00:00Imagine riding aboard a spacecraft, pushing toward the very edge of our solar system.
00:06You check your navigation console, and there is absolutely no signal.
00:11Earth's GPS network is billions of miles behind you.
00:15This massive Earth-based radio dish is part of the deep space network.
00:20For over six decades, every single probe we have sent into the dark
00:25has relied on this localized hardware to keep us connected.
00:29These antennas fire powerful radio signals across the solar system to a traveling probe.
00:35By measuring exactly how long it takes for that ping to bounce back to the dish,
00:41ground control calculates the spacecraft's exact position.
00:44This remote control approach works well enough for local flights to the Moon or Mars.
00:50But as we push deeper into the void,
00:52it creates a dangerous tether that prevents our ships from navigating themselves.
00:57The problem comes down to the physical speed limit of the universe.
01:02Radio signals travel at the speed of light.
01:05That sounds incredibly fast, until you start measuring distance on a cosmic scale.
01:12When you look at an isolated planet like Neptune,
01:16it takes a message from Earth over four hours just to reach it.
01:20If a probe is heading toward the nearest neighboring star system,
01:25that same radio ping takes more than four years.
01:29In this diagram, you can see how dangerous that delay becomes.
01:33As a radio ping crawls slowly toward a fast-moving spacecraft,
01:38the ship's actual position becomes an expanding cone of guesswork.
01:43By the time a course correction finally arrives,
01:47the probe could already be thousands of miles off target.
01:51To survive out there, spacecraft have to cut the cord entirely.
01:55To build a truly independent system, we can borrow the math right out of your pocket.
02:02This 3D geometry shows how terrestrial GPS works.
02:07Your phone calculates its location by measuring signal arrival times from four intersecting satellites.
02:14Deep space probes need this system,
02:17but we obviously cannot build a satellite network across the Milky Way.
02:21These bright, rhythmic slashes are millisecond pulsars.
02:27They are the crushed, super-dense cores of dead stars
02:31that rapidly sweep powerful beams of X-ray energy across the void
02:36hundreds of times every single second.
02:39Because an entire giant star's mass is compressed into a sphere roughly the size of a city,
02:46their rotation is incredibly stable.
02:49The arrival times of their pulses can be predicted down to the nanosecond,
02:54making them the most reliable atomic clocks in nature.
02:59By mapping these permanent, perfectly timed beacons,
03:02we can take the localized math of GPS and scale it up to cover the entire universe.
03:09Spacecraft will tap into this network using a technology called X-ray Pulsar-Based Navigation, or XNAV.
03:16Here is how it functions in flight.
03:19An onboard detector tracks pulse arrival times from four distant pulsars.
03:24Moving toward one, pulses arrive a fraction of a millisecond early.
03:30Drifting away, they arrive late.
03:33Cross-referencing these times against a galactic map
03:37lets the ship instantly calculate its exact 3D position.
03:42It is a totally self-contained, passive calculation.
03:46The ship never has to send a signal.
03:49And it never has to wait for Earth to tell it where to go.
03:53This concept has already moved out of the theoretical physics phase and into actual orbit.
04:00In 2017, NASA proved it works with an experiment called Sextant.
04:06Mounted right here on the exterior of the International Space Station is an X-ray telescope called NICER.
04:14During the test, engineers instructed this instrument to track five specific millisecond pulsars.
04:20As the station zipped around the Earth at 17,500 miles per hour,
04:27the system used those pulsar beams to actively calculate its own location in real time,
04:33staying accurate to within just a few kilometers.
04:36That successful test marked the very first time humanity navigated a spacecraft using cosmic objects located entirely outside our own
04:49solar system.
04:50As our X-ray detectors become smaller, lighter, and more sensitive,
04:56XNAV is positioned to become the standard guidance system for all deep space missions.
05:01We will use it to pilot crewed habitats to Mars and guide robotic probes all the way to Alpha Centauri.
05:10There is something highly poetic about the mechanics of this system.
05:15The deadest, most extreme stellar remnants in the cosmos have become the most vital map we possess.
05:22By listening to the steady rhythm of these cosmic lighthouses, tomorrow's starships can finally cut the tether to Earth,
05:31venturing into the interstellar dark without ever losing their way.
05:36The deadest, most extreme
05:36The deadest, most extreme
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