In reaction propulsion engines and rockets thrust is created by very hot gases products of the combustion of chemical fuel,flowing from them with great velocity. the amount of thrust mainly depends on the mass of the exhausted material and the axhaust velocity. In ordinary engines working on chemical fuels the exhaust velocity of the wastes gases does not exceed 3000 to 5000 metres a second . consequently the only way to increase the thrust developed by jet engines of any type is to increase the mass of the combustion products ejected per unit of time,or to raise the exhaust velocity considerably,or to increase both simultaneously . An exhaust velocity approaching the speed of light would be the ideal, but it is unlikely that men will ever succeed in creating substances developing combusting temperatures of tens and hundreds of thousands of degrees, and only such temperaturs, and the exhaust velocities corresponding to them, would make it possible to dream of rocket speeds, giving men the chance some day to escape into the interstellar space and visit other worlds.
So, in order that the whole problem should not became hopelessly pessimistic, chaining man forever to the limits of his nearest neighbours or, at best, within the solar system, engines must be created, based on quite different principles.
In recent years, with the building of charged-particle accelerators and the development of plasma generators that convert heat directly into electricity with no need for boilers or turbo-generators, and at high efficiency (70 percent and over), intensive work has begun on what are called ionic propulsion or ion-plasma jet engines for rockets. Their main attraction is the possibility of converting a substance first into a high temperature plasma, i.e. of ionizing a gas, and then accelerating the ions produced to velocities comparable with that of light, thereby increasing the thrust of engines as many times as the exhaust velocity of the ions exceeds that of the gases produced by the combustion of ordinary chemical fuel, if given equal quantities. Hence there would be a considerable increase in the lift, volocity, and range of rockets, and other, advantages no less decisive.
The mass of a proton is 1836 times that of an electron, while the mass of an jon, in turn, exceeds the mass of a proton by as much as the atomic weight of the fuel used exceeds that of hydrogen. Consequently the most important thing in designing an ion engine for the mass of the ions ejected from the rocket.
But our present-day charged-particle accelerators, even the superpowerful ones, are of little use for the purpose, for it is not a fine invisible ray even of heavy particles, with a current measured in micro-amperes,that is to be accelerated, but a powerful flux of particles, measured and thousands of amperes and maybe even in millions
It is not easy to construct accelerators of such high current intensity.
To make it possible to ionize a fabulously large number of atoms of gas, and then accelerate the mass of positively charged particles obtained to velocities around 10000 or 100000 kilometres a second, it would be necessary to mount powerful energy sources on a rocket, whose weight and volume would naturally eat up much of the advantage of the enormous gain in exhaust velocity.
But scientists have calculated that the game is definitely worth the candle.
As a result of long research several working models of such engines have been developed.
The design of an ionic propulsion engine is extremely simple. Its main part is an electric generator creating a strong high-voltage electrics field.positively charged ions can be produced from gases like hydrogen or helium, or the light metal caesium, or other substances capable of being ionized, i.e. of losing electrons, at comparatively low temperatures of the order of 2000-5000 c .
On entering the electrics field of the accelerator, the ions are accelerated to cosmic velocities and then ejected from the tail unit of the engine, building up a jet thrust.
This thrust is not large compared with that of existing rocket engines burning chemical fuel, so it would be better to launch rockets, powerd by an ionic propulsion engines, not from Earth, but from an orbit around Earth into which they had been put by means of an ordinary multistage rocket.
Once launched into speace however, a rocket powerd by an ion-plasma jet engine could work for days and weeks, and in the future (when it is possible to use atomic power unit) for years.
Suppose a spaceshipe weighing 1000 tons has been put into orbit. An ionic propulsion engine developing a thrust of only about 100 kilograms (which is more than modest, compared with the weight of the ship) would be able to impart an acceleration to it of about 6000-7000 kilometres a dey, until it attained a speed around 40 kilometres a seconde or three or four million kilometres a day.
For such acceleration the consumption of fuel(ionized gas) would be only around six kilograms an hour.
This velocity is far below that of the ejected particles, let alone of light.
But it could be increased as the density of the flux of particles accelerated in the beam of the linear accelerator rose,taking into account that more than one accelerator could be installed in the rocket, and more compact types of accelerators employed.
On long flights, when the rocket could be accelerated gradually, other sources of power could be used such as thermoelectric or solar batteries