Comparative Study of Plastics as Propellants for Laser Ablation Plasma Thrusters

Abstract

NEW analysis and comparison of laser ablation propulsion(LAP) parameters like specific impulse and coupling coef-ficientobtainedwhileablatingdifferentprospectiveplasticmaterialsis presented inview ofselecting themost suitable ofthem. Thetestsinvolved a medium–low energy pulsed laser along with a free-moving ballistic pendulum with a target pasted on it. In a novelapplication of 2-D position-sensitive detectors (PSDs) in LAP, thedisplacement measurements were taken by the noncontact opticaltriangulationwithalaser.Theirusegavetheadvantagesofdetectingany unwanted lateral movement of the pendulum. The study shouldhave high utilization for the future LAP applications.Laser ablation propulsion technique, introduced by ArthurKantrowitzin1972,dependsuponthecharacteristicsoflasersourceaswellasthoseofthetargetmaterial,asthemomentumofthetargetis produced in reaction to the generated momentum of the ejectingparticles [1–3]. Specific impulse values up to several thousandseconds are possible by properly choosing the propellant, that is,targetmaterialandthelaserpulsecharacteristics.Themomentumofthe object may well also depend on the coupling coefficient ofmaterial–laser interaction. Earlier worksinclude ablation with someof the materials included in this study, but here a list of threecommonly available plastics is analyzed and compared [3–6].Additionally, most researchers have employed mechanical forcesensingforthrustmeasurementorcharge-coupleddeviceimagerfordisplacement measurement [5], whereas others have used electro-magneticcoilsforsensingtorqueonthesuspendedtarget[3].Ontheother hand, here a noncontact optical triangulation method is beingemployed using a precision PSD with 1 m resolution and a stableHe-Ne laser. This yields direct measurement and better accuracyalongwithlateral-shifterrorreduction,andthususefuloutputcurveshave been obtained.