1 00:00:00,934 --> 00:00:03,269 - NASA's Jet Propulsion Laboratory presents 2 00:00:03,302 --> 00:00:04,837 the von Kármán Lecture, 3 00:00:04,870 --> 00:00:07,273 a series of talks by scientists and engineers 4 00:00:07,306 --> 00:00:09,575 who are exploring our planet, 5 00:00:26,492 --> 00:00:19,652 our solar system, and all that lies beyond. 6 00:00:26,525 --> 00:00:28,027 - Good evening, ladies and gentlemen. 7 00:00:28,060 --> 00:00:29,128 How's everyone tonight? 8 00:00:29,161 --> 00:00:30,563 - Good. - Excellent. 9 00:00:30,596 --> 00:00:31,798 [applause] 10 00:00:31,831 --> 00:00:34,200 Really want to thank you guys for coming out tonight, 11 00:00:34,233 --> 00:00:35,735 especially in that weather. 12 00:00:35,768 --> 00:00:37,036 We didn't expect a house anywhere near this full 13 00:00:37,069 --> 00:00:39,806 so thank you very, very much. 14 00:00:39,839 --> 00:00:41,207 So, shall we? 15 00:00:41,240 --> 00:00:44,677 Mission planning is a core strength of JPL engineering, 16 00:00:44,710 --> 00:00:45,845 along with deep space communications, 17 00:00:45,878 --> 00:00:47,980 and navigation. 18 00:00:48,013 --> 00:00:49,449 Tonight, we're going to take a look back 19 00:00:49,482 --> 00:00:52,552 at the various scenarios and contingency plans 20 00:00:52,585 --> 00:00:55,188 that the Cassini team made as they steered the spacecraft 21 00:00:55,221 --> 00:00:59,459 into unexplored space during its 2017 grand finale. 22 00:00:59,492 --> 00:01:02,595 Our guest will discuss how the possible scenarios, 23 00:01:02,628 --> 00:01:04,764 some of which could've been mission ending, 24 00:01:04,797 --> 00:01:07,533 compared to the mission as it was actually flown, 25 00:01:07,566 --> 00:01:09,402 along with sharing some science highlights 26 00:01:09,435 --> 00:01:10,937 from the finale. 27 00:01:10,970 --> 00:01:14,107 Tonight's guest was the mission planning lead 28 00:01:14,140 --> 00:01:15,308 for the Cassini mission. 29 00:01:15,341 --> 00:01:17,176 Prior to joining Cassini, he served 30 00:01:17,209 --> 00:01:19,879 as a mission engineer and mission architect 31 00:01:19,912 --> 00:01:21,747 for the Mars Advanced Formulation Office 32 00:01:21,780 --> 00:01:25,318 and for other various planetary mission concepts. 33 00:01:25,351 --> 00:01:27,019 He joined JPL in 2005, 34 00:01:27,052 --> 00:01:30,189 fresh out of Cal Poly, San Luis Obispo, 35 00:01:30,222 --> 00:01:32,325 where he received his B.S. in Aerospace Engineering, 36 00:01:32,358 --> 00:01:33,759 a B.A. in Physics, 37 00:01:33,792 --> 00:01:36,562 and a Masters degree in Aerospace Engineering. 38 00:01:36,595 --> 00:01:37,997 Ladies and gentlemen, please help me welcome 39 00:01:38,030 --> 00:01:40,333 tonight's guest, Mr. Erick Sturm. 40 00:01:40,366 --> 00:01:47,707 [applause] 41 00:01:47,740 --> 00:01:50,176 - HI. 42 00:01:50,209 --> 00:01:52,245 Thank you very much and let me second the thanks 43 00:01:52,278 --> 00:01:53,980 for coming out in the rain. 44 00:01:54,013 --> 00:01:55,348 That's very impressive. 45 00:01:55,381 --> 00:01:57,049 Thanks to the smarter ones who are online, 46 00:01:57,082 --> 00:02:01,120 who are watching from a nice warm, dry area. 47 00:02:01,153 --> 00:02:03,923 Okay, so yeah, as was said, I'm Erick Sturm 48 00:02:03,956 --> 00:02:06,392 and I am Cassini's Lead Mission Planner. 49 00:02:06,425 --> 00:02:08,794 And I say am, not was, because while the Cassini mission 50 00:02:08,827 --> 00:02:11,631 ended six months ago the project is still going. 51 00:02:11,664 --> 00:02:13,199 We're still archiving, we're still closing out, 52 00:02:13,232 --> 00:02:14,534 we're still writing reports. 53 00:02:14,567 --> 00:02:18,871 It's not as fun as it was, but it's not past tense yet. 54 00:02:18,904 --> 00:02:22,041 So, I have the honor of speaking to you guys tonight 55 00:02:22,074 --> 00:02:25,278 as Cassini's last Mission Planner but I'm certainly not 56 00:02:25,311 --> 00:02:28,214 Cassini's only Lead Mission Planner. 57 00:02:28,247 --> 00:02:31,517 In fact, I share that title with five other people, 58 00:02:31,550 --> 00:02:33,786 and you can see them all here. 59 00:02:33,819 --> 00:02:36,189 And so, without the hard work of these people 60 00:02:36,222 --> 00:02:37,590 Cassini wouldn't have gotten off the ground, 61 00:02:37,623 --> 00:02:39,125 it wouldn't have gotten into space, 62 00:02:39,158 --> 00:02:40,693 wouldn't have made it out to Saturn, 63 00:02:40,726 --> 00:02:43,262 and it certainly wouldn't have made it through its tour 64 00:02:43,295 --> 00:02:45,097 and let me be here tonight to talk to you 65 00:02:45,130 --> 00:02:48,334 about the end of that tour, Cassini's grand finale. 66 00:02:48,367 --> 00:02:51,771 And as you can see, Cassini's been around a long time. 67 00:02:51,804 --> 00:02:55,808 It first got a Lead Mission Planner back in 1991, 68 00:02:55,841 --> 00:02:58,711 but the beginnings of Cassini actually go back 69 00:02:58,744 --> 00:03:01,781 even before that, back to 1982. 70 00:03:01,814 --> 00:03:04,116 That's when Cassini was born. 71 00:03:04,149 --> 00:03:07,620 And at that time a working group was formed between 72 00:03:07,653 --> 00:03:09,322 the European Science Foundation 73 00:03:09,355 --> 00:03:11,257 and the National Academy of Sciences 74 00:03:11,290 --> 00:03:13,125 and they were supposed to come up 75 00:03:13,158 --> 00:03:17,330 with a joint concept for exploring the planets. 76 00:03:17,363 --> 00:03:20,199 And eventually what came out of that was a concept 77 00:03:20,232 --> 00:03:23,202 that involved a U.S. Saturn orbiter 78 00:03:23,235 --> 00:03:24,971 and a European probe that later 79 00:03:25,004 --> 00:03:27,006 became Cassini and Huygens. 80 00:03:27,039 --> 00:03:29,308 And you can actually Cassini and Huygens over there. 81 00:03:29,341 --> 00:03:32,144 That's our half scale model. 82 00:03:32,177 --> 00:03:34,146 And just to give you more of an appreciation 83 00:03:34,179 --> 00:03:38,484 of just how long ago 1982 was... 84 00:03:38,517 --> 00:03:40,453 that's me back in 1982. 85 00:03:40,486 --> 00:03:42,455 [laughter] 86 00:03:42,488 --> 00:03:46,726 So, Cassini and I were born in the same year. 87 00:03:46,759 --> 00:03:51,897 So yeah, it was a long time ago. 88 00:03:51,930 --> 00:03:56,202 Okay, so jumping ahead a few years, Cassini launched in 1997 89 00:03:56,235 --> 00:03:58,271 and it followed this nice loopty-loop green path 90 00:03:58,304 --> 00:03:59,672 out to Saturn. 91 00:03:59,705 --> 00:04:02,408 That's actually two and a half revolutions around the Sun. 92 00:04:02,441 --> 00:04:04,644 It flew by Venus twice, 93 00:04:04,677 --> 00:04:07,246 Earth and Jupiter all on its way out there, 94 00:04:07,279 --> 00:04:10,149 and seven years later it arrived at Saturn 95 00:04:10,182 --> 00:04:12,251 in July of 2004. 96 00:04:12,284 --> 00:04:13,653 And at that time, it began its prime mission, 97 00:04:13,686 --> 00:04:15,354 which was a four year mission to tour Saturn 98 00:04:15,387 --> 00:04:18,758 and explore it and its moons and the rings. 99 00:04:18,791 --> 00:04:21,494 It got a mission extension in 2008 100 00:04:21,527 --> 00:04:23,663 to go an additional two years out to 2010, 101 00:04:23,696 --> 00:04:25,498 that was the Cassini Equinox mission. 102 00:04:25,531 --> 00:04:27,233 And then, it did such a good job there 103 00:04:27,266 --> 00:04:28,968 it got a seven year mission extension, 104 00:04:29,001 --> 00:04:31,504 the Cassini Solstice mission, which was so named 105 00:04:31,537 --> 00:04:33,072 because it extended the mission all the way out 106 00:04:33,105 --> 00:04:35,474 to the northern summer solstice, 107 00:04:35,507 --> 00:04:40,746 and that ended six months ago. 108 00:04:40,779 --> 00:04:44,116 So here you can see the entire Solstice mission trajectory. 109 00:04:44,149 --> 00:04:46,919 This is from when it started in October of 2010 110 00:04:46,952 --> 00:04:50,623 up until the end of November of 2016. 111 00:04:50,656 --> 00:04:53,993 And at that time, Cassini began it's penultimate phase, 112 00:04:54,026 --> 00:04:55,461 which were the ring-grazing orbits. 113 00:04:55,494 --> 00:04:58,664 These lighter gray orbits that you see here. 114 00:04:58,697 --> 00:05:01,033 And so, this was a series of 20 orbits. 115 00:05:01,066 --> 00:05:04,603 The farthest they get from Saturn is out near Titan's orbit 116 00:05:04,636 --> 00:05:07,640 and the closest they get is just outside the ring system, 117 00:05:07,673 --> 00:05:11,243 Saturn's F Ring, thus their name the ring-grazing orbits. 118 00:05:11,276 --> 00:05:15,614 So these 20 orbits took a little over a week to complete. 119 00:05:15,647 --> 00:05:17,917 They started at the beginning of December of 2016 120 00:05:17,950 --> 00:05:22,822 all the way through the middle of April, 2017. 121 00:05:22,855 --> 00:05:26,359 And here is the last of those ring-grazing orbits. 122 00:05:26,392 --> 00:05:28,928 So, it's the last time that it's going to pass outside 123 00:05:28,961 --> 00:05:30,463 Saturn's ring system. 124 00:05:30,496 --> 00:05:32,665 And this time, as it comes back out towards Titan's orbit, 125 00:05:32,698 --> 00:05:34,667 Titan's actually going to be there 126 00:05:34,700 --> 00:05:36,469 and what we're going to do is we're going to form 127 00:05:36,502 --> 00:05:40,005 our last targeted Titan flyby. 128 00:05:40,038 --> 00:05:42,908 This is 127th close flyby of Titan. 129 00:05:42,941 --> 00:05:45,177 We came within 600 miles of the moon 130 00:05:45,210 --> 00:05:47,913 and that changed our orbit just enough 131 00:05:47,946 --> 00:05:50,182 that now as it comes back through towards Saturn, 132 00:05:50,215 --> 00:05:52,718 instead of being outside the ring system, it's inside, 133 00:05:52,751 --> 00:05:58,124 and it'll be between the planet and the rings. 134 00:05:58,157 --> 00:06:01,660 And so, that dive happened on April 26th, 2017, 135 00:06:01,693 --> 00:06:08,300 so just about a year ago now. 136 00:06:08,333 --> 00:06:10,870 Okay, so that's what started Cassini's grand finale. 137 00:06:10,903 --> 00:06:13,038 It's a series of 22 and a half orbits 138 00:06:13,071 --> 00:06:14,840 that dove between Saturn and the rings 139 00:06:14,873 --> 00:06:16,942 in a gap of about 1,200 miles wide, 140 00:06:16,975 --> 00:06:19,211 and it did it at 76,000 miles per hour, 141 00:06:19,244 --> 00:06:22,815 which would get you to D.C. in about three minutes, 142 00:06:22,848 --> 00:06:24,116 or to the moon in a couple days. 143 00:06:24,149 --> 00:06:25,985 So, it was going pretty fast. 144 00:06:26,018 --> 00:06:29,422 Also, periodically, as it came back out to Titan's orbit, 145 00:06:29,455 --> 00:06:32,124 Titan would be there far away, not as close at the 600 miles 146 00:06:32,157 --> 00:06:33,526 but it would give it a little tug 147 00:06:33,559 --> 00:06:36,429 and change exactly where we flew through the gap. 148 00:06:36,462 --> 00:06:37,963 The last of those distant flybys, 149 00:06:37,996 --> 00:06:40,733 which is happening right there, was on September 11th, 150 00:06:40,766 --> 00:06:43,068 and that's where Titan gave us a goodbye kiss, 151 00:06:43,101 --> 00:06:45,604 some may call it a shove, and it actually made it, 152 00:06:45,637 --> 00:06:48,674 so instead of passing safely through the gap four days later, 153 00:06:48,707 --> 00:06:50,976 on September 15th, 2017, 154 00:06:51,009 --> 00:06:54,747 we are permanently captured by Saturn. 155 00:06:54,780 --> 00:06:57,183 Okay, so one of the first questions I get 156 00:06:57,216 --> 00:06:58,918 when I tell people that we did this, 157 00:06:58,951 --> 00:07:01,086 they're like, "Well, why did you do that? 158 00:07:01,119 --> 00:07:03,522 "Cassini was a cool spacecraft." 159 00:07:03,555 --> 00:07:05,291 So, first, why we had to do it at all 160 00:07:05,324 --> 00:07:07,293 was for planetary protection. 161 00:07:07,326 --> 00:07:09,895 The Saturn system has two protected moons 162 00:07:09,928 --> 00:07:12,665 and protected just means that they have environments 163 00:07:12,698 --> 00:07:15,668 that could possibly be habitable for life. 164 00:07:15,701 --> 00:07:18,003 So, one of those is Enceladus. 