1 00:00:00,200 --> 00:00:05,599 The SpaceX Starship is currently humanity's best hope for setting foot on the planet Mars 2 00:00:05,679 --> 00:00:09,839 in your lifetime. The feature that makes the starship so well suited for this 3 00:00:10,000 --> 00:00:14,359 job is, of course, it's incredible power. There's no doubt that a 4 00:00:14,439 --> 00:00:21,039 future starship will have more than enough muscle to send both crews and massive amounts 5 00:00:21,079 --> 00:00:26,280 of supplies on their path towards Mars. Going up is one thing, but 6 00:00:26,719 --> 00:00:31,519 what about coming back down on the Martian surface. We are talking about the 7 00:00:31,640 --> 00:00:36,920 most complicated maneuver of the entire journey, the make or break moment, and 8 00:00:36,960 --> 00:00:41,640 there's a lot more involved in figuring it out than you might think. This 9 00:00:42,000 --> 00:00:47,560 is how the SpaceX Starship will land on Mars. Let's establish right now that 10 00:00:47,640 --> 00:00:52,799 we are not all rocket scientists or physicists. I'm definitely neither of those things. 11 00:00:52,840 --> 00:00:57,920 But luckily we do not need to be geniuses to understand the basic principles 12 00:00:57,960 --> 00:01:02,600 behind interplanetary travel. So we're going to keep this all at a very accessible 13 00:01:02,679 --> 00:01:06,079 level. Before we can talk about landing on Mars, we need to know 14 00:01:06,159 --> 00:01:10,159 how the starship got there in the first place. The thing that we always 15 00:01:10,159 --> 00:01:15,280 have to remember about space travel is that everything is always in motion, and 16 00:01:15,319 --> 00:01:19,359 within the context of a solar system, everything is moving in an orbit around 17 00:01:19,519 --> 00:01:23,079 the Sun. We are currently held in the gravity well of the Sun, 18 00:01:23,159 --> 00:01:27,599 and the only thing that prevents us from falling down any deeper is the orbital 19 00:01:27,719 --> 00:01:34,040 velocity of the Earth, which is approximately thirty kilometers per second. That's how 20 00:01:34,120 --> 00:01:38,319 fast we are traveling right now in a big circle around a star that takes 21 00:01:38,439 --> 00:01:42,959 three hundred and sixty five days to complete. Mars is further away from the 22 00:01:42,000 --> 00:01:46,879 Sun than the Earth, meaning that it isn't as far down into the gravity 23 00:01:46,920 --> 00:01:51,560 well as we are, and therefore Mars can travel at a slower orbital velocity 24 00:01:51,799 --> 00:01:57,159 without falling in so Mars orbits the Sun at around twenty four kilometers per second. 25 00:01:57,959 --> 00:02:00,319 Now, if we want to leave the Earth in a spaceship and explore 26 00:02:00,359 --> 00:02:06,439 the planets, we will become yet another object spinning around in the gravity well 27 00:02:06,519 --> 00:02:08,960 of the Sun. And just like the planet Earth, if we were to 28 00:02:09,039 --> 00:02:14,719 slow down our orbital velocity, we would start to fall into that gravity well. 29 00:02:15,159 --> 00:02:19,759 This will change our orbit in the direction of an inner planet like Venus, 30 00:02:20,039 --> 00:02:23,800 and by the same mechanics, if our spaceship starts moving faster than the 31 00:02:23,800 --> 00:02:28,280 planet Earth, we will rise up the gravity well, bringing our orbit towards 32 00:02:28,280 --> 00:02:32,520 an outer planet like Mars. So traveling through the Solar System is all about 33 00:02:32,599 --> 00:02:38,840 changing your velocity relative to your starting point. The technical term that we use 34 00:02:38,919 --> 00:02:44,960 to describe this is delta V, where delta means change and V means velocity. 35 00:02:45,840 --> 00:02:50,039 We typically measure delta V in kilometers per second. So if the Earth 36 00:02:50,120 --> 00:02:53,520 is moving at thirty kilometers per second and you accelerate your spaceship to thirty one 37 00:02:53,599 --> 00:02:59,000 kilometers per second, you have a delta V of one. By the same 38 00:02:59,039 --> 00:03:02,439 measure, if you decelerate your spaceship relative to the Earth and travel at twenty 39 00:03:02,599 --> 00:03:07,120 nine kilometers per second, you also have a delta V of one. And 40 00:03:07,199 --> 00:03:10,479 yet, if you blast off from the surface of the Earth at one kilometer 41 00:03:10,560 --> 00:03:15,360 per second, you are not going to begin rising up through the Solar System. 