whole process of slowing down from the outer atmosphere to touchdown was supposed to take seven minutes. 

And during those seven minutes, all NASA’s team can do is sit there, in a stew of helplessness, waiting for a signal to find out if the rover is still alive.

Internally, NASA calls this  period the “seven minutes of terror.”

Montage of announcers and spokespeople:

“Seven minutes of terror”

“That’s the riskiest part of the mission”

“The most elaborate and challenging feat”

“Seven minutes of terror”

“So treacherous it’s known as…”

“The seven minutes of terror”

David So you’re at JPL. By the time it’s all over, by the time you get word of what’s happened on Mars, it could be a smoking heap of wreckage. 

Allen That’s correct. 

David Is that actually a possibility, or has it been so tested and so dekinked that no one really thinks that’s going to happen? 

Allen No, it’s always a possibility.   Every time that you think you have everything figured out when you’re going to Mars, Mars will get you.   there are going to be things that you miss, right? Because things are so complicated.   There’s a reason why we’re all sweating in there. 

OK, so let’s think about how NASA could solve this problem. Your 3-billion-dollar robot enters the Martian atmosphere at 12,000 miles an hour. You need to set it down at under 3 miles an hour. For comparison, 3 mph how fast you hit the ground when you jump …from the height of a physics textbook.

So how do you do that? You can’t splash down in the ocean; they don’t have those on Mars.

You’re probably thinking: Well, duh! Just use a rocket engine. But no, you can’t use rockets down to the surface.

Allen:   There’s a lot of force coming out, those engines pushing into the ground.   you’re worried about the engines basically creating your own tomb, right? You’re digging your own grave. If you are disturbing the ground too much and creating a crater for you to not be able to get out of,   as you’re trying to put the rover down. 

The first time NASA solved this problem, it was 2004, when it sent the twin rovers Spirit and Opportunity to Mars. It used a parachute for initial braking. But then it got nutty: each rover was entombed in what looks like a pyramid-shaped bouncy house, with big bubble balloons bulging out of all sides—the effect looks like a huge freaky clump of white grapes. When the bubble thing hits the ground, 

Airbags

— it does a bunch of big, high, slow-motion, low-gravity bounces. 

(we hear 2-3 bounces)

When it finally comes to a stop, the balloons deflate, the pyramid opens up like flower petals, and the rover drives out. You can watch a computer-animated rendition of this process on YouTube; I put the link up at UnsungScience.com. It’s quite a sight.

Allen Yeah, yeah. We call those airbags, right?  but Spirit and Opportunity were kind of the biggest things that we thought we could touch down with airbags. If you go back to Spirit and Opportunity, you’ll see that development was fraught with problems of us tearing airbags. And now those rovers were about 170 kilos each. 

In case you’re American and not a scientist, I’ll be translating the metric units for you in this episode. The 2004 rovers weighed 375 pounds. The new one, Perseverance, weighs 2270 pounds. Six times as heavy.

Allen So we kind of had reached the end of the line with what we thought we could do with modern airbag technology in terms of landing heavy things. You know, this was just too big a jump. 

So for the heavier rovers like Curiosity and Perseverance, clearly, the airbags weren’t gonna cut it . On the other hand, one reason they were heavier was that they were built to withstand bigger shocks driving along the rocky Mars surface. Maybe, NASA thought, that ruggedness could be the key to a new landing system.

Allen (cont’d)   we’re beginning to build such a big rover that has   the ability to conform to the ground, and deal with rocks, and has the strength to fall off rocks when it’s driving around on Mars— why don’t we just slow the whole thing down to the point that the loads, that kind of impact forces that we see a touchdown, are the same as what the rover might see when just driving around on Mars?   We don’t need those airbags anymore, because we have a landing gear—it’s already on the rover.

That realization was the beginning of the design for the Sky crane maneuver, which NASA ultimately used for Curiosity in 2012 and Perseverance this year. To the untrained eye, this system looks improbable and convoluted, absurdly over-engineered; it seems crazy that there’s not a simpler solution. It’s a four-step series of braking technologies that slow the falling rover to a gentle bump down on the surface.

