Emission Spectra of Hydrogen-Seeded Helium Arcjets
Abstract
With currently available space electric power systems, the optimum specific impulse for electrically propelled satellite transfers from low Earth orbit to geosynchronous Earth orbit appears to be in the 1000 to 1200 second range. Arcjets operating with helium as a propellant may be the most efficient electric thruster capable of operating in this specific impulse range. This work reports on a recent set of experiments in which emission spectra of the plume of a helium arcjet were acquired and analyzed to obtain information on the internal energy modes of the arcjet. Of particular interest is the population of electronically excited helium states, as these carry a large energy, and would have a significant negative impact on arcjet performance if highly populated. Experiments were conducted using pure helium as a propellant, and using helium seeded with small amounts (<= 5%) hydrogen. Data are presented which show that the intensity of emissions from the excited helium states falls off rapidly as the hydrogen concentration is increased. Electron temperatures, as determined by Boltzman plots of three different series of helium lines, remain constant within limits of uncertainty as the hydrogen concentration is varied. It is also observed that, as a function of distance from the exit plane, the emission intensities of several lines in the helium spectrum fall off proportionally, indicating that the emission observed does not derive from re-emission of photons originating in the arc which were absorbed by the plume.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 21, 2000
- Accession Number
- ADA380663
Entities
People
- R. P. Welle
Organizations
- The Aerospace Corporation