Fiber-Optic Sensors for the Study of Spacecraft-Thruster Interactions: Ion Sputtering

The FOCS principle of operation has been verified in a proof-of-principle demonstration. A decrease in transmitted signal strength was observed as the optical fiber cladding thickness decreased during the HF sub aq solution etch. The experimental results obtained in this study simulated the sputtering of optical fiber cladding material by energetic ions in the plume of ion electric thrusters. The repeatability of the HF sub aq etch results indicate that the sensor can be calibrated for transmitted light intensity as a function of cladding thickness. Measured and calculated sputter rates for a SPT-100 plume impacting a SiO sub 2 surface were used to calculate values for the FOCS effect time based on correlations with the measured HF sub aq etch characteristics. Results indicate that the transmitted light intensity will go from maximum to zero signal in approximately 6.5 h if the sensor is placed 1 m downstream of an SPT-100 on the thruster centerline. This effect time is shown to increase as the divergence angle from the thruster centerline increases. Placing the optical fiber perpendicular to the thruster centerline can reduce the predicted effect time at high plume angles. In the perpendicular configuration effect times less than one-tenth of the design lifetime of a typical Hall thruster (approx 2000 h) can be achieved for almost any plume angle.