S.1 Spacecraft Propulsion Systems Chapter 1: Introduction to ...

- 15 -
Potential increase in performance of existing space propulsion systems – Electric Propulsion
Most promising for further increase of propulsive performance capabilities is the use of
electric propulsion. This technology, although still under development, has proven to
achieve thruster exhaust velocities ve an order of magnitude higher than the best
performing chemical thrust engines.
Although electric propulsion leads to substantial propellant mass savings compared with
chemical propulsion, considerable power consumption will require increased mass of
power supply systems. Therefore, for electric propulsion, the determination of the systemspecific
impulse, Issp, requires also the consideration of contained mass of the power
supply/power processing systems and thruster, mEl. Here high performance is not dictated
by maximum but rather by optimum values of thruster exhaust velocity, ve-opt.
For electric propulsion, high values of Issp will be achieved mainly for high values of ve-opt.
which requires particularly high values of overall specific power γ, overall power
conversion efficiency η and thrust operation time τ .
From parametric investigations it is obvious, that for deep space missions mainly power
supply systems with high specific power γ need to be further developed to achieve high
values of Issp. For high optimum thruster exhaust velocity, ve-opt, e.g. Field Emission Electric
Propulsion (FEEP) will have to be used.