Any object, being tossed up, sooner or later ends up on the earth's surface, be it a stone, a piece of paper or a simple feather. At the same time, a satellite launched into space half a century ago, a space station or the Moon continue to rotate in their orbits, as if they were not affected by the force of gravity of our planet at all. Why is this happening? Why does the Moon not threaten to fall to the Earth, and the Earth does not move towards the Sun? Are they not affected by gravity?
From the school physics course, we know that universal gravitation affects any material body. Then it would be logical to assume that there is a certain force that neutralizes the effect of gravity. This force is called centrifugal. Its action is easy to feel by tying a small load to one end of the thread and spinning it around the circumference. In this case, the higher the rotation speed, the stronger the tension of the thread, andthe slower we rotate the load, the more likely it is to fall down.
Thus, we are very close to the concept of "cosmic speed". In a nutshell, it can be described as the speed that allows any object to overcome the gravity of a celestial body. A planet, its satellite, the solar system or another system can act as a celestial body. Every object that moves in orbit has space velocity. By the way, the size and shape of the orbit of a space object depends on the magnitude and direction of the speed that this object received at the time the engines were turned off, and the altitude at which this event occurred.
Space velocity is of four kinds. The smallest of them is the first one. This is the lowest speed that a spacecraft must have in order for it to enter a circular orbit. Its value can be determined by the following formula:
V1=õ/r, where
µ - geocentric gravitational constant (µ=39860310(9) m3/s2);
r is the distance from the launch point to the center of the Earth.
Due to the fact that the shape of our planet is not a perfect ball (at the poles it is sort of flattened), the distance from the center to the surface is greatest at the equator - 6378.1 • 10(3) m, and least at the poles - 6356.8 • 10(3) m. If we take the average value - 6371 • 10(3) m, then we get V1 equal to 7.91 km/s.
The more the cosmic velocity exceeds this value, the more elongated the orbit will acquire, moving away from the Earth for allgreater distance. At some point, this orbit will break, take the form of a parabola, and the spacecraft will go to surf space. In order to leave the planet, the ship must have the second space velocity. It can be calculated using the formula V2=√2µ/r. For our planet, this value is 11.2 km/s.
Astronomers have long determined what the cosmic velocity, both the first and the second, is equal to for each planet of our native system. They are easy to calculate using the above formulas, if we replace the constant µ with the product fM, in which M is the mass of the celestial body of interest, and f is the gravitational constant (f=6.673 x 10(-11) m3/(kg x s2).
The third cosmic speed will allow any spacecraft to overcome the gravity of the Sun and leave the native solar system. If you calculate it relative to the Sun, you get a value of 42.1 km / s. And in order to enter the near-solar orbit from the Earth, you will need to accelerate to 16.6 km / s.
And, finally, the fourth cosmic speed. With its help, you can overcome the attraction of the galaxy itself. Its value varies depending on the coordinates of the galaxy. For our Milky Way, this value is approximately 550 km/s (when calculated relative to the Sun).
