Laser ignition of an experimental cryogenic reaction and control thruster: Ignition energies

An extensive experimental investigation has been conducted to assess the feasibility of implementing laser ignition in a cryogenic reaction and control system and orbital and maneuvering system thrusters. A 400 N experimental thruster, with a single-coaxial injector element, was designed for a steady-state pressure of 2 bar and was tested using two laser ignition systems: a tabletop laser as well as a miniaturized laser, which was mounted onto the thruster. Chamber pressures in the thruster before ignition varied from 200 mbar for liquid oxygen/gaseous methane to 450 mbar for liquid oxygen/gaseous hydrogen. The locations of energy deposition and the energy deposited were varied to determine the associated ignition probabilities for the propellant combinations liquid oxygen/gaseous hydrogen and liquid oxygen/gaseous methane. Plasma ignition and ablation ignition were both examined. For 100% ignition success, minimum energies measured were lower for liquid oxygen/gaseous hydrogen (72 mJ) than for liquid oxygen/gaseous methane (92 mJ), and they were lower for ablation (14.5 mJ for liquid oxygen/gaseous hydrogen and 61.7 mJ for liquid oxygen/gaseous methane) than plasma ignition. The feasibility of laser ignition for cryogenic thrusters was demonstrated, and further investigation needs were revealed.