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1,000km Cable to the Stars – The Skyhook

1,000km Cable to the Stars – The Skyhook

Getting to space is hard Right now, it’s like going up on a mountain on a unicycle With a backpack full of explosives Incredibly slow, you can’t transport a lot of stuff, and you might die A rocket needs to reach a velocity about 40,000 km an hour to escape from Earth To get to that speed rockets are mostly containers for fuel with a tiny tip of payload This is bad if you want to go to other planets because you need a lot of heavy stuff if you want to survive and maybe even come back So, is there a way to get to space with less fuel and more payload? A nice thing that solved most of our transport problems on Earth is what-you-call infrastructure Whether it’s roads for cars, ports for ships, or rails for trains We’ve made it easier to get to places We can apply the same solution to space travel Space infrastructure will make getting into orbit and out to the Moon, Mars, and beyond easier and cheaper Great, but what exactly is space infrastructure? Unlike an Earth space elevator, which is currently science fiction, There is a simple yet promising technology that does not require new science, magic materials, or huge investments And that has been tested successfully in orbit already A cable and a weight Known as a tether The concept’s is so simple; it’s surprising What if we put tethers hundreds or thousands of kilometers long — into space, and had spacecraft use them as ladders to climb to higher altitudes and gain speed? This concept is known as the Skyhook. It works even better if we make it spin. A counterweight holds a long cable in place while it rotates around a circle. A rotating tether slows down its tip relative to the ground at the bottom and speeds it up at the top like a catapult. This means that you can transfer energy from the tether and get a massive boost when released, more-or-less for free, equal to twice the tether’s rotation velocity. Specialized fibers already exist that can survive the extraordinary stresses a Skyhook would be faced with. To protect against cuts and collisions from debris and meteorites, we can thread our tether into a web of redundant fibres. Since our Skyhook would pass over the same spot many times a day, this would allow small, reusable shuttles to catch up with it. Of course, it’s not that easy. At its lowest point, the tether’s tip is dashing through the atmosphere at around 12,000km/h. Because of Earth’s atmosphere, we can’t lower the Skyhook too much or it will get too hot from air friction. So it will dip to a height of 80 to 150 kilometers and no lower. To match this, we’ll need specialized spacecraft that can get to the tether. While this isn’t exactly easy, it’s still much cheaper than getting a big tin can, filled with rocket fuel, to go 40,000km/h. Catching the tip will be a challenge too. There’s only a short time window of 60 to 90 seconds to find a tiny thing in the sky, moving at Mach 12. To make this easier, the tip could have a sort of fishing line a kilometer long with a navigation drone that helps the spacecraft connect. Another challenge is keeping our Skyhook in orbit. As more and more ships latch onto it and pull themselves up, they use up the momentum that keeps it in place. If we don’t do anything, it will slow down and crash into the atmosphere. And here, we can cheat the universe a bit. The Skyhook is a battery of orbital energy. It’s possible to balance the payloads coming in and being sent off. Arriving ships bringing humans and materials home to earth add energy to the tether, which it can give to other ships departing into space. This way, the tether doesn’t lose any energy. The more we use it, the cheaper it gets. If we’re still losing energy with each boost, we can recover it with small electric or chemical engines that regularly correct the tether’s position. A set of tethers, one around earth and one around Mars, could make trips between the planets fast, straight-forward and low cost compared to rockets. The Earth tether would sit in low earth orbit to grab people and payloads and fling them off to Mars. The Mars tether catches them and slows them down for a landing on the surface. In the opposite direction, the tether could pick up a vehicle travelling through Mars’ thin atmosphere at only about 1,000km/h not much faster than our airliners on Earth, and fling it back to Earth to be caught and lowered down. The tethers could shorten trips between both planets, from nine months down to five or even three, and reduce the scale of the rockets required by between 84 and 96 percent. Even better: people may be able to travel in relative luxury as we could afford to invest in passenger comfort. Tether travel would be first-class seats to Mars! Together, tethers around Earth and Mars could provide the rapid and cost-efficient transportation backbone that would make space travel affordable. But let’s go further. Starting from low Mars orbit, a tether could boost ships to the asteroid belt. The first craft sent to a new asteroid would need rockets to slow down at its destination. Subsequent arrivals might find a tether waiting to catch them and send them back for free. Getting to asteroids cheaply is a major factor in opening up the resources of the solar system. Precious metals and valuable minerals could be delivered to Mars just weeks after they were cut out of their asteroid. They would be the perfect building blocks for our interplanetary civilization. But why stop here? Mars moons are very convenient. No other moons in the solar system orbit that close to their planet. Phobos is so heavy that we don’t need to worry about slowing it down, making it the perfect attachment point for super-tethers just under 6,000km long. The lower tip would fly just over the surface of Mars and be very easy to catch. The upper tip can fling ships all the way to Jupiter and Saturn. The same super-tether can also bring the inner solar system closer. Venus and Mercury are a single swing away. Unlike Mars, they’re bursting with solar energy and are rich in minerals. In the long term, nothing is stopping humanity from constructing a zero-propellent transport network for the terrestrial planets, centered on the Martian moons. Tethers are a comparably cheap and sustainable solution to making space travel affordable and the rest of the solar system accessible for exploitation and exploration. Considering that we have the technology to build them today, there’s really no good excuse to wait any longer. Parts of the solar system are far away, but they could be very close. Speaking of stuff that is hard to reach, but doesn’t have to be: Knowledge. Our friends from Brilliant can hook you up to a universe full of explosive ideas and fun courses. Brilliant is a website that helps you tackle science in a practical way, with interactive problem-solving courses and daily problems in maths, logic and engineering. Each problem gives you all the tools you need to crack complex topics all by yourself. It’s learning-by-doing, but with your brain instead of your hands. Use your curiosity to get to the bottom of puzzles and courses about things like classical mechanics, astronomy, gravitational physics and much more. If you click the link in the description, or visit, you can sign up for free and learn more things than you can imagine. And there’s an extra perk for Kurzgesagt viewers: The first 688 people to use the link get 20% off their annual membership, which lets you view all the daily problems in the archives and unlock every course. Brilliant helps you end your day a little smarter. You might… get ‘hooked’ on the experience!

