Mars 2020 Lecture: The Thrill and Terror of Landing a Spacecraft on Mars

good evening and welcome to this evening's program i am tom prince a bone professor of physics at caltech and director of the wm keck institute for space studies your host for this evening's event back in july on the eve of the successful launch of the mars 2020 mission and its perseverance rover katie stack morgan uh gave us an excellent tour of the landing site for perseverance giselle crater well here we are several months later on the eve of the landing itself and we are glad to have another great speaker for this evening uh by my count uh we are this will be the biggest audience we have ever had for a tech institute event so since many of you are new uh to the kekkids too uh what is the keck institute for space studies well in ask are thankful for new ideas about future space exploration we carry out our work jointly with the caltech's jet propulsion laboratory and we endeavor to bring together bus scientists and engineers from the u.s and around the world to participate in our studies we undertake studies in planetary science earth science astronomy and astrophysics and space engineering our goal is simple to come up with new concepts that have the potential for significantly changing the future direction of space exploration we have been consistently rated among the best u.s science and technology think tanks each year over the last 10 years if you would like to learn more about the work of the keck institute please visit our website and also maybe consider supporting our work which includes programs such as the one we are hosting tonight i'd like to also say that great talks like these uh have a lot of people working behind the scenes to make them possible i'd like to especially thank this evening kathleen alva and michelle jugg of the keck institute and i'd also like to thank wesley maxfield the caltech video and audio wizard for her work on the production of this and many other webinars and lastly we are very grateful to the caltech space innovation council for their continuing support of the tech institute so turning to tonight's program one of the goals of the keck institute is to help develop the next generation of space scientists and engineers among the activities of the keck institute is therefore what we call the affiliates program a fabulous group of cal tech graduate students and post docs with a passion for space science and engineering the affiliates come together for pizza about once a month to hear a talk by a prominent space scientist or engineer tonight is just such a get-together the affiliates have had their pizza already tonight and they will now be your host for the rest of the evening so i'd like to call on one of the leads of the affiliates affiliates group mike o'connell a caltech graduate student in aerospace engineering there is uh his research is at the intersection of engineering control design and machine learning to understand how to apply safety analysis of classical techniques to modern computing methods and also in a lighter vein his new hobby during the covet period is brewing beer so since this is a affiliates event mike will be introducing the speaker and also directing the question the answer period afterwards and he'll be your host for the rest of the evening thanks for joining the tech institute affiliates for this talk and enjoy the evening mike take it away yeah thanks tom welcome everyone and thank you for tuning in and joining with us tonight to gear up for the mars landing tomorrow i don't think there's a better person to tell us about the thrill and terror of landing on mars than our speaker tonight rob manning so rob has been working on mars spacecraft at jpl since the early 1980s just after he graduated from caltech he spent the first decade of his career working on avionics software and guidance navigation and control systems then in the early 90s he became the chief engineer for the mars pathfinder and he was the entry descent in landing or edl team lead um this work uh really struck a chord with rob as edl requires pulling together multiple disciplines and talented engineers to solve a really difficult problem as we'll learn more about tonight since his time as chief engineer for the mars pathfinder mission rob has had a hand in nearly every u.s mars mission in the last 20 years he's received numerous awards from nasa and other professional organizations uh one of those uh that really stood out to me was being included as one of the 100 people who made a difference in civil commercial and military space named by space news magazine uh but that was in 2004 uh so now you know that was over 15 years ago you know he's worked on so many more missions and only continued to push the frontiers of space exploration possibly like many people uh rob's passion for space started when he was young growing up reading national geographic magazines uh time life books on space exploration and there's even going to now be a national geographic special on this i think this this weekend um when rob is not pushing you know the boundaries of space exploration at jpl he does other things like play jazz trumpet paints and skis uh and he spends time with his wife and daughter uh so to help us all learn about the thrill and terror happening tomorrow on mars uh please help me welcome dr rob manning oh mike thank you but i'm not a doctor i'm just rob um so thank you very much i really appreciate this is what a great privilege is to be here uh with all of you and and i know a lot of my friends are watching me friends who know edl almost as well as i do are going to be watching here tonight so i have to be careful what i say um but this is a great thrill so thank you and i love sharing this stuff because you know this is this is pretty cool this is fun stuff you know we talk about thrill and terror you know if people have talked before you know this is rob this isn't terror this is just you know anxiety well i have to admit i guess i get anxious what can i say i've had i've had some a lot of wonderful experiences and and uh and so i tell people you know this is not you know what you see is this looks like happiness but it's not happiness it's great relief uh and hopefully tomorrow we'll have more great relief uh because of this because these these efforts to do this require a huge team of people thousands of people and the team at jpl and across nasa have done an amazing job and i'm so proud of them they're really great group and uh probably just let you know how it started for me um i grew up uh in the 60s and uh my view of space i really my expectation was that by the 80s we'd be flying people uh to land on mars just as verner von braun and others and and chesley bonestell argued in in in magazines like uh collier's magazine with these wonderful paintings of now this is really cool when this is uh this is a based on a 1950s design by von braun uh where um a uh he envisioned that we would be able to land a massive glider on mars on skids um he thought the atmosphere was thicker than it really turns out to be and can you imagine so if this thing would really land on mars they'd probably be landing roughly you know 800 900 maybe a thousand miles an hour on skids and unprepared services i don't think the outcome would be that pretty but anyway i didn't know that when i was young and i just i assumed i assumed that all this stuff would be easy well the real truth of the matter is that we've had a landing on mars has been a real challenge and we've had a lot of missions that worked some a lot of them have failed um we being the human species and we've had a nice run of successes lately in the united states um but uh you know it's it's we're one single failure away from uh one the simplest little thing going wrong and uh i can tell you it's uh you know it it's there's an enormous amount of effort to make sure that we've didn't miss that one thing out of thousands and i'll talk more about that as we go but it's been an interesting ride and look at the diversity of stuff that's been sent to mars look how different they all look yeah it's like you make it makes you wonder whether or not we know we know what we're doing um but and so so we mars has been splattered with mars with human uh debris some of it is some of it real uh stuff that worked some of it not so worked some of it sort of worked um but uh it's been quite it's been uh mars is uh i probably think a little inundated by now uh and there's more coming um ours is coming uh tomorrow and there's a is a chinese later coming in a in a month or two so here's the timeline uh you can see we've had um uh the uh uh uh the story started with the mars three which which which is a ussr mission which apparently