42 00:03:15,639 --> 00:03:19,680 You aren't going to rise up above the Earth's surface because gravity and atmospheric 43 00:03:19,800 --> 00:03:23,840 drag are holding you down. These natural forces will affect the amount of delta 44 00:03:23,919 --> 00:03:30,199 V required to maneuver the spaceship. This is why it's so hard to get 45 00:03:30,240 --> 00:03:34,360 from the surface of the Earth to outer space. The delta V required to 46 00:03:34,400 --> 00:03:38,759 reach a typical low Earth orbit is going to be around nine point four kilometers 47 00:03:38,800 --> 00:03:43,360 per second. That's a lot of acceleration, and that's why our starship requires 48 00:03:43,400 --> 00:03:47,520 the massive power of the super heavy booster at launch. This is also why 49 00:03:47,520 --> 00:03:53,120 the starship needs to stop for a refilling session in Earth orbit before it can 50 00:03:53,159 --> 00:03:57,479 continue on to Mars, because we're going to need a lot more delta V 51 00:03:57,879 --> 00:04:00,879 to complete this journey. In order to change velocity, we need propulsion, 52 00:04:00,960 --> 00:04:06,360 and propulsion needs fuel. The advantage of filling up in orbit is that it 53 00:04:06,520 --> 00:04:12,039 resets our starting point. From here, we only need another nine point five 54 00:04:12,120 --> 00:04:16,560 kilometers per second of delta V to reach the surface of Mars, so basically 55 00:04:16,639 --> 00:04:21,319 equal to the change required just to escape the Earth's atmosphere. But there is 56 00:04:21,399 --> 00:04:26,240 going to be a big difference in the approach we take for the next leg 57 00:04:26,319 --> 00:04:30,439 of the journey, because while escaping the Earth was all about speeding up, 58 00:04:30,879 --> 00:04:34,560 landing on Mars is going to require a lot of slowing down and this can 59 00:04:34,600 --> 00:04:41,160 be just as difficult to achieve. A fully fueled starship in low Earth orbit 60 00:04:41,240 --> 00:04:46,360 is imagined to have enough thrust for somewhere between six and seven kilometers per second 61 00:04:46,519 --> 00:04:50,439 of delta V. This obviously is a bit short of our nine point five 62 00:04:50,519 --> 00:04:56,439 kilometers per second necessary to reach Mars. But that's okay, because the same 63 00:04:56,480 --> 00:05:00,720 forces that made it so difficult to escape Earth's atmosphere, gravity and aerodynamic drag, 64 00:05:01,000 --> 00:05:04,600 are going to work to our advantage when we come in for a landing, 65 00:05:04,759 --> 00:05:10,839 effectively increasing the delta V potential of our starship. So here's how it's 66 00:05:10,879 --> 00:05:14,319 going to go down. Okay, we are in orbit around the Earth, 67 00:05:14,360 --> 00:05:17,759 but even a few hundred kilometers above the surface, we are still firmly caught 68 00:05:17,759 --> 00:05:21,240 in the Earth's gravity. Well, the only thing keeping us up right now 69 00:05:21,480 --> 00:05:26,720 is velocity. If the starship were to slow down at all, it would 70 00:05:26,720 --> 00:05:30,920 start falling back towards the Earth. By that same reasoning, if we do 71 00:05:30,000 --> 00:05:34,879 the opposite and speed up, then we will continue to rise up into space. 72 00:05:35,439 --> 00:05:39,519 Because we are still so close to the Earth, we need a lot 73 00:05:39,560 --> 00:05:44,279 of delta V to fight against gravity. The ship will have to accelerate by 74 00:05:44,319 --> 00:05:48,399 two point four to four kilometers per second just to reach a height of geostationary 75 00:05:48,519 --> 00:05:53,800 orbit. Another zero point sixty eight gets us through the height of the Moon. 76 00:05:54,160 --> 00:05:57,240 Up Here, we are finally on the edge of the Earth's gravity. 77 00:05:57,279 --> 00:06:01,199 Well, the force of gravity is infinite, but the power of attraction dissipates 78 00:06:01,279 --> 00:06:06,800 relatively quickly as you move further away. Now, all we need is another 79 00:06:06,959 --> 00:06:14,120 zero point nine kilometers per second of velocity to escape the Earth's influence completely. 