How long can the body rotate in space?
Alexander V. Bagrov
The reader asked the Space Colonization Journal to answer the question: how long can the body rotate in space. This debate unfolded in .
In fact, this question is important for understanding the spacecraft design and astronauts motion in open space. Therefore, this note was decided to be written.
Thus, the laws of the universe are such that if no forces act on the body, it can not change its state. The body rotating in vacuum will always maintain the rotation velocity and the rotative axis position in space.
In fact there are so many bodies in the universe, that it is impossible to be isolated from them so some external influence on any body will always be in evidence. The external influence appears differently for the bodies rotation than for its spatial movement. To change the body’s rotation a couple of forces createsing a moment of force about the rotative axis must act on it. Perhaps if the planet had zero dimensions, the Sun gravitation could not create a pair of forces in the body having no size. A large body can be regarded as a variety of small connivent ones; the solar gravitation of the Earth’s parts, located further and closer about on its center, creates a pair of forces changing the planet’s rotation. Because of the such forces existence the Earth’s axis does not keep a permanent position, but precesses.
Another type of impact on the rotation is its acceleration or deceleration. The moment of force is also necessary for its appearance but but it must be asymmetrical about the rotative axis. Such a moment of force is artificially created in the engine rotor, which they spin up or down with. In the gyroscopes – navigation devices – the rotor spins up to the velocities of thousand revolutions per second, so that the energy of its rotation surpasses multiply the small impacts from the outside forces on it. Any friction creates a spinning down moment, therefore especially precise gyroscopes are being evacuated to avoid even the air friction of smooth rotor. In the vacuum gyroscope rotor, like any other solid rotating body, will rotate indefinitely.
Even in the vacuum the forces causing braking of the rotating body may exist. Perhaps a liquid body will be braked by tidal forces in the gravitational field of another body. Due to the action of gravitational tidal forces of the Moon and the Sun, the Earth slowly spins down its rotation. Solid bodies are not braked by tidal forces due to its their elasticity, so all the asteroids and planet satellites that have no liquid substance rotate without braking. Single stars, having nothing to cause the tidal forces appearance in their material also retain the rotation velocity for the whole lifetime, although the structure of their material acts as a fluid.
Leviton is not the device isolated from other bodies. It is in the field of electromagnetic forces that affect it constantly. The Foucault currents that appear from the rotation of the normal conductor in a magnetic field will spin down its rotation, and this effect will persist even in a vacuum. But if the leviton is made of superconducting material, the brakeage will not appear, and such leviton will rotate without stopping indefinitely.
The author thanks Walter Myers , the talented American artist and astronomer, for providing space art for the title of this article.