lasted for a few seconds on the surface of mars before dying but the real first missions was viking and then there's a huge gap a 20-year hiatus when we have to realize that there was nothing uh alive on mars um no little green men uh no no plants no no no water flowing as many scientists already suspected um and we got a chance to do pathfinder and then and then a few years later after some interesting failures i'll talk about um spirit opportunity uh phoenix curiosity and insight uh and uh there will they will be there will be more coming so including this one so entry descent landing that's what edl st we call it edl we've been calling edl for a while um so it kind of rolls off a tongue it's sort of i look at well what could go wrong well you know as well as i do it's there's a lot can go wrong but before we get needles edl actually starts well before we even get to mars um i think a lot of people want to know i don't understand this whole business of why is it why is it we uh why can't we go to mars anytime why the why is our fleet of mars spacecraft leaving now arriving at mars now um why wasn't there one last year well let me show you so here there's this this is a simplified schematic of our solar system there's the sun there's earth and there's mars earth is in the in the blue orbit mars is in the appropriately orange orbit and the ice show as earth goes around what we do is we we and so don't let me tell you you can go to mars orbit anytime you like but mars may not be there when you get there that's a key detail so so imagine you've launched your vehicle and your vehicle up and it goes in this big looping elliptical orbit starts off fast as you go past the closest part of the sun gets as it goes further way up to the top it slows down then comes back to ground in a big loop well the real key for landing of course is you would like mars to be there when you get there so what you do is you time it so that you time your departures so that mars will be there when you get there um mars comes around the band uh and then uh with the fascinating thing about this and i always love sharing this with people is that because we're in elliptical orbit we're slow at that top part but mars is kind of cruising around in this big circular orbit mars actually comes around hits us from behind and so we have to kind of leap around uh and take a look so so the reason we can't go uh at any time we like is because mars is only in this configuration where we can launch and arrive there um every every mars about it is roughly um a little over mars uh roughly mars year or so so every 26 months and and the window of launch is only about three weeks long you could you could really stretch it you know a lot of you you'll see if you saw the actual orbit i mean sometimes those ellipses are actually bigger much bigger than the orange circle which means you can get there pretty quick um but so i thought we so once you once you do get there oh now the trick is a little bit something about entry um so uh e is the for entry and i'll talk a little bit about that so we have um so it's fun to think about so there's a picture of mars and i show to scale there's i put mount everest in there to scale um and we define an entry point 120 kilometers above the surface nothing nothing magic about that it's kind of an arbitrary altitude uh that is defined to be above where the atmosphere starts so what we do is we overlay some trajectories on top of this is our entry so entries coming from the upper right right there and it comes in so i show three trajectories in parallel in this case for this picture i show three because um often people say well we're trying to get the angle right you're trying to get that you get as much atmosphere as you can uh so if you go come in too steep you'll come in to whack the ground if you come in too shallow you'll bounce off the atmosphere but what i'm showing here is that oftentimes we talk about the entry angle being off it's not the angle being off it's the position the angle is is really nothing more than uh where you hit the atmosphere so all so in this case this was a real problem for us on mars pathfinder than that 90s because mars hadn't been we hadn't as i mentioned before it hadn't been explored for 20 years um and in that in that in that ensuing since viking and so in ensuing time it basically kind of locked lost track exactly where mars was so on our way to mars we were trying to aim for mars to do this direct entry thing just like uh pure perseverance is doing tomorrow and so we so we were very we were very concerned that um we could be off and so the uncertainty in our entry angle really corresponded to an uncertainty where mars was and mars could have been off as far as eight kilometers which in and it doesn't sound like much but that's quite a bit of difference got a bit of variation and and it leads to a large large error downstream because you can see there's the entry angle right there see where the arrows pointed something around 10 11 to 12 degrees and then as you get closer into the atmosphere you eventually get thicker and thicker and then you start really slowing down now it doesn't because you're really going fast between 12 13 000 miles an hour in that window here it doesn't take very long only it takes about a minute or so to get from the entry point down to the uh to the peak deceleration point down below um because you're going so fast then the brakes really hit you um and and and you know our vehicle is slowing down somewhere between eight and 14 g's which slightly between the angle and a bunch of other things um it's still a really it's quite a it's quite a neck breaking event and if you were on board you would make sure you'd be wearing a very uh lying pretty darn flat because it could be very hard on your back um and then um we would get to really close the ground there look at that that when we get to that line i've shown just above the surface that's about that's about nine kilometers above the surface that's um that's by the time you're there you've gone from thirteen thousand you're still going a thousand miles an hour a thousand miles an hour and look how close the ground you are holy smokes um you gotta pull that parachute because otherwise you're gonna hit it and so uh so that's about where we open the parachute right there and you can see though just the variation of uncertainty position leads to a large uncertainty of where you're landing insert lips now there's that and that's the only one of two inserts the other big uncertainty uncertainties even even if you came in really right where that little circle is in the up on the right there at the top of the atmosphere um the atmosphere variation of the density itself is very large at mars it's much uh it's it's it's significant which means that sometimes depending on the density you could be way down down track or up track that means uh left or right on this picture um uh quite a bit just due to death variations in the density so if you're if you're uh so if you're just a ballistic means it means you're ungodly just a a a rock like pathfinder a spirit an opportunity where um then you then you're gonna have some uncertainty and where you're gonna land now we could do which is what we're doing tomorrow and what we did on on on on on curiosity and that is we instead of flying this straight line this way we flew it we stayed um we're coming tomorrow we're coming a little bit differently we're coming in steeper and what we're doing is we're coming in and uh diving into the atmosphere and then we're pulling out imagine an aircraft with lift as you get closer to the bottom you pull up i'll show another picture about a lift a little bit later but then you actually fly remarkably horizontal in fact you even gained some altitude before you ultimately open your parachute so then you can see so i've just annotated this this picture here so the result is you end up with a much smaller uncertainty ellipse of where you're landing uh and and so a lot of our challenges on mars have to do the fact that density of of mars atmosphere is only one percent of earth it's very very small it's like landing trying to land a space shuttle 130 000 feet you're still doing entry at 130 thousand feet of the space shuttle um so it's really hard to slow down um when you don't have when your air is that thin there's something else about mars that you should know and it's and it's a lot like earth so i know you've heard of something called the hypsometric curve i love that word it's a it's called bimodal which means got two big bumps and those bumps what those represent so what this is is that elevation zero elevation in the middle it means at sea level everything to the right of that zero is above