During the break, see if you can guess how it’s all supposed to work. 

[theme music]

BREAK

OK. Before the break, we were talking with NASA’s Allen Chen, who was in charge of the Perseverance rover’s Entry, Descent, and Landing, aka EDL, aka the “Seven minutes of terror.” 

Allen We pretty much have one job, which is to make sure that the rover lands safely in the place that we want to land it. In this case,   We went to Jezero Crater, a place that was so challenging that we weren’t willing to ever go there before, with past missions. 

David So what is dangerous about Jezero Crater?

Allen you can see this giant cliff running through the middle of it. You see lots of big craters out there that are places that even if we were to land there successfully, the rover might not be able to get out of. 

you see all sorts of rocks all over the place that are really dangerous—things that you wouldn’t want to land on.  So that’s kind of that internal conflict there in the mission. We want to go somewhere that we really don’t want to land in. 

David so basically—the Jezero Crater used to be water. Is that what we think? 

Allen Yeah. The scientists believe that Jezero Crater used to be an ancient lake.   if you go to any river delta, you know,   anywhere here on Earth, you’d be hard pressed to not find the signs of life here on Earth. So that’s kind of the idea on Mars, that if we if we find signs of life well-preserved here on Earth in deltas, maybe that’s true, too, at Mars. 

So now, at last, Allen Chen and I shall reveal the answer to the mother of all physics problems: How NASA intended to slow down this plummeting projectile, so gently that it wouldn’t even stir up dust.

Allen We hit the top of the atmosphere going about 12,000 miles an hour or so. At that point, we’re about 125 kilometers off the, off the surface of Mars. 

That’s 77 miles up. And now, meet the first braking mechanism: The Mars atmosphere. Unfortunately, there’s not much of it.

Allen The atmosphere is about one percent, the— the density of Earth.  the lower density is painful. Here on Earth, we have a nice thick atmosphere to use for slowing down. That’s why, you see when the Apollo capsule splashed down, right, there’s only parachutes. They don’t have retrorockets or anything like that because we have a nice, thick, soupy atmosphere to use. 

At this point, the rover is nestled inside what looks like a typical space capsule, with a gently curved heat shield on the bottom. After about a minute and a half of plowing through the Mars air, that shield is insanely hot—like 2300 degrees Fahrenheit, glowing like fire. But inside the capsule, the rover itself rests comfortably at room temperature.

Allen: We hit peak deceleration, about eleven earth Gs of deceleration. So about the amount of deceleration that would certainly cause even fighter pilots to black out. 

Little thrusters start going off, adjusting the capsule’s angle and direction to keep it on track when it hits pockets of denser air.

Allen: The first three-ish minutes of flight through the atmosphere, is really about survival and about steering toward the landing target. 

Allen: At that time,   we deploy this big supersonic parachute. At this point, we’ve slowed down enough to get to the supersonic period where we could safely deploy our 21-and-a-half-meter parachute still going about Mach 1.75 or so. So, nearly two times the speed of sound. 

That parachute is over 70 feet across. Its design has big orange-and-white sections and stripes—which those sly dogs at NASA arranged in such a way that they spell out a binary code. It took internet nerds about six hours to figure out that was an Easter egg, a secret message that said, “Dare mighty things.” It comes from a Teddy Roosevelt quote, and it’s sort of a JPL motto. Google it.

Anyway—it’s a really big parachute. 

David So, so even at 1 100th the density of Earth, the atmosphere is still enough to make the parachute worth it. 

Allen That’s right. It’s still useful. Somebody once told me that Mars has just enough atmosphere to be annoying. That’s not quite right.   we use the atmosphere to slow down.   

Next, a set of explosives is supposed to blast away the heat shield.

Allen: So popping off that heat shield off is like popping off a lens cap. We finally get to be able to see where we’re going. 

