Opening new worlds with space navigation

Transcript

I consider it to be the frontier of our generation. High above the clouds, the International Space Station orbits the Earth every 90 minutes. It serves as a reminder of how far we’ve come. It orbits the very same Earth that we spent centuries navigating, discovering, and mapping. And the mapping continues today in the outer solar system.

So how do we get to this point? We’ve mapped our own world. Now we’re moving on the map other distant worlds beyond our own. I’d like to make the argument that it’s through navigation. Not necessarily the methods we use to navigate, but the precision with which we can navigate.

Navigation is all about building maps. More and more detailed maps that we can hand down to the next set of explorers so they can go explore more interesting places. So today, I’ll be talking about a story. It’s a story of building maps.

So let me take you back to 1492. The map of the world looked very different during that day than it does today. It included parts of Europe, North Africa, the Mediterranean. But beyond that was the unknown, it was left to the realm of imagination. It was full of monstrous creatures and exotic peoples and grand treasures.

And so around that time, Europeans for the first time were setting out to the open seas. They were attracted by the spice trade, trying to get to India to bring back these valuable spices to Europe. And while most of them were trying to go around the Horn of Africa to get there, Christopher Columbus came along and he had a very bold idea. He said, “I will go west. I will sail off the known map of the world into the darkness because I believe I will get to India through the West.”

So how did Columbus do this? Well, Columbus was a fair navigator of the day. He knew about the trade winds in the sea, and he knew how to use his senses to know it was going around, going on around him as he sailed in the open seas.

And he used a very primitive form of navigation called dead reckoning. And that form of navigation, if you know your heading, you know how fast you’re going along that heading, and you know the amount of time you spent going on that heading, you can log that along your travel and get a reasonable reconstruction of the path you’ve taken.

So what sort of instrumentation did Columbus have at his disposal during that day? Well, to determine the heading of the ship, he had your standard magnetic compass. Of course, during that day, the explorers were not aware that the magnetic north of the Earth actually differs from the true north, depending on what part of the globe you’re on.

This is my favorite one for determining the speed of the ship. The ship’s mate would pull a piece of driftwood, he would go off to the bow of the ship, he’d tie a rope around it, and he’d throw it overboard. And he’d begin chanting, and he would measure how many chants he could recite by the time this piece of wood would get to the back end of the boat. Based on the number of chants, that’s how fast the boat was going.

And last, time. Time is ever important, to keep track of our time. And so during that day they didn’t have any clocks, so what they used was a handy sand glass. And so you start the time like this, you turn over the sand glass, and every 30 minutes or so one of the shipmates would have to come up and turn it over and announce to the ship that he had turned over the sand glass and logged this, and this would go on for a multi-month journey.

So I don’t think I need to convince you that this was not the most precise way to navigate, and you can see that with the map that was built after Columbus returned from his voyages back to Europe. Columbus vastly underestimated the size of the Earth. He thought that he had reached Asia. He thought this was all one, part of one megacontinent. And what’s even more astounding is that even after his third voyage, Columbus believed that he had reached Japan when he was going around the island of Cuba. So that’s how far off he was.

So along came another explorer. His name was Amerigo Vespucci, he was from Portugal. He studied under Henry the Navigator in Portugal, and he saw what Columbus had done. He said, “Yes, I would like to do that as well.” But the difference was is that Vespucci was a cartographer. His profession was building maps. And so along the way, he was very curious about the path he was taking.

And so he had a few other tools at his disposal. He had a tool similar to this, it was called a quadrant, and you could use that to align it to the horizon. And of course, the ship was rocking back and forth, but they could make a reasonable estimate of the elevation of the sun in the sky above the horizon. And with that measurement, you could reasonably determine your latitude.

But the challenge of the day was determining longitude, and most sailors did this by measuring the amount of time they had traveled east or west through their time glass.

But Vespucci had a different idea. He brought along with him to South America this detailed log of the known planetary occultations, when planets would pass in front of each other, and he knew a very precise time when the moon was going to pass in front of Mars.

At that very precise time he looked up in the sky and he said, “Holy smokes, it’s not passing in front of the moon at this point, it’s three and a half degrees away. That means I’m very far to the West than what anyone ever thought it was before. This is a new land, a new continent.”

And so he went back to Europe and a new map was drafted up, and for the first time there was this new continent on the map, a continent we all live in today that’s called America, after Amerigo Vespucci, and that’s why it’s called America and not Colombia.