80 00:06:14,639 --> 00:06:17,519 From this point, floating in the vacuum of space far beyond the Moon, 81 00:06:17,839 --> 00:06:24,240 we only require zero point three nine meters per second of delta V to achieve 82 00:06:24,360 --> 00:06:29,800 our Earth to Mars transfer velocity. This second leg of the journey has used 83 00:06:29,879 --> 00:06:33,040 up three point six kilometers per second of delta V, which is at least 84 00:06:33,160 --> 00:06:38,519 half of the potential energy in our starship, if not more, and that 85 00:06:38,560 --> 00:06:43,160 means that we do not have enough fuel left to successfully land on Mars with 86 00:06:43,319 --> 00:06:47,839 engines alone. And here comes the problem that we need to solve. All 87 00:06:47,959 --> 00:06:53,399 of the velocity that we acquired to escape Earth's atmosphere and gravity well has got 88 00:06:53,480 --> 00:06:58,079 us traveling around the Sun at a significantly higher speed than the planet Earth, 89 00:06:58,319 --> 00:07:01,920 which was already traveling at thirty kilometers per second to begin with. The planet 90 00:07:01,959 --> 00:07:05,480 Mars, on the other hand, is orbiting at a speed of just twenty 91 00:07:05,560 --> 00:07:12,720 four kilometers per second, so we are moving significantly faster than our target planet, 92 00:07:12,920 --> 00:07:15,759 which means that we are going to overshoot the planet Mars and end up 93 00:07:15,800 --> 00:07:21,959 stuck somewhere in the asteroid belt unless we start slowing down. After several months 94 00:07:21,959 --> 00:07:27,720 of coasting through the vacuum of space, we need to execute our first deceleration 95 00:07:27,879 --> 00:07:31,399 burn After flipping the starship around and getting the Raptor engines back up to speed, 96 00:07:31,720 --> 00:07:35,319 we have to shave off zero point six to seven kilometers per second of 97 00:07:35,399 --> 00:07:42,000 velocity in order to become captured in the gravity well of Mars. This is 98 00:07:42,040 --> 00:07:46,480 the first step in what's about to become a very rough ride. If we 99 00:07:46,560 --> 00:07:51,040 burn off another zero point three to four kilometers per second of velocity, then 100 00:07:51,079 --> 00:07:56,680 we reach the height of the outer moon demos. Zero point four kilometers per 101 00:07:56,720 --> 00:08:01,879 second of further delta V gets us down to the inner moons. Here's where 102 00:08:01,920 --> 00:08:07,279 things get really tricky. By slowing down this much, we've already expended over 103 00:08:07,360 --> 00:08:11,279 five kilometers per second of the potential delta V in our fuel tanks, and 104 00:08:11,319 --> 00:08:16,240 that leaves us with somewhere between one and two remaining. But we need at 105 00:08:16,360 --> 00:08:22,680 least another four and a half kilometers per second of delta V to safely reach 106 00:08:22,079 --> 00:08:28,079 the surface. In theory, this is still possible as long as we are 107 00:08:28,240 --> 00:08:31,679 very strategic about how we use our last bit of fuel, and it's important 108 00:08:31,799 --> 00:08:39,039 to remember that everything from here on out is purely speculative. This is our 109 00:08:39,120 --> 00:08:45,919 interpretation of the most logistically feasible Mars landing. If we want to conserve as 110 00:08:46,039 --> 00:08:50,440 much fuel as possible for our landing burn, then we need to take advantage 111 00:08:50,480 --> 00:08:56,320 of some external forces to slow our ship down to a reasonable velocity. Getting 112 00:08:56,399 --> 00:09:01,279 down into a circular lo Mars orbit would use up most of our remaining fuel, 113 00:09:01,360 --> 00:09:05,399 so we probably shouldn't do that. In this case, we might be 114 00:09:05,399 --> 00:09:09,440 better served by inserting the ship into an elliptical orbit, so instead of flying 115 00:09:09,480 --> 00:09:13,440 in a circle, we're moving in an oval pattern with a low spot or 116 00:09:13,600 --> 00:09:18,879 peragy close to the planet and a high spot or apogey deeper out into space. 117 00:09:20,440 --> 00:09:24,600 By using this maneuver, we can start to take advantage of both aerodynamic 118 00:09:24,679 --> 00:09:30,360 drag and Mars gravity to help us slow down. The Mars atmosphere is still 119 00:09:30,480 --> 00:09:35,080 very thin, but we'll take any help that we can get. We can 120 00:09:35,200 --> 00:09:39,320 lower the peragy of our orbit down to the point where the ship actually dips 121 00:09:39,399 --> 00:09:43,639 into the upper atmosphere of the planet. By doing this very carefully, we 122 00:09:43,679 --> 00:09:48,200 can actually catch some atmospheric drag and lose a small amount of velocity before getting 123 00:09:48,200 --> 00:09:52,320 flung back out to our apogee, where if we've done this properly, the 124 00:09:52,360 --> 00:09:56,399 gravity of Mars will pull us back in to repeat the process over again. 