Как Спутники Летают Вокруг Земли?（原声文稿）

Right over your head, the International Space Station is hurtling past It weighs about 420 tons, is roughly a football field long, and people live and work inside This station is constantly falling toward Earth It's been falling nonstop for over 25 years, yet never actually fallen What saves it isn't altitude, it's speed If it suddenly stopped in orbit, it would crash within minutes And it's not just the station.

Thousands of satellites circle Earth Every single one is falling right now too Today we'll talk about the solar storm of 2022 And why it dragged nearly 40 new satellites out of orbit You'll also learn that in space, to catch up with another spacecraft You don't speed up, you brake Plus, which year the station will be taken out of the sky All of it hinges on one simple principle After this video, you can explain it to anyone in half a minute If you ask people why astronauts float inside the station Most will confidently say, there's no gravity in space That's one of the most common space misconceptions Busting it is easy, because gravity weakens with altitude far slower than you'd think The International Space Station flies at about 400 kilometers up Gravity there is still about ninety percent Same as what you're feeling right now If we built a tower straight to the station and climbed it with a scale A 70-kilogram person would show about 62 on it So gravity in orbit hasn't vanished at all Weightlessness has another cause, and it's way more interesting than most people think Astronauts float because they're constantly falling They fall along with the whole station, same speed, same direction When you and the floor beneath you fall together The floor stops pressing on you, and your body feels no weight Even though gravity is still working at full force Anyone who's ridden an elevator has felt a weaker version of this An elevator lurches downward, and for a moment your body feels clearly lighter Drop tower rides give you a much stronger version The seat lifts you to the top of the tower Then it lets go, and you free-fall for several seconds In those seconds, riders feel almost exactly like astronauts in orbit Except the astronauts' fall lasts for months Astronaut training uses the same principle Special planes fly high arcs, like a thrown ball At the top of the arc, the plane is basically falling along with everything inside People in the cabin float freely for twenty to twenty-five seconds Then the pilot levels out, climbs again, and repeats One flight can do dozens of these parabolas The space station is in this state all the time Except its fall doesn't end after half a minute—it goes on around the clock, year after year Engineers can create similar conditions on the ground too NASA has a deep air-evacuated shaft in Ohio An instrument capsule drops 132 meters down it That fall lasts just over five seconds Scientists use it to check how liquids, flames, and machines behave in weightlessness By the way, experts call this microgravity, not weightlessness Because with equipment running and people moving, there are always tiny vibrations A hundred kilometers is usually taken as the boundary of space The space station orbits at about four hundred A car on the highway would cover that in about four hours Airliners usually cruise at ten to eleven kilometers The space station is only about forty times higher—which is close, by space standards So the biggest challenge of spaceflight isn't getting high—it's staying up there without falling To see how satellites and space stations pull that off we first need to figure out what falling actually means Best to start with a ball Everyone's thrown one in the yard—it follows the same rules as a satellite Just let go, and the ball drops straight down Throw it forward, and it flies a few meters in an arc before landing anyway The harder you throw, the farther it lands Same with a garden hose—the higher the pressure, the farther the water shoots Here's a key point physicists have verified many times However fast you move forward, it doesn't affect how fast you fall Ignoring air resistance, drop one ball straight down and throw another horizontally at the same moment—they hit the ground together The second one just travels farther In the first second of falling, anything drops about five meters Whether it's sitting still or racing forward—it's the same Now a second detail we run into every day but rarely notice The ground isn't flat—it curves gently Because of that curve, for every eight kilometers you go the ground dips about five meters below a straight line Say something flies incredibly fast—eight kilometers per second In that same second, it falls 5 meters as usual But the ground under those 8 kilometers also curves down 5 meters So its height above the ground is exactly the same as a second earlier It falls every second, but the ground keeps dodging downward So it keeps missing the Earth, circling around it That's an orbit.

