|
|
plasma engine
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.
Editor by :
Prof-mn.chegenie