Evaluation and Characterization of Laser Ignition Conditions for RCS Thruster Using Green Propellants

Paper number

IAC-08.C4.3.8

Author

Dr. Shinichi Moriya, Japan Aerospace Exploration Agency (JAXA), Japan

Year

2008

Abstract

Future rocket engine systems will require more reliable ignition systems than conventional spark plugs. RCS (Reaction Control Systems) in particular with their multiple thrusters configuration and high-repetition operation will require the most reliable and durable ignition systems. Laser ignition may be an option for such systems. Gaseous oxygen (GO2)/gaseous hydrogen (GH2) and GO2/gaseous methane (GCH4) were selected as green propellants, due to the environmental and handling problems of conventional propellants ordinarily used for RCS, such as hydrazine and NTO/MMH.
   There are two methods for laser ignition; one is the use of ablation plasma produced on a solid target material with pulsed-laser irradiation. The other is the use of breakdown of the ambient gas by focusing the pulsed-laser beam in the gas. In the preliminary tests, it was clarified that the ablation method needed smaller energy than that of the breakdown method. A high-intensity laser pulse focused on the target surface generates a high-temperature metal vapor and caused ignition of the mixture gas. In the experiment, a conventional Nd:YAG pulse laser was used to ignite a small thruster (with an inner diameter of 1 cm). It was found that the ignition energy decreases as the chamber pressure increases as the result of single-pulse tests, the minimum ignition energy was lower than 2 mJ, and at the optimum chamber pressure and mixture ratio, GO2/GH2 mixture gas and GO2/GCH4 mixture gas can be ignited at 30 ?J and 230 ?J, respectively. This means that fiber-optic transmitted laser ignition can be applied to both GO2/GH2 and GO2/GCH4 propellants. One hundred cyclic pulse mode operation was also successfully demonstrated for the RCS. However, the conventional laser unit used in the preliminary tests was unsuitable for RCS ignition system application because of large size and weight.
   The fiber optic is a useful element for the distribution of the laser pulse with high reliability. On the other hand, the micro chip laser is a promising candidate put in each thruster because of its small size and higher power density. In this study, ignition conditions by using a fiber laser and a micro tip laser were evaluated and characterized to realize a small size and weight RCS system.

Abstract document

IAC-08.C4.3.8.pdf

Manuscript document

IAC-08.C4.3.8.pdf (🔒 authorized access only).

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