165 00:07:18,036 --> 00:07:19,271 Enceladus is pretty cool. 166 00:07:19,304 --> 00:07:22,341 It has a global subsurface ocean under a thick ice shell 167 00:07:22,374 --> 00:07:25,077 and it's in direct contact with an active rocky core, 168 00:07:25,110 --> 00:07:27,713 very much like environments found in our-- 169 00:07:27,746 --> 00:07:30,783 near our deep ocean events. 170 00:07:30,816 --> 00:07:33,419 And then, there's Titan with its thick atmosphere. 171 00:07:33,452 --> 00:07:36,055 It has rivers and lakes of liquid methane and ethane. 172 00:07:36,088 --> 00:07:38,624 And both of these are thought to be environments 173 00:07:38,657 --> 00:07:40,426 where we could find life, and because of that 174 00:07:40,459 --> 00:07:42,194 it means we have to absolutely ensure 175 00:07:42,227 --> 00:07:44,196 that Cassini would never impact these 176 00:07:44,229 --> 00:07:46,699 and possibly contaminate those environments 177 00:07:46,732 --> 00:07:47,733 with our own life. 178 00:07:47,766 --> 00:07:48,801 Because the last thing we'd want to do 179 00:07:48,834 --> 00:07:51,003 is send a future mission there and discover life, 180 00:07:51,036 --> 00:07:53,305 only to find out, no, that's life that we just 181 00:07:53,338 --> 00:07:55,441 brought when we crashed Cassini into one of them. 182 00:07:55,474 --> 00:07:57,943 So, that meant Cassini needed to be removed 183 00:07:57,976 --> 00:08:01,080 from the Saturn system one way or the other, 184 00:08:01,113 --> 00:08:05,417 either through leaving it or through crashing into Saturn. 185 00:08:05,450 --> 00:08:07,720 The reason it needed to happen now 186 00:08:07,753 --> 00:08:11,891 is actually because of Cassini's gas tank. 187 00:08:11,924 --> 00:08:13,526 We were running low on fuel. 188 00:08:13,559 --> 00:08:15,995 So, here's our spacecraft 189 00:08:16,028 --> 00:08:18,030 and this is not an engineering representation, 190 00:08:18,063 --> 00:08:20,266 but a good representation of our gas tank 191 00:08:20,299 --> 00:08:23,269 and we're going to fill this up with gas right now. 192 00:08:23,302 --> 00:08:25,170 I should say, when I asked my wife what color 193 00:08:25,203 --> 00:08:27,339 is Cassini's gas she said, 194 00:08:27,372 --> 00:08:29,408 "It's orange. It's definitely orange." 195 00:08:29,441 --> 00:08:32,678 So, we're going to fill it up now with definitely orange. 196 00:08:32,711 --> 00:08:35,681 It's a little like cerulean blue, but definitely orange. 197 00:08:35,714 --> 00:08:36,949 So there it is. 198 00:08:36,982 --> 00:08:39,051 And another nice thing about it actually being orange, 199 00:08:39,084 --> 00:08:42,354 well, think of this as 100 oranges, okay? 200 00:08:42,387 --> 00:08:45,758 So, this is 100 oranges worth of fuel, okay, at launch. 201 00:08:45,791 --> 00:08:49,295 Okay, now, just getting out to Saturn 202 00:08:49,328 --> 00:08:53,732 we used 24 oranges, so we're down to 76. 203 00:08:53,765 --> 00:08:55,668 Okay, now we want to go into orbit around Saturn, 204 00:08:55,701 --> 00:08:58,704 all right, well that's another 45 oranges. 205 00:08:58,737 --> 00:09:00,506 Now, we're down to 31. 206 00:09:00,539 --> 00:09:03,442 Four years after the start of our prime mission, 207 00:09:03,475 --> 00:09:06,211 used another 17, only 14 left. 208 00:09:06,244 --> 00:09:07,279 Okay, two year mission extension, 209 00:09:07,312 --> 00:09:10,583 we can do this, 8.5 oranges. 210 00:09:10,616 --> 00:09:12,818 Okay, seven year mission extension, 211 00:09:12,851 --> 00:09:15,321 we've got 5.5 oranges left. 212 00:09:15,354 --> 00:09:18,057 All right, well, we can use them all, and okay, 213 00:09:18,090 --> 00:09:19,658 now we have the ring-grazing orbits and the grand finale 214 00:09:19,691 --> 00:09:22,628 for the last year and I think you can see 215 00:09:22,661 --> 00:09:24,129 some propellant still in there. 216 00:09:24,162 --> 00:09:27,399 That's-- Oranges have about 10 to 11 wedges, 217 00:09:27,432 --> 00:09:29,535 that's a common knowledge, right? 218 00:09:29,568 --> 00:09:33,906 Okay, that's one orange worth of fuel-- 219 00:09:33,939 --> 00:09:36,008 Or, one orange wedge worth of fuel, 220 00:09:36,041 --> 00:09:37,109 that's how much we had left. 221 00:09:37,142 --> 00:09:41,413 We started with 100 oranges, we ate 99, 222 00:09:41,446 --> 00:09:43,682 opened that 100th and ate 10 of the 11 wedges. 223 00:09:43,715 --> 00:09:45,751 That's what we were left with. 224 00:09:45,784 --> 00:09:51,824 Okay, so that's what we flew the last year of the mission on. 225 00:09:51,857 --> 00:09:54,026 Okay, and so why did we do it by going in to Saturn? 226 00:09:54,059 --> 00:09:55,527 Like I said, we could've tried to 227 00:09:55,560 --> 00:09:57,496 get out of the Saturn system, 228 00:09:57,529 --> 00:10:00,766 but by going into Saturn it gave us the opportunity 229 00:10:00,799 --> 00:10:02,901 to collect a bunch of unique science. 230 00:10:02,934 --> 00:10:04,536 So, we were going closer to Saturn than ever before 231 00:10:04,569 --> 00:10:07,339 so we could get lots of information 232 00:10:07,372 --> 00:10:09,041 about Saturn's internal structure, 233 00:10:09,074 --> 00:10:11,343 like gravity, magnetic field. 234 00:10:11,376 --> 00:10:13,178 We were also going inside the rings for the first time, 235 00:10:13,211 --> 00:10:14,913 which would let us see their structure 236 00:10:14,946 --> 00:10:15,814 and possibly estimate their mass 237 00:10:15,847 --> 00:10:18,884 and get an idea of how old they are. 238 00:10:18,917 --> 00:10:20,152 Also, because of how close we were, 239 00:10:20,185 --> 00:10:22,087 we were flying through the auroras, 240 00:10:22,120 --> 00:10:24,556 through radiation belts, through ring dust, 241 00:10:24,589 --> 00:10:26,592 so we were going to get direct measurements 242 00:10:26,625 --> 00:10:28,627 of all of those things. 243 00:10:28,660 --> 00:10:30,596 And then, simply because we were so close, 244 00:10:30,629 --> 00:10:32,231 we'd get really high resolution images, 245 00:10:32,264 --> 00:10:33,966 and these images are amazing 246 00:10:33,999 --> 00:10:36,268 and these aren't even the ones from the grand finale. 247 00:10:36,301 --> 00:10:42,474 We got better, higher resolution images than these. 248 00:10:42,507 --> 00:10:45,444 Okay, so that's a long windup of the grand finale 249 00:10:45,477 --> 00:10:46,779 and why we did it. 250 00:10:46,812 --> 00:10:49,815 As Cassini's Mission Planner for the four years 251 00:10:49,848 --> 00:10:51,550 before the end of mission 252 00:10:51,583 --> 00:10:54,720 I spent all my time worrying about this gap. 253 00:10:54,753 --> 00:10:58,257 Minding the gap-- So the region between the rings 254 00:10:58,290 --> 00:11:01,527 and the planet, and here you can see where the 22 orbits passed 255 00:11:01,560 --> 00:11:03,062 and you can see the final orbit in orange 256 00:11:03,095 --> 00:11:06,065 that actually impacts Saturn. 257 00:11:06,098 --> 00:11:08,867 And you can compare that to an actual image 258 00:11:08,900 --> 00:11:15,407 that was taken by Cassini. 259 00:11:15,440 --> 00:11:17,676 And so, you can see we're flying 260 00:11:17,709 --> 00:11:20,879 right where that D Ring dust 261 00:11:20,912 --> 00:11:23,115 and the atmospheric haze just sort of fade into 262 00:11:23,148 --> 00:11:24,650 the background of the image. 263 00:11:24,683 --> 00:11:30,155 So, like really going right where we think it's safest. 264 00:11:30,188 --> 00:11:31,423 And so, those really were our two concerns 265 00:11:31,456 --> 00:11:32,991 for these orbits-- 266 00:11:33,024 --> 00:11:35,794 how much dust was the spacecraft going to encounter 267 00:11:35,827 --> 00:11:37,763 and how thick of an atmosphere was it going to fly through. 268 00:11:37,796 --> 00:11:39,398 And that meant that each of the 22 orbits 269 00:11:39,431 --> 00:11:41,600 could be characterized by two points. 270 00:11:41,633 --> 00:11:43,902 The first was the ring-plane crossings, 271 00:11:43,935 --> 00:11:45,337 so this is how high into the ring-plane 272 00:11:45,370 --> 00:11:48,140 did they go and how much dust was potentially 273 00:11:48,173 --> 00:11:50,976 going to impact the spacecraft. 274 00:11:51,009 --> 00:11:54,313 Now, the second point was how close did they get to Saturn. 275 00:11:54,346 --> 00:11:56,215 They're at minimum altitude, how much atmosphere 276 00:11:56,248 --> 00:11:59,184 were they going to fly through and how much drag and torque 277 00:11:59,217 --> 00:12:04,089 was going to be imparted on the spacecraft. 278 00:12:04,122 --> 00:12:05,290 And you can get a little better idea 279 00:12:05,323 --> 00:12:08,360 of how these are distributed through the gap 280 00:12:08,393 --> 00:12:10,295 by looking at them down from above. 281 00:12:10,328 --> 00:12:12,564 So now you can see Saturn down below, 282 00:12:12,597 --> 00:12:13,866 we got the rings up above, 283 00:12:13,899 --> 00:12:16,368 and you can see the orbits going through. 284 00:12:16,401 --> 00:12:18,237 And what's neat about looking at it in this-- 285 00:12:18,270 --> 00:12:19,705 from this perspective, 286 00:12:19,738 --> 00:12:21,640 these are actually in chronological order, 287 00:12:21,673 --> 00:12:24,676 so the first one's on the left and the last one's on the right. 288 00:12:24,709 --> 00:12:27,179 And so, you can see each of the ring-plane crossings 289 00:12:27,212 --> 00:12:29,414 and the minimum altitude points. 290 00:12:29,447 --> 00:12:31,450 You can also see how there's the variations 291 00:12:31,483 --> 00:12:32,885 and those are caused, like I said, 292 00:12:32,918 --> 00:12:36,288 by the distant Titan flybys that we're having periodically 293 00:12:36,321 --> 00:12:37,923 as we flew the grand finale. 294 00:12:37,956 --> 00:12:40,526 And to get a better idea of those variations, 295 00:12:40,559 --> 00:12:42,795 we can take all those points and plot them up. 296 00:12:42,828 --> 00:12:44,797 I'm an engineer, I've got to put things into Excel, 297 00:12:44,830 --> 00:12:47,399 I can't just look at pictures. 298 00:12:47,432 --> 00:12:49,802 And so, now we have time on the horizontal axis, 299 00:12:49,835 --> 00:12:51,036 starting at the end of April 300 00:12:51,069 --> 00:12:52,938 going to the middle of September. 301 00:12:52,971 --> 00:12:56,074 Again, D Ring dust up above, atmosphere down below, 302 00:12:56,107 --> 00:12:58,644 and we have distance from the center of Saturn 303 00:12:58,677 --> 00:13:00,779 and kilometers on the horizontal axis. 304 00:13:00,812 --> 00:13:02,447 And I know everybody is familiar with kilometers 305 00:13:02,480 --> 00:13:05,417 and 63,000 kilometers makes perfect sense 306 00:13:05,450 --> 00:13:06,552 to everybody in the room. 307 00:13:06,585 --> 00:13:08,620 But just in case is doesn't, we're also familiar 308 00:13:08,653 --> 00:13:10,355 with how wide the Earth is, right? 309 00:13:10,388 --> 00:13:11,757 So that's about five Earth diameters 310 00:13:11,790 --> 00:13:13,458 from the center of Saturn. 311 00:13:13,491 --> 00:13:15,294 Another very common measurement. 312 00:13:15,327 --> 00:13:17,963 Okay, so these are our ring-plane crossings 313 00:13:17,996 --> 00:13:19,798 at minimum altitudes. 314 00:13:19,831 --> 00:13:21,900 You can see at the end we get low in the atmosphere, 315 00:13:21,933 --> 00:13:23,635 but for the 17 orbits before that 316 00:13:23,668 --> 00:13:25,737 we're actually much higher up 317 00:13:25,770 --> 00:13:28,574 and we're more concerned about the dust environment 318 00:13:28,607 --> 00:13:29,842 than the atmosphere. 319 00:13:29,875 --> 00:13:32,110 And so, we're going to start by looking at that. 320 00:13:32,143 --> 00:13:33,946 So what do we know about the dust environment? 321 00:13:33,979 --> 00:13:35,647 This is literally everything we knew about 322 00:13:35,680 --> 00:13:36,682 the dust environment. 