125 00:09:58,120 --> 00:10:01,960 Every time that we dip into the app hemisphere, we gain a little more 126 00:10:01,039 --> 00:10:05,679 of that precious delta V, bringing us closer to the velocity we need for 127 00:10:05,799 --> 00:10:11,080 a soft touchdown on the planet's surface. But we can't keep this maneuver up 128 00:10:11,159 --> 00:10:16,399 indefinitely. Eventually we need to transition from a shallow dip to a full on 129 00:10:16,679 --> 00:10:22,159 dive through the Martian atmosphere. It's actually pretty difficult to achieve a landing trajectory 130 00:10:22,240 --> 00:10:26,759 from Mars because the planet is only around half the size of the Earth. 131 00:10:26,080 --> 00:10:31,399 That means the angle of attack necessary to get down below the sky is pretty 132 00:10:31,440 --> 00:10:35,840 steep. This means you need a lot of energy pushing the vehicle down in 133 00:10:35,960 --> 00:10:41,159 order to prevent it from skipping off and shooting back up into space again. 134 00:10:41,360 --> 00:10:46,399 We want to save our engines until the last possible moment, so that forced 135 00:10:46,440 --> 00:10:50,039 to push the ship down deeper into the atmosphere needs to come from somewhere else. 136 00:10:50,720 --> 00:10:56,759 This is why the original SpaceX, designed for an interplanetary transport system in 137 00:10:56,840 --> 00:11:01,679 twenty sixteen, had an aerodynamic lifting body in the upper stage. Starship is 138 00:11:01,840 --> 00:11:07,039 much smaller than its so it doesn't need as much aerodynamic force, but the 139 00:11:07,080 --> 00:11:13,559 methodology is still pretty much the same. On its final approach, starship is 140 00:11:13,639 --> 00:11:18,039 actually going to flip over and come into the atmosphere upside down, so that's 141 00:11:18,080 --> 00:11:22,320 what the belly and tail pointed up and the nose pointed down. This way, 142 00:11:22,360 --> 00:11:26,399 the lift generated by the body is going to push the vehicle towards the 143 00:11:26,480 --> 00:11:31,320 surface on a steeper angle to achieve entry. We're also going to start losing 144 00:11:31,360 --> 00:11:37,559 a lot of velocity thanks to aerodynamic drag. Once the angle of attack is 145 00:11:37,639 --> 00:11:41,080 set, the starship is going to flip around into the more traditional belly flop 146 00:11:41,120 --> 00:11:48,120 maneuver that we've seen on Earth. This is all about creating the maximum amount 147 00:11:48,159 --> 00:11:52,559 of drag that is physically possible and getting the velocity down. But this force 148 00:11:52,799 --> 00:11:58,960 can only accomplish so much. The maximum speed of a free fall is something 149 00:11:58,960 --> 00:12:03,840 that we call terminal velocity. Imagine you jump into a bottomless hole. Your 150 00:12:03,840 --> 00:12:07,360 body will accelerate as you fall up until a certain point when the drag and 151 00:12:07,399 --> 00:12:13,720 bullyancy of your body equalizes with the force of gravity and your speed becomes constant. 152 00:12:13,279 --> 00:12:18,440 One way that we cheat terminal velocity is by using a parachute. This 153 00:12:18,519 --> 00:12:24,399 greatly increases drag and slows down our terminal velocity. Starship isn't going to use 154 00:12:24,480 --> 00:12:28,320 parachutes, so there's going to come a point where the aerodynamic drag of the 155 00:12:28,399 --> 00:12:33,279 vehicle has done all that it's going to do, and we reach terminal velocity. 