THIS PROPOSAL SEEKS TO INVESTIGATE THE FEASIBILITY AND PERFORMANCE OF LASER-SUSTAINED PLASMA (LSP) PROPULSION USING AN ON-BOARD LASER AND WATER PROPELLANT AS A BREAKTHROUGH IN-SITU RESOURCE UTILIZATION (ISRU) SOLAR ELECTRIC PROPULSION (SEP) TECHNOLOGY. PREVIOUS WORK HAS SHOWN THAT LSP THRUSTERS OFFER UNIQUE MISSION BENEFITS FILLING THE GAP BETWEEN SPECIFIC IMPULSE-LIMITED CHEMICAL PROPULSION AND THRUST-LIMITED ELECTRIC PROPULSION. SUCH A THRUSTER'S POTENTIAL SPECIFIC IMPULSE UP TO 1 000 S WITH WATER AN INERT ISRU PROPELLANT MAKES IT UNIQUELY SUITED TO REPLACE CURRENT PROPULSION TECHNOLOGIES FOR STATION-KEEPING ORBITAL TRANSFER VEHICLES AND A WIDE VARIETY OF DEEP-SPACE MISSIONS. THE POSSIBILITY OF ON-BOARD LSP PROPULSION IS ENABLED BY A NEW GENERATION OF HIGH EFFICIENCY SOLID STATE LASERS WHICH UP UNTIL NOW HAVE NOT BEEN CAREFULLY STUDIED FOR THIS APPLICATION. IN LSP PROPULSION A HIGH-POWERED LASER IS FOCUSSED TO PROVIDE MAXIMUM POWER DENSITY IN A REGION JUST INSIDE THE THROAT OF A DE-LAVAL NOZZLE. POWER DENSITY IS SUCH THAT PLASMA DISCHARGE OCCURS INCREASING OPTICAL ABSORPTIVITY TO NEAR UNITY AND ALLOWING HEATING OF THE PLASMA TO TEMPERATURES ON THE ORDER OF 10^4 K. KEY INNOVATIONS ARE: 1. TO MAKE THE LSP THRUSTER VIABLE BY USING MODERN HIGHLY EFFICIENT LASERS WHICH HAVE UNDERGONE A REVOLUTION SINCE MAJOR LSP RESEARCH WAS LAST CONDUCTED ABOUT 30 YEARS AGO 2. TO APPLY LSP PROPULSION TO ISRU BY TAKING ADVANTAGE OF ITS UNIQUE CAPABILITY TO ACHIEVE HIGH SPECIFIC IMPULSE USING WATER PROPELLANT. MOST OF THE RESEARCH INTO LSP PROPULSION WAS CONDUCTED IN THE 1980S ALTHOUGH ONE DIMENSIONAL MODELING WORK TO UNDERSTAND LASER-SUSTAINED PLASMAS WAS PUBLISHED AS EARLY AS 1970. RELATIVELY FEW LSP THRUSTERS HAVE BEEN CONSTRUCTED AND EXPERIMENTALLY CHARACTERIZED BUT SIGNIFICANT MODELING WORK HAS BEEN DONE. A REALISTIC UPPER LIMIT BASED ON KINETIC FLOW MODELING PUTS SPECIFIC IMPULSE USING HYDROGEN PROPELLANT AT 1900 S. TWO-DIMENSIONAL KINETIC SIMULATION PERFORMED FOR THIS PROPOSAