Status and Perspectives of Laser Ignition of a Cryogenic Research RCS Thruster

Kurzfassung

The ignition of cryogenic rocket engines is a critical step towards a reliable functioning of the engine. This process is characterized by the injector head geometry, the ignition method, the thermodynamical condition of the injected propellants and the sequencing of the propellant injection. This article reports on the advances towards the laser ignition of a cryogenic research reaction control system (RCS) thruster with 5 coaxial injectors. In the last years, laser ignition of a single injector configuration has been investigated with hundreds of ignitions performed for in vacuum injection and the two propellant combinations LOx/CH4 and LOx/H2 at the test bench M3.1 of the DLR Institute for Space Propulsion [11, 12]. For future applications of laser ignition in upper stage launcher engines or RCS engines, a broader background knowledge of the laser ignition processes of multi-injector configurations is needed but which is not available today. An injector head consisting of five individual but identical coaxial injectors has been designed and qualified for this purpose. In this configuration, one injector is surrounded by four injectors for boundary effect shielding. The combustion chamber used for the single injector configuration tests is foreseen for the upcoming tests and is optically accessible from three sides. Multiple optical diagnostics like high-speed Schlieren, highspeed OH* imaging and laser induced breakdown spectroscopy have been installed at the test bench and can be operated simultaneously. Cold flow checks with LOx and gaseous H2 have recently been carried out and are presented in this paper. Finally, a brief outlook is given on further laser ignition research activities at the test bench M3.1.