156 00:12:33,759 --> 00:12:37,159 Due to the thinner atmosphere, terminal velocity on Mars is around five times 157 00:12:37,279 --> 00:12:41,879 faster than on Earth. In other words, that means you only get one 158 00:12:43,080 --> 00:12:48,320 fifth the delta v accomplished by belly flopping through the air on Mars compared to 159 00:12:48,360 --> 00:12:52,399 what we've already seen Starship do on Earth, which means that it's going to 160 00:12:52,480 --> 00:12:56,360 require more engine power to land on Mars than it does on Earth. This 161 00:12:56,600 --> 00:13:03,000 is why fuel is such a made your concern here. Assuming that everything up 162 00:13:03,039 --> 00:13:07,679 until this point has gone correctly, the Starship's engines will fire up one last 163 00:13:07,720 --> 00:13:11,440 time and flip the tail towards the surface at which point the fuel in the 164 00:13:11,519 --> 00:13:18,200 rocket's header tanks will provide just enough delta V to bring our ship perfectly in 165 00:13:18,360 --> 00:13:24,639 sync with the surface of Mars and we touch down softly. Now that's a 166 00:13:24,679 --> 00:13:28,399 lot of stuff that has to go right, and there is zero margin for 167 00:13:28,600 --> 00:13:31,759 error. You either score one hundred percent on the exam or you die. 168 00:13:33,039 --> 00:13:37,000 So by knowing all of that, we can appreciate that landing on Mars is 169 00:13:37,039 --> 00:13:41,759 going to be incredibly difficult in a massive vehicle like the Starship. It's much 170 00:13:41,799 --> 00:13:46,919 easier for NASA to land smaller and lighter vehicles on Mars because the potential delta 171 00:13:46,960 --> 00:13:50,679 V of your fuel is determined by the mass of the vehicle and the efficiency 172 00:13:50,759 --> 00:13:56,360 of the engine. So one pound of fuel accomplishes more change in velocity for 173 00:13:56,480 --> 00:14:00,360 a lighter ship than it does for a heavier ship, and there is a 174 00:14:00,399 --> 00:14:03,240 limit on the amount of fuel that we can bring to Mars. Starship would 175 00:14:03,279 --> 00:14:07,480 be much easier to land on Mars if it were lighter, but SpaceX needs 176 00:14:07,480 --> 00:14:11,879 it to be so gigantic to accomplish the goal that Elon Musk has set out, 177 00:14:11,120 --> 00:14:16,039 which is building a self sustaining city of one million people on Mars. 178 00:14:16,679 --> 00:14:22,480 SpaceX is working hard on increasing the delta V of the starship. They want 179 00:14:22,519 --> 00:14:26,440 to make starship be too longer with bigger fuel tanks, while also making it 180 00:14:26,519 --> 00:14:31,559 lighter at the same time and adding three more Raptor vacuum engines. The third 181 00:14:31,639 --> 00:14:35,799 version of the Raptor is currently in design and will probably offer higher efficiency and 182 00:14:35,879 --> 00:14:41,519 therefore more delta V potential. Now there are other more long term solutions as 183 00:14:41,559 --> 00:14:46,799 well. Remember Mars's outer moon Demos. The delta VI required to move from 184 00:14:46,879 --> 00:14:50,360 low Earth orbit to the orbit of Demos is only around five point three kilometers 185 00:14:50,399 --> 00:14:54,519 per second. That's a lot more manageable. And imagine if you could build 186 00:14:54,559 --> 00:15:00,720 an outpost or a Mars gateway at the orbit of Damos. Now we have 187 00:15:00,799 --> 00:15:03,519 the potential to refuel the ships so that it can make the hardest part of 188 00:15:03,559 --> 00:15:07,600 the journey with more than enough delta vie to spare. This buys you a 189 00:15:07,639 --> 00:15:13,360 margin of error that would increase the safety of a Mars landing by orders of 190 00:15:13,480 --> 00:15:18,200 magnitude. So yes, landing a fully loaded starship on Mars is going to 191 00:15:18,240 --> 00:15:22,480 be logistically insane. This is one of those situations where SpaceX won't know anything 192 00:15:22,519 --> 00:15:28,039 for certain until they try. We've seen this twice now with just launching the 193 00:15:28,080 --> 00:15:31,879 starship, and both times it exploded in mid air. Learning to land on 194 00:15:31,960 --> 00:15:37,440 Mars is more than likely going to be a similar affair. They are much 195 00:15:37,480 --> 00:15:41,120 more likely to fail before they succeed. They could fail multiple times. It's 196 00:15:41,240 --> 00:15:46,960 going to require a spectacular amount of willpower to make this work, to not 197 00:15:46,080 --> 00:15:50,279 give up, and probably more than a lot of people are genuinely prepared for. 198 00:15:50,679 --> 00:15:56,240 And then eventually we try to do this with people on board, and 199 00:15:56,559 --> 00:16:03,360 calling this ambitious seems like an incredible understatement, But over the history of humanity, 200 00:16:03,480 --> 00:16:07,960 we've accomplished the impossible many times over, So what's one more