IONIC ROCKETS

IONIC ROCKETS
(An Alternate Method for Rocket Propulsion)


Wondering and bit he
arting thing in the field of rocketry science is that, the type which we are using for the rocket propulsion that is chemical combustion engines. This is the only kind of propulsion method we are using till from the birth of rockets as we know which is a very costly process and also leads to many other technical problems. That is different thing that we are successfully using these kinds of propulsion systems in satellite launching but further if we want to chose the same one for long journeys such as a mission to mars or such as study of universe beyond our solar system this method no more going to work at all because their will be many problems such as maintaining high speed [with exhaust velocity 31.5 Km/sec], the supply of tones of fuel, high cost, increasing payload etc.

So at this stage we need to think of other type of propulsion systems, one of them is IONIC ENGINES. Which is one of the effective method for propulsion which also over comes the many deficiencies from that of chemical propulsion system. Thou the basic concept were given many decades back it’s held back due many political and economical problems, their need to be lots of development required and an up growing country like India should also concentrate upon the new methods like this.

Let me specify initially some of the areas that I want to concentrate upon:

To improve initial thrust, which is very low in this case.
Storage and supply of fuel for long journeys.
The power supply.
The type of field system (grid system).

The basic definition and working principles are given below:

As by title it self says that we are doing something with ions (either + or -). Hence the ion rocket is one which develops thrust by expelling ions rather than hot gases as done in chemical propulsion systems.

Here the fuel or propellant gas that we are using should have high charge to mass ratio i.e. its atoms should be heavy. So that we can achieve high specific impulse.

Initially from the fuel chamber a heavy gas like xenon is supplied into the discharge chamber where the ionization process starts. Here xenon atoms are ionized by bombardment with electrons emitted from the main hollow cathode as shown in above diagram. As ions they will be having some amount of velocity and further they are accelerated electro statically with an ion accelerating grid system and finally these ions are ejected outwards with high force to produce required amount thrust.
Here magnetic rings on the walls of the discharge chamber act to contain the ions as they are accelerated. The ion accelerating system consists of two grids with many holes. A positive voltage, usually 1000 V, is applied to the inner grid (the screen grid) and a negative low voltage to the outer grid (the accelerator grid). The neutralizer emits electrons into the ion exhaust to prevent the spacecraft from acquiring an electric charge. This allows very high exhaust velocities and specific impulses.

ADVANTAGES:
As it has very high specific impulse the amount of fuel required is very small near about 1.8 kg of xenon for 8000 hrs. of operation of engine.
Since the space acquired by the fuel is very low hence the payload area can be increased.
Heavy gases like argon, krypton etc are available in other planets so we can make a plan of long journeys using these gases as refills on other planets.
Experiment had shown that high speed of almost half of the speed of the light can be achieved in space.
After all listing to the theory and its advantages you may ask me one question that if it is so efficient than why this system is used in common rocketry activities? The answer is Thou it has very good efficiency it also consists of many problems too. Some of them are given below.
Since the thrust is inversely proportional to specific impulse the thrust is very low.
In grid accelerating system since there is a chance of collision of ions with grids the grid efficiency decreases and ultimately engine fails.
The power supply. It needs near about 3000 watts of power which is not suitable even by using modern solar cells.