Despite the fact that domestic cosmonautics is going through hard times, to put it mildly, more and more people of different ages and educational levels are interested in space today. Through the efforts of private investors and popularizers of science, the space outside our planet is becoming more interesting, accessible and understandable, attracting curious citizens to acquire new knowledge.

In this material, we will briefly, avoiding complex explanations and formulations, talk about the cosmic velocities that are necessary to overcome the gravitational fields of astronomical objects. In news stories, we often hear such a phrase as “the first (second, third, fourth) cosmic speed”, but not every man in the street understands what speeds are in question and how they are defined.

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## What is space speed

Space velocities in cosmonautics (we are talking not only about manned flights, but for convenience we will call all launches of artificial spacecraft astronautics) are used to calculate the minimum required speed for:

1. Entry of spacecraft into Earth orbit;

2. Spacecraft going beyond the Earth’s gravitational field;

3. Spacecraft going beyond the solar system;

4. The exit of spacecraft outside the Milky Way galaxy.

Naturally, the formulas for calculating cosmic velocities are applicable not only to our planet, but also to any other object in the Universe, however, we will consider only the values that are relevant for terrestrial spacecraft.

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## The first space speed – 7.9 km / s

In order to orbit the Earth, the satellite must have the first cosmic or circular speed, which for our planet is approximately 7.9 km / sec. In this case, the object in orbit will be held by the force, which is popularly called centrifugal, and the movement of the Earth and the force of gravity will not allow the satellite to leave the gravitational field of the planet.

A rather interesting and simple conclusion follows from this: what will happen if in the formula for calculating the first cosmic velocity (V1 = (GM / R) to the 1/2 power, where M is the mass of the object, R is the radius, and G is the gravitational constant) to play with the numbers and substitute data that will determine the first cosmic speed for an invented object, as equal to the speed of light (slightly less than 300,000 km / s)?

We will get an object of huge mass and small radius, on which light can fall, but photons are no longer able to leave its gravitational field, because this requires a second cosmic speed, which in this case will exceed the speed of light, which is impossible in the known universe. This is the object that everyone has heard of and which astrophysicists call a “black hole”.

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## Second space speed – 11.2 km / s

In 1959, the USSR launched the automatic interplanetary station Luna-1 – the first artificial object that left the Earth’s gravitational field and became a satellite of the Sun. To do this, the spacecraft had to accelerate to the second cosmic velocity (it is the escape velocity), which for the Earth is about 11.2 km / sec. Having left the Earth at such a speed, the object enters a parabolic orbit, which, provided there were no other bodies in the Universe, would allow it to move infinitely far from the planet.

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## Third space speed – 16.6 km / s

It is impossible to determine the exact value of the third cosmic velocity, as it can fluctuate over a fairly wide range. What matters is the angle of the launch direction to the Earth’s orbital trajectory and contact with the gravitational fields of other planets, which can both accelerate and decelerate the spacecraft. The minimum value of the third cosmic speed is estimated as 16.6 km / sec.

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## The fourth space speed – 400-600 km / s

A rarely used term due to the inaccessibility of the values determined by it for our cosmonautics in the foreseeable future. The fourth space velocity implies spacecraft departure outside the galaxy, which is impossible in principle at the current and expected level of technology development. Considering that our solar system revolves around the galactic center at a speed of about 220 km / s, the approximate estimated speed of an artificial vehicle for leaving the Milky Way can be defined as 400-600 km / s.

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