sea level everything to the left is below sea level and what you show under those curves is the fraction of the earth's surface that's in that rate roughly that range of of of elevations look how much of our surface is under water well that's not a surprise two-thirds of our planet is underwater and remarkably even that big peak remarkably most of that is uh places like nebraska which is not very high up um so only a little fraction of earth's surface is actually well above sea level well mars is the same way it's like it's shaped differently in fact it's got two humps just like earth does um and specifically um if there's it's almost like there's there are there's an ocean on the left you can see the big bump where there's something low and on the right mountainous regions but unlike earth where the spike is near sea level there's a big bump right there around one and a half two kilometers of up uh where a large fraction of mars is now the trouble with that so let me see show you where we've landed historically we've landed the highest mission we've landed was opportunity it was about minus one kilometer uh one point something kilometers everything else has been to the left of that in other words built way below sea level so we said well yeah so so you might say well rob why won't just go higher well it's that whole problem was just talking about you got to stop above the ground key detail um so we have this so the problem the ancient highlands on the right um have a lot less air because he's sticking up into that very thin atmosphere the low northern lowlands there's some air there in fact there's a lot more the lower you go the more air it is just like on this planet uh the atmosphere is exponential that means it's you get more atmosphere quicker the lower you go and you can sort of imagine this so here's here's here's um here's the full globe of mars and then so imagine if you had a lander that could go that can land as high as two and a half kilometers well that was that would rule out all the area in black well that's not too bad you miss out olympus mods you'll miss some of the highlands there but the good news by the way we learned water flows downhill and if you're looking for ancient life water and looking for where water once was you can go downhill which is actually very relieving thing but but uh but if you're if you're trying to get uh if your vehicle can only go say oh say minus two kilometers like uh curiosity perseverance um look how much of mars that you can't get to mars is a tough place um it's almost like if we're going to explore mars we're going to have to drive through these blue areas and i mean land in the blue areas and drive to the highland highlands if you want to get there it's going to be tough to land there if we if we're using atmosphere as our primary mechanism and parachutes and things like that there's other messages you could also use more fuel and do something supersonic direct propulsion that's much harder well this all started um with the viking projects in the 1970s and what's cool about the vikings from an entry descent landing perspective and by these missions were very successful um they did not discover life but uh they they did see interesting hints of of odd things in the service odd chemical reactions um but but uh but the cool thing from an engineer's perspective is that that these very smart people who were who were our inspiration early in the 1990s who were and they were still alive back then uh they no longer are um who who gave us that uh not just information inspiration but actual technical and not advice and knowledge that allows us to use their supersonic parachutes and this in the in the hypersonic entry space capsule and the thermal protection system that we use for mission after mission as well as the idea of the propulsive throttle engines that that very much like the apollo landers used uh for landing humans on mars and you can see so we adopted those so vikings on the left the the helico all these pictures these are all the space capsules um with heat shields on the left and all of them and they all the heat shields look identical don't they they're all the same angle in the same geometry well that's no coincidence um uh is tabec this guy right here in the in the glasses in the middle there told us doubles to do that and we had some good data to say that was a good idea and so the only thing we might have to do is make sure you make that heat shield as big as you possibly can relative to the mass um and to make sure that the mass to heat shield area isn't too high um what we've what we've been doing with our vehicle larger vehicles like curiosity and perseverance is that even though we've made a bigger aeroshell look how big they are compared to person uh it's it's it's still getting heavier and heavier and denser denser and so that ratio of mass to heat shield area is getting higher and higher which means you have to do these tricks like aim deep into the atmosphere cut it high and then pull up like a pilot um uh kind of a in a very kind of uh dramatic uh uh entry so anyway so um so 20 years later um we we took their ideas unfortunately we on on 20 and mars pathfinder in the early 60s we didn't have uh the wherewithal the money or the time or the technology to reinvent the throttled engine in the 20-year interval that throttled engine had really all but vanished as a capability uh so you know we could you know know when we needed them i mean you you don't land on the moon or mars very often that's the only application that was around for this thing so nobody was doing it so all the people who knew how to do it the companies who made it all disappeared so we said well how about this with just some silly solid rocket motors attach it to the back shelf the space cap so lower vehicle down on airbags and fire these rockets that stop it's just above the ground some meters above the ground and then we'll bounce on the surface and that's exactly what we did in in the uh in the in the 1990s with pathfinder and and delivering little sojourner to the to the uh to the surface of mars and a fun little mission for lasting three months uh in the process we learned all about soft goods and fabric and ropes i learned i didn't know i would have to learn about ropes and fabric and denier and and other attributes of fabric but we had to learn all those things um but um meanwhile um after pathfinder we were there was still the idea well we can drop we can use the the the throttle engines the the but the throttle engines technology wasn't around so so uh a group of people um led out at lockheed martin and um some other and there and some of their colleagues at jbl developed this idea of using existing thrust thrusters that just on off thrusters putting 12 small thrusters together and firing them on and off in a pulse mode like a like a bunch of little machine guns so 12 imagine 12 machine guns strapped to the bottom of your chair if you fire them off and on fast enough you can land this you can you can you can land your chair and it's it's about as dramatic too because the ride is very dark it's pretty darn rough but that actually worked and that's how a mars polar lander worked uh was intended to work how phoenix worked how insight worked and they all succeed the phoenix and insight also succeeded with that technique and it worked very well however the bad news for mars polo lander in late 1999 is that it it after after we had a uh long long story about mars climate orbiter just a few months a couple months earlier um we can't we just uh this vehicle in interest we we saved some money by not having a communication system on during entry descent landing unlike what we're doing tomorrow and uh it came in quiet and we didn't we weren't watching when it landed but when it finally landed we were hoping to get a signal back but we never did and um subsequently a team uh using the highrise camera uh on on on the mars reconnaissance orbiter has taken something like 50 to 60 gigabytes worth of of i'm sorry terabytes i'm mistaken terabytes or jp2 files of that of that area and we've seen no sign of it anywhere i think i we think we know what may have happened to it um i i suspect as some of my colleagues could suspect that we didn't make it through the entry phrase but but uh uh even though the official cause is that it failed on landing but we don't see any sign of it on the surface uh it doesn't mean it's not there it could be covered up in uh in dust but uh but uh i i suspect that's not what happened well so after that failure we had to come up with something um in a hurry so uh because as you know you can only launch every 26 months and and the next opportunity was to launch a vehicle just like that we didn't