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  • so many years ago my family visited Cape Canaveral in Florida and we went on some boring bus tour.

  • And then there was an alligator, which was exciting.

  • And then at some point, my parents said, Hey, Erica, do you want to go see the decommission Saturn five?

  • It looks like this.

  • And it was hot and humid and I wanted to go back to Disney World.

  • So I said, Will it be air conditioned?

  • And they said Yes.

  • So I said, OK, let's go.

  • So we go over there and the problem with these pictures everyone is seeing these pictures, right?

  • The problem with these pictures is they don't prepare you for the fact that rockets are actually really big, like they're actually just enormous.

  • And you can imagine my surprise when this happens.

  • This is 14 year old Erica and the smallest dimension of the Saturn five.

  • It is unbelievably large.

  • It confused me.

  • I didn't realize this was a real thing that happened.

  • And I think this was the moment when it occurred to me that may be space was big and on, and also that maybe space was interesting.

  • And today I'm going to talk to you about human space travel.

  • Specifically, some of the challenges of human space travel faces when it comes to fuel.

  • So let me sort of introduce the problem to you now.

  • So suppose we wanna have a human mission to Mars, and then we want to bring our humans back from Mars.

  • That's the hard part.

  • So with the Saturn five, big as it is, it will get you to hire Thorpe it and then at high earth orbit indeed, more fuel.

  • Okay, so let's say we have more fuel and you get to Mars, Then it mars.

  • You need more fuel to come back to Earth.

  • But whatever fuel you're using at Mars, you had to get it there in the first place.

  • And to do that you need more fuel.

  • And you see we have a problem, which is that the farther away from Earth you venture, the more calm, pounding fuel costs you face as you use fuel to transport fuel and it's prohibitive.

  • And maybe you can think of some ways around this.

  • Maybe we could use solar sails and not need to use fuel it all.

  • Maybe we could mine asteroids for fuel and not have to carry it with us.

  • There's all sorts of really interesting ideas, and one of them was something I encountered during my high school science competition days, which is called the Interplanetary Transit Network.

  • And the basic idea here is a, rather than using some big rocket to blast our way from Point A to point B.

  • Instead, we're going to think really carefully about the path we're going to take so that the gravity and movement of all the planets in the solar system will pull us toward our destination.

  • And that's very abstract.

  • So let me give you a example of the consequences is has in the in the solar system Today.

  • Here's a graph of some stuff in our solar system.

  • The horizontal access is distance from the sons, the sons on the left.

  • Then we have some planets.

  • Vertical access is just how elliptical the orbit is, and somewhere in between Mars and Jupiter is the asteroid belt.

  • But we know more about the asteroid belt, then just this.

  • We know the orbits of lots of asteroids in the asteroid belt, and something unbelievably cool happens when you plot each asteroid as a dot on this graph.

  • Look at this.

  • Isn't this the coolest graph like what is going on there?

  • There are gaps in the asteroid distribution, their particular distances from the sun, where there are no asteroids.

  • What is going on?

  • And here's what's happening.

  • So if we look at this big gap at two and 1/2 astronomical units from the sun, if there wasn't asteroid there, it would go around the sun once every four Earth years.

  • Meanwhile, Jupiter orbits the sun once every 12 Earth years, and that means Jupiter and our asteroid are in sync.

  • Every 12 years.

  • Our asteroid wills will see Jupiter off in the same spot.

  • Then it'll go around the sun three times.

  • Jupiter will go around once, and it will see Jupiter off in the same spot again.

  • There will be a pattern of Jupiter's gravity pulling and pushing on that asteroid, and over hundreds of thousands of years, that pattern will repeat itself and push that asteroid off of its orbit so that the pattern goes away and they're no longer in sync.

  • And each of these gaps there, called Kirkwood gaps, is caused by a resonance between the orbit of an asteroid in the orbit of a heavy planet.

  • Think how many sad and fives this would take.

  • There are many asteroids that are just way heavier than anything we're thinking about sending into space, and they run propelled.

  • Yet Jupiter is able to move them around with its gravity.

  • And this is the effect that the interplanetary transit network is taking advantage of the fact that you can use the gravity of planets to manipulate the orbits of objects.

  • And, of course, there's a catch, which is that it takes forever.

  • So in the top maneuver, this is something it'll save you 20% of your original fuel costs, but it takes over 200 days, as opposed to the original 4 to 5 days, and in another sort of unrelated but also a fuel saving strategy.

  • You can save almost 90% of the original fuel, but it takes years rather than days.

  • But the fact that the numbers in this time required column are high does not mean that these past they're useless.

  • The fact that we're thinking about these past now means where, considering new types of space missions that we just never never thought of before and with our our human space travel problem, we can solve our com pounding fuel issue like this.

  • So remember I said the problem was we're using fuel to transport fuel.

  • So instead, we're going to use these really slow but very fuel efficient paths to transport our fuel.

  • So before we launch our humans, we start launching booster packs, chemical rockets into space, and we slowly preposition them along the path we're going to take later, like bread crumbs.

  • And then five years later, we launch our humans.

  • They blast right through picking up all the chemical boosters, enjoying the benefits of fast chemical rockets without the compound ing fuel costs.

  • And I'm gonna close by giving you an idea of just how much this helps.

  • So if our spacecraft, with all the humans and all the cargo, weighs 50 metric tons, this is very conservative, by the way, then we would need to launch 3000 tonnes into low earth orbit if we're not pre placing our fuel, which is a lot if we do pre place the fuel sort of using the strategy.

  • I I suggested we only have to launch 600 metric tons into low earth orbit.

  • And that is an order of magnitude different that is bringing space travel, human space travel to the far reaches of our solar system.

  • An order of magnitude closer to reality.

  • Thank you.

so many years ago my family visited Cape Canaveral in Florida and we went on some boring bus tour.

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エリカ・デベンディクティス燃料効率の高い宇宙旅行のための戦略 (Erika DeBenedictis: Strategies for fuel-efficient space travel)

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    林宜悉 に公開 2021 年 01 月 14 日
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