And so I hope I’ve driven my point home that precision drives capability. Our ability to navigate precisely directly drives our exploration capability to visit more and more interesting places.

So today, why do we need such ultra-high precision? Well, we’re going out into space, and it’s driven by the scale of space. We have destinations that are separated by hundreds of millions of kilometers. And you may be traveling hundreds of millions of kilometers to reach a destination that’s only a few kilometers wide. So what’s that like? That’s like heading out from Los Angeles to New York to find something the size of a quarter.

So how do we deal with this? Well, over the last few decades, the amount of computational power has increased exponentially, and electronics have miniaturized. So we have ever more precise instrumentation to use as we take our voyages to the outer solar system.

Here’s some examples. So for the, an upgrade to the handy-dandy compass of the day, we have the inertial stellar compass. It has a camera and it can look out at the starfield that it sees and it matches up that starfield with a star catalog that’s on board. Now combine that information with internal gyroscope data, kind of like what you have in your iPhone, and based on that it can get a very detailed orientation fix of how the spacecraft is oriented in space. This instrument can determine the orientation at all times down to a precision of less than a tenth of a degree.

Now for velocity, we have the tried-and-true deep space network. It’s an array of satellite dishes that we’ve been using since the Apollo era. It was built during Apollo and we’ve, over the last few decades, been getting it better and better by moving to higher-frequency bands and calibrating out systematic errors. So today we can send a signal up to a spacecraft and have it returned to us and we can measure the transmission time of that signal down to a precision of one nanosecond.

So to give you some perspective, Voyager 2 is our most distant spacecraft, it just passed beyond the edge of the solar system last year. And they can send a roundtrip signal that takes over 24 hours round-trip, they can measure that down to one nanosecond.

If we want to measure the velocity of the spacecraft, we can measure the Doppler shift through the changing velocity of the spacecraft in its orbit. We can measure that down to a tenth of a millimeter per second. So to give you perspective on that, a tenth of a millimeter is the width of the human hair. So very precise.

And lastly, for time, we have a new instrument called Deep Space Atomic Clock. For the first time we’re gonna have very stable atomic clocks onboard a spacecraft. This atomic clock you see behind me is stable to one nanosecond over a ten-day period. It does that by synchronizing the clock with the electronic transition frequency of mercury atoms onboard this clock. So we have very incredible clocks onboard our spacecraft. We can take a lot of computations that used to happen on the ground and move those up to the spacecraft, so it’s a very different way of navigating.

So I hope I convinced you now that we have immense precision now to venture out beyond our own world.

There’s another point I want to make. It’s the point that people think of space exploration is a very macro type of endeavor. But it’s both macro and micro because you do go out further than ever before, but once you get to your destination, you may have to navigate closer than ever before. So let me give you a few examples of that.

So as we approach an object out in the distant solar system, we’ll perform celestial navigation on the way in. So we’ll take a picture of this object and we’ll compare where the object is relative to the starfield around it. And that’ll give us a relative position fixed relative to this destination. Once we get even closer, we can map the shape of this object using stereo imagery. And then we can start to populate this object with landmarks. And as we orbit this object, we can track these landmarks to give us a very high position fix relative to this object.

There’s other devices we use. We use what’s called a lidar system, our laser ranging system. It’s very simple. We just take a laser beam and we send this pulse of energy down to the surface of an asteroid or comet, and it returns back up to us and we can get a measurement of the range of that surface down to a precision of 10 centimeters. And so not only can this instrument help us determine where we are relative to the surface using terrain-relative navigation, but we can also build a detailed topographic map of these objects in space.

So if you take all of these items I’ve talked about, if you take the deep space atomic clock, you take the laser range finder, you take the optical navigation, you put them all together, we can create a smarter spacecraft using algorithms onboard. We can do autonomous navigation, which is a smarter spacecraft that navigates itself. It determines where it is relative to its destination and it autonomously maneuvers to where it needs to go.

So why do we want this technology? Well, a major goal of ours is planetary landings. We want to land on new worlds. But it’s not just good enough to land. We want to land in very interesting places. It could be the difference between landing in Los Angeles and landing in the barren Mojave Desert. I think you all think that Los Angeles might be a better place to go explore.