Back with Curiosity, we had just a radar, so we can kind of see how fast we were going and how high we were. With Perseverance, we had that plus a camera. This time we could actually take a look at the ground. 

So we’re taking pictures of the ground rushing up at us, comparing those pictures with an onboard map. This is our new terrain-relative navigation system. So we’ve got a picture of the place we’re going. We’ve got pictures we’re taking on the way down. We’re trying to match those up to figure out exactly where we are. 

This new nav system is what NASA thought would let Perseverance land in such a dangerous place. The Mars 2020 team, in advance, had picked out flat spots around the Jezero Crater where it’d be safe to land—and programmed Perseverance to choose one of those spots on its own.

 With one minute until landing, the third braking device is supposed to kick in.

Allen: The parachute’s kind of done its job. You know, the parachute is just not enough to slow us down because the atmosphere is so thin. 

So at about two kilometers above the ground, that’s about six minutes into our seven minutes of terror. That’s when we do the this backshell separation. We drop off from the, from the parachute backshell and let that go, light up those engines and begin that descent toward the ground on engines. 

OK, whoa, whoa, whoa. This is gonna take some description.

[music]

Remember, the rover is inside a capsule, which is hanging from the parachute. The bottom of the capsule, the heat shield, is gone now.

So now, the rest of the capsule, the backshell, is going to detach and just float away somewhere, parachute and all, never to be seen again. Or at least not until Elon Musk’s arrives in a couple of years and stumbles across it. 

But what falls out of that backshell is not recognizable as the rover. That’s because the rover is enclosed inside this crablike superstructure called the Descent Stage. It’s a jetpack for the rover. 

Imagine a deck of cards in a box on the table, and you clutch it with your hand. Well, the card box is the rover; your hand is the jetpack grabbing it. Oh, and I forgot to mention—your fingertips all have rocket thrusters, pointing down. Also, you have eight fingers.

Allen: So light up those engines, turn the vehicle to fly there, and slow down even more till we’re coming down directly over that site. 

At 70 feet off the ground, the jetpack is supposed to activate the fourth braking maneuver.

Allen: That’s when we begin that Skycrane period, separate that rover from the descent stage, that rocket-powered jet pack that’s been slowing us down. 

This is the part where it gets really absurd-looking. So your fingers are shooting retro rockets, right? And now—your hand lets go of the card box. It drops straight down,  falling.

What your hand just did? That’s what the descent stage does on Mars at this point. It lets go of the rover—but the rover is hanging from a set of three 21-foot nylon ropes, known as the bridle. That’s what keeps it from smashing onto the ground. Ropes!

Allen It’s a, it’s like a rope. It’s braided. And then there’s an umbilical with a bunch of cables running in there that passes data and power between—mostly data at this point—between the two vehicles. 

And here, finally, we find the ultimate secret of the gentle landing. Yes, retro rockets are involved—but they never get near the ground. The descent stage is going to carry the rover down on ropes. This is the Skycrane maneuver.

Somewhere, Rube Goldberg is smiling.

Allen: Send the rover down below that descent stage and deploy   our landing gear at this point, to put that rover down safely at about 0.75 meters per second. 

That’s 3 miles an hour—and in theory, the rover is now on Mars, fully intact.

Oh, but wait a second—we’re not out of the woods yet. The jetpack thing is still attached to the rover! By those ropes. It’s hovering overhead.

David At this point the— the tethers somehow get cut or disconnected and the descent stage flies away. 

Allen That’s right. 

David What, what makes the decision that it’s time to do that? 

Allen Oh, good question. Let me first backtrack and kind of give you  how we used to do this and how we still do it with landers.

When he says landers, he means three-legged tripod things, like the Viking landers in 1976.  

Allen: And now I’m going to geek out on you. So watch out here a little bit. 

With legged landers, right,   If you touch down on a slope, one leg is going to hit first. And if it hits first, you start pivoting about that point.  you’re going to start flying away from that slope if you accidentally left your engines on. So the, all of these legged landers  have hair triggers—like, you know, really fast detection of, has any leg hit. As soon as the leg hits, we want to shut those engines off and hit the ground. 