323 00:13:36,715 --> 00:13:39,785 This is our best picture of the D Ring dust. 324 00:13:39,818 --> 00:13:41,553 And so, what we did is we took this picture 325 00:13:41,586 --> 00:13:44,723 and we overexposed it and you can draw a line and say, 326 00:13:44,756 --> 00:13:47,993 "Hey, outside that line there's dust. 327 00:13:48,026 --> 00:13:50,829 "Inside that line, we're not really sure, 328 00:13:50,862 --> 00:13:52,364 "but we think there's not dust." 329 00:13:52,397 --> 00:13:55,367 And if we go back to-- Oh, and compare that 330 00:13:55,400 --> 00:13:59,071 to the range through which we flew the orbits, 331 00:13:59,104 --> 00:14:00,205 you can see that our highest orbit's 332 00:14:00,238 --> 00:14:01,440 actually one above it. 333 00:14:01,473 --> 00:14:04,309 They went into a region that we knew there'd be dust. 334 00:14:04,342 --> 00:14:08,013 And so, going back to our corridor chart 335 00:14:08,046 --> 00:14:09,948 and adding that line, we can see it was 336 00:14:09,981 --> 00:14:11,316 actually our four highest crossings. 337 00:14:11,349 --> 00:14:13,785 So, those four crossings flew through a region 338 00:14:13,818 --> 00:14:15,721 that we knew there would be dust. 339 00:14:15,754 --> 00:14:16,788 And so, what does that mean? 340 00:14:16,821 --> 00:14:18,290 Well, it doesn't particularly mean a whole lot 341 00:14:18,323 --> 00:14:20,993 because Saturn is a dusty place. 342 00:14:21,026 --> 00:14:24,663 We've flown through dust a lot before, and so whenever the dust 343 00:14:24,696 --> 00:14:27,165 was such that it could've posed a risk to the spacecraft 344 00:14:27,198 --> 00:14:29,067 what we would do is we'd take the entire thing-- 345 00:14:29,100 --> 00:14:30,435 again, you can look at it over there. 346 00:14:30,468 --> 00:14:32,638 We'd take that huge antenna and we'd turn it into 347 00:14:32,671 --> 00:14:35,207 the direction that the dust was coming from and you can see 348 00:14:35,240 --> 00:14:38,677 that that shields all of the spacecraft behind it 349 00:14:38,710 --> 00:14:40,545 so all of our sensitive electronics and instruments 350 00:14:40,578 --> 00:14:45,083 were protected behind the high gain antenna. 351 00:14:45,116 --> 00:14:49,521 So, good, we have a shield, we will use it. 352 00:14:49,554 --> 00:14:51,423 So, there we go. 353 00:14:51,456 --> 00:14:55,227 Our four highest crossings were shielded. 354 00:14:55,260 --> 00:14:58,030 But then the question is, well, what about 355 00:14:58,063 --> 00:15:00,565 those other 13 crossings? 356 00:15:00,598 --> 00:15:03,402 Like I said, if we go back to this picture, 357 00:15:03,435 --> 00:15:04,603 we don't necessarily know what's happening 358 00:15:04,636 --> 00:15:07,506 inside that purple line. 359 00:15:07,539 --> 00:15:09,207 It could be that there's no dust there, 360 00:15:09,240 --> 00:15:11,376 but it could be the nature of the dust is changing 361 00:15:11,409 --> 00:15:12,611 and reflecting less light. 362 00:15:12,644 --> 00:15:15,981 As an example, think about if it's nighttime 363 00:15:16,014 --> 00:15:17,716 and it's foggy and you're driving, 364 00:15:17,749 --> 00:15:19,084 you have your headlights on. 365 00:15:19,117 --> 00:15:21,320 The fog is just reflecting everything back at you, 366 00:15:21,353 --> 00:15:22,454 all you can see is fog. 367 00:15:22,487 --> 00:15:23,956 You can see the fog very easily. 368 00:15:23,989 --> 00:15:26,525 But then, if it's raining instead of foggy, 369 00:15:26,558 --> 00:15:28,794 you have still lots of droplets in the air 370 00:15:28,827 --> 00:15:29,928 but they're much bigger 371 00:15:29,961 --> 00:15:31,697 and they don't reflect as much light back to you. 372 00:15:31,730 --> 00:15:35,734 So, we couldn't know for sure if it was foggy outside 373 00:15:35,767 --> 00:15:38,203 and not foggy inside, or if instead of foggy 374 00:15:38,236 --> 00:15:40,639 it just started raining and if it just started raining 375 00:15:40,672 --> 00:15:43,108 that meant there were large dust particles there 376 00:15:43,141 --> 00:15:46,645 that could pose a risk to the spacecraft. 377 00:15:46,678 --> 00:15:50,449 So given that information, I know what you're all thinking. 378 00:15:50,482 --> 00:15:53,385 Okay, well, we have a shield, let's just use this. 379 00:15:53,418 --> 00:15:55,387 We're going to Captain America this sucker 380 00:15:55,420 --> 00:15:57,522 and we're good, we're done. 381 00:15:57,555 --> 00:15:59,791 And if you thought that, "Great." 382 00:15:59,824 --> 00:16:01,960 You'd probably make a very good spacecraft engineer, 383 00:16:01,993 --> 00:16:03,962 but you'd probably upset a lot of scientists. 384 00:16:03,995 --> 00:16:07,933 The reason being, everything on Cassini is body fixed, 385 00:16:07,966 --> 00:16:09,901 it can't point in two directions at once. 386 00:16:09,934 --> 00:16:12,037 So, if we're using our antenna as a shield it means 387 00:16:12,070 --> 00:16:13,405 the cameras can't look over here 388 00:16:13,438 --> 00:16:14,840 at this very interesting thing. 389 00:16:14,873 --> 00:16:17,909 And so, while that may not seem like a big problem, 390 00:16:17,942 --> 00:16:20,545 because hey this is only for ring-plane crossing, 391 00:16:20,578 --> 00:16:23,482 that's just this small little piece of the orbit. 392 00:16:23,515 --> 00:16:27,386 Cassini is the size of a school bus and it's not 393 00:16:27,419 --> 00:16:30,655 very nimble and it doesn't have very large thrusters. 394 00:16:30,688 --> 00:16:31,823 And so, what that means is it takes a lot of time 395 00:16:31,856 --> 00:16:33,025 to turn the spacecraft, 396 00:16:33,058 --> 00:16:35,027 and when you factor that in the time to 397 00:16:35,060 --> 00:16:38,296 turn to that shielded direction and then the time 398 00:16:38,329 --> 00:16:40,732 to turn back to our nice science friendly attitude, 399 00:16:40,765 --> 00:16:41,733 suddenly we wipe out 400 00:16:41,766 --> 00:16:44,436 all of our high priority science areas. 401 00:16:44,469 --> 00:16:48,407 So, okay, we know this is a bad idea, 402 00:16:48,440 --> 00:16:50,208 but it's possible this is a bad idea too 403 00:16:50,241 --> 00:16:51,576 because we don't actually know what's there. 404 00:16:51,609 --> 00:16:54,146 So what we did was we came up with a contingency plan 405 00:16:54,179 --> 00:16:56,915 that said, hey, we're going to shield 406 00:16:56,948 --> 00:16:59,017 that very first crossing and when we do that 407 00:16:59,050 --> 00:17:00,018 we're going to use an instrument, 408 00:17:00,051 --> 00:17:01,953 the radio and plasma wave science instrument 409 00:17:01,986 --> 00:17:04,122 to detect the dust particles that are there. 410 00:17:04,155 --> 00:17:05,857 When the dust hits the spacecraft it creates 411 00:17:05,890 --> 00:17:08,026 plasma waves and that instrument can detect those waves 412 00:17:08,059 --> 00:17:13,098 and from that we can see if the environment is safe or not. 413 00:17:13,131 --> 00:17:17,369 But, the catch here is that those-- that first orbit 414 00:17:17,402 --> 00:17:20,906 and that second orbit are only six and a half days apart, 415 00:17:20,939 --> 00:17:22,674 so we had to get the data back, analyze it, and decide 416 00:17:22,707 --> 00:17:24,709 what to do with the spacecraft in six and a half days 417 00:17:24,742 --> 00:17:27,646 if we were going to keep everything else unprotected. 418 00:17:27,679 --> 00:17:28,914 And so, this is what this looked like. 419 00:17:28,947 --> 00:17:31,917 So here we have our first ring-plane crossing in green, 420 00:17:31,950 --> 00:17:34,886 coming around to the second one in red, and then we have 421 00:17:34,919 --> 00:17:37,089 all of our communications passes in blue 422 00:17:37,122 --> 00:17:39,291 out on the far side. 423 00:17:39,324 --> 00:17:42,294 And so, after we came through that first crossing it took 424 00:17:42,327 --> 00:17:44,196 a whole day before we even got to talk to the spacecraft, 425 00:17:44,229 --> 00:17:45,630 so that wiped a day out. 426 00:17:45,663 --> 00:17:46,665 We only have five days left. 427 00:17:46,698 --> 00:17:50,435 The spacecraft gave us back all of the radio 428 00:17:50,468 --> 00:17:53,338 and plasma wave science instrument data. 429 00:17:53,371 --> 00:17:56,641 And then, we wanted two opportunities to tell 430 00:17:56,674 --> 00:18:00,078 the spacecraft if it needed to go to the safe attitude, 431 00:18:00,111 --> 00:18:01,480 and so that's what you see there, 432 00:18:01,513 --> 00:18:03,048 those next two opportunities. 433 00:18:03,081 --> 00:18:06,518 And had it seen hazardous dust, it could've turned 434 00:18:06,551 --> 00:18:11,423 the spacecraft and gone in the next one shielded. 435 00:18:11,456 --> 00:18:12,524 Okay, so that was the plan. 436 00:18:12,557 --> 00:18:13,558 That was our contingency plan. 437 00:18:13,591 --> 00:18:15,193 And what actually happened? 438 00:18:15,226 --> 00:18:17,963 Well, in order to understand what happened 439 00:18:17,996 --> 00:18:20,198 let's take a step back to our ring-grazing orbit. 440 00:18:20,231 --> 00:18:22,801 Okay, these are the 20 orbits before the grand finale. 441 00:18:22,834 --> 00:18:26,071 During the third ring-grazing orbit 442 00:18:26,104 --> 00:18:27,305 the radio and plasma wave science instrument 443 00:18:27,338 --> 00:18:29,674 was on and it took data for us. 444 00:18:29,707 --> 00:18:32,944 And the data it gives us is this and what this is 445 00:18:32,977 --> 00:18:36,248 is time on the horizontal axis, 446 00:18:36,281 --> 00:18:39,351 it is dust particle size on the vertical axis, 447 00:18:39,384 --> 00:18:42,654 and it is the density we see at that time 448 00:18:42,687 --> 00:18:45,457 at that size of that dust particle. 449 00:18:45,490 --> 00:18:48,326 So, this is how thick of a dust cloud do we fly through? 450 00:18:48,359 --> 00:18:50,662 And so, you can see on this third ring-grazing orbit, 451 00:18:50,695 --> 00:18:52,264 the ring crossing should probably 452 00:18:52,297 --> 00:18:53,265 jump right out at it you. 453 00:18:53,298 --> 00:18:55,534 What happened, happened right there. 454 00:18:55,567 --> 00:18:59,237 And on this scale of less dense to more dense, 455 00:18:59,270 --> 00:19:00,939 the red that we're seeing here 456 00:19:00,972 --> 00:19:03,208 actually isn't even dangerous to the spacecraft. 457 00:19:03,241 --> 00:19:06,211 So this is what we saw when we went through the first time. 458 00:19:06,244 --> 00:19:07,379 We wouldn't even have to shield it. 459 00:19:07,412 --> 00:19:09,948 It'd have to go into a nice deep, dark maroon for us 460 00:19:09,981 --> 00:19:11,516 to be worried about it. 461 00:19:11,549 --> 00:19:13,885 So, what did we see? 462 00:19:13,918 --> 00:19:16,454 We saw this. 463 00:19:16,487 --> 00:19:17,956 We almost literally saw nothing. 464 00:19:17,989 --> 00:19:19,691 You can't even tell a ring-plane crossing happened. 465 00:19:19,724 --> 00:19:23,962 It happened there, but there was just no dust. 466 00:19:23,995 --> 00:19:26,631 And so, we didn't have to invoke the contingency. 467 00:19:26,664 --> 00:19:29,401 The scientists-- there was much rejoicing. 468 00:19:29,434 --> 00:19:31,469 And so, this is what it looked like. 469 00:19:31,502 --> 00:19:34,673 And in fact, we didn't see a noticeable amount of dust 470 00:19:34,706 --> 00:19:38,143 until that first orbit above the line, 471 00:19:38,176 --> 00:19:41,479 and there the dust wasn't hazardous. 472 00:19:41,512 --> 00:19:43,682 And so, it turns out we did use our contingency, 473 00:19:43,715 --> 00:19:46,284 but we used it in reverse. 474 00:19:46,317 --> 00:19:48,653 We took-- we were able to take that third orbit 475 00:19:48,686 --> 00:19:52,657 and unshield it, and what that meant was-- 476 00:19:52,690 --> 00:19:54,125 on the left we have the original design, 477 00:19:54,158 --> 00:19:56,261 on the right we have what we did. 478 00:19:56,294 --> 00:19:58,663 And so, instead of turning and pointing straight down 479 00:19:58,696 --> 00:20:01,099 to look at the dust and shield us as we came in, 480 00:20:01,132 --> 00:20:02,834 we kept rotating past. 481 00:20:02,867 --> 00:20:05,837 And this let our cosmic dust analyzer peek out 482 00:20:05,870 --> 00:20:09,708 from beside the antenna and directly sample 483 00:20:09,741 --> 00:20:11,042 the D Ring dust particles. 484 00:20:11,075 --> 00:20:13,345 So, we were actually able to get more science 485 00:20:13,378 --> 00:20:17,916 than we thought we were going to. 486 00:20:17,949 --> 00:20:20,285 Okay. 487 00:20:20,318 --> 00:20:24,823 So, that brings us back to our corridor. 