The work on laser propulsion at the Institute of Technical Physics covers both basic investigations on pulsed thermal laser propulsion with stationary high power laser sources and the development and qualification of laser ablation based micro rockets.
The principle of thermal laser propulsion is based on a repetitively pulsed propulsion mechanism. A thrust chamber in the form of a parabolic reflector concentrates the received laser energy into the focal spot. There, from the propellant, for example air, a high density plasma is formed, which detonates and rapidly expands. A spherical shockwave is produced at high pressure and high temperature, which accelerates the gas. By means of a metallic ignition pin on the axis of symmetry of the thrust chamber, a consistent reproducible ignition of the detonation process is ensured. High speed camera recordings of pulsed free flights of the laser rocket indicate that the craft exhibits beam riding properties within certain limits of lateral offset and inclination. Based on calculations of the intensity distribution inside the thrust chamber this highly nonlinear dynamic system and the resulting forces have been numerically modelled. Thus suitable starting parameters for stable flight as well as critical boundary conditions can be derived by the calculations. Active flight control has been implemented by tilting the ignition pin or the propellant cylinder with respect to the axis of symmetry of the thrust chamber.
For micro propulsion by laser ablation the (compact) laser source is integrated in the thruster device. The thrust is generated as a result of the recoil of the ablated propellant.
Precise thrusters require highly accurate impulse bits and high specific impulse. Different metallic propellants made from aluminium to gold are promising candidates to meet these requirements.
Experimental investigations are carried out at a test bed employing a solid state laser. The experiments are supported and complemented by theoretical calculations on the propulsion process. The experimental setup includes a highly sensitive thrust gauge under vacuum conditions as well as devices for the analysis of the expansion velocity of the ablation jet. The development of an active optical system that allows for momentum conserving beam steering across the target surface is a prerequisite for the vibration free integration of the thruster in the satellite system. For future missions the long term stability and the reproducibility of the system performance have to be proven in extended endurance tests.