DIRECTIONS OF POTENTIAL INCREASE IN IMPULSE PERFORMANCE OF SPACECRAFT PROPULSION SYSTEMS

This paper outlines directions of potential increase in performance of spacecraft propulsion systems with regard to their mission impulse and velocity-increment capabilities. Performance evaluations have concentrated on today’s most commonly used spacecraft propulsion system designs, comprising chemical and electric propulsion. For the determination of related propulsion system performance capabilities, the reference number ‘System-specific Impulse’, Issp is applied, which takes into account all parameters influencing the impulse-dependent part of the propulsion system mass 1. The magnitude of potential increase in propulsion performance has been outlined in parametric investigations by some examples. Actual designs of chemical propulsion systems are well developed and only small increases in performance can be expected by e.g. further improvements in light weight tank design, possibly in combination with propellant pump-fed systems for lower propellant tank pressure or use of propellants with higher densities. For electric propulsion, being still under development, results of the parametric investigations show that for increase in propulsion impulse capability, thruster optimum exhaust velocity ve-opt should be as high as possible in order to achieve maximum values of Issp. This requires that power supply systems with high specific power need to be further developed especially for deep space missions where solar electric propulsion cannot be used any more. In addition, this should be supported by a further development of power processing units and electric thrusters with high specific power and high efficiencies. Thruster exhaust velocities should be fully adaptable to the optimum exhaust velocity. In addition, thrust operation time should be always a maximum within the frame of mission manoeuvre time.