Satellite propulsion spectral signature detection and analysis
Space Situational Awareness (SSA) is of utmost importance in today's space dependent, congested and contested environment. The health of a propulsion system is vital to ensure proper function and thus proper mission placement. Electric propulsion is gaining popularity for satellite propulsion systems due to higher efficiencies, specific impulse, and the savings it offers in both spacecraft mass and launch costs. Electron temperature is a commonly used diagnostic to determine the efficiency of a Hall thruster. Recent papers have coordinated near infrared (NIR) spectral measurements of ionization lines in xenon and krypton to electron temperature measurements. This research will characterize NIR plume emissions for a 600 Watt Hall thruster using both xenon and krypton propellants for a variety of observation angles and operating power levels. By determining spectral differences when altering these variables, it would be possible to identify angle, power level, and propellant in order to provide information on electron temperature and thus efficiency. Although they have a high specific impulse, electric propulsion systems provide lower thrust than chemical alternatives. This means that the firing times needed for spacecraft maneuvers can be on the order of hours to months. This provides an opportunity for this characterization to not only be put to use in chamber experiments but on-orbit as well. Ground-based observations of these spectral lines would allow for identification of the type of thruster as well as the health of the system while the satellite is in operation on-orbit. The current SSA architecture is limited and task saturated. If smaller telescopes, like those at universities, could successfully detect these signatures they could augment data collection for the SSA network. To facilitate data collection, precise atmospheric modeling must be used to identify the signature. Within the atmosphere, the NIR has a higher transmission rate and typical HET propellants are approximately 3x the intensity in the NIR versus the visible spectrum making it ideal for ground based observations. This research will combine emission measurements with atmospheric and plume models to develop a single end-to-end model that will determine xenon and krypton signatures through the atmosphere, discernable differences in power level and viewing angle of Hall thruster systems, and estimate the efficacy through ground-based observations.
Emission-Excitation Cross Sections Relevant to Krypton-Propelled Electric Thrusters
Emission-excitation cross sections for collision processes relevant to krypton-propelled Hall effect and ion thrusters are measured using optical emission spectroscopy in the 350–1000 nm spectral range. Absolute spectral radiances were recorded for collisions between beams of krypton ions (either singly or doubly charged) and electrons with a Kr gas at charged particle energies relevant to electrostatic thruster plasmas. The most prominent emissions observed are in the near-infrared region from a low-lying excited electronic state of neutral Kr. In the case of Kr+/Kr2++Kr systems, the emission-excitation cross section from this low-lying excited electronic state of neutral Kr has a threshold at approximately 12.5 eV in the center-of-mass frame, and it increases with collision energy until 200 eV, where it remains constant through 600 eV. The energy dependence of cross sections for emission from Kr II varies with the colliding charged particle. The threshold for the radiative emission of Kr II is estimated...
The General Theory of Relativity
THE WORD “SPECIAL” IN “SPECIAL THEORY OF RELATIVITY” means that the theory is restricted to those frames of reference for which the law of inertia holds, that is, inertial frames of reference.* Einstein sometimes referred to them as Galilean frames of reference. At first glance, it does not seem reasonable to expect that the principle of relativity can be extended to non-inertial frames. The reasons are fairly obvious. The principle of relativity that we have been using states that the laws of physics have the same form in all frames of reference to which the principle applies. In other words there should be no way to determine by an experiment which of two frames of reference is in motion relative to the other.