1 00:00:00,000 --> 00:00:09,000 Throughout humankind's early history, the quest for greater knowledge and understanding 2 00:00:09,000 --> 00:00:11,560 fueled the need for exploration. 3 00:00:11,560 --> 00:00:16,720 For centuries, the vehicle most early explorers used to achieve this exploration was a ship 4 00:00:16,720 --> 00:00:18,240 with sails. 5 00:00:18,240 --> 00:00:23,280 But because these ships depended on wind pushing against the sails for forward motion, they 6 00:00:23,280 --> 00:00:27,520 were generally very slow, unpredictable, and often very dangerous. 7 00:00:27,720 --> 00:00:32,800 Today, with the multitude of ways that humans now possess to travel, the sail, with all 8 00:00:32,800 --> 00:00:38,040 of its limitations, has been relegated to recreational status rather than a serious 9 00:00:38,040 --> 00:00:40,360 tool for exploration. 10 00:00:40,360 --> 00:00:43,720 But a new idea might change the way we think about sails. 11 00:00:43,720 --> 00:00:48,960 NASA researchers are actually developing a new type of sail that will use the sun's light 12 00:00:48,960 --> 00:00:51,860 to propel spacecraft deep into space. 13 00:00:51,860 --> 00:00:56,800 These solar sails are so promising that someday they may replace slower, more costly propulsion 14 00:00:56,800 --> 00:00:59,100 systems for deep space exploration. 15 00:00:59,100 --> 00:01:04,060 I spoke with Dr. Keith Belvin at NASA Langley Research Center to find out more. 16 00:01:04,060 --> 00:01:07,020 The idea for solar sails has been around for a very long time. 17 00:01:07,020 --> 00:01:12,620 Maxwell, back in 1873, predicted the existence of solar pressure lights. 18 00:01:12,620 --> 00:01:16,540 So we've known about solar pressure for a long time. 19 00:01:16,540 --> 00:01:20,340 But it wasn't until recently that we were able to build solar sails with the lightweight 20 00:01:20,340 --> 00:01:22,700 materials and structures that are needed. 21 00:01:22,700 --> 00:01:24,940 Tell me about these lightweight materials and structures. 22 00:01:24,940 --> 00:01:25,940 How are they being used? 23 00:01:26,080 --> 00:01:30,160 Well, the key to building a solar sail is, of course, to make it very large and very 24 00:01:30,160 --> 00:01:31,940 lightweight. 25 00:01:31,940 --> 00:01:38,240 For a useful solar sail, it has to have a weight of less than 10 grams per square meter. 26 00:01:38,240 --> 00:01:42,980 For example, copier paper has a weight of 70 grams per square meter. 27 00:01:42,980 --> 00:01:46,400 So we're talking about some materials that are much lighter than that. 28 00:01:46,400 --> 00:01:50,860 One of the things that NASA's done over the last decade is to work on materials that can 29 00:01:50,860 --> 00:01:53,540 be processed to just a couple microns. 30 00:01:53,540 --> 00:01:56,860 That's a couple millionths of a meter thick. 31 00:01:56,860 --> 00:02:01,700 And these lightweight, thin materials then are made space-durable so they can withstand 32 00:02:01,700 --> 00:02:04,340 the radiation and temperatures of space. 33 00:02:04,340 --> 00:02:07,300 Dr. Belvin, tell me how a solar sail works. 34 00:02:07,300 --> 00:02:12,020 The basic principle is much like a ship on the sea that uses sails to capture the wind. 35 00:02:12,020 --> 00:02:17,100 The sun is constantly emitting light, or photons, in all directions. 36 00:02:17,220 --> 00:02:22,700 Since the photons have mass and are in motion, their momentum produces a pressure when reflected 37 00:02:22,700 --> 00:02:23,700 by a surface. 38 00:02:23,700 --> 00:02:30,180 When a spacecraft uses a solar sail for propulsion, the sail's reflective surface transfers a 39 00:02:30,180 --> 00:02:35,640 continuous force from the photons to propel the craft through space, much like a sailing 40 00:02:35,640 --> 00:02:39,020 ship uses wind to push it across the water. 41 00:02:39,020 --> 00:02:43,860 Since the pressure being emitted from the photons is very low, the force is small. 42 00:02:43,860 --> 00:02:49,220 And because the sail will have a constant source of energy, it is continuously accelerating 43 00:02:49,220 --> 00:02:53,980 and can reach speeds upwards of 155,000 miles per hour. 44 00:02:53,980 --> 00:02:59,260 This speed could cut years off travel time during long-duration interstellar flights. 45 00:02:59,260 --> 00:03:04,460 In addition, the constant propulsive force provided by the sun's light allows the spacecraft 46 00:03:04,460 --> 00:03:08,860 to travel in orbits that are not affordable using conventional propulsion. 