Early in the space age, it was found out
that the maximal net velocity change that can be achieved using chemical
rocket propulsion systems is too low. Therefore, missions requiring a higher
velocity change could only be accomplished successfully with staging of the rockets and
with a small payload ratio. The reason for this weakness is to be found
in the energy content of the propellants limiting the maximum achievable
exhaust velocity to 4 up to 5 km/s.
One possibility to overcome this limit is the coupling of
additional energy into the system, i.e. in the form of electrical energy.
This fact has already been published by Goddard in 1906 and later by Hermann Oberth in
his book "Die Rakete zu den Planetenräumen" (The Rocket into Interplanetary Space).
Due to the fact that the development of launchers, possible not earlier than World War II,
enabled the possibilities of spaceflight, it was mainly the work of Ernst Stuhlinger that appointed again
the advantages of electric propulsion and that lead to R&D programs all over
the world since the 1960ies.
A huge variety of different concepts were studied, especially
regarding the acceleration process as the propellant can be accelerated
electrothermally, electromagnetically or electrostatically when using electrical
energy. To benefit from electromagnetic or electrostatic acceleration forces
charged particles have to be formed by means of ionisation of the propellant.
In case of nearly all electric propulsion systems
the exhaust velocity can be varied in a broad range by means
of adjustment of applied power and mass flow as well as by choice of
propellant. However, the thruster classes differ in
the maximum exhaust velocity achievable, the thrust density, the
thrust-to-power-ratio as well as the requirements on the propellant.
|
email
| © Universität Stuttgart
| legal notice
|| intern: Webmail | Literatur
| Groupware
| MoonWiki