In a thermal arcjet the main heating of the propellant takes place in
the constrictor. To gain more insight into arcjet operation and to obt
ain experimental data on the shape, size, and stability of the arc cha
nnel inside the constrictor, a modified arcjet thruster was built. Thr
ough a window in the nozzle throat the discharge channel in the constr
ictor was observed. With a fast CCD camera, images of the arc were tak
en, and using image processing methods a hydrogen arc was analyzed. Th
e camera system was calibrated to measure absolute intensities. Thus,
it was possible to determine the two-dimensional temperature profiles
from electron continuum and from the line intensity ratio of the H(alp
ha) and the H(beta) line. In the second section, an analytical method
to calculate the flow conditions inside the constrictor is described.
The first version of the model is developed for hydrogen as propellant
. The calculation results are compared with measurements.