47 00:03:08,860 --> 00:03:11,620 So can solar sails be used on all types of missions? 48 00:03:11,780 --> 00:03:17,060 Well, in addition to solar sails having to be lightweight for various missions, the spacecraft 49 00:03:17,060 --> 00:03:19,540 they're propelling has to be very lightweight. 50 00:03:19,540 --> 00:03:24,460 But there are many missions where, with the miniaturization of electronics, that the spacecraft's 51 00:03:24,460 --> 00:03:27,560 science sensors are very small and lightweight. 52 00:03:27,560 --> 00:03:32,020 And those systems are very amenable to being propelled by a solar sail. 53 00:03:32,020 --> 00:03:37,140 For example, we're looking at missions in the future where we do interstellar transfer 54 00:03:37,140 --> 00:03:40,900 of science instruments using solar sails. 55 00:03:40,900 --> 00:03:44,900 So do we see solar sails only being used in deep space? 56 00:03:44,900 --> 00:03:50,700 Well, there are missions where solar sails can be used close to the Earth's orbit. 57 00:03:50,700 --> 00:03:54,260 They don't all have to be long-duration, interstellar-type missions. 58 00:03:54,260 --> 00:03:59,420 The constant acceleration that a solar sail produces gives it an orbit trajectory that 59 00:03:59,420 --> 00:04:02,340 is not achievable by some other means. 60 00:04:02,340 --> 00:04:09,220 For example, we can fly a science payload to measure the magnetic storms emanating from 61 00:04:09,220 --> 00:04:10,220 the sun. 62 00:04:10,220 --> 00:04:13,220 How do you deploy such a large structure into space? 63 00:04:13,220 --> 00:04:16,220 To deploy a solar sail in space is quite a challenge. 64 00:04:16,220 --> 00:04:22,020 First of all, the sail has to be packaged in a small size to fit into the launch vehicles. 65 00:04:22,020 --> 00:04:27,980 Near-term sail missions are on the order of 70 meters to up to 150 meters in size. 66 00:04:27,980 --> 00:04:32,400 And so it's a real challenge to package those tightly and then deploy in space. 67 00:04:32,400 --> 00:04:36,100 Two aspects probably are most important for deploying a solar sail. 68 00:04:36,100 --> 00:04:40,460 The first is deploying the booms that hold the membranes in place. 69 00:04:40,460 --> 00:04:46,060 We're using inflation to push the booms out and to the right location. 70 00:04:46,060 --> 00:04:48,960 And then we cool the booms to rigidize them. 71 00:04:48,960 --> 00:04:54,400 The second aspect is deploying the sail, the thin-film membranes that we've talked about. 72 00:04:54,400 --> 00:04:58,420 Those will incorporate ripstop so that if there's a small tear, it doesn't propagate 73 00:04:58,420 --> 00:04:59,420 very far. 74 00:04:59,420 --> 00:05:04,980 In addition, we have to deploy those so that we don't affect the sail's reflective performance. 75 00:05:04,980 --> 00:05:09,100 And so special measures are taken to maintain the integrity of that sail. 76 00:05:09,100 --> 00:05:10,820 What is the future of this program? 77 00:05:10,820 --> 00:05:15,140 I would say within the next dozen years or so, solar sails will be used routinely to 78 00:05:15,140 --> 00:05:17,300 propel spacecraft. 79 00:05:17,300 --> 00:05:22,260 Continual improvements in the sail technology will allow them to be used for extreme environments 80 00:05:22,260 --> 00:05:24,140 like near-sun missions. 81 00:05:24,140 --> 00:05:29,140 Over the next 20 years, most importantly, we'll have the technology in hand to do interstellar 82 00:05:29,140 --> 00:05:30,980 missions. 83 00:05:30,980 --> 00:05:35,820 These are kilometer-sized solar sails that weigh only one to two grams per square meter. 84 00:05:35,820 --> 00:05:40,420 The technology being developed today at NASA is going to enable us to unlock a lot of the 85 00:05:40,420 --> 00:05:42,380 secrets of the universe. 86 00:05:42,380 --> 00:05:47,500 Not only will we be able to look at distant places using telescopes, we'll actually be 87 00:05:47,500 --> 00:05:53,260 able to send science instruments to some of those locations using solar sails. 88 00:05:53,260 --> 00:05:57,260 Did you know that the inspiration for solar sail technology came from the 17th century 89 00:05:57,260 --> 00:05:59,500 astronomer Johannes Kepler? 90 00:05:59,500 --> 00:06:03,780 Kepler deduced that winds blew objects around in space after he observed comet tails blown 91 00:06:03,780 --> 00:06:06,860 by what appeared to be a solar breeze. 92 00:06:06,860 --> 00:06:10,940 Kepler suggested that eventually ships might navigate through space using sails that could 93 00:06:10,940 --> 00:06:13,500 catch this wind.