A great example of this is the Mars Curiosity rover, which landed two years ago, and it didn’t just land in any plain in Mars, it landed inside the ring of Gale Crater within a footprint that was 12 miles by four miles. That’s how good we are today, but we can get better tomorrow. This was so good that we landed within driving distance of a very interesting mountain on Mars. And so that’s really the driver of all this.

So it’s all about building new maps. So let me give you a few examples of some maps that I’ve been a part of building. We’ve built a few comet maps, and these maps are built by very high velocity flybys. In the example I have behind me, which is the comet Hartley 2, we flew by this comet at a velocity of twelve kilometers per second. So we only saw the comet for a very few brief instances during this travel. But it went from being just this bright light in the sky with a tale of dust beyond it to being a very detailed world. We always thought of comets as just being round balls of dust, but it turned out that this comet was actually a bowling pin or peanut-shaped comet.

Not only that, but there was all this activity going on around it. It was spurting gases and materials from all different sorts of all different edges of this comet. And it turns out that these jets were jets of carbon dioxide or dry ice that were spurting out as the sun warmed it, and it was spurting out with the ice particles. And these ice particles were conglomerating together. And so it turns out that we observed and flew through the first recorded snowstorm in space. What’s really changed perceptions, you know, going to these places, really changed the perceptions. And so we had a full new map of this comet.

I’ve also been on an asteroid mission. This is the asteroid Vesta. It’s the second-largest asteroid in the asteroid belt. It’s about the size of California. And prior to visiting it with the Dawn spacecraft, the best map we had of this object was from the Hubble Space Telescope, a blurry image in the sky. But after visiting and orbiting for nine months, we had a full 3D topographic map of the surface, something that might be enough quality for Google Maps today.

In addition to that, you — we often think of maps as just topographic maps, but we are also able to build a gravity map by observing the tugs and pulls of the gravity field on the spacecraft as we orbited. And so the gravity map helped us understand the mineralogy below the surface of this asteroid. So we actually knew a lot more about it than just the surface, we could see below the surface.

So here’s a movie just showing the comet flyby, it’s happened a few brief instances, and then the great map of the comet of the asteroid Vesta, with the mineralogy down below the surface. So now that we have better maps, the next visitors to this place can find more and more interesting places to explore.

There’s other more interesting places we’d like to explore in the solar system. There’s several moons that harbor subsurface oceans. And so if we have more precise navigation in the future, we can go explore these oceans and map them out. Several of these oceans have geysers that are spurting up from the surface. We may want to fly through these geysers to sample the material within them. It’s thought there might be life in some of these oceans, and so this is what’s driving our future exploration.

So we built all these maps. But how do we get our maps back home? Back in Columbus’ day, he would sail back to Europe and he would report on what he found. But today we need to transmit all the information back home.

There is a new technology called laser communications. It’s basically sending information over laser beams instead of radio waves, and it promises to increase data rates in space by a factor of 1000. It’s like going from using a modem in space up to using DSL. And so if we use this, we’re able to get our information back and we get even more detailed high-definition maps back to the Earth in this method.

What you see behind me is the payload OPALS, was just arrived at the space station this month. In the coming weeks, we’re going to demonstrate laser communications using this payload. This animation here shows what we’re going to do. From our ground station, we’ll be firing a laser beam up at the space station. The payload will lock onto that laser beam to point back at the ground station and it will modulate a signal over that laser beam for transmission to the ground. It’ll be transmitting much higher data rates than available data rates using radio waves. So I hope I’ve convinced you that using precision can lead to greater exploration in the future.

You may not be aware, but next year is going to be a very important year in the year of exploration mapping. The dwarf planet Pluto, which used to be a planet, for the first time will be mapped out. We’ve never seen this object up close, which really surprised a lot of people. And there’s a spacecraft on its way right now that will be mapping it next year. It was launched in 2006 and takes ten years to get out there. And so next year, look for the news, you’ll see Pluto for the first time.

In addition, the largest object in the asteroid belt is a dwarf planet called Ceres. And the Dawn spacecraft will also reach Ceres next year. Now, Ceres is a very interesting planet because they think that Ceres has more water on it than all of the freshwater on Earth, which again would really change the perceptions.

And so I’m very excited about the mapping going forward and how we continue to navigate through our, through deep space. So lastly, I want to return to my final point, that through navigation precision, we can build ever more detailed maps. And as we build more and more detailed maps, it can only lead to our prosperity. Thank you. And cheers.