know what to do with that why it failed so we couldn't launch that one so so a couple of colleagues and i got together and we proposed the idea of of modifying mars path on a path on the left see that little white box the jpl letters and the us flag and then missing nasa meatball sorry about that um and and uh imagine if you just got rid of that white box and replaced it with a touch rather than a tetrahedral shaped box replace it with a tattoo touch with a little shape rover and get rid of the sojourner and add some little bat wing ramps to get this rover off and then you can just take the same design and land it and that's exactly what we did with spirit and opportunity actually three years and a month from the date that we proposed it from about a 24-page powerpoint package as mark adler who's listening will remember um i think it's 24 page anyway so we put that pulled it off we landed those things now we used the same idea this rocket sweep but we had all dickens of a time one of the trouble with the same tetrahedral shaped land or the same airbags as pathfinder it turns out this little rover was denser and it was heavier than pathfinder so we had to stuff more stuff in there so it turns out we start testing our airbags they're all being torn to shreds so we had to do something we said what are we going to do we need to we need to find some way to to slow down that control the velocity better is there some way we control those rockets better and it's not the rocket's fault it's the fact that the that the wind pushes that back shell around it it puts all these different angles plus the parachute itself can move across across the ground at a good clip if there's a horizontal wind and so we came to ideas what if we added a small camera to the to the radar bracket and we added three small rocket motors and fired them um just when we fired the big rockets and and to adjust the angle to make up for that velocity and that's exactly what happened a little video you were seeing there on the right if you could make it out um you notice that's actually spirits landing dance or reconstruction um that's what we we figured out exactly what happened and we pushed that the parachute was pulling us to the right we go we had to do something we had to push that back shell over by firing two rockets and push it on over and get get it to slow down and that's exactly what happened uh on to august january 3rd 19 uh i know 2004. so uh d is for descent um and so just point out though this this what's interesting is that that so that's the first time we'd use a camera for using kind of image kind of processing on board with the camera still just using that we use that camera strictly to get velocimetry basically measure horizontal velocity to help so we can use that information to help cancel the the the effects of wind so we did that and so you know one of our problems has always been one of our uh this is classic thing called a parachute which this is how it's supposed to oh shoot that's not the one i wanted to show that one all ripped up well of course it's ripped up that's the that's we did these are wind tunnels these are parachute tests we performed that we performed some years ago in the world's largest wind tunnel uh it it's called the nfac it's a hundred by uh 80 by 100 uh uh cross section up at nasa ames research center uh it's currently run by the uh the uh i believe the army but it's it's it's uh an incredible facility but uh but we've used it for testing parachutes uh and very successfully for many for many years oh shoot this isn't supposed to happen and we're using basically use it because this is subsonic test but we're using it for strength testing in these parachutes to try to reproduce the environment and so we said let's let's we need to do this right let's take some bigger bigger parachutes we want to push the envelope and these are these are two tests to reform your part in hawaii over the pacific and what you see there's a drag device ignore that here's the parachute open up oh ow oh shoot oh what's oh oh that wasn't supposed to happen well so um what did we learn well we learned that parachutes are hard to get right and it's easy to to um underestimate the forces that are on a parachute when it opens up supersonically and uh so so we since that time we we redesigned parachutes we built them um we we tested them and this is what it's supposed to look like and that's about the speed of inflation you remember that's a 21.5 meter parish you just saw open up there it's really big a person's really tiny look how fast this thing opened up anyway um so uh so parachutes have been one of our buggy bugaboos and it's probably the one i still think it's among the most risky aspects of entry descent landing um uh because you know on earth we never open up parachutes going you know approaching a thousand miles an hour that's that's crazy so l is for landing you've seen a lot of diversity in the landing you see uh airbags the the uh the viking style phoenix and insight landers and of course this new funny business thing called sky crane thing that showed up with curiosity what's that all about what were we thinking and so um so it really started when in early 2000's um even before uh mars polo lander arrived we were wondering how how we're going to get large rovers to the surface we we knew about how to get soldier there and we you know we we had some ideas how to get something like the size of a small golf cart there um or large coffee table as a spirit and opportunity are there um and of course the question is how do you get something as big as this a real laboratory to mars or a thing that's going to collect samples like like perseverance is going to do starting hopefully this next week and or even bigger you know you can imagine something bigger maybe not quite that big um but they're big you can see the mass grows um as each iteration of these missions and mass and volume so the question is how do you land this and then you can imagine all sorts of techniques you know stork delivery you can imagine so what happened was in 2000 just even before spirit and opportunity were invented or conceived we were playing with some groups a small group of us were working on various um enumerated ways to think about how to land how do you enter to st landing is in its in totality we and we looked at all these different options in about january into 2000 and we came up some with some ideas that that were you know just modifications of existing design there's a one with outriggers what about you could imagine you can land your rover underneath a lander with really long legs and just kind of like a land uh and just have it lowered to the ground once it's landed like this you can even use big airbags you can imagine big airbags with a more liquid propulsion system is when things we conceived um and to try to try to land a big rover there and so that by controlling the velocity you wouldn't have to bounce as much you might not even need to put airbags all the way around him or he could do the kinds of things with that that that that the uh soyuz capsule does in uh in the in the desert just before it lands some solid rocket motors fire stopping the vehicle just before it hits the ground another possibility is just to use a pallet lander with a very flexible lander that that could that could adapt itself to the surface and we worked on that for a while there's another wild idea we have is what if we just use a propulsive to descent stage helicopter thing to land it on its wheels nah that's just crazy and so we actually this is actually a view graph from that period that we were playing around with it and that interesting of those velocities down the lower right is pretty much the velocities we actually end up flying well after some time in around july we uh 2002 it took us a while a pathfinder uh uh i'm sorry a spirit opportunity with these struggle with these little rockets i told you about earlier we said well we really need some way to control the velocity really well like and if we if we could lower it down on a rope we could be very gentle and we wouldn't have to have uh airbags or lander at all uh stop screen and i'm going to give you a little demo so one of the biggest challenges we had i think can you guys all see me okay so so this is hey i'm careful not to hurt myself this is you know very dangerous um so one of the things we thought was well you know what this this system is really a pendulum and we said to herself early on it's like it's really hard to land something on a pendulum so especially on its wheels because if you if you have any angle like this you'll you'll damage the wheels and you wouldn't you'd it just it's wheels would be a terrible landing gear but then