Remember how I said NASA has landed eight out of nine spacecraft successfully on Mars? The one that got away was the Mars Polar Lander, in 1999.

Allen: One of the leading theories behind why we lost the Mars Polar Lander is that that hair trigger was set off prematurely. That didn’t detect the impact of touchdown, but instead detected the impact of the legs deploying themselves prior to hitting the ground. 

So one nice thing about the Skycrane is, we don’t actually have to detect the instant of touchdown. We don’t have a hair trigger. Once the rover really settles down on the ground, the, the descent stage jetpack is no longer carrying that weight. And that’s a really strong signal. Really strong, slow signal, right? The weight is gone for about a second to make that decision, which is an eternity in in computer speak. 

that’s when we order the rover to cut the bridle that’s connecting the descent stage and the rover. It uses these little explosive cutters that fire these knives through the, through the nylon bridles and through the electrical connection between the two vehicles. 

David Oh, man, I am geeking out so hard right now. OK, so the descent stage presumably now knows that the cables have been cut and the NASA videos always just say, ‘And the descent stage flies safely away.’ 

Allen Not safely for the descent stage, as it turns out, but it executes about a five or six seconds of, of a turnaround. It first goes up, and then turns, and then flies away about six hundred meters. 

That’s about two blocks away. 2000 feet.

Allen: And going that far ensures that when the descent stage hits the ground,   won’t have any detrimental effect on the rover, right? That’s far enough that when those things explode or rupture, there won’t be a problem. 

David OK,   —so the first slowing down is friction of the atmosphere. 

The second slowing down is the parachute. 

The third slowing down are the jet pack’s rockets. 

Allen That’s right. 

David The fourth slowing down is the crane cables. 

Allen That’s right. 

David And are all of those necessary? For example, as I sit here in my Connecticut living room and try to improve on NASA’s system, why then do you need the parachute? Could the rockets not do the same job as that?

Allen Yeah. You certainly could use rockets to go all the way. However, that requires a lot more fuel.  You need that much bigger a launch vehicle to get it off the ground from from Earth and toward Mars. Everything balloons as you try to try to put more fuel on there.

So there’s a couple of reasons why the, why the parachute still a really good deal for us, although, you know, it certainly provides a lot of heart-stopping moments for us, too, right? 

The parachute? The parachute is the scary part? Of all that sophisticated, autonomous robotics, the jetpack and the heat shield and the pyrotechnic rope cutters—the last thing I’d think would give NASA heartburn is the parachute! I mean, it’s a parachute! There’s nothin’ to it!

But no. The parachutes were the Mars 2020 migraine. 

Allen We wanted to make sure that these parachutes would really work, so we went and tested them supersonically, out over the Pacific Missile Test Range, PMRF, down in Kauai. So a lot of people had a good time hanging out in Kauai for months on end. 

[music]

So, you know, when it came time to test these parachutes, we went, went ahead and shot them up high in the atmosphere. So to get to the right density, the low density you see on Mars, we have to go up really high in the atmosphere, and I mean 130,000 feet high. 

But when the when that day came and we tested those parachutes, they turned into confetti cannons. As we deployed those parachutes, they shredded themselves in a matter of, you know, less than a second. The parachute just disappeared. It deploys cleanly, you see it open, and then it’s gone. The whole thing is shredded and torn to pieces. 

So that’s really a heart-stopping moment. I mean, you know, not very proud of having watched that. You know, I was kicking chairs around the room because, you know, suddenly you realize, you know, you make it makes you question everything you’ve been doing.   And then just because we didn’t believe it the first time, we actually kind of made some tweaks to the parachute design   and tested it again. And the same thing happened again, right? That we blew up, blew up this giant parachute again. 

So suddenly, you know, everything was in question, right?   one of the things that we thought we got for free was the parachute . 

So we strengthened our parachute, redesigned it, and then took it up to– to those supersonic conditions high in the atmosphere and proved that it worked. So that took a couple of years of our life that we didn’t expect to have to use there. 

