Techniques for Spectroscopic Measurements in an Arcjet Nozzle

A successful attempt has been made to gain optical access to the inside of an arcjet nozzle without changing internal thruster design or affecting performance characteristics. Both fiber optics and small open holes have been used for emission spectroscopy of a small, confined, high-temperature plasma source. The plasma was found to be in a highly nonequilibrium state, with electron excitation temperatures more than double the rotational or vibrational temperatures.