on spirit opportunity when we were working on those little rockets we started developing the algorithm people like miguel san martin would would say hey rob you know we should we can we can control this thing and one of the things that we discovered is that this is that this the algorithm for damping and the the motion is very simple because this is not a pendulum this is the descent stage is up here it's very agile it can make little turns back and forth especially as miguel pointed out if you put it in the middle of the center of mass of the descent stage so one of the things we do is that you can move like your fingertips you can move it around like this so imagine you're swinging like this how is the longest suppose it takes you suppose it would take to damp out that motion ready see one two three stop one two three stop stop it's really easy you can do with your eyes closed so see we realized that that was actually a really easy problem to solve but the algorithm was very easy so once we realized this and we put it to use and figured out how to lower the rover down we actually had a design and uh uh adam steltzer and others dubbed this designed uh uh sky crane the sky cream maneuver the lower the from a dense descent stage and there we had it it was our design and we did have some other problems along the way but uh uh it worked uh uh with a heat shield uh falling apart we had to get rid of our viking technology we had to go to a to a phenolic and blader uh as opposed to the uh the tps we developed on viking thermal protection system but let me talk to you quickly about uh first of inter viruses edl so what's new about tomorrow so we're landing in chester crater it's 45 kilometers across about 28 miles um we're aiming for any upper left of that picture um and i'll show you but first let me show you remember these ellipses the big ellipse on the uh the lips we had for like pathfinders or the spirit and opportunity were or where it was beside the area of of rhode island um well we when we added guidance we were able to on curiosity we were able to really reduce that quite a bit to an area the size of oh of of uh much smaller um something the size of greater the what the the the washington beltway um uh or greater washington's uh washington d.c and so so uh but now we've added another trick um because we're coming in horizontal with a parachute if you time the parachute inflation we can stop the vehicle more carefully over their landing site simply by timing when we inflated the parachute because we're coming in from the left horizontally boom open the parachute when we're over that lending ellipse and we'll fall straight the parachute then slow straightens out and we start fault descending straight down so there's that same ellipse it's zooming in there gives a sense of scale against uh manhattan that's so a new landing area is about the size of manhattan about an eight and a half by uh by nine kilometers uh ellipse more of a circle this time um they're mostly driven by what the winds will do to us and if it's not a windy day we're gonna come pretty close near the middle of that thing but you know look at that there are hazards here they're all headsets all over that landing ellipse so one of the things that we needed to do so how are we going to find it so scientists want to go this place because there's some great um there's some great mineralogy here there's this is an ancient water outflow clearly it was water right you can see the water had there's a river right we're on our plan is to drive up toward that river and uphill to the left so we want to get as close as that as possible so so the real trick here is figuring out how to avoid obstacles even though you're going to land anywhere in that you don't know where in that red or orange circle you'll land on you need to be able to somehow find a safe spot in that for any place in that circle so we're on thursday at about 2 12 36 10 minutes before entering the atmosphere the cruise taste is going to separate like we talked about we we got we'll get rid of it um we'll use uh we'll we'll get rid of throw away some extra mass on the vehicle on the bottom half the vehicle that will cause the vehicle to tip a little bit so as it flies through the atmosphere almost horizontally it'll get lift just like when you stick your hand out the window when you're driving your car at an angle your hand will be lifted up this same thing here we can use that lift by steering that vehicle by rolling it back and forth to get to to to glide ourselves with big s turns to our destination to control the dr how well we're going to target test bus so so um not just left and right but up and down but the tighter the s turns the the the less distance you need to travel you're going to travel even if you're going too fast and next so then we open up a 21 meter diameter parachute that's motor launched on a mortar cannon a mortar can check out that that's a real mortar this is what it actually looks like if you were there you'd see a big flash of flame um and then seconds but some seconds later we'll we'll open about you know we're still going 200 miles an hour we open up the each heat shield falls away we have a for the first time in history we're going to use a camera not just to take pictures of velocity but actually to figure out the rover on its own it's going to figure out where it is it's going to take it's got onboard images of the site that it's already that's taken from earth we gave it to them to the rover and it's going to take images from its camera and compare its images with the onboard images and with this two-dimensional image correlation will be able to deduce its location well from that we can also use another map effectively to look up to see whether there's a hazard there or not and if it turns out vehicles look it's gonna it's gonna be a hazard the rover makes a plan to land someplace else the next safest place and that's that's this technique we called uh train relative navigation uh and uh we'll we'll we'll do a meter up to 600 meter divert maneuver to avoid obstacles and find a safe place so hopefully that'll be tried out tomorrow too and uh so the engine swear to rifle life about a mile up and then um and we use a radar just like curiosity did on the way down uh and then slows down to about two and a half miles an hour and and about when it's about 70 feet up and gently lowers the rover down the wheels deploy and at uh at the same time we're taking images now we have a camera looking up the parachute when inflates we have a camera on the descent stays looking down and the rover is deployed we have a camera looking up at the distance we have another camera looking down from the rover it's just amazing um we're gonna have more video not tomorrow necessarily but in the coming days uh and maybe some snippets tomorrow uh of edl than we've ever had before and hopefully we'll learn something and so uh once we land it'll come to a stop and it uh it will uh uh cut the cables and the descent stage will fly away and crash land about 600 meters away so a lot of stuff has to work three sets of batteries multiple computers i won't want 79 close explosive devices i say it all the time mortar cannon thermal tiles 16 rocket motors ah boy it's like a partridge in a pear tree it's amazing how much stuff is in there and uh it all has to work it's there's very little in the way of redundancy from much many of these devices and mechanisms particularly um so we're gonna we're gonna be listening to uh tomorrow the new space network as well as madrid spain uh and um and we're getting signals directly from the vehicle up until just before cruising separation in which case we'll get rather than getting ones and zeros we'll get tones and uh so we get tones most of the way in from just from x-band signal which is not very much it's basically a bright flashlight but the cool thing is that um you can see that line coming on horizontally there um that's uh mars 2020 has perseverance turns out maven and mars reconnaissance orbiter are strategically placed so that they're flying overhead and in view and what's great about that is that mars 2020 will be able to send uh about just before entry will start sending ones and zeros to mars with constant orbit which orbiter which then relay those ones and zeros all the way to the jdl to the via the deep deep space network and we'll be able to hear what's going on and listen in to what the rover thinks it's doing and and get in it what it senses and so that's going to be very cool and so so with luck we'll be doing this in a um just in a few months times we'll be we'll be doing drilling and and decoring rock um we'll also be doing this [Music] okay so there's here's a here's an animation