David Well, so that’s the other thing. To what extent are you able to run tests on Earth? 

Allen Yeah,  people always ask us, right, Why can’t you run a full end-to-end test, right?  Why is the first time you do this going to be on Mars? 

And it’s because  things are just too wrong here on Earth. The atmosphere is wrong, right?  You know, Earth does not have the three-eighths gravity that that Mars has. 

Everything is different between gravity, atmosphere, winds, terrain, everything is different. 

So we’ll test engines on their own and characterize how they work and build a software model of that. We’ll test the radar and  try to put together these little building blocks of things we can test, in this end-to-end simulation. And that’s the best we can do, which is pretty disconcerting when it comes down to it.

David I think of computer hardware and software and robotics as– on Earth as a as a process of iteration and beta testing and iteration and selling hundreds of thousands of iPhone 4’s before you make the iPhone 5. You guys are making one-offs. 

Allen Yeah, I mean,  even after developing our new supersonic chute and strengthening it, we only tested it twice. If you take a look at how violent that parachute deployment is, right—you think of parachutes here on Earth as being as being soft, you know, slow, slow inflations here on Earth. On Mars, the parachute inflates in about .7 seconds. So, you know, we have a parachute that’s roughly the size of a Little League infield or so, inflating, you know, in a, in an instant there. If you blink, you’ll miss it. So –and we only tested it twice. So, you know,   there’s a reason my hair is graying much faster than my age. I think it takes it out of you, right. To to think about all those things that can go wrong. 

In any case, you now know, step by step, what was supposed to happen on February 18. Want to know what actually went down? Let’s set the scene for you:

David You are sitting there at—where are you, mission control? 

Allen Yep, that’s right, what we call the crew’s mission support area. 

David Are you, as a person,  able to not completely crunch into a psychological puddle , or are you human like anyone else? 

Allen You know, try not to show it as much as possible. But, you know, everybody’s dying a little bit on the inside, right? That you can’t do anything. And, you know  you’re taking this test in front of the world, right, in terms of whether what you’ve done is going to pass muster or not. What did we get wrong? All those things are racing through your head as it’s going down. So it’s, it’s definitely a coronary event. My blood pressure is probably spiking.

Now, in mission control, someone passes out the peanuts. Oh yeah! You didn’t know about the peanuts thing?

[Music fades out]

 Yeah—so, in the mid-60s, NASA had tried six times to launch its Ranger probe to  the moon—Ranger 1 through Ranger 6—and every single time, they malfunctioned, and we lost the spacecraft.

On launch day for the seventh attempt, engineer Dick Wallace handed out peanuts to the team before the launch—and this time, Ranger 7 lifted off without a hitch. He brought peanuts for Ranger 8 and Ranger 9—flawless missions. So, a tongue-in-cheek superstition was born, and it carries on to this day.

OK, back to Perseverance mission control: 

[music resumes] 

Ten years of work have led to this moment. Al Chen gives a little speech.

Chen: We’re ready to roll.   Thanks for literally and figuratively putting us into the right position to succeed. And let’s land on Mars together. (applause)

And now…there’s absolutely nothing left to do. It takes 11 and a half minutes for the news from the rover to reach the team. Maybe it’s safely on Mars, maybe it’s a twisted pile of smoking metal. Either way, it’s out of the NASA’s hands. They can do nothing but wait out the seven minutes of terror.

B thrusters

BEEP! 

Seven minutes to touchdown. Altitude, 80 miles. The capsule enters the Mars atmosphere. Speed, 12,000 miles an hour. Little thruster puffs keep the capsule on target as it falls. 

BEEP!

3 minutes to touchdown. Altitude, 7 miles. Speed, 940 miles an hour. Parachute opens.

C chute

Parachute

NASA: Navigator has confirmed that the parachute has deployed, and we’re seeing significant deceleration…

BEEP! 

2 minutes, 40 seconds to touchdown. Altitude: 6.5 miles. Speed, 350. Explosives blast the heat shield off.