488 00:20:24,856 --> 00:20:25,991 And now, now we're done with dust. 489 00:20:26,024 --> 00:20:27,025 We're done with those first 17. 490 00:20:27,058 --> 00:20:29,661 Nobody's worried about dust anymore, right? 491 00:20:29,694 --> 00:20:31,029 Okay, good, good. 492 00:20:31,062 --> 00:20:33,365 No one's worried about dust. 493 00:20:33,398 --> 00:20:35,767 Now we're worried about the atmosphere for those last five 494 00:20:35,800 --> 00:20:37,202 and this is not the first time Cassini 495 00:20:37,235 --> 00:20:38,603 flew through atmosphere. 496 00:20:38,636 --> 00:20:39,771 Titan has a very thick atmosphere 497 00:20:39,804 --> 00:20:44,242 and we flew by Cassini I would say lots of times. 498 00:20:44,275 --> 00:20:47,112 So again, 127 times we flew by Cassini 499 00:20:47,145 --> 00:20:52,183 and during those low Titan flybys 500 00:20:52,216 --> 00:20:55,720 we switched from reaction remote control 501 00:20:55,753 --> 00:20:57,355 to thruster control. 502 00:20:57,388 --> 00:20:59,858 And the reason we do that is the thrusters can provide 503 00:20:59,891 --> 00:21:02,260 about ten times the control authority 504 00:21:02,293 --> 00:21:03,762 that the reaction wheels do. 505 00:21:03,795 --> 00:21:05,330 And that means that we can fly through 506 00:21:05,363 --> 00:21:06,798 a ten times thicker atmosphere 507 00:21:06,831 --> 00:21:08,700 and still point the spacecraft in the direction 508 00:21:08,733 --> 00:21:11,036 we wanted to point it. 509 00:21:11,069 --> 00:21:12,804 Now, if the atmosphere was so thick 510 00:21:12,837 --> 00:21:14,706 that it would overwhelm our thrusters, 511 00:21:14,739 --> 00:21:17,609 what we could actually do is perform a maneuver, 512 00:21:17,642 --> 00:21:18,877 change the trajectory, and fly through 513 00:21:18,910 --> 00:21:20,478 a less dense part of the atmosphere. 514 00:21:20,511 --> 00:21:22,681 So, these are our two options when it comes to 515 00:21:22,714 --> 00:21:26,251 dealing with Saturn's atmosphere. 516 00:21:26,284 --> 00:21:27,619 So what did we have to do? 517 00:21:27,652 --> 00:21:29,654 Well, first, we needed to know what do we know 518 00:21:29,687 --> 00:21:31,790 about Saturn's atmosphere at the time. 519 00:21:31,823 --> 00:21:33,425 Well, everything we knew came from 520 00:21:33,458 --> 00:21:34,859 solar and stellar occultations, 521 00:21:34,892 --> 00:21:38,430 which is having Cassini watch the Sun and stars 522 00:21:38,463 --> 00:21:39,864 set into Saturn's atmosphere 523 00:21:39,897 --> 00:21:43,168 and see how their light gets filtered through it. 524 00:21:43,201 --> 00:21:47,672 And from that, the scientists derived a density model. 525 00:21:47,705 --> 00:21:50,342 So this is-- this gives us density as a function 526 00:21:50,375 --> 00:21:53,178 of radius and latitude on Saturn. 527 00:21:53,211 --> 00:21:56,881 And so, we can use that model and go back to 528 00:21:56,914 --> 00:22:00,485 the proximal corridor and start adding some boundaries. 529 00:22:00,518 --> 00:22:04,422 So, the first is our spacecraft capture boundary, 530 00:22:04,455 --> 00:22:06,791 so this is the region that we had to get to in order to 531 00:22:06,824 --> 00:22:10,128 ensure that Cassini would not come back out of Saturn again. 532 00:22:10,161 --> 00:22:13,698 And you can see the very last plus on September 15th 533 00:22:13,731 --> 00:22:16,868 is well below that region. 534 00:22:16,901 --> 00:22:20,238 Above that, we have the tumble boundary for thrusters, 535 00:22:20,271 --> 00:22:22,741 so this is the point where the density of the atmosphere 536 00:22:22,774 --> 00:22:25,377 is such that if we were on thruster control 537 00:22:25,410 --> 00:22:26,411 we couldn't point in the direction 538 00:22:26,444 --> 00:22:29,447 we wanted to point and we'd start to drift. 539 00:22:29,480 --> 00:22:30,815 And then, above that, we have that same boundary 540 00:22:30,848 --> 00:22:32,083 but for the reaction wheels, 541 00:22:32,116 --> 00:22:34,519 so this is where the atmosphere is ten times less dense 542 00:22:34,552 --> 00:22:36,020 than the boundary for the thrusters. 543 00:22:36,053 --> 00:22:39,357 And you can see that our final five 544 00:22:39,390 --> 00:22:41,726 are right between those two. 545 00:22:41,759 --> 00:22:45,363 So what that meant was we flew those last five 546 00:22:45,396 --> 00:22:49,200 on thruster control, and you also see that two others 547 00:22:49,233 --> 00:22:51,102 were on thruster control earlier than that. 548 00:22:51,135 --> 00:22:52,837 That wasn't because of atmosphere, it was actually 549 00:22:52,870 --> 00:22:55,373 because of science observations that wanted 550 00:22:55,406 --> 00:22:58,543 to take advantage of the higher turn rates that were allowed 551 00:22:58,576 --> 00:23:03,515 thanks to the thrusters higher torque. 552 00:23:03,548 --> 00:23:07,185 Okay, so to get an idea of just how close we're coming 553 00:23:07,218 --> 00:23:09,254 to not just having to use thrusters but potentially 554 00:23:09,287 --> 00:23:12,791 having to use a maneuver and get out of this region. 555 00:23:12,824 --> 00:23:16,161 We can zoom up on the final five. 556 00:23:16,194 --> 00:23:19,030 And so, here you can see about how close we're getting 557 00:23:19,063 --> 00:23:20,398 to the tumble point. 558 00:23:20,431 --> 00:23:26,871 And so, we thought we had about 120 miles of margin 559 00:23:26,904 --> 00:23:30,008 between where we were going to fly and where we would tumble. 560 00:23:30,041 --> 00:23:31,543 And to get a better idea of just what this meant 561 00:23:31,576 --> 00:23:33,845 for the spacecraft in terms of the thrusters, 562 00:23:33,878 --> 00:23:35,380 we can convert that altitude margin 563 00:23:35,413 --> 00:23:38,349 into a thruster duty cycle margin. 564 00:23:38,382 --> 00:23:42,654 And so, here thruster duty cycle is the percentage of time 565 00:23:42,687 --> 00:23:45,723 that the thrusters are on while they're in the atmosphere. 566 00:23:45,756 --> 00:23:47,692 So if they're on 0% it means they didn't really 567 00:23:47,725 --> 00:23:49,093 encounter atmosphere. 568 00:23:49,126 --> 00:23:51,262 If they're on 100% it means they're flying through 569 00:23:51,295 --> 00:23:53,064 more atmosphere than they can handle 570 00:23:53,097 --> 00:23:55,300 and we're about to lose pointing control. 571 00:23:55,333 --> 00:23:59,437 And you can see that our worst case scenario 572 00:23:59,470 --> 00:24:01,639 had us at just over 30%. 573 00:24:01,672 --> 00:24:05,143 And as a point of reference, Titan flybys-- low Titan flybys 574 00:24:05,176 --> 00:24:08,680 in the past were designed to have a 70% worst case, 575 00:24:08,713 --> 00:24:11,282 so we were even less than half of that. 576 00:24:11,315 --> 00:24:13,985 So, we felt pretty comfortable going in, but again, 577 00:24:14,018 --> 00:24:15,286 we were prepared to be surprised. 578 00:24:15,319 --> 00:24:17,755 So, just like with dust we had a contingency plan, 579 00:24:17,788 --> 00:24:20,725 for the atmosphere we had a contingency plan. 580 00:24:20,758 --> 00:24:25,897 So, the plan was to fly that very first one just as planned. 581 00:24:25,930 --> 00:24:27,765 It has the lowest duty cycle of all of them. 582 00:24:27,798 --> 00:24:29,267 It was the highest in the atmosphere, 583 00:24:29,300 --> 00:24:31,302 it was the least likely to lose control, 584 00:24:31,335 --> 00:24:33,905 but if what we saw there was more atmosphere 585 00:24:33,938 --> 00:24:38,209 than we thought we could perform a maneuver in between 586 00:24:38,242 --> 00:24:41,646 the two passages and pop up into a safer part 587 00:24:41,679 --> 00:24:42,814 of the atmosphere. 588 00:24:42,847 --> 00:24:44,782 We could then fly this blue trajectory to the end 589 00:24:44,815 --> 00:24:48,520 all by performing one maneuver. 590 00:24:48,553 --> 00:24:51,589 Okay, so again, all of you wanted to shield 591 00:24:51,622 --> 00:24:54,459 absolutely every crossing, so now you're all just ecstatic, 592 00:24:54,492 --> 00:24:57,862 hey, we have lots of margin here and we have a contingency plan, 593 00:24:57,895 --> 00:24:59,030 so we're good. 594 00:24:59,063 --> 00:24:59,898 We're going to sit back, relax, 595 00:24:59,931 --> 00:25:02,667 and enjoy these last five orbits. 596 00:25:02,700 --> 00:25:05,069 Again, you're going to upset a lot of scientists. 597 00:25:05,102 --> 00:25:06,237 The scientists came back and they said, 598 00:25:06,270 --> 00:25:08,573 "Well, you know, that's only 25%. 599 00:25:08,606 --> 00:25:10,942 "You can go to 70, so you can go lower, right?" 600 00:25:10,975 --> 00:25:15,647 Well, that really depends on how much fuel we have 601 00:25:15,680 --> 00:25:18,349 and what actually we saw in the atmosphere. 602 00:25:18,382 --> 00:25:21,185 But, let's just go ahead and take a look at it. 603 00:25:21,218 --> 00:25:23,621 We can go lower and specifically they want to 604 00:25:23,654 --> 00:25:26,190 go lower for those last two because those are the ones 605 00:25:26,223 --> 00:25:29,894 where we're doing a direct sampling of the atmosphere. 606 00:25:29,927 --> 00:25:35,567 And so, looking at the higher of those two, the rev 291, 607 00:25:35,600 --> 00:25:38,102 now we're changing the horizontal axis. 608 00:25:38,135 --> 00:25:40,438 Now the horizontal axis is the size of the burn we'd need 609 00:25:40,471 --> 00:25:43,374 to perform to get lower into the atmosphere 610 00:25:43,407 --> 00:25:45,143 and to hit different duty cycles. 611 00:25:45,176 --> 00:25:47,812 It's in meters per second, which is speed. 612 00:25:47,845 --> 00:25:49,847 It's how much do we have to change the speed 613 00:25:49,880 --> 00:25:52,517 of the spacecraft to get lower in the atmosphere? 614 00:25:52,550 --> 00:25:53,418 Four and a half meters per second 615 00:25:53,451 --> 00:25:55,987 is about 10 miles per hour. 616 00:25:56,020 --> 00:25:58,990 And so, as we start to change the speed of the spacecraft 617 00:25:59,023 --> 00:26:02,560 out near Titan's orbit we get lower in the atmosphere 618 00:26:02,593 --> 00:26:05,863 and we find that it would take about 2.25 meters per second, 619 00:26:05,896 --> 00:26:08,833 about 5 miles per hour of speed change 620 00:26:08,866 --> 00:26:10,735 in order to get low enough in the atmosphere 621 00:26:10,768 --> 00:26:12,637 that we'd hit that 70%, 622 00:26:12,670 --> 00:26:14,606 which also corresponds to a best guess, 623 00:26:14,639 --> 00:26:18,409 best estimate of a 40% duty cycle. 624 00:26:18,442 --> 00:26:21,846 To give you some idea of the size of that burn, 625 00:26:21,879 --> 00:26:26,250 we're going 3,700 miles per hour out at Titan 626 00:26:26,283 --> 00:26:29,754 and we need to change the speed by 5 miles per hour, 627 00:26:29,787 --> 00:26:30,955 so it's kind of like sticking your head 628 00:26:30,988 --> 00:26:32,657 out of the car window and blowing backwards 629 00:26:32,690 --> 00:26:34,292 to see how much speed that adds to you. 630 00:26:34,325 --> 00:26:36,628 [laughter] 631 00:26:36,661 --> 00:26:37,829 So, not a lot. 632 00:26:37,862 --> 00:26:40,331 We are one wedge-- or one orange wedge of propellant. 633 00:26:40,364 --> 00:26:41,699 It was going to be enough to do this. 634 00:26:41,732 --> 00:26:45,370 So, this in fact became a viable option and what it meant 635 00:26:45,403 --> 00:26:47,538 for the scientists was now if we're looking at 636 00:26:47,571 --> 00:26:49,240 change in altitude on the left 637 00:26:49,273 --> 00:26:51,142 and change in orbit period on the right, 638 00:26:51,175 --> 00:26:52,644 or the amount of time it takes to get back around 639 00:26:52,677 --> 00:26:57,582 to the same point in the orbit as we do different burn sizes, 640 00:26:57,615 --> 00:27:00,184 what it meant was they got a little over 100 miles deeper 641 00:27:00,217 --> 00:27:02,787 into the atmosphere, 176 kilometers, 642 00:27:02,820 --> 00:27:04,589 and it only changed their orbit period by 2 minutes. 