Last year, Yuri Milner and Stephen Hawking teamed up to create Breakthrough Starshot. Their plan is to use a huge array of lasers to accelerate a very light laser sail. The sail, with the "ship on a chip" attached to it, will accelerate to a speed exceeding 20% of the speed of light, and head to one of the nearest stars. With this speed, he must arrive at his goal in one human life - an amazing achievement! Although there are an incredible amount of economic and technical obstacles in the way of this project, Alex Stockton, hoping for success, asks a question about the arrival of the ship:
My father and I discussed the possibilities of the spacecraft proposed by Milner and Hawking. The father believes that the atmosphere of the planet will be able to slow him down when he reaches his target. I believe that it will not be possible to appreciably slow it down, and all this will end in a powerful explosion. Who is right?
Indeed, the purpose of sending a spacecraft several light years away, to the nearest planetary system, cannot be simply sending space debris across the galaxy.
We would like to reach a system teeming with other worlds, with the ability to study them, obtain data, and return it back to those people who will still live on Earth. We've already received an incredible amount of information about alien solar systems from our exoplanet research program, but - as the New Horizons, Dawn and Cassini missions have shown in our solar system - there is no substitute for close examination of worlds.
If we can get there, it will already be a feat. If we can aim well enough and accelerate with the right precision and values, our speed will be about 60,000 km / s relative to any planet or solar system we arrive at. Think about it: 60,000 km / s, 216 million km / h. If this speed exceeds anything you can imagine, then it is. It exceeds the speed of any macroscopic object known to us, and it is hundreds of times faster than the speeds required to escape from the gravitational pull of our galaxy. If you fly into a small area of scattered inert gas along the way, the heating will be incredible. Indeed, at speeds thousands of times slower, entry into our atmosphere can only be tolerated by the most advanced heat shields.
Astronaut Bob Cripen with the Gemini-B capsule and its battered but whole heat shield
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But if you move a thousand times faster, the situation becomes a million times worse. If you opened the car window while driving, you might have noticed something interesting: if you go twice as fast, the drag force will be four times greater. The energy, friction, and heating of the spacecraft are subject to the same problem; if you move at twice the speed, you warm up four times faster, and if you move tenfold, then a hundred times. To understand what Starshot can experience in the atmosphere, consider the closest analogy to this: a meteor.
Most of the meteors hitting the Earth during a meteor shower are comparable in mass to our device - from 0.1 to 10 grams. The amount of kinetic energy of a meteor is proportional to its mass and the square of its velocity relative to the atmosphere. These meteors travel fast: from 20 to 110 km / s, and usually burn up in the atmosphere in a split second. During a plentiful and beautiful meteor shower, dozens or even hundreds of bursts can be seen in the sky overnight.
Now we come to a spaceship: its mass is comparable to a meteor, but its speed is 1000 times greater. This means that its kinetic energy to be dissipated will be 1,000,000 times greater than that of a typical meteor. A planet colliding with a 1 gram spaceship moving at 60,000 km / s will experience the same catastrophe as a planet collision with a 1 ton asteroid moving at 60 km / s: the equivalent of Earth happens every ten years.
1860 Meteor by Frederick Edwin Church
At such speeds, the substance of the spacecraft will turn into plasma when the atoms / molecules are stripped of their electrons. A ship as thin and distributed as it is planned to be built will disintegrate in microseconds - which is good, since it will only take 1,000 microseconds to traverse the thickness of the Earth's atmosphere.
In an effort to keep the spacecraft intact, it is best to rely on the same array of lasers present at the point of arrival, which can irradiate the spacecraft with light of the same frequency that accelerated it. We are excellent at creating materials that can reflect about 99.999% of the light incident on them of a certain frequency - thanks to this, the concept of such an apparatus has the right to life. But if you bump into anything other than light of this frequency - any other radiation, or matter - you will absorb a huge amount of energy. And at such speeds, it would mean disintegration. So, with regret, I inform you and your father, Alex, that atmospheric resistance will slow down your spacecraft, but it will do so in the form of a fiery catastrophe that will destroy everything on the ship, down to individual atoms.