D shell

2 heat shield

NASA: Heat shield sep.

NASA: And the heat shield has been separated. Both the radar and the cameras get their first look at the surface.

1 minute to touchdown. Altitude: 1.3 miles. Speed: 200 miles an hour. The backshell and parachute detach and float away…

E backshell sound

3 backshell

NASA: Backshell sep. 

NASA: We have confirmation that the backshell has separated.

Beep!

…and the jetpack’s eight engines light up—for about 40 seconds.

F jetpack

18 seconds to touchdown. Altitude: 70 feet. Speed: 3.7 miles an hour. The rover drops out of the jetpack on its nylon ropes. The rover’s wheels unfold to serve as landing gear.

G crane

skycrane

NASA: Skycrane maneuver has started, about 20 meters off the surface.

And then…and then…after ten years, and after seven months, and after 11 and a half minutes…

NASA: Touchdown confirmed! Perseverance safely on the surface of Mars! Ready to begin seeking the signs of past life. (cheers)

The explosive guillotine cutters cut the bridle. 

H explosive.aiff

The jetpack flies off at a 45 degree angle and eventually crashes.

F jetpack.

Music concludes.

Altitude: zero. Speed: 0. Allen Chen’s heart rate: 140. Probably.

Allen: We touched down actually on Perseverance in six minutes and 59 seconds. So just one second shy of our seven minutes of terror. So little less terror than—than advertised. 

David And then you go on vacation. 

Allen That’s right. 

David the complexity of this thing just absolutely fries my brain. I just don’t know how you pulled it off. 

Allen Yeah, it gives me heartburn every time I think about it, so sometimes you’ve got to think about it a piece of time, right? Break it down and into manageable chunks. Otherwise, you get that paralysis from not knowing where to start. 

David I guess everything’s working. Helicopters work and everything. 

Allen Yeah. So far, it’s gone smoother than any surface mission that I can remember. So—knock on something.

At Mars.nasa.gov, you can see some of the incredible pictures and videos the Perseverance has taken—it, and its little helicopter companion. And remember how Perseverance has microphones on it? For the first time in history, you can actually listen to sounds recorded on another freaking planet!

Mars wind

You can hear the Martian wind…

Laser zaps

There’s the rover’s laser, zapping rocks to see how hard they are.

Rover noise

And that’s Perseverance rolling along the surface on its aluminum tires. I don’t know…something there sounds like it needs oiling.

These days, Allen Chen and the gang at JPL are already working on the next project: Getting those sample tubes of soil and air back from Mars in the coming decade.

But for the Skycrane maneuver, Mars 2020 was the end of the line. The spacecraft that NASA is building to retrieve the sample tubes will rocket its way all the way down to the Martian surface—no detachable jetpack necessary. Because it’s going to be a lander, not a rover.

Allen So that’s something that we may not do again. I’d be surprised if we land the rocket with the Skycrane again. 

And you know what? By the time we get those samples back to earth, two missions from now, today’s middle schoolers will be in their mid-20s. Including Alex Mather, the seventh-grade kid who came up with the name Perseverance.

So it’s only fitting that I give him the last word. This is what he said during NASA’s broadcast of the Perseverance landing on Mars:

[music]

MATHER: Hello, space nerds! Space is the future, and kids are the future. Learning about space and watching the story of humanity spread to the stars happen is watching the future happen and seeing future unfold. I am currently applying to a science and tech school for high school, with my ultimate goal to join the incredible team of scientists and engineers who are about to make this happen.

Something tells me…he’s got a pretty good shot.

Full landing animation, with all sound effects: https:  www.youtube.com watch?v=rzmd7RouGrM

Mission control voices for the final sequence:

https:  www.youtube.com watch?v=4czjS9h4Fpg&t=16s 

Timeline of EDL:

https:  eyes.nasa.gov apps mars2020 # home?rate=0&id=cruise_stage_separation&time=2021-02-18T15:26:48.003-05:00