643 00:27:04,622 --> 00:27:06,824 So all the other science observations we were doing 644 00:27:06,857 --> 00:27:08,893 during the orbit other than right there where we're at 645 00:27:08,926 --> 00:27:11,095 the lowest point really weren't affected 646 00:27:11,128 --> 00:27:14,399 because 2 minutes over 6.5 days, not too bad. 647 00:27:14,432 --> 00:27:17,368 And so, this became our third viable path 648 00:27:17,401 --> 00:27:21,839 through these final five. 649 00:27:21,872 --> 00:27:23,107 All right. 650 00:27:23,140 --> 00:27:26,744 So now the question is, well, what really happened? 651 00:27:26,777 --> 00:27:29,714 So, we flew through that first time 652 00:27:29,747 --> 00:27:32,183 and it came in right there, 30%. 653 00:27:32,216 --> 00:27:35,520 And doing some quick math, that is two to three times thicker 654 00:27:35,553 --> 00:27:37,455 than we thought the atmosphere should be. 655 00:27:37,488 --> 00:27:40,058 And if you use that data point to update our model 656 00:27:40,091 --> 00:27:43,728 the other predicts do this. 657 00:27:43,761 --> 00:27:45,697 So, wow, that's 70% line, 658 00:27:45,730 --> 00:27:46,898 we didn't fudge the numbers for that. 659 00:27:46,931 --> 00:27:50,034 That second one is actually 69.7%, 660 00:27:50,067 --> 00:27:51,736 so it came in just under it. 661 00:27:51,769 --> 00:27:53,438 But needless to say, the scientists were like, 662 00:27:53,471 --> 00:27:54,939 "Okay, we don't need to go deeper." 663 00:27:54,972 --> 00:27:58,543 [laughter] 664 00:27:58,576 --> 00:27:59,444 And then the Project Manager said, 665 00:27:59,477 --> 00:28:01,312 "Hey, you know what? 666 00:28:01,345 --> 00:28:05,249 "We're still below the line and that's our worst case, 667 00:28:05,282 --> 00:28:07,385 "so we're going to stay the course 668 00:28:07,418 --> 00:28:10,121 "and we're just going to not perform any maneuver." 669 00:28:10,154 --> 00:28:13,791 So turns out that was the right call. 670 00:28:13,824 --> 00:28:15,393 The next four came in here. 671 00:28:15,426 --> 00:28:17,395 So, you can see they were actually below 672 00:28:17,428 --> 00:28:18,963 what the updated model would've said. 673 00:28:18,996 --> 00:28:21,365 So, we flew through some thick clouds that first time 674 00:28:21,398 --> 00:28:23,134 and scared ourselves. 675 00:28:23,167 --> 00:28:26,504 But they were still above the original estimate, so-- 676 00:28:26,537 --> 00:28:28,106 and this is still a mystery. 677 00:28:28,139 --> 00:28:29,107 We're still trying to figure out 678 00:28:29,140 --> 00:28:31,442 exactly why our stellar occultations 679 00:28:31,475 --> 00:28:33,811 and the direct measurement of the atmosphere 680 00:28:33,844 --> 00:28:37,248 didn't quite line up. 681 00:28:37,281 --> 00:28:39,884 So, going back to our final five chart, we can update this 682 00:28:39,917 --> 00:28:41,786 for where the atmosphere actually was 683 00:28:41,819 --> 00:28:43,421 and we think it was about there. 684 00:28:43,454 --> 00:28:48,025 And so, that was our as-flown final five. 685 00:28:48,058 --> 00:28:50,361 And then we come back out again, now we've done dust, 686 00:28:50,394 --> 00:28:51,763 we've done atmosphere, 687 00:28:51,796 --> 00:28:54,298 and here's the as-flown grand finale. 688 00:28:54,331 --> 00:28:57,201 So, four shielded crossings instead of five, 689 00:28:57,234 --> 00:29:02,273 and no maneuvers in those final five. 690 00:29:02,306 --> 00:29:06,344 Okay, so that's the end of my talk as a Mission Planner. 691 00:29:06,377 --> 00:29:08,980 Now, I'm going to try and play scientist, 692 00:29:09,013 --> 00:29:10,348 which can be interesting. 693 00:29:10,381 --> 00:29:12,450 Or, maybe just space enthusiast, 694 00:29:12,483 --> 00:29:15,052 that's probably a better way to put it. 695 00:29:15,085 --> 00:29:16,621 Okay, so some fun science stuff. 696 00:29:16,654 --> 00:29:18,823 So what was the result of all this? 697 00:29:18,856 --> 00:29:21,225 Well first, before we even got to the grand finale 698 00:29:21,258 --> 00:29:24,428 one of my favorite images was taken during 699 00:29:24,461 --> 00:29:26,531 the seventh ring-grazing orbit. 700 00:29:26,564 --> 00:29:29,901 And here it's Daphnis orbiting in the Keeler gap. 701 00:29:29,934 --> 00:29:32,837 Yeah, you're having some trouble seeing it, huh? 702 00:29:32,870 --> 00:29:36,340 Here. 703 00:29:36,373 --> 00:29:38,743 Here's the actual image that was taken. 704 00:29:38,776 --> 00:29:41,512 And so, here you can see Daphnis, one of Saturn's moons, 705 00:29:41,545 --> 00:29:44,048 orbiting in the Keeler gap between the rings 706 00:29:44,081 --> 00:29:45,416 and the main ring system. 707 00:29:45,449 --> 00:29:48,753 And you can see as the ring particles go by Daphnis 708 00:29:48,786 --> 00:29:52,390 it actually creates a wake, and you can get an even better 709 00:29:52,423 --> 00:29:55,626 view of this by applying some false motion. 710 00:29:55,659 --> 00:30:00,498 And so you can see that as Daphnis orbits to the right, 711 00:30:00,531 --> 00:30:01,899 the rings below are orbiting slower 712 00:30:01,932 --> 00:30:03,734 and appear to move to the left. 713 00:30:03,767 --> 00:30:06,804 The rings above are orbiting faster and go to the right. 714 00:30:06,837 --> 00:30:10,007 And so you have a wake on the outside ring 715 00:30:10,040 --> 00:30:12,343 going out to the left, and on the inside ring 716 00:30:12,376 --> 00:30:15,746 you may just be able to make out the start of a wake 717 00:30:15,779 --> 00:30:22,286 going in the other direction because of the relative motions. 718 00:30:22,319 --> 00:30:28,025 So very analogous to that is this other fun image 719 00:30:28,058 --> 00:30:30,228 of a ring propeller. 720 00:30:30,261 --> 00:30:31,762 So a ring propeller is very much like Daphnis 721 00:30:31,795 --> 00:30:33,698 only on a very, very small scale. 722 00:30:33,731 --> 00:30:35,499 It's orbiting in the main ring system. 723 00:30:35,532 --> 00:30:39,670 It's a very small moonlet, and it creates that similar wake 724 00:30:39,703 --> 00:30:42,406 where you have these wakes coming off the opposite edges. 725 00:30:42,439 --> 00:30:45,343 What's really neat about this particular set of images 726 00:30:45,376 --> 00:30:47,211 is because of the way the ring grazing orbits came in 727 00:30:47,244 --> 00:30:49,413 over the top and then exited down below, 728 00:30:49,446 --> 00:30:51,582 we're able to photograph the same propeller 729 00:30:51,615 --> 00:30:52,817 in a relatively short amount of time 730 00:30:52,850 --> 00:30:55,786 from both the lit side and the unlit side of the rings. 731 00:30:55,819 --> 00:30:59,657 And so that's what you're seeing there. 732 00:30:59,690 --> 00:31:01,859 And scientists are interested in these because they think 733 00:31:01,892 --> 00:31:06,163 that they are analogous to a baby planet 734 00:31:06,196 --> 00:31:08,532 in a protoplanetary disk and how it can start 735 00:31:08,565 --> 00:31:15,907 to accrete mass in an early solar system. 736 00:31:15,940 --> 00:31:17,875 Okay, so now we're actually at the grand finale. 737 00:31:17,908 --> 00:31:20,378 This is grand finale orbit number one. 738 00:31:20,411 --> 00:31:23,681 We're a day out from the first dive through the rings, 739 00:31:23,714 --> 00:31:26,050 and we're over Saturn's north pole. 740 00:31:26,083 --> 00:31:29,520 And so we've got this series of images of Saturn's 741 00:31:29,553 --> 00:31:32,757 hexagonal jet stream and hurricane at its north pole. 742 00:31:32,790 --> 00:31:34,325 And you can see it's really neat. 743 00:31:34,358 --> 00:31:36,260 What's even more interesting is we have a similar 744 00:31:36,293 --> 00:31:39,196 set of images from four years earlier. 745 00:31:39,229 --> 00:31:40,932 And these are true color images. 746 00:31:40,965 --> 00:31:44,235 And you can see that the hexagon has very clearly changed 747 00:31:44,268 --> 00:31:47,004 from blue to this nice yellowish orange. 748 00:31:47,037 --> 00:31:49,507 And the reason for that is in 2013, 749 00:31:49,540 --> 00:31:52,176 the hexagon had only just become exposed to light. 750 00:31:52,209 --> 00:31:56,347 And 2017 now we're at the northern summer solstice, 751 00:31:56,380 --> 00:31:58,349 so sunlight's been hitting this region for a long time. 752 00:31:58,382 --> 00:32:01,419 And this region is full of photochemical aerosols, 753 00:32:01,452 --> 00:32:04,088 and so when the ultraviolet light from the sun hits them, 754 00:32:04,121 --> 00:32:07,992 they form a smoggy haze that turns the hexagon 755 00:32:08,025 --> 00:32:11,796 from blue to yellowish orange. 756 00:32:11,829 --> 00:32:13,531 As for why that hurricane in the center stays blue, 757 00:32:13,564 --> 00:32:15,032 there's a couple thoughts. 758 00:32:15,065 --> 00:32:16,667 One is that that hurricane is actually at 759 00:32:16,700 --> 00:32:18,736 a lower altitude than the surrounding clouds, 760 00:32:18,769 --> 00:32:21,205 and so they're shading it from the sun. 761 00:32:21,238 --> 00:32:24,742 So given enough time, they could eventually form a haze. 762 00:32:24,775 --> 00:32:28,546 However, if it acts at all like Earth hurricanes, 763 00:32:28,579 --> 00:32:30,514 it actually creates a downwelling that's right there. 764 00:32:30,547 --> 00:32:32,416 And so it's sucking any haze particles that are formed 765 00:32:32,449 --> 00:32:34,652 back down into the deep atmosphere. 766 00:32:34,685 --> 00:32:39,790 And so that keeps it that nice pristine blue color. 767 00:32:39,823 --> 00:32:42,426 Okay, so day after this, 768 00:32:42,459 --> 00:32:44,929 we did our first dive through the gap. 769 00:32:44,962 --> 00:32:46,297 And while we were doing it, 770 00:32:46,330 --> 00:32:48,933 we were taking images with our camera from the north pole 771 00:32:48,966 --> 00:32:50,634 all the way down to the equator. 772 00:32:50,667 --> 00:32:54,238 And you can see the images in the lower right there. 773 00:32:54,271 --> 00:32:56,540 At the end of this animation, the spacecraft will actually 774 00:32:56,573 --> 00:32:59,510 turn, because we had to go to our shielded attitude. 775 00:32:59,543 --> 00:33:02,113 And so you can see it turning in order to protect itself 776 00:33:02,146 --> 00:33:03,180 during that first crossing. 777 00:33:03,213 --> 00:33:04,415 We still didn't know that there was 778 00:33:04,448 --> 00:33:07,118 absolutely no dust there. 779 00:33:07,151 --> 00:33:08,119 But you can take all those images, 780 00:33:08,152 --> 00:33:09,553 and you can stitch them together, 781 00:33:09,586 --> 00:33:11,122 and you get a Saturn noodle. 782 00:33:11,155 --> 00:33:14,025 So this is a thin little strip all the way from 783 00:33:14,058 --> 00:33:18,596 Saturn's north pole down to its equator. 784 00:33:18,629 --> 00:33:22,266 On our second dive, we were in a high rate spin 785 00:33:22,299 --> 00:33:25,336 to get high resolution magnetic field data. 786 00:33:25,369 --> 00:33:26,537 And here you can see the spacecraft 787 00:33:26,570 --> 00:33:27,805 diving through the graph, 788 00:33:27,838 --> 00:33:30,641 and that colored line is Saturn's magnetic field line 789 00:33:30,674 --> 00:33:32,843 that passes through the spacecraft. 790 00:33:32,876 --> 00:33:34,979 And so you can see where that field line both hits Saturn 791 00:33:35,012 --> 00:33:36,580 and intersects the ring plane. 792 00:33:36,613 --> 00:33:41,085 And that can give a lot of interesting results as far-- 793 00:33:41,118 --> 00:33:43,287 there are particles that travel along that field line, 794 00:33:43,320 --> 00:33:46,057 and this kind of shows you what the source of those 795 00:33:46,090 --> 00:33:49,326 particles may be as far as the latitudes on Saturn, 796 00:33:49,359 --> 00:33:56,867 or the exact distance into the ring plane that they are. 797 00:33:56,900 --> 00:33:58,269 On our third dive-- I'm not going to go through these 798 00:33:58,302 --> 00:34:00,838 one by one, but the first three were pretty cool. 799 00:34:00,871 --> 00:34:02,973 On the third dive, we were on Earth point, 800 00:34:03,006 --> 00:34:06,343 and communicating with Earth as we dove through. 801 00:34:06,376 --> 00:34:11,449 And Earth is above the ring plane relative to Saturn. 802 00:34:11,482 --> 00:34:12,750 And so you can see here, 803 00:34:12,783 --> 00:34:14,085 we're pointing up above the ring plane, 804 00:34:14,118 --> 00:34:16,287 but as we dive through it, what that means is the signal's 805 00:34:16,320 --> 00:34:18,989 actually going to pass through those rings. 