Its been a week and here i am with a new post.
This time its rockets. Yes those giant devices that put man on the moon.
Well rockets dont always have to be that huge.Any entity that pushes a stream of fluids and propels itself using Newton's third law of motion is called a rocket. Rockets carry their own fuel and an oxidizer to burn the fuel. They differ from jet engines in this respect that jet engines rely on surrounding air hence they are air breathing.
Rocket engines usually consist of a combustion area, a nozzle and a diffuser.
As the fuel burns hot expanding gases eject through the nozzle giving thrust to the rockets
Rockets usually use combustion or some other chemical reaction that provides huge volumes of gases. This class of rockets are called chemical rockets. It is possible to use other mechanisms to power rockets.
One such method is "Ion propulsion system" or "Ion thrusters".
In this method charged ions are accelerated using coulumbic force or lorentz force and ejected through a nozzle. This propels the craft. In this method the amount of impulse obtained per unit volume of propellant used or the specific impulse is extremely high. This means that the rocket is at maximum efficiency. Specific impulse is not to be confused with the total thrust or maximum thrust. Thrust is the effective force acting on the engine. Ion thrusters have very low thrusts. Thrust is directly proportional to the power spent in accelerating the ions. Since we need extremely high power to provide high thrusts the use of these engines for propulsion is not viable inside the atmosphere. But in the vacuum of space ion thrusters are very useful. Ion thrusters are used in satellites to correct orbits, compensate spins.etc.
There is usually a mechanism for providing plasma. This is achieved by using electrons to ionize gases and form plasma or microwave hearing of propellant to form plasma. Once the plasma is formed it is accelerated using Electrostatic forces(by using a cathode-anode pair to provide the accelerating potential and making the electrodes as grids to only eject high speed ions) or Magnetic forces(by using electromagnets to provide the required accelerating potential) or even a combination of both. This accelerated plasma is let out through the nozzle and thus provides thrust. Near the nozzle there is also a spray of electrons to ensure that the engine doesn't accumulate a charge. Since these thrusters work for years, such build up of charges might harm the internal electronics or even impair the propulsion system.
One specific variant of ion thrusters is called the Hall Effect Thruster uses magnetic field to trap electrons. These electrons further ionize the propellant gas. These use heavy gases like xenon.etc. One such engine used solar radiation to power the engine and ejected around 59kgs of xenon. It achieved a total change in velocity of 2400m/s in around a year. It doesn't provide instant acceleration but can be used to achieve high velocities from relatively small mass of propellant.
Conventional chemical rockets are still the preferred mode of escaping earth. But once out there, these ion thrusters provide high efficiency for small propellant payload.