of everything i just explained here there's the uh there's the vehicle coming at us there um uh the [Music] uh the cruise stage is separated and it's separated such a way that it stays away from us and it burns up parallel with us we fly a little bit away from it as we enter and there's our those are reaction control jets which helps steer do those roll maneuvers i was telling you about as it enters the atmosphere and slows down from about 12 and a half thousand miles an hour to about a thousand miles an hour when the parachute comes up and uh there it is right there with the uh uh the heat shield's about to come off uh well actually the parachute has to open up first and uh there's now we're we're just finishing that up now we align the vehicle the right direction we're getting on the alignment repair sheet opens up just like you saw in the other video and uh about uh 30 seconds later the heat shield has popped out and we'll get our first few the rover will get its first view of mars meanwhile we've got a vehicle a marshmallow orbiter is not only relaying data it's also going to take a snapshot from orbit but like we try to miss out in with phoenix and we tried it again with insight but we missed but hopefully we'll get this and then then we do this divert maneuver so if there's an obstacle away that descent stage moves out of the way and uh i mean uh it moves and moves the vehicle we call it super pulsing descent configuration the pdp and then it's just and we just slow down slow down slow down and eventually go straight down once we get over our safe landing zone and and lower the rover down straight and about 70 feet above the ground or so we lower the rover down there's the helicopter nested below and it's protective shell three cables are cut as well as electrical cable and off the center case goes and we're on mars okay that is our story in a nutshell and hopefully um great thing we didn't have to climb off a road lander we didn't have to uh no there were no ramps involved we were directly on the surface so this this landing and technique of using the sky crane maneuver really is a very effective way to get a rover of this size and shape and configuration on the surface of mars so i'm going to stop right there and uh stop sharing so thank you very much i spoke fast i hope it was not too fast yeah thanks rob uh for taking us through the uh the thrill and terror of landing on mars uh we have a ton of questions that were submitted so i'm going to get right to it um so the first question uh is um how do you define sea level on mars uh and this one was a popular question so this so it turns out um mars global surveyor carried an instrument called the mola instrument the mars orbiter laser altimeter and what they did was they very carefully over 100 meter resolution they mapped the whole globe elevation-wise and they arbitrarily selected sort of what they thought was the middle ground in terms of elevation subtracting the measured elevation with a uh ellipsoid um that that defined the shape at the mean shape of mars and so that that shape variation became the definition of a lip of elevation and that's been the standard that we've used ever since and i think it's sort of become the de facto standard for mars for everybody uh because all the maps and everything are based on the mola map based on the mola instrument well um so the next question is from uh raphael avila from ecmsg in los angeles and the question is uh do you think it might be possible to live on mars uh will the rover be able to gather evidence to see if we might be able to um well in fact yes as a matter of fact one of the one of its instruments is the moxie instrument its job its mission is to um to extract atmosphere um from mars which is uh even though it's only one percent of earth's still got quite a lot of it's carbon dioxide co2 and it's possible to to pull apart the carbon from the oxygen and use and create oxygen from that which is a useful very useful thing for surviving on earth surviving on mars as you can imagine because once you have oxygen it's possible also to grab hydrogen from other sources and put it together to create water and so uh so you can use oxygen you can create oxygen oxidizer fuel for your fuel and there's a lot of things you can do so so so that's one key part about the possibility of eventual habitation that this project will will uh endeavor to solve but its primary objective and i didn't spend a lot of time talking about is the main objective of this mission is not edl even though i make it sound like it it's it's to go to mars to study uh the possibility for ancient life and particularly not just to do in situ exploration of mars with these fabulous new instruments on the end of its robotic arm but also going to collect core samples and put them in sterile ultra clean sample tubes that are sealed up with core samples or soil samples or even atmosphere samples and we'll leave them we'll leave them on mars in a pristine way so a more dirty rover could come along in a few in a future mission called sample return grab those tubes put them in a rocket and send them into space and so this is the step one of the sample return mega mega story um that that we hope to have happen because ultimately even though we send these fabulous instruments to mars the equipment we have on earth the ability to analyze things with incredible precision and to double check using ultimate methods is so much more powerful here on this planet scientists in this planet are just pining to have real samples from mars pristine samples that we know it's we know their their gen we know their uh uh their uh where they came from the conditions in which the uh they were sampled in collection what what what was the context that they were created in by looking at the surroundings uh the environment yeah that will be uh great to have back here on earth one day so the next question is uh from ruby ann vallejo who's a student at norma combs elementary school and she asked how do you program a rover to go to mars and what kinds of coding do you use to control it well you know it is uh if uh if some of you focus on first robotics you guys know how to program something it's you just write software and you put it inside your inside the computer and you hit go um and and the trick is that sounds it makes it sound easy but um you just have a lot of people work very hard working with these sensors and testing all all the time we we've tested uh the amount of testing required to pull us together is unbelievable really but but it's it's no different than uh trying to control uh writing software for your own personal robot your first robotics experience with with the various robots that you can buy yourself and so it's just a lot more elaborate with far many more lines of software and many more hands working on it too and many more hands hundreds and hundreds if not thousands um so the next question is as a spacecraft is approaching the landing site uh do you need to check the weather conditions uh we're landing on mars in fact we did we had our weather uh we have weather reports we have where we we collect weather data from instruments on uh our orbiters and particularly mars for constance orbiter um uh we we we look at we we get thermal um uh we look at grazing angles through the atmosphere to get the temperature and the and the and the uh uh absorption of various uh colors of light to give us a sense of what how the atmosphere is doing whether there's dust accumulation in the atmosphere uh we're taking we've got pictures that look down they can see clouds and dust build up and so yes we do in fact we just had who did this it turns out at our landing site tomorrow it's going to be pretty clear and cool and so we're not too worried about that um it's a the weather is great um had there been a serious serious dust storm go though we would have adjusted and tuned up some of the software parameters that we can tell the spacecraft here how did how to do edl tomorrow but we wouldn't be worried because we have we've convinced ourselves that this design with especially with this guided system and the robust thermal protection system is relatively impervious to dust and because we're not solar powered on the surface even if it's a a a solar ro a solar rover solar ray rover killer such as what happened with poor opportunity rover where it got so dark and so dusty it had no virtually no electricity was going to solar powers we have a separate plutonium powered um source of energy of perpetual electrical energy that can get us through even the darkest darkest dust storm so um the good news is this system is really robust to that and so i'm but that wasn't always true um some some some of our missions were not