806 00:34:19,022 --> 00:34:21,659 And from that, we can look at what that does to the signal 807 00:34:21,692 --> 00:34:23,094 and get some information about the rings. 808 00:34:23,127 --> 00:34:25,096 It looks a little like this, which is a messy plot, 809 00:34:25,129 --> 00:34:28,332 but it's basically the transmission strength 810 00:34:28,365 --> 00:34:30,267 of the signal as it goes through. 811 00:34:30,300 --> 00:34:31,635 And it lets us see how thick the rings are, 812 00:34:31,668 --> 00:34:38,142 how sharp those edges are between the ringlets. 813 00:34:38,175 --> 00:34:41,112 Okay, so jumping ahead now to the 12th orbit. 814 00:34:41,145 --> 00:34:43,747 Here we got a really good look, a really high resolution 815 00:34:43,780 --> 00:34:46,717 picture of Saturn's B Ring, which the rings are made up 816 00:34:46,750 --> 00:34:47,852 of mostly water ice. 817 00:34:47,885 --> 00:34:48,953 And if they were pure water ice, 818 00:34:48,986 --> 00:34:50,154 they'd probably look like this, 819 00:34:50,187 --> 00:34:52,523 but in this particular opportunity, we were actually 820 00:34:52,556 --> 00:34:54,725 able to get this image in color. 821 00:34:54,758 --> 00:34:59,130 And here, the color comes from impurities in the water ice. 822 00:34:59,163 --> 00:35:01,098 And the source of those impurities is actually 823 00:35:01,131 --> 00:35:02,733 still debated by the scientists. 824 00:35:02,766 --> 00:35:05,269 It could have been rocks and minerals that were part of 825 00:35:05,302 --> 00:35:06,737 the accretion disk of Saturn as it was forming, 826 00:35:06,770 --> 00:35:09,240 or it could have also been meteorites that are 827 00:35:09,273 --> 00:35:10,841 coming in and impacting the ring system 828 00:35:10,874 --> 00:35:17,448 and getting obliterated and orbiting with it. 829 00:35:17,481 --> 00:35:21,118 Okay, on the 14th orbit, a day or two after we passed through 830 00:35:21,151 --> 00:35:25,556 the gap for the 14th time, we look back at Saturn, 831 00:35:25,589 --> 00:35:27,224 and specifically at the south pole 832 00:35:27,257 --> 00:35:29,326 and we got to watch the aurora. 833 00:35:29,359 --> 00:35:32,329 This is a false color image, but it's reproduced with what 834 00:35:32,362 --> 00:35:34,965 should be a somewhat natural color for the aurora. 835 00:35:34,998 --> 00:35:38,302 And so here you have Saturn as the big black body up top. 836 00:35:38,335 --> 00:35:41,572 You can see the starry sky sweeping by in the background 837 00:35:41,605 --> 00:35:44,542 and the aurora orbiting the south pole. 838 00:35:44,575 --> 00:35:46,610 If you look close, you can also see that the stars 839 00:35:46,643 --> 00:35:48,145 sort of take a sharp right turn 840 00:35:48,178 --> 00:35:50,314 just before they set behind Saturn. 841 00:35:50,347 --> 00:35:51,916 That's because their light actually is refracted 842 00:35:51,949 --> 00:35:58,122 by Saturn's atmosphere as it travels back to Cassini. 843 00:35:58,155 --> 00:36:00,057 Okay, so next is one of my favorite observations 844 00:36:00,090 --> 00:36:03,160 because I actually had a hand in helping plan it, 845 00:36:03,193 --> 00:36:05,362 which as a Mission Planner I don't normally do. 846 00:36:05,395 --> 00:36:06,597 That's science planning's job. 847 00:36:06,630 --> 00:36:09,333 And what we did is we actually were able 848 00:36:09,366 --> 00:36:11,602 to have the spacecraft, as it was diving through, 849 00:36:11,635 --> 00:36:13,470 take pictures of the rings from the inside out, 850 00:36:13,503 --> 00:36:15,973 and create this movie where we got to see the lit side, 851 00:36:16,006 --> 00:36:18,375 the unlit side, and even neater, 852 00:36:18,408 --> 00:36:20,945 we got to see the entire ring system in one frame 853 00:36:20,978 --> 00:36:24,181 because of the foreshortening. 854 00:36:24,214 --> 00:36:30,387 See, as you watch it go by again. 855 00:36:30,420 --> 00:36:34,558 So there, the entire ring system in one camera frame. 856 00:36:34,591 --> 00:36:37,728 Pretty neat. 857 00:36:37,761 --> 00:36:41,298 Okay, an orbit later, we got to watch one of 858 00:36:41,331 --> 00:36:44,468 the protected bodies of the Saturn system. 859 00:36:44,501 --> 00:36:46,003 So this is in Enceladus. 860 00:36:46,036 --> 00:36:48,305 Again, it has that global subsurface ocean and contact 861 00:36:48,338 --> 00:36:50,741 with an active rocky core. 862 00:36:50,774 --> 00:36:54,445 And as it orbits Saturn, squeezes it, and it creates 863 00:36:54,478 --> 00:36:57,414 these geysers that shoot out of its south pole. 864 00:36:57,447 --> 00:37:00,150 So these are water geysers shooting out of the south pole. 865 00:37:00,183 --> 00:37:02,453 This is about 14 hours of observation 866 00:37:02,486 --> 00:37:07,358 and it was taken from half a million miles away. 867 00:37:07,391 --> 00:37:15,432 And this was our last dedicated observation of Enceladus. 868 00:37:15,465 --> 00:37:18,969 Okay, Grand Finale Orbit 21, so just one and a half to go. 869 00:37:19,002 --> 00:37:20,771 We got some really great pictures of 870 00:37:20,804 --> 00:37:22,339 the dawn side of Saturn's atmosphere. 871 00:37:22,372 --> 00:37:24,908 So here you can see some of the structure in the clouds, 872 00:37:24,941 --> 00:37:27,211 and once again, like with the B Ring, 873 00:37:27,244 --> 00:37:28,312 we got the images in color. 874 00:37:28,345 --> 00:37:29,947 And it's a little hard to make out, 875 00:37:29,980 --> 00:37:32,016 but you actually have these multi-hued bands 876 00:37:32,049 --> 00:37:33,951 of green and red in the clouds. 877 00:37:33,984 --> 00:37:35,653 And again, this is a true color image. 878 00:37:35,686 --> 00:37:41,992 That is actually what you would see if you were there. 879 00:37:42,025 --> 00:37:44,595 All right, getting close to the end now. 880 00:37:44,628 --> 00:37:47,965 On the final plunge, so this is our last half orbit. 881 00:37:47,998 --> 00:37:52,136 Last trip from Titan's orbit down into Saturn, 882 00:37:52,169 --> 00:37:56,173 we took a series of seven image sets 883 00:37:56,206 --> 00:37:59,677 of different objects in the rings. 884 00:37:59,710 --> 00:38:03,147 And so these are the final seven sets of images 885 00:38:03,180 --> 00:38:04,948 that Cassini took. 886 00:38:04,981 --> 00:38:07,985 And this was about a day before we plunged into Saturn. 887 00:38:08,018 --> 00:38:11,288 Also at the end of that, we had Cassini image 888 00:38:11,321 --> 00:38:13,457 what would eventually become its impact site, 889 00:38:13,490 --> 00:38:14,658 which was a little bit morbid, 890 00:38:14,691 --> 00:38:16,060 but very scientifically interesting. 891 00:38:16,093 --> 00:38:19,029 [laughter] 892 00:38:19,062 --> 00:38:21,031 So this gave us some context for what we would 893 00:38:21,064 --> 00:38:25,135 later be seeing with our other instruments as we were 894 00:38:25,168 --> 00:38:27,905 plunging into Saturn's atmosphere. 895 00:38:27,938 --> 00:38:30,641 Okay, so a little before 5 a.m. 896 00:38:30,674 --> 00:38:33,143 on September 15th, 2017, 897 00:38:33,176 --> 00:38:36,046 Cassini entered Saturn's atmosphere. 898 00:38:36,079 --> 00:38:39,049 And within a minute, our thrusters saturated 899 00:38:39,082 --> 00:38:41,118 and we couldn't point the spacecraft anymore. 900 00:38:41,151 --> 00:38:43,220 It only took 20 more seconds for our S band signal, 901 00:38:43,253 --> 00:38:47,391 which you can see there, to completely disappear. 902 00:38:47,424 --> 00:38:49,893 And within the next minute, 903 00:38:49,926 --> 00:38:53,397 Saturn's atmosphere destroyed the spacecraft, 904 00:38:53,430 --> 00:38:57,201 and Cassini became a part of Saturn. 905 00:38:57,234 --> 00:39:01,004 So end of mission was called at 4:56 a.m. JPL time, 906 00:39:01,037 --> 00:39:03,374 September 15th, 2017 when we lost 907 00:39:03,407 --> 00:39:11,215 the S band carrier signal. 908 00:39:11,248 --> 00:39:12,216 Okay, so with that, 909 00:39:12,249 --> 00:39:14,485 I just want to say thank you for coming. 910 00:39:14,518 --> 00:39:26,029 [applause] 911 00:39:26,062 --> 00:39:30,434 I would also like to thank all of my Cassini family, 912 00:39:30,467 --> 00:39:31,602 all of my predecessors, 913 00:39:31,635 --> 00:39:35,272 and also everybody here who helped put this on. 914 00:39:35,305 --> 00:39:37,975 It takes a lot of work, and I get the easy part. 915 00:39:38,008 --> 00:39:39,610 I just come up here and talk to you guys. 916 00:39:39,643 --> 00:39:40,577 So they all did a lot of work, 917 00:39:40,610 --> 00:39:41,979 so give them a round of applause too. 918 00:39:42,012 --> 00:39:53,690 [applause] 919 00:39:53,723 --> 00:39:55,592 Okay, so with that, I have time for questions. 920 00:39:55,625 --> 00:39:56,860 However, if you want to ask a question, 921 00:39:56,893 --> 00:39:59,096 I ask that you go up, 922 00:39:59,129 --> 00:40:02,366 form a line at that microphone there. 923 00:40:02,399 --> 00:40:03,700 That way everybody in here can hear you, 924 00:40:03,733 --> 00:40:05,169 and also everybody online can hear you. 925 00:40:05,202 --> 00:40:06,804 And I also I will preface this with: 926 00:40:06,837 --> 00:40:08,439 I will answer these to the best of my knowledge. 927 00:40:08,472 --> 00:40:11,341 If you remember those dates at the beginning, 928 00:40:11,374 --> 00:40:14,545 2013 to 2017 is my reign of terror. 929 00:40:14,578 --> 00:40:16,046 [laughter] 930 00:40:16,079 --> 00:40:18,015 And it went all the way back to 1991 931 00:40:18,048 --> 00:40:21,418 with Mission Planners and even farther than that. 932 00:40:21,451 --> 00:40:22,719 Like I said, I was a baby when it was born, 933 00:40:22,752 --> 00:40:24,288 so I will do what I can. 934 00:40:24,321 --> 00:40:26,056 I may rely on some friendly faces in the audience 935 00:40:26,089 --> 00:40:27,624 to help me out. 936 00:40:27,657 --> 00:40:29,593 - Well, the first one is actually kind of a remark, 937 00:40:29,626 --> 00:40:31,028 not a question. 938 00:40:31,061 --> 00:40:34,298 The birth of Cassini goes a bit back before 1982. 939 00:40:34,331 --> 00:40:36,934 In the mid-'70s, Donna Pivirotto noticed 940 00:40:36,967 --> 00:40:39,570 that essentially every Mariner was different. 941 00:40:39,603 --> 00:40:40,737 And she said, "We ought to construct 942 00:40:40,770 --> 00:40:42,573 "some building blocks." 943 00:40:42,606 --> 00:40:45,776 And she proposed a project called Mariner Block II. 944 00:40:45,809 --> 00:40:47,845 And then they stopped calling it Mariner, 945 00:40:47,878 --> 00:40:49,580 because all the Mariners were solar powered. 946 00:40:49,613 --> 00:40:52,683 And then later on they were nuclear powered. 947 00:40:52,716 --> 00:40:55,752 But Mariner Block II is where Cassini got started. 948 00:40:55,785 --> 00:40:57,254 And, of course, Cassini was supposed to have a twin 949 00:40:57,287 --> 00:41:00,257 called CRAF, the Comet Rendezvous Asteroid Flyby, 950 00:41:00,290 --> 00:41:02,459 and that got axed long before 951 00:41:02,492 --> 00:41:05,195 Cassini actually got going along. 952 00:41:05,228 --> 00:41:07,564 So Cassini's a bit older than 1982. 953 00:41:07,597 --> 00:41:09,566 It goes back to the mid-'70s. 954 00:41:09,599 --> 00:41:10,767 - Okay, we'll have to update a couple books. 955 00:41:10,800 --> 00:41:12,202 And I'm going to keep telling that story because 956 00:41:12,235 --> 00:41:14,404 my picture before 1982 was not as good. 957 00:41:14,437 --> 00:41:16,073 - No pictures of you before then, yeah. 958 00:41:16,106 --> 00:41:19,042 Yeah. No, the question I have: 959 00:41:19,075 --> 00:41:24,715 In the mid-'90s, before the Neptune flyby for Voyager, 960 00:41:24,748 --> 00:41:28,352 I asked Fred Billingsley with such a long baseline, 961 00:41:28,385 --> 00:41:30,954 are the Voyager cameras good enough to do 962 00:41:30,987 --> 00:41:33,957 any decent astrometry, to measure the distance 963 00:41:33,990 --> 00:41:36,193 to nearby stars using parallax? 964 00:41:36,226 --> 00:41:38,662 And he said the cameras on Voyager aren't good enough 965 00:41:38,695 --> 00:41:41,999 for astrometry even with that enormous baseline. 