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Can the atmosphere slow down the spacecraft? / SurprizingFacts

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Last year, Yuri Milner and Stephen Hawking teamed up to create the project Breakthrough Starshot. Their plan is to use a huge array of lasers that will accelerate a very light laser sail. The sail, with the "ship on the chip" attached to it, will accelerate to a speed exceeding 20% ​​of the speed of light, and will go to one of the nearest stars. With such speed, he must come to his goal within one human life – an amazing achievement! And although there is an incredible amount of economic and technical obstacles on the way to this project, Alex Stockton, hoping for success, asks the question about the arrival of the ship:

My father and I discussed the possibilities of a spacecraft offered by Milner and Hawking. Father believes that he will be able to slow down the atmosphere of the planet when he reaches his goal. I think that it will not be possible to significantly slow down it, and all this will end with a powerful explosion. Who is right?

Indeed, the purpose of sending a spaceship a distance of several light years, to the nearest planetary system, can not be a simple transfer of space debris along the galaxy.

We would like to get to the system , Replete with other worlds, with the opportunity to study them, get data, and return them back to those people that will still live on Earth. We have already received an incredible amount of information about foreign solar systems thanks to our program for studying exoplanets, but – as the missions of New Horizons, Dawn and Cassini, working in our solar system showed, a close examination of the worlds can not be replaced by anything.

If we can get there, it will already be a feat. If we can aim well enough and accelerate with the appropriate accuracy and with the right values, our speed will be about 60,000 km / s relative to any planet or solar system that we arrive at. Think about it: 60,000 km / s, 216 million kilometers per hour. If this speed exceeds anything you can imagine, it is. It exceeds the speed of any macroscopic object known to us, and it is hundreds of times faster than the speeds necessary to escape from the gravitational attraction of our galaxy. If on the way you fly into a small area with a scattered neutral gas, the heating will be incredible. After all, at speeds thousands of times smaller, only the most advanced of thermal shields can move into our atmosphere.


Astronaut Bob Crypen with Gemini-B capsule, and her shabby, but whole Thermal shield

But if you move a thousand times faster, the situation becomes a million times worse. If you opened a window in the car on the go, you might notice something interesting: if you go twice as fast, the resistance force will be four times that. The energy, friction and heating of the spaceship are subject to the same problem; If you move at twice the speed, you warm up four times faster, and if with ten times – then a hundred times. To understand what Starshot can experience in the atmosphere, let's present the closest analogy for this: meteor.

Most meteors crashing into the Earth during a meteor shower are comparable in mass to Our apparatus – 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 fly quickly: from 20 to 110 km / s, and usually burn in the atmosphere in a fraction of a second. During a profuse and beautiful meteor shower, you can see dozens or even hundreds of bursts in the sky per night.

Now we come to the spacecraft: its mass is comparable to a meteor, but the speed In 1000 times more. This means that its kinetic energy, which will have to be dispelled, will be 1,000,000 times greater than that of a typical meteor. A planet that collides with a spacecraft weighing 1 gram, moving at a speed of 60,000 km / s, will experience the same catastrophe as a collision of a planet with an asteroid weighing 1 ton, moving at a speed of 60 km / s: the equivalent of that on The Earth occurs once every ten years.


The meteor of 1860, the artist Frederick Edwin Church

At such speeds, the substance of the spacecraft will turn into plasma when Atoms / molecules will be torn off their electrons. Such a thin and distributed ship as it is planned to build will disintegrate for microseconds – which is good, since it will need only 1,000 microseconds to overcome the thickness of the atmosphere comparable to that of the Earth.

In trying to keep the spacecraft intact, it will be best to rely on the same array of lasers present at the point of arrival, which can irradiate the ship with light of the same frequency as it disperse. We are perfectly coping with the creation of materials capable of reflecting about 99.999% of the light incident on them at a certain frequency – thanks to this the concept of such a device has the right to life. But if you crash into anything other than light of this frequency – in any other radiation, or matter – you will absorb a huge amount of energy. And at such speeds this will mean disintegration. So, I regret to inform you and your father, Alex, that the resistance of the atmosphere will slow down your spaceship, but it will do it in the form of a fiery catastrophe that will destroy everything that is on the ship, up to individual atoms.

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