so robust to it but this one certainly is um the next question is how long does a mars rover last until it dies eluding uh alluded to by the uh solar panels on opportunity uh well see this one since this doesn't have solar panels it has it has this uh um uh uh radiothermal isotope generator electric generator uh it's it's it it it produces only about a little over 100 watts electricity doesn't sound like very much for such a big rover i mean you know you get 100 watt in the old days you know before led lights we would get 100 watt light bulbs and just put it in your in you know in the middle of your room and that would be one little light source um but uh but it's enough to charge the battery and that's what we use it for recharge the battery it basically trickle charges the battery all day long um so we but that thing will last to last now it does it does degrade with time uh just like your curiosities has degraded at a time it was it landed it's a little over 100 watts when it landed uh and now it's somewhere um south of 90 watts i think something like that now um it's a lot it's getting worse and worse over time but it's really slow and what's more is that we know how to if it gets the weaker it gets the we just do less on a given day and just spread it out the energy out the good news so that's the good news in terms of design life the other hand things can break and we have had our vehicles break um and uh either through through wear or issues with lubricant or even design flaws that we didn't catch before we launched which are very common and so and i just gotta warn you tomorrow and for all of us is that we gotta remember that we're only human beings we're not we um even with thousands with thousands and thousands things to go right even the best of us can make a mistake and and and miss something and so uh you know i hope you hope we don't come along come away thinking that that this is slam dunk it isn't a slam dunk it's very hard and the good news is we figure out over the years how to find ways around to keep things going as we do with spirit opportunity literally when we design spirit and opportunity i could i i swear we we really didn't think it could make it through the winter i i thought maybe morning it was designed for 90 mars days but you know i said i said i was talking now i remember talking to jake matia back who was our assistant at the late jake material wonderful fellow who who said rob i think we can get i think we can get to 120 days maybe if we're lucky um but we didn't count on something that showed up on mars it took us we were able to squeak out longer than 120 days but we had something that happened on mars that was very unusual uh it wasn't that we had dust cleaning events these best these this high-speed wind that essentially sand blasted the fine particles of dust that accumulated in the solar panels but we can't count on that um insight is on mars right now it's got dust accumulating on our solar panels and there hasn't been a dust cleaning event there's not those those and by the way you call them dust cleaning events it's a secret way of saying little you know uh martian monkeys with windex going kicks cleaning out the top of your solar panels no it's it's it's wind but but we but it we can't count on it and so the great thing about this power supply that we have on this vehicle is that we can count on it um as long as it doesn't break and doesn't short out or we don't have um uh electro electrical failures or shorts or things go wrong which could happen um all right so the next question is from finnegan keller who's a high school student how if at all does the climate of mars affect the design of perseverance's instruments um well the the the the climate that plays a big role particularly um the the the changes from uh summer to winter mars uh is is gets has has very large temperature swings in a single day but they're very predictable if you know the weather today it's going to be much the same tomorrow but over the course of the season though it can get very very cold and even but and and even though we're not that far from the equator um it can get pretty warm in the summer time too on the surface now the fascinating thing about mars is that you you can say it's you know it's getting really hot the surface it's room temperature on the surface it's boiling um but uh but you know at this at your nose or even higher up it could be it could be you know 40 degrees below zero uh just a few meter a couple meters away from the surface and so uh uh but but but on in the winter it seems it's even worse than that so you for instruments or other things that have to expect especially the ones have to stick out in the breeze they have to be designed to handle those temperature extremes uh as in over the whole annual cycle because this vehicle's designed to last to march tomorrow's year or longer so it's it's got to be able to handle a mars winter and by design from the beginning that was not a requirement on spirit and opportunity because we're only going for 90 days in the summer time even though we managed to hunker down and survive the winters uh several several winters for each of the rovers uh so the next question is what happens to the vehicle that delivers the rover so the sky the descent stage oh the poor descents day someday i'm going to put we're going to put software on it we're going to take it fly it away and then have it kind of try to land safely so it doesn't explode or anything um but this this the sense stage will uh like it like likes curiosities end up uh crashing into the ground and so it does crash unfortunately because it's it's unfortunate because we put a lot of money and time and effort into it it's kind of sad to see something you that you just be very very careful with your fingers and polished up so perfectly crashing the ground same with the cruise stage um which melts on the way to the surface so unfortunately our technology is still pretty messy in that respect and uh now the good news it's not that hard to clean up if i was there at the pickup truck i probably could get most of it in a in an afternoon but it's still um some of these some days we'll make it we'll come up with a descent stage that that doesn't that has a more graceful landing even if even if it's ugly graceful just as long as it doesn't explode one day there will be reusable descent stages on mars yes you can imagine you could put more fuel in it and if you're lucky you can fly it off somewhere else or if and if now it'd be really hard you have to really feel a fuel in order to get it completely out of mars and bike into orbit again but you can't you can imagine that idea yeah um so our next question is what kind of time delay is there between uh instrument observations made during like observations during landing uh and the time it takes to get back to earth and does that complicate the landing sequence it uh well i i'll answer though the second part first it doesn't because everything about the laning sequence is pre-programmed in advance in fact the view we gave the command the do edl command um which is what we call it um since pathfinder days um um last week uh late last week um and we so the rover once it gets that command it says okay i'm ready to land and with that duty command you tell it when lane it couldn't happen and where we want it to go and everything so it has all the information it needs to land um what we're doing now is updating that information tweaking it every little bit but if we don't tweak it anymore if we don't talk to anymore the vehicle is on its own there is no need for us to talk to it and so when you see us all in the room tomorrow or you'll still see the team you know jumping up and down or staring at the consoles what we're doing is we're monitoring different parts of it because different parts of the of the rover communicate to have different parts to talk about they have different things to talk about in different areas so so the team is able to monitor what's going on but there's we're not involved in it at all so that that delay is not a problem at all in fact when we're leaping up and down or when we say oh look at the the cruise stage uh that we hit that we're entering the top of the atmosphere well on mars it's actually already over because it happened 11 minutes earlier because that's how long it took for the radio signals from both our space from our rover as well as the one data that's been relayed from mars preconcepts orbiter to get back to earth so but when you're operating a rover on mars that time delay is significant but another delay is even more significant it turns out our rovers because we don't get we only have 100 watts electricity we don't have enough energy to stay