966 00:41:42,032 --> 00:41:45,402 Were the Cassini cameras good enough to get better parallax 967 00:41:45,435 --> 00:41:47,971 measurements with an enormous baseline than we can get 968 00:41:48,004 --> 00:41:51,575 with just using the Earth baseline for astrometry? 969 00:41:51,608 --> 00:41:53,143 - I don't know that we ever did that with Cassini. 970 00:41:53,176 --> 00:41:54,211 I'm going to look at a friendly face here. 971 00:41:54,244 --> 00:41:56,713 - Yeah, we never did that. 972 00:41:56,746 --> 00:41:59,583 - Yeah, I think we were too busy with Saturn science. 973 00:41:59,616 --> 00:42:01,785 But, yeah, so I'm not sure if the cameras 974 00:42:01,818 --> 00:42:03,887 are good enough or not to do parallax. 975 00:42:03,920 --> 00:42:07,791 - No star images, huh? - We can get back to you. 976 00:42:07,824 --> 00:42:10,761 - Thank you. - Yeah. 977 00:42:10,794 --> 00:42:12,496 - I have an attitude control question. 978 00:42:12,529 --> 00:42:13,730 - Yeah. 979 00:42:13,763 --> 00:42:15,933 - It looked like the tumble boundaries that you showed 980 00:42:15,966 --> 00:42:17,901 for RCS thrusters were not flat. 981 00:42:17,934 --> 00:42:19,870 - Right. - Why is that? 982 00:42:19,903 --> 00:42:22,573 - So the tumble boundary is not just a function 983 00:42:22,606 --> 00:42:25,042 of the density of the atmosphere. 984 00:42:25,075 --> 00:42:27,544 It's also a function of how fast you're going 985 00:42:27,577 --> 00:42:29,746 and the attitude of the spacecraft. 986 00:42:29,779 --> 00:42:33,083 A good way to think about this is if you're driving in a car, 987 00:42:33,116 --> 00:42:34,551 you put your hand out the window, 988 00:42:34,584 --> 00:42:37,154 and put it face-on to the wind, and start driving faster, 989 00:42:37,187 --> 00:42:39,289 it's going to push you harder. 990 00:42:39,322 --> 00:42:41,325 Also if you change the pointing of your hand 991 00:42:41,358 --> 00:42:43,727 so that it's like this, it's going to push you less. 992 00:42:43,760 --> 00:42:45,629 So in that one where it bumped up, 993 00:42:45,662 --> 00:42:47,264 we weren't necessarily going any faster. 994 00:42:47,297 --> 00:42:48,665 They were all about the same speed. 995 00:42:48,698 --> 00:42:50,667 But we were at an attitude that was more like having 996 00:42:50,700 --> 00:42:53,070 an open palm out the window than a closed palm out the window. 997 00:42:53,103 --> 00:42:56,239 And so the atmosphere turned us harder, 998 00:42:56,272 --> 00:42:58,442 which meant the thrusters had to fight it more. 999 00:42:58,475 --> 00:43:00,978 - Thank you. - Yep. 1000 00:43:01,011 --> 00:43:04,047 - So what were some of the most difficult decisions 1001 00:43:04,080 --> 00:43:08,118 that you had to make as a planner? 1002 00:43:08,151 --> 00:43:11,822 - Well, I think the first one was just coming up 1003 00:43:11,855 --> 00:43:13,790 with the fact that we could have a contingency plan, 1004 00:43:13,823 --> 00:43:15,759 and not just Captain America it, and just say, 1005 00:43:15,792 --> 00:43:18,261 "Hey, shields. Shields everywhere!" 1006 00:43:18,294 --> 00:43:19,896 But to actually have to prove that, you know what, 1007 00:43:19,929 --> 00:43:22,499 we could take data, analyze it, 1008 00:43:22,532 --> 00:43:26,069 and make a decision and uplink a contingency 1009 00:43:26,102 --> 00:43:29,039 to the spacecraft all within six and a half days. 1010 00:43:29,072 --> 00:43:30,607 Because these orbits were much, much shorter 1011 00:43:30,640 --> 00:43:32,476 than anything we'd ever done before. 1012 00:43:32,509 --> 00:43:35,379 The ring-grazing orbits were just over a week. 1013 00:43:35,412 --> 00:43:37,114 These were just under a week. 1014 00:43:37,147 --> 00:43:39,516 The closest we got to that before was nine days, 1015 00:43:39,549 --> 00:43:41,485 and we weren't inside the ring system. 1016 00:43:41,518 --> 00:43:44,554 So proving that we could turn something around fast enough 1017 00:43:44,587 --> 00:43:47,457 I think was the biggest challenge as far as 1018 00:43:47,490 --> 00:43:48,692 mission planning goes. 1019 00:43:48,725 --> 00:43:50,927 - Thank you. - Yeah. 1020 00:43:50,960 --> 00:43:52,729 - Thanks so much for the awesome presentation. 1021 00:43:52,762 --> 00:43:53,930 - You're welcome. 1022 00:43:53,963 --> 00:43:56,400 - How do you know how many orange peels you have left 1023 00:43:56,433 --> 00:43:58,502 in the tank on a spacecraft? 1024 00:43:58,535 --> 00:43:59,736 [laughter] 1025 00:43:59,769 --> 00:44:00,871 - Yeah, that's a good question. 1026 00:44:00,904 --> 00:44:03,774 I actually didn't say-- we have some uncertainty 1027 00:44:03,807 --> 00:44:06,243 in that estimate, right? 1028 00:44:06,276 --> 00:44:08,445 The uncertainty in that one orange wedge was about 1029 00:44:08,478 --> 00:44:10,080 plus or minus 1.5 orange wedges. 1030 00:44:10,113 --> 00:44:13,216 [laughter] 1031 00:44:13,249 --> 00:44:17,788 So we really needed to-- We couldn't go any longer. 1032 00:44:17,821 --> 00:44:19,990 And so it really all comes to two things. 1033 00:44:20,023 --> 00:44:22,459 First, it's very accurate measurements on the ground 1034 00:44:22,492 --> 00:44:27,397 when we load up the spacecraft and take its weight. 1035 00:44:27,430 --> 00:44:30,634 And so we have some idea with a relatively small uncertainty 1036 00:44:30,667 --> 00:44:32,002 of how much fuel we put in it. 1037 00:44:32,035 --> 00:44:34,404 Then that small uncertainty actually just grows 1038 00:44:34,437 --> 00:44:36,406 and grows and grows, because from there, 1039 00:44:36,439 --> 00:44:37,541 each time we perform a maneuver, 1040 00:44:37,574 --> 00:44:39,476 we have a model on the ground that says 1041 00:44:39,509 --> 00:44:41,411 about how much fuel we thought we burned, 1042 00:44:41,444 --> 00:44:43,013 but that model has some uncertainty. 1043 00:44:43,046 --> 00:44:46,216 So each time you use that model, what may have been 1044 00:44:46,249 --> 00:44:48,585 a fraction of an orange wedge of uncertainty is just 1045 00:44:48,618 --> 00:44:49,753 growing and growing and growing. 1046 00:44:49,786 --> 00:44:52,289 So by the end, not only is our uncertainty bigger, 1047 00:44:52,322 --> 00:44:55,092 but the amount of fuel we have left is smaller. 1048 00:44:55,125 --> 00:44:59,563 And so things start to look a lot scarier. 1049 00:44:59,596 --> 00:45:03,633 - Thank you. - Yep. 1050 00:45:03,666 --> 00:45:07,971 - I guess my question is there must've been 1051 00:45:08,004 --> 00:45:10,907 a lot of discussion about what to do. 1052 00:45:10,940 --> 00:45:15,712 You know, what-- and there must have been some observations 1053 00:45:15,745 --> 00:45:19,049 that would've been nice that you couldn't do. 1054 00:45:19,082 --> 00:45:21,051 Could you tell us about some of those? 1055 00:45:21,084 --> 00:45:24,020 - Yeah, I can tell you a little. 1056 00:45:24,053 --> 00:45:25,388 So that's all science planning, 1057 00:45:25,421 --> 00:45:27,224 which is right after mission planning happens. 1058 00:45:27,257 --> 00:45:29,292 I'm the bigger picture, and then science planners 1059 00:45:29,325 --> 00:45:31,228 go down and divvy up the individual orbits. 1060 00:45:31,261 --> 00:45:33,530 But what I can say is that science was split up 1061 00:45:33,563 --> 00:45:35,499 into different disciplines. 1062 00:45:35,532 --> 00:45:37,501 And each of those disciplines and instruments were given 1063 00:45:37,534 --> 00:45:40,003 the opportunity to say what they thought they needed 1064 00:45:40,036 --> 00:45:43,740 in the Grand Finale in order to get this really great science 1065 00:45:43,773 --> 00:45:45,709 that we were promising everyone. 1066 00:45:45,742 --> 00:45:48,545 And luckily when we added all those orbits up, 1067 00:45:48,578 --> 00:45:51,181 it came out to 35 out of 22. 1068 00:45:51,214 --> 00:45:53,416 And so that's a little bit over. 1069 00:45:53,449 --> 00:45:56,153 But at JPL, we know how to make 35 fit into 22. 1070 00:45:56,186 --> 00:45:57,320 [laughter] 1071 00:45:57,353 --> 00:45:59,322 We were able to get 1072 00:45:59,355 --> 00:46:01,691 the instrument scientists together to talk things out 1073 00:46:01,724 --> 00:46:03,326 and figure out where we could share orbits, 1074 00:46:03,359 --> 00:46:04,661 where we could have more than one instrument on 1075 00:46:04,694 --> 00:46:06,696 at the same time and both get the same science. 1076 00:46:06,729 --> 00:46:08,465 And then we also had to push back a little bit and say, 1077 00:46:08,498 --> 00:46:10,300 "Do you really need that many orbits? 1078 00:46:10,333 --> 00:46:11,668 "Could you do with one less?" 1079 00:46:11,701 --> 00:46:14,371 And so, it was just a series of negotiations 1080 00:46:14,404 --> 00:46:17,140 with the project and the science teams that went back and forth 1081 00:46:17,173 --> 00:46:20,744 like that to get it all fit into the 22.5 orbits. 1082 00:46:20,777 --> 00:46:24,815 - Thank you. - Yeah. 1083 00:46:24,848 --> 00:46:32,556 - Hi, my question would be for future missions, 1084 00:46:32,589 --> 00:46:37,260 what sort of guidance do you have for people 1085 00:46:37,293 --> 00:46:39,162 that will be in your shoes five years, 1086 00:46:39,195 --> 00:46:41,231 ten years and fifteen years from now. 1087 00:46:41,264 --> 00:46:44,000 What sort of-- maybe you can think of, like, one, or two, 1088 00:46:44,033 --> 00:46:46,469 or three things that-- what sort of guidance do you have 1089 00:46:46,502 --> 00:46:50,707 for them learning what you learned on this mission 1090 00:46:50,740 --> 00:46:54,077 where it seemed like there were a lot of options that 1091 00:46:54,110 --> 00:46:58,915 you may not have thought you had that you did have? 1092 00:46:58,948 --> 00:47:02,786 - Yeah, so the first one is: plan for what you think 1093 00:47:02,819 --> 00:47:06,523 you're never going to do, because you're going to do it. 1094 00:47:06,556 --> 00:47:08,992 We never thought we'd fly inside the ring system, 1095 00:47:09,025 --> 00:47:13,330 and so being able to do that was actually a pretty big deal. 1096 00:47:13,363 --> 00:47:14,764 It took a lot of work. 1097 00:47:14,797 --> 00:47:16,533 We had to change a lot of tools in order to 1098 00:47:16,566 --> 00:47:19,336 actually get them to function inside the rings, 1099 00:47:19,369 --> 00:47:20,971 because we never thought we'd be there. 1100 00:47:21,004 --> 00:47:23,506 But what that really gets to is-- 1101 00:47:23,539 --> 00:47:25,475 I'd say a couple other lessons, it's: 1102 00:47:25,508 --> 00:47:29,846 you got to keep the spacecraft simple and robust. 1103 00:47:29,879 --> 00:47:33,450 And that makes it so that you have something that lasts 1104 00:47:33,483 --> 00:47:36,586 a long time so that you can just keep doing this great science. 1105 00:47:36,619 --> 00:47:38,755 And also, you need to keep your system flexible, 1106 00:47:38,788 --> 00:47:40,991 so that you can react to new discoveries 1107 00:47:41,024 --> 00:47:42,425 and going new places. 1108 00:47:42,458 --> 00:47:43,560 And so I think those are the two key things about 1109 00:47:43,593 --> 00:47:46,963 the Cassini spacecraft and the project 1110 00:47:46,996 --> 00:47:48,465 that made it so that we could do this. 1111 00:47:48,498 --> 00:47:49,833 - Got you. Thank you so much. 1112 00:47:49,866 --> 00:47:52,235 - Yeah. 1113 00:47:52,268 --> 00:47:56,573 - How come some of the pictures that Cassini took 1114 00:47:56,606 --> 00:47:59,342 were black and white and others were color? 1115 00:47:59,375 --> 00:48:01,978 - Yeah, so Cassini's cameras actually 1116 00:48:02,011 --> 00:48:03,780 are just black and white. 1117 00:48:03,813 --> 00:48:05,749 And the way it works is we put different color filters 1118 00:48:05,782 --> 00:48:08,151 in front of them, so that just that color of light 1119 00:48:08,184 --> 00:48:09,386 comes through. 1120 00:48:09,419 --> 00:48:11,187 And depending on the science we're doing, 1121 00:48:11,220 --> 00:48:12,923 and how much time we have, 1122 00:48:12,956 --> 00:48:14,291 that determines how many filters 1123 00:48:14,324 --> 00:48:16,426 we're able to put in front of the camera 1124 00:48:16,459 --> 00:48:17,928 when we make a given observation. 