Space propulsion

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Space propulsion
The propulsion of spacecraft is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and the propulsion of the spacecraft is an active area of ​​investigation.
However, most of today’s spacecraft are propelled by forcing a gas from the rear / rear of the vehicle at a very high speed through a Laval supersonic nozzle. This type of engine is called a rocket engine.
All current spacecraft use chemical rockets for launch, although some have used breathing engines in their first stage. Most satellites have simple and reliable chemical propellers or resistojet rockets for maintenance of the orbital station and some use impulse wheels for attitude control.

The satellites of the Soviet bloc have used electric propulsion for decades, and new spacecraft in western geological orbit are beginning to use them for the maintenance of the station and the north-south orbit. Interplanetary vehicles also use chemical rockets, although some have used ion thrusters and Hall effect impellers with great success.
Requirements
Artificial satellites must be launched into orbit and, once there, must be placed in their nominal orbit. Once in the desired orbit, they often need some kind of attitude control to correctly aim at the Earth, the Sun and possibly some astronomical object of interest.

They are also subject to the drag of the thin atmosphere, so that to stay in orbit for a long period of time, sometimes some form of propulsion is needed to make small corrections.
Many satellites need to move from one orbit to another from time to time, and this also requires propulsion. The lifetime of a satellite usually ends once it has exhausted its ability to adjust its orbit.
Spacecraft designed to travel further also need propulsion methods. They need to be thrown out of Earth’s atmosphere just like satellites. Once there, they need to leave the orbit and move.

For interplanetary travel, a spacecraft must use its engines to exit Earth’s orbit. Once you have done so, you must somehow reach your destination. Current interplanetary spacecraft do this with a series of short-term trajectory adjustments. Among these adjustments, the spacecraft simply falls freely along its trajectory.

The most efficient means of fuel consumption to move from one circular orbit to another is with a Hohmann transfer orbit: the spacecraft begins in a more or less circular orbit around the Sun. A short period of thrust in the direction of movement accelerates or decelerates the spacecraft in an elliptical orbit around the Sun that is tangential to its previous orbit and also to the orbit of its destination.

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