A satellite in orbit isn't hovering—it's falling all the time It just never hits the ground Isaac Newton thought up this experiment long ago Mount a cannon on a very tall peak and fire horizontally, harder and harder A weak shot lands nearby, a strong one flies past the horizon At just the right speed, the cannonball circles the Earth and flies back over the mountaintop from the other side It has to skim right above the ground With no air resistance, that speed is about 7.9 kilometers per second That's roughly 23 times the speed of sound For comparison: A commercial airliner flies at about 900 kilometers per hour Reaching orbit takes more than 30 times that speed This is called the first cosmic velocity Any slower, the path sooner or later meets the ground, and the thing falls A bit faster, it doesn't fly away—it takes an elliptical orbit Close to Earth on one side, far on the other The International Space Station's orbit isn't a perfect circle either Its highest and lowest points differ by a few kilometers Only at about 11.2 kilometers per second Can gravity no longer pull it back It leaves Earth forever But you can't fly that close to the ground Because dense air would slow a craft down And heat it red-hot.

That's why satellites go up hundreds of kilometers The biggest surprise is comparing satellites at different heights Because here the rule works in reverse Seems like the higher you fly, the faster you go?

Actually, the farther out a satellite, the slower it flies Because the farther from Earth's center, the weaker gravity gets Double the distance, and only a quarter of the gravity remains The weaker the gravity, the less speed you need Plus, one loop around Earth up high is a much longer trip The International Space Station sits at about 400 kilometers up Its speed is about 7.7 kilometers per second That's about 28,000 kilometers per hour It orbits Earth in about ninety-two minutes So in a day you see sixteen sunrises—and sixteen sunsets Each orbit it flies about forty-two thousand five hundred kilometers A little longer than the equator Orbital speed has nothing to do with weight A big space station and a small wrench fly at the same speed at the same altitude So when astronauts step outside They fly right along with the station—though thousands of times lighter The safety tether is just for accidental collisions Much higher up—about twenty thousand two hundred kilometers That's where GPS navigation satellites are—built and maintained by the United States They travel about three point nine kilometers per second One orbit takes almost exactly half a day About eleven hours fifty-eight minutes These satellites are spread across six orbits, evenly spaced around Earth So from any point on Earth you can see several satellites at once Europe's Galileo system is similar—at about twenty-three thousand kilometers up Many phones can pick up signals from several systems at once Higher still, thirty-five thousand seven hundred eighty-six kilometers above the equator There's a special geosynchronous orbit—satellites there travel about three kilometers per second An orbit there takes twenty-three hours fifty-six minutes That's how long Earth takes to rotate relative to the stars So the satellite flies in sync with Earth—and seen from the ground It seems motionless, hanging over the same spot on the equator That's why home satellite dishes only need to be pointed once In the northern hemisphere they almost all face south All satellites like this must hover above the equator So they line up in a thin chain around Earth Positions on that chain are coordinated in advance by the ITU So neighboring satellites don't interfere with each other's signals The farthest and most famous satellite is the Moon On average it's three hundred eighty-four thousand kilometers away, moving at only about one kilometer per second The Moon takes a bit over twenty-seven days to circle Earth—and just like the space station It's always falling, yet never hits the ground The key to a rocket isn't flying high But accelerating sideways to extreme speed—that shapes its structure and trajectory To reach low orbit, a rocket has to accelerate to about nine point four kilometers per second in total Orbital speed itself is under eight kilometers per second The extra is spent fighting gravity during the climb Plus pushing through the drag of the thick lower atmosphere So the rocket only flies straight up for the first few seconds To get off the launch pad and punch through the thick air near the ground as fast as possible Then it starts tilting slowly toward the horizontal Earth's gravity naturally bends it into an arc — this is called a gravity turn By the time the engines cut off The rocket is already flying almost parallel to the ground In long-exposure launch photos, the light trail bends into a clearly visible arc About a minute after liftoff, the rocket hits its most intense phase Speed is high, air is still dense — the vehicle takes the most stress here In this stretch, the engines often throttle back slightly Easing the load on the structure, then going full power once the air thins out Reaching that kind of speed takes a huge amount of fuel In modern rockets, fuel makes up about ninety percent of liftoff weight For example, the Falcon 9 weighs about five hundred fifty tons at liftoff And can send about twenty tons to low orbit That's just a small fraction of its own weight Many rockets use refined kerosene as fuel, with liquid oxygen as the oxidizer Liquid oxygen only stays liquid at around minus one hundred eighty-three degrees Here's the tricky part Fuel doesn't just push the payload — it has to push itself too So every extra kilometer per second takes far more fuel The fix is staging — dropping empty shells and heavy engines along the way No carrying dead weight all the way to orbit Falcon 9's first stage separates after about two and a half minutes The second stage uses one engine to speed up for another six minutes or so After separation, the first stage flips around Fires its own engines and lands back on the ground or a sea platform, ready to fly again Launch direction matters too — Earth spins from west to east Launching that way gives you speed for free At the equator, the ground spins at about four hundred sixty-five meters per second The Florida launch site gets about four hundred So launch sites are built as close to the equator as possible For example, European rockets launch from French Guiana That's about five hundred kilometers from the equator On the Atlantic coast, rockets fly straight out over open sea Finally, the rocket usually enters an elliptical orbit first At the highest point, the engines fire once more Circularizing the orbit and raising the perigee above the atmosphere Once in orbit, some things can really mess with your head Even if you know your physics — because flying in space is nothing like driving Fire the engine along the direction of flight The spacecraft doesn't just speed up—it climbs, clearly higher half an orbit later But the higher you go, the slower you move So the accelerated spacecraft ends up in a higher orbit, yet slower Slower than before the burn If you slow down, the spacecraft drops to a lower orbit Shorter orbit, faster speed—it overtakes everything flying higher This is the greatest paradox of spaceflight maneuvering To catch up with a station ahead in the same orbit, you must first slow down and drop lower It's like a running track The inner-lane runner finishes a lap faster, because the lap is shorter Except in orbit, the inner lane is simply faster So spacecraft bound for the International Space Station enter a lower orbit after launch and slowly catch up over several laps When the distance is right, the spacecraft fires precisely twice The first burn raises the apogee, the second circularizes the orbit at the target altitude This fuel-saving transfer method is called a Hohmann transfer Named after a German engineer He worked it out back in 1925 The precision required here is extreme One extra meter per second of burn and the far side of the orbit rises about three and a half kilometers This chase begins at the launch pad The rocket must lift off at a moment precise to the second The station's orbital plane passes right over the launch site Launch a bit late, and the station is off target The launch is usually pushed to another day The Dragon takes about a day from launch to docking In the final meters, it moves at just a few centimeters per second Several times slower than walking The spacecraft approaches automatically using laser rangefinders and cameras The crew and mission control monitor it, ready to take over if needed Some cargo ships, like Cygnus, don't dock themselves They stop ten meters out, and a robotic arm gently grabs them New spacecraft use a unified international standard for docking mechanisms So ships from any maker can dock at the same port Keeping a spacecraft in the right attitude is another discipline Solar panels face the sun, antennas face Earth, telescopes lock onto target stars Sharp turns use small attitude control thrusters But fuel in orbit is worth its weight in gold, so spinning flywheels do most of the work The International Space Station stays stable thanks to four huge gyro flywheels They spin at about 6,600 rpm, powered by the solar panels Like a spinning-top toy, fast-spinning flywheels hold their attitude rock steady Just give their axis a gentle tilt And the station turns smoothly, without a drop of fuel If Earth were a perfect airless sphere Low-orbit satellites could circle it almost forever But in reality several forces stir up trouble—mainly the leftover atmosphere At 400 km up, the air is hundreds of billions of times thinner than at ground level, but it's still there At orbital speed, even sparse gas molecules noticeably slow the station It loses about 2 km of altitude per month on average The lower the orbit, the denser the air, the faster it falls Around 200 km, a spacecraft without engines lasts only days to weeks So the station's altitude is a compromise Any lower and it brakes too hard; any higher and ships struggle to reach it Crews would also take more radiation The Sun has the biggest impact When solar activity ramps up, the upper atmosphere heats up And expands to greater heights Result: more molecules at the same altitude, and drag shoots up Satellites fall faster than engineers expected Solar activity cycles roughly every 11 years In peak years, satellite operators have to fire thrusters more often to raise orbits The best example: a batch of Starlink satellites SpaceX launched on February 3, 2022 Forty-nine of them in one go The new satellites were deliberately sent into a very low initial orbit About 210 kilometers Bad ones burn up fast; good ones fire their thrusters and climb But the day after launch, solar activity triggered a geomagnetic storm Air resistance at that altitude jumped about 50 percent Engineers put the satellites into safe mode Flying edge-on like sheets of paper to cut drag But many couldn't be saved In the end, as many as forty satellites failed to raise their orbits They fell into the atmosphere and burned up completely, just as designed The Hubble telescope has a similar problem—it has no engines of its own to raise its orbit It used to rely on Space Shuttle crews to boost its orbit during servicing missions The Shuttle was retired back in 2011 The telescope's orbit has slowly decayed, from an initial 600-plus kilometers It's now well below 500 kilometers The science institute that manages Hubble estimates that without outside help the telescope would plunge into the atmosphere around mid-2033 Besides the air, Earth's own shape affects orbits too It's a bit flattened—the equatorial radius is about 21 kilometers more than at the poles The extra mass at the equator slowly rotates a satellite's orbital plane Engineers learned to make use of this effect In so-called sun-synchronous orbits a satellite passes over every location at the same local time That way the surface is photographed in consistent lighting Distant geostationary satellites feel more pull from the Moon and the Sun Their orbital inclination drifts by nearly a degree a year on its own Engineers can't switch off air drag or lunar gravity So satellites that need to hold position for a long time have to rely on engines to keep their orbit The International Space Station boosts its orbit regularly using the engines of docked cargo ships A single burn raises it by one to several kilometers American cargo ships do this too Cygnus has already performed such boosts while Dragon added an aft engine module in 2024 Every boost is calculated in advance by mission control, so that when the next ship arrives the station is exactly at the required altitude and orbital position Geostationary satellites must stay within a very narrow window usually about 0.1 degrees, or fixed ground antennas will lose the signal So these satellites make regular small burns to offset the pull of the Moon and Sun, and Earth's uneven gravity Many satellites use hydrazine as fuel It breaks down into hot gas when it touches a catalyst which jets out of the nozzle to produce thrust This kind of engine is extremely simple and reliable No oxidizer or ignition system needed—just open the valve But hydrazine is highly toxic.

When fueling a satellite ground crews have to wear fully sealed protective suits More and more are now using electric engines A gas, like xenon, krypton, or argon becomes a stream of charged particles, accelerated by electric fields The energy comes from solar panels The particles shoot out several times faster than from a normal rocket Such engines have tiny thrust—like the weight of a sheet of paper on your palm But they can run for months on end and save a lot of fuel Starlink satellites use exactly this kind of engine They burn krypton or argon—much cheaper than rare xenon There are also all-electric geostationary satellites The first batch launched in 2015, taking about six months to reach operating orbit Fuel reserves often determine a satellite's lifespan So geostationary satellites are usually designed for fifteen years The usual scenario: the electronics are still fine but the fuel runs out, and the satellite can't hold its orbital slot That's where space tugs come in In 2020, Northrop Grumman's first tug docked with Intelsat 901 This satellite had been in orbit since 2001, nearly out of fuel, and the tug grabbed it It inserted a special rod into the main engine nozzle After docking, the tug took over control and sent the satellite back to its original slot It held station for about five years, keeping the satellite in service In 2025, the tug moved the satellite to a safe orbit, detached, and headed off on a new mission In other words, satellites can not only be launched but also serviced in space Sooner or later, every satellite runs out of fuel—or life Then engineers have to decide how to clear the orbit safely In low orbit, there's a simple way The satellite fires retrograde and slows down Its lowest point drops down close to the atmosphere Then it's the air's turn Compressed hard in front of the vehicle, it turns into glowing plasma The surface heats up past 1,500 degrees At around eighty kilometers up, most satellites start breaking apart Small craft burn up almost completely, leaving nothing that could reach the ground Large, sturdy structures like titanium fuel tanks are deliberately steered toward the most desolate place on Earth—a remote stretch of the South Pacific This is Point Nemo, about 2,700 kilometers from the nearest land Debris falling here harms no one An uncontrolled fall is another story The impact point depends on air density and solar activity Only in the final hours can the landing spot be pinned down Geostationary satellites can't use this trick Descending from 36,000 kilometers would burn a huge amount of fuel So instead, they're raised by about 300 kilometers into the so-called graveyard orbit The last bit of fuel is saved specifically for this The rules for low orbit keep tightening—the US is a good example In 2022, the US Federal Communications Commission required satellites to leave orbit within five years of retirement The old standard was 25 years, but with the satellite boom, that's no longer enough The International Space Station will take this step too — it's set to retire in 2030 NASA chose SpaceX The contract is worth up to 843 million dollars, converting a Dragon spacecraft into a dedicated tug In the final months, the orbit will be gradually lowered The crew evacuates early, and the tug makes its final braking burn over remote waters Most of the structure burns up along with the tug The debris falls into the sea, far from land Properly disposing of dead spacecraft matters, because space around Earth is already crowded According to the European Space Agency, about 40,000 objects were being tracked in orbit in 2025 around 11,000 of them still operational Plus an estimated 1.2 million more pieces of debris, each one to ten centimeters across Too small to track one by one The station has multi-layer protective shields The thin outer layer shatters small particles into dust, and the next layer catches what's left For big known targets, the station maneuvers out of the way Starlink automatically dodges tens of thousands of times a year The most interesting part is satellites are visible to the naked eye — no telescope needed You just need clear skies and the right timing The International Space Station is easiest to spot in the first hours after sunset, or before dawn By then the ground is dark, but the station up high is still lit by the sun At those times, it's one of the brightest objects in the night sky Usually only the Moon and Venus outshine it It's easy to tell apart from a plane — it flies smooth and steady No blinking colored lights, and it crosses the sky in just a few minutes Sometimes it suddenly vanishes halfway across the sky That's when it enters Earth's shadow, and the sun no longer reaches it To know when the station passes overhead, just use NASA 's Spot the Station — that's it It shows you the pass times, direction, and elevation A few days after new Starlinks launch, you can see a string of bright dots They travel in single file like train cars, until each one reaches its assigned spot But satellites in geostationary orbit are too far to see with the naked eye Still, without them, satellite TV and lots of communications would grind to a halt And navigation satellites — we use them almost every day Yet you never wondered how it works Every GPS satellite runs on atomic clocks They constantly beam out precise time signals, and your phone compares when each one arrives From those time differences, it calculates the distance to each satellite For an accurate fix, you need signals from at least four satellites at once Three satellites can pinpoint a spot The fourth corrects your phone's clock error—it's nowhere near as accurate as an atomic clock But there's an even more mind-blowing correction Because satellites move fast and gravity up there is weak Their clocks run about 38 microseconds faster per day than clocks on Earth Sounds trivial, but without correcting for it position errors would pile up by roughly ten kilometers a day So engineers pre-adjust the satellite clocks to offset this effect Next time you see a bright light streaking across the sky or open the maps app on your phone, just think about this Those machines overhead are falling every second—and missing the Earth every second Tell us in the comments: have you ever spotted the International Space Station with your own eyes?

Which engineering puzzle should we tackle next episode?

If you enjoyed it, hit like and share it with friends and family And be sure to subscribe to the Hidden Horizons channel Don't miss more fun videos on life, history, and engineering