1125 00:48:17,961 --> 00:48:20,530 In order to get one in color as we see it, 1126 00:48:20,563 --> 00:48:23,466 we need three filters, the red, the green, and the blue. 1127 00:48:23,499 --> 00:48:25,335 And so for those particular ones, we were able to get 1128 00:48:25,368 --> 00:48:27,370 all three filters in front of the camera 1129 00:48:27,403 --> 00:48:33,143 and reproduce true to life images. 1130 00:48:33,176 --> 00:48:34,277 - Hello, thanks for your lecture tonight. 1131 00:48:34,310 --> 00:48:35,312 - Yeah. 1132 00:48:35,345 --> 00:48:36,246 - You showed a beautiful picture of the moon, 1133 00:48:36,279 --> 00:48:37,981 Daphne going through the ring plane. 1134 00:48:38,014 --> 00:48:39,049 - Yeah. 1135 00:48:39,082 --> 00:48:40,083 - How big is that moon in comparison to ours 1136 00:48:40,116 --> 00:48:42,085 or something else that we can reference. 1137 00:48:42,118 --> 00:48:45,221 - Ooh! - It's about 150 miles across. 1138 00:48:45,254 --> 00:48:48,024 - Okay, my friendly face says that's it's about 1139 00:48:48,057 --> 00:48:49,559 150 miles across. 1140 00:48:49,592 --> 00:48:51,161 - So it's tiny. - It's tiny, yes. 1141 00:48:51,194 --> 00:48:55,298 - Thank you. - Yeah. 1142 00:48:55,331 --> 00:48:57,467 Okay, I'm getting some blue card questions from online, 1143 00:48:57,500 --> 00:48:58,935 but yeah? 1144 00:48:58,968 --> 00:49:02,305 - So as Cassini gets extended 1145 00:49:02,338 --> 00:49:06,276 over all these years, does it have an arc? 1146 00:49:06,309 --> 00:49:08,912 Like, did you know you were going to dive into the rings 1147 00:49:08,945 --> 00:49:10,981 this-- you know, all these years later as the mantle 1148 00:49:11,014 --> 00:49:14,217 gets passed, they're making up new missions as they're 1149 00:49:14,250 --> 00:49:16,219 seeing what kind of science they're gathering? 1150 00:49:16,252 --> 00:49:17,554 Could you talk a little bit about that? 1151 00:49:17,587 --> 00:49:22,525 - Yeah, so, I think it was 2008 or 2009 when we first thought 1152 00:49:22,558 --> 00:49:26,463 of doing this Grand Finale, so, you know, 1153 00:49:26,496 --> 00:49:28,198 eight or nine years before it. 1154 00:49:28,231 --> 00:49:30,367 As far as how Cassini kept getting extended, 1155 00:49:30,400 --> 00:49:32,435 we would submit a proposal 1156 00:49:32,468 --> 00:49:35,438 and go through a review process every two years. 1157 00:49:35,471 --> 00:49:37,874 And that would say, "Hey, here's what we're doing. 1158 00:49:37,907 --> 00:49:38,775 "Here's our status. 1159 00:49:38,808 --> 00:49:40,010 "Here's all this great stuff we did. 1160 00:49:40,043 --> 00:49:41,077 "And if you give us this much more money, 1161 00:49:41,110 --> 00:49:42,779 "here's this much more great stuff 1162 00:49:42,812 --> 00:49:44,914 "that we think we're going to be able to do." 1163 00:49:44,947 --> 00:49:46,950 And so it was sort of on this rolling two-year basis 1164 00:49:46,983 --> 00:49:48,718 that we were able to try and plan out 1165 00:49:48,751 --> 00:49:51,021 what the next two years would be. 1166 00:49:51,054 --> 00:49:52,155 - Thank you. 1167 00:49:52,188 --> 00:49:54,424 I'm just in awe of what humans can do. 1168 00:49:54,457 --> 00:49:55,725 So thank you. - Yeah. 1169 00:49:55,758 --> 00:50:02,198 [laughter] 1170 00:50:02,231 --> 00:50:04,134 - Okay, so now we have questions from online. 1171 00:50:04,167 --> 00:50:07,303 So this one's from YouTube from OneHeart. 1172 00:50:07,336 --> 00:50:13,376 "How small could Cassini be made with today's technology?" 1173 00:50:13,409 --> 00:50:15,712 Actually interestingly, I don't think it could be made 1174 00:50:15,745 --> 00:50:18,615 too much smaller. 1175 00:50:18,648 --> 00:50:20,316 Yeah, that graphic that I showed you where it was 1176 00:50:20,349 --> 00:50:23,586 filled up with propellant, that wasn't accurate, 1177 00:50:23,619 --> 00:50:25,021 but it was a lot closer to accurate 1178 00:50:25,054 --> 00:50:27,157 than you may think it was. 1179 00:50:27,190 --> 00:50:30,226 Most of that spacecraft body that you see there 1180 00:50:30,259 --> 00:50:31,928 is filled with fuel. 1181 00:50:31,961 --> 00:50:33,730 And so that's really where it gets its size. 1182 00:50:33,763 --> 00:50:35,031 The other thing that sizes it 1183 00:50:35,064 --> 00:50:37,700 I'd say is the antenna up on top, 1184 00:50:37,733 --> 00:50:40,403 and Saturn hasn't gotten any closer to Earth as far as 1185 00:50:40,436 --> 00:50:43,706 I know, and so the antenna would need to be about 1186 00:50:43,739 --> 00:50:45,642 the same size in order to communicate with Earth. 1187 00:50:45,675 --> 00:50:47,911 So the part that would get smaller, if you look at 1188 00:50:47,944 --> 00:50:50,480 the spacecraft, there's a ring going around the top, 1189 00:50:50,513 --> 00:50:52,515 below the antenna, but above the probe. 1190 00:50:52,548 --> 00:50:54,551 That's where all our electronics are. 1191 00:50:54,584 --> 00:50:59,556 And those could probably get a little bit smaller. 1192 00:50:59,589 --> 00:51:01,791 Okay, yes, taking them from-- here we go. 1193 00:51:01,824 --> 00:51:04,861 Okay, also from YouTube, from AstronomyNation. 1194 00:51:04,894 --> 00:51:08,198 "Was the contamination of Titan by the Huygens probe 1195 00:51:08,231 --> 00:51:09,299 "taken into consideration." 1196 00:51:09,332 --> 00:51:13,069 Yes, so we knew that the Huygens probe 1197 00:51:13,102 --> 00:51:15,605 was going to Titan. 1198 00:51:15,638 --> 00:51:18,174 And so we built it with that in mind. 1199 00:51:18,207 --> 00:51:21,177 And so it went through a much more stringent 1200 00:51:21,210 --> 00:51:23,546 planetary protection process than the orbiter did. 1201 00:51:23,579 --> 00:51:26,716 And so that made it safe to go down to Titan, 1202 00:51:26,749 --> 00:51:28,818 but Cassini-- it's very expensive to do that. 1203 00:51:28,851 --> 00:51:31,020 And so Cassini was not built to those standards. 1204 00:51:31,053 --> 00:51:32,722 It wasn't going to go down to Titan. 1205 00:51:32,755 --> 00:51:38,094 And so that's why it could not be crashed on Titan. 1206 00:51:38,127 --> 00:51:43,166 Okay... 1207 00:51:43,199 --> 00:51:45,668 Okay, YouTube from Eric Lamplanta, "What was 1208 00:51:45,701 --> 00:51:50,840 "the biggest surprise that came out of Cassini's discoveries?" 1209 00:51:50,873 --> 00:51:52,709 I think this is an opinion, but in my opinion, 1210 00:51:52,742 --> 00:51:54,577 the biggest surprise was Enceladus. 1211 00:51:54,610 --> 00:51:57,847 I don't think anybody expected to find 1212 00:51:57,880 --> 00:51:59,782 this global subsurface ocean 1213 00:51:59,815 --> 00:52:01,985 that actually had, like, activity where you have 1214 00:52:02,018 --> 00:52:04,087 these jets coming out of the south pole, 1215 00:52:04,120 --> 00:52:05,221 and then we later find out, 1216 00:52:05,254 --> 00:52:07,123 hey, it's in contact with a rocky core. 1217 00:52:07,156 --> 00:52:08,691 Oh, and guess what? 1218 00:52:08,724 --> 00:52:10,827 We think there's actually evidence that there could be 1219 00:52:10,860 --> 00:52:14,564 the chemicals in that ocean necessary to support life. 1220 00:52:14,597 --> 00:52:17,700 And so that is definitely by far the biggest surprise. 1221 00:52:17,733 --> 00:52:22,505 Also because Enceladus at Saturn is very much 1222 00:52:22,538 --> 00:52:24,274 like Europa at Jupiter. 1223 00:52:24,307 --> 00:52:28,311 It's almost identical in that it's an icy moon 1224 00:52:28,344 --> 00:52:30,680 with a subsurface ocean in contact with a rocky core. 1225 00:52:30,713 --> 00:52:34,284 And discovering two of these in one solar system means that 1226 00:52:34,317 --> 00:52:37,120 these potentially habitable environments outside 1227 00:52:37,153 --> 00:52:41,391 of the sun's habitable zone is-- are not rare. 1228 00:52:41,424 --> 00:52:43,660 If you have it twice in one solar system, it means 1229 00:52:43,693 --> 00:52:45,962 in the whole universe it could be occurring a lot. 1230 00:52:45,995 --> 00:52:47,697 So it really increases the probability 1231 00:52:47,730 --> 00:52:54,637 that we could someday find life beyond Earth. 1232 00:52:54,670 --> 00:52:58,241 Okay, on YouTube from Claudia. 1233 00:52:58,274 --> 00:53:02,078 "What kind of-- 1234 00:53:02,111 --> 00:53:04,547 "Oh, what kind of cameras were on Cassini?" 1235 00:53:04,580 --> 00:53:08,818 So the cameras on Cassini were basically telescopes. 1236 00:53:08,851 --> 00:53:10,887 So, like I said, that one picture of Enceladus 1237 00:53:10,920 --> 00:53:12,889 was taken from half a million miles away. 1238 00:53:12,922 --> 00:53:16,626 So the cameras are digital cameras. 1239 00:53:16,659 --> 00:53:19,562 The highest resolution one is what? 1240 00:53:19,595 --> 00:53:20,797 One megapixel? - Yeah. 1241 00:53:20,830 --> 00:53:23,733 - Yeah, one megapixel camera. It was launched in '97. 1242 00:53:23,766 --> 00:53:25,034 Give us a break. 1243 00:53:25,067 --> 00:53:27,170 [laughter] 1244 00:53:27,203 --> 00:53:29,405 - Operates in the freezing cold. 1245 00:53:29,438 --> 00:53:31,674 - But then it has this huge lens put on it so that 1246 00:53:31,707 --> 00:53:33,576 the fields of view are really, really small. 1247 00:53:33,609 --> 00:53:35,411 Like you could not use them in this room. 1248 00:53:35,444 --> 00:53:37,680 It'd be like using binoculars in your bedroom. 1249 00:53:37,713 --> 00:53:39,349 You're not going to see a whole lot. 1250 00:53:39,382 --> 00:53:40,383 So yeah, so that's what it was. 1251 00:53:40,416 --> 00:53:44,654 It was a one megapixel telescope. 1252 00:53:44,687 --> 00:53:48,858 All right, any other questions from the room, from online? 1253 00:53:48,891 --> 00:53:50,793 Oh, I'll repeat it, yes. 1254 00:53:50,826 --> 00:53:55,031 - What's the baud rate that data was transmitted at? 1255 00:53:55,064 --> 00:53:58,167 - Okay, so he asked what the baud rate or the data rate 1256 00:53:58,200 --> 00:54:01,037 that Cassini was able to transmit at. 1257 00:54:01,070 --> 00:54:03,439 And again, I'm going to look at my friendly face. 1258 00:54:03,472 --> 00:54:04,707 [laughter] 1259 00:54:04,740 --> 00:54:06,509 - Look at your other friend. 1260 00:54:06,542 --> 00:54:07,577 That one back there. 1261 00:54:07,610 --> 00:54:09,145 - Oh, yeah, yeah, I have another friendly face. 1262 00:54:09,178 --> 00:54:14,550 You want to come to the microphone? 1263 00:54:14,583 --> 00:54:16,152 - So the highest data rate we could transmit at 1264 00:54:16,185 --> 00:54:20,156 was 142,000 bits per second. 1265 00:54:20,189 --> 00:54:21,758 From a billion miles away. 1266 00:54:21,791 --> 00:54:22,692 - Yeah. 1267 00:54:22,725 --> 00:54:23,693 [laughter] 1268 00:54:23,726 --> 00:54:24,827 - It may not seem like fast, but from 1269 00:54:24,860 --> 00:54:30,733 a billion miles away that's doing pretty good. 1270 00:54:30,766 --> 00:54:32,201 - Okay, if there are no more questions, 1271 00:54:32,234 --> 00:54:33,569 you're still welcome to stay here. 1272 00:54:33,602 --> 00:54:34,671 You'll be warm and dry. 1273 00:54:34,704 --> 00:54:36,973 [laughter] 1274 00:54:37,006 --> 00:54:38,608 [applause] 1275 00:54:38,641 --> 00:54:44,180 Oh! 1276 00:54:44,213 --> 00:54:46,849 - How big was your Cassini team? 1277 00:54:46,882 --> 00:54:50,053 And I'm talking your dates when you were planner? 1278 00:54:50,086 --> 00:54:51,254 How many people? 1279 00:54:51,287 --> 00:54:54,157 - When I was the planner, I think we had 1280 00:54:54,190 --> 00:54:56,526 50 to 100 part-time people. 1281 00:54:56,559 --> 00:55:00,096 We didn't have a whole lot of full time. 1282 00:55:00,129 --> 00:55:02,632 - Well, there's 250 scientists. 1283 00:55:02,665 --> 00:55:04,100 - Oh, sure, yeah, sorry. 1284 00:55:04,133 --> 00:55:06,703 [laughter] 1285 00:55:06,736 --> 00:55:07,704 - Those other people. 1286 00:55:07,737 --> 00:55:10,206 - Yes, the project people at JPL, sorry. 1287 00:55:10,239 --> 00:55:12,208 The project people at JPL. 1288 00:55:12,241 --> 00:55:14,077 I believe there are about 100 part-timers that 1289 00:55:14,110 --> 00:55:20,283 all fit into about 50 full time equivalents. 1290 00:55:20,316 --> 00:55:22,018 All right, you can clap again, if you want. 1291 00:55:22,051 --> 00:55:32,729 [applause] 1292 00:55:32,762 --> 00:55:36,499 - Outstanding, Erick.