100 comments on “1,000km Cable to the Stars – The Skyhook

  1. To support Kurzgesagt and learn more about Brilliant, go to and sign up for free. The first 688 people that go to that link will get 20% off the annual Premium subscription.
    Thanks to our friends from Brilliant for supporting this channel.

  2. I, have a suggestion that could you do a video about hurricanes and how they work and explaining about storm quakes and what they are and about global warming and sea levels rising.

  3. I wondering .. space trash (which is in Earth orbit ) bumped THE SKYHOOK.. so skyhook lost Energy or get energy .. but I heard that a lot of space trash is existed .. So Can manager of skyhook change Ek. Ep immediate?

  4. That’s a catapult…not a tether…and it sounds good in theory but one miscalculation and people or equipment could get launched into deep space. Accidents happen. I sure wouldn’t wanna be a tourist who got launched into deep space

  5. Dear future people, this is stupid idea, we work hard to colonize our solar system but we can't. You may laugh at us, it's okay, we are stupid, i am dead now, but if there's any way you can make death things live again, please wake me up, i want to see your world. Thank you

  6. There is hope for the space age. There were so many concern about traditional rocket usage and the exponential relationship between fuel and cargo.

  7. A great solution, possible with today's tech… until someone asks the usual question: "Who's gonna pay for it?" Then everything will shelved and forgotten…

  8. What about the gravitational force? Isn't it going to be greater than 10g while you get lunched out of the orbit?

  9. 3:51 Question PLEASE READ THIS : Is the skyhook in that picture sideways? Because if it’s really like that the skyhook is just throwing the rocket out of the orbit

    Q2 : if the answer is yes in Q1 then how come the rocket that is trying to go to mars going at the same way? Because it looks like the rocket is going the opposite direction to mars.

    Please look at this comment I’m so confused, I also want to know how do they place the skyhook in what direction
    Sorry I love astronomy XD

  10. @Kurzgesagt this is the only video that i disliked in your channel , unlike road which is efficient because it allow car to travel with less fuel while repairing the road itself didnt cost as much fuel as it saves , skyhook didn't reduce fuel usage to go to space , it could also be a wasteful way to travel and cost more than just launching space rockey with rocket, skyhook is just another type of way to travel , why ? because everytime the tip of the skyhook is used to launch a spacecraft , it require energy to do so , and energy cannot be created out of nowhere , so everytime skyhook tip is used to launch a spacecraft , the velocity of the skyhook is used to create energy that launch the spacecraft , which mean the skyhook velocity is slowed everytime it is used to launch a spacecraft , which in return the orbit height of the skyhook is also descend to earth everytime it is used to launch spacecraft , to the certain limit that skyhook must be sent back up again to the orbit where the skyhook is supposed to be there or it will fall to earth when used.

  11. Hi,
    Just an important point to make.
    Kurzgesagt please do not partner up with What If. We enjoyed your content on important science topics. However now there is not much information in your videos that could help us it is just an analogy of scenarios.
    I hope we can enjoy the same type of videos that we were

  12. This is the coolest method by far to get into space (unless you really like rockets like me), but the most practical is an orbital ring.

  13. Please tell me any sort of space agency has seen this. I don't care if it's NASA or SpaceX, just get this damn tether into orbit!

  14. Hi! I’m a big fan. I love outer space, and I love this channel, so one month ago, as soon as the space age calendar vid came out, I sent a link to the vid to my mom and told her “mom. I’m doing really good in school this year. If I promise to fix that A-, will you get me this calendar for Christmas? It would make me so happy!”
    And she said “that’s an expensive calendar.. we’ll see! 😂”
    Just now, I asked her if she ordered it.
    She looked at me and said “you mean that silly video with the calendar for 10,000 years from now? I thought that was a joke.”
    She thought it was a joke.
    Immediately, I tried to get to her computer, but it was already too late.
    You’re out of stock.
    And your words echoed through my head, like the banging of a cruel gong “we’ll sell them till they’re gone, and then never again.”
    This is not just some made-up sob story. I am a 16 year old, and all of my money is currently trying desperately to pay for an educational trip to France (je parle Français), so I could not buy it for myself. I have high ambitions for my future and I love space. The universe calls me. I was so excited to looking at all your beautiful animation-styled space art on my wall.
    Please. Take pity on my soul, oh rare kind hearts of youtube. Please lift me up… please.

  15. This cool and all but what if the ship doesn't catch the giant thing. The ships still need to have emergancy slow down system. Just saying.

  16. But instead we'd rather spend money on useless things and NASA is only losing money. But space exploration can only be the future of mankind.Can power sources such as solar or radiation be used?

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