awake all the time so what we do is um do we imagine if you were if you were comfortably at home and you had a a team down in the in the antarctic uh antarctica who who's who's doing all this do the scientific work for you they would do all this work during the day they would send you the results and overnight you and your team here in in your in your comfort of your living room would figure out what you wanted that team to do tomorrow while they were sleeping and you would come up with a whole script of what you want to do and in the morning the first thing you do just before they wake up you s just when they wake up you send them a list of things to do that's what our rovers get in the morning when they wake up they get a list of things to do and uh sometimes that list goes a day sometimes that list may go for several days but nevertheless they wakes up as okay this is what they want me to do okay let's get going and the rover operates with us without us being involved at all for several hours before itself it gets sleepy or runs out of energy and it shuts itself down and sleeps for another 10 hours or more more like more like 16 hours until next morning and it repeats repeats the next day but so so so in some sense that the time delay due to the actual distance from ours is not as not as important as the fact that we don't have enough energy to communally communicate and allow us to interact with it in a more dynamic way like you do on a telephone it's much more like email versus a telephone uh so that actually was our next question from tallua so we will go on to the last question now so this is from ella at john muir high school uh what is the experience of mission control and the relief felt after a successful landing during the pandemic well you're so you're yeah it's it's a great relief i might i can see it looks like it kind of looks it feels like it looks um you you imagine you've spent uh not you know six months but you've spent oh maybe four five six years working on something that you've been trying to visualize and work out and argue with people with how to do it and they'll say no i want to do this wait no that makes you should do it this way and you would you would talk about different ways and you finally get the design right so okay let's try it out oh it didn't work we have to fix this and then you're just on it and just and oh i didn't oh i didn't look oh look at this we made a mistake here we got to find that we got to fix that and you're doing that all the time because well what if this doesn't work well that doesn't work we can do this that's the kind of thing of people's goes through their mind all the time and you're basically thinking about all the ways that things not going to work in fact we spend far more time thinking about our way our machines aren't going to work than we do thinking about how they are going to work kind of weird huh but but you know but when actual landing happens you've been thinking about all these things that have gone could go wrong and all the things you thought through and all the designs and now the the information you're getting tells you it's over it's all in the past it all worked but in your mind you're still worrying about them and you may still worry about them like oh shoot i didn't do that i didn't set up that parameter i was going to set up did we oh shoot i was going to do that it doesn't matter now does it it's all over with so there's it's it's a very strange sense of feeling of um it's a bit it's a bit traumatic um even when it works it can be very bit traumatic um so it's a very very strong emotional feelings especially when you spent that much part of your life and especially not just during the weekdays but for many from many of these team are my team members these folks worked week not me because i was i was the chief engineer of jpl and just watching this stuff um this this team worked hours and hours evenings weekends nights days leaving their fam four families behind uh and just struggling to make this all work it's been um it's it's hard i know what that feels like i've been there but it's i tell you it's hard and it's harder on this team and that's why seeing this thing come through tomorrow will mean so much to them uh but also if it goes well it just tells reminds you just how much when people come together and they work hard with a toward a vision and and they and they and their and they and their they work with honesty and integrity uh and and work hard and they have perseverance they can make something happen you can solve problems it's possible for human beings to solve problems whether they're natural problems that we create for ourselves like laying on mars or the natural the problems that we created for our own planet uh that we have to solve as people and i think this is a reminder that solutions are there if you work at it and you come together and you and you listen to each other and learn from each other and and do it honestly and openly yeah well thank you rob so much for your time um tonight so i think we sent you a small gift hopefully that'll uh go with the relief and that you're feeling with the landing finally approaching tomorrow yeah this just arrived thank you uh this is the gift right yeah just double checking what is this i think i know what this is peanuts that's right so if people don't know uh but jpl isn't normally that superstitious but we have this tradition going back since the 60s after a series of failures of mars i'll mention that tomorrow during our during the the the nasa tv thing of of of opening peanuts and sharing peanuts uh the night before that during just before a big event kind of for good luck but also it's just a tradition but it's it's a wonderful tradition so i want to thank you oh my gosh there's more i'm not done yet oh my goodness look at this this is important for all of us a mars bar these are hard to find on mars i tell you and they're actually almost as hard to find on this planet too but thank you very much this is fabulous oh oh oh hi this one cracks me up can you see what this is loaded dice and you know if you know this this is this is maybe more appropriate for airbag landers to have to roll people wondering how can you keep landing on the base pedal down no but this is how we this is how we deal with uncertainty we try to stack the deck low the dice in our favor and that's and that's exactly what we try to do uh we do it without cheating but we but we do definitely try to win because it isn't it's not a precise game we can't be positive that we've done it right and there's residual risk and almost everything we do i'd like to tell people that that our designs are the least unsatisfactory designs we can come up with and never the best that's impossibly the best this is also cool look at this oh this is a playing card oh my gosh look at that oh this is really cool check these cart playing cards out i've never seen these before that's that's a big smiling rover you can probably can't tell but there's a big smile on that rover oh we can tell i think the cards might be one-of-a-kind is that right oh this is priceless thank you oh i love this this is so great thank you so much wow that is amazing thank you so much i didn't deserve that but i really appreciate it and it's it's so fun to share all this stuff with so many people and uh of course i'll be getting emails tomorrow with all the all things rob you got this wrong that's not the right number yeah sorry you'll have some bigger things to be excited about yeah i count up i count on my colleagues to correct my mistakes and vice versa and uh and that's how we succeed by the way we catch each other and and look out for each other yeah well uh thank you again rob uh so much for your time um i think we're we're a little bit over but i think that's okay because we're all excited for tomorrow for lucky people i am too thank you very much mike and thank you for the to the kiss team for inviting me to come and speak with all of you today um so i just want to remind everyone in the audience uh if they could just please take the time to fill out the survey when you leave the lecture and then also a quick announcement which is that we hope you attend our next kiss webinar on march 17th uh that's with dr sarah spangelo discussing swarm a new paradigm for communication satellites and of course we also ask that you attend some of the other mars landing events tomorrow uh and i think the one you alluded to rob was nasa's landing live stream beginning at 11 15. so we will see you all there thank you so much everyone and thank you rob thank you see you tomorrow everybody

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Length: 69min 44sec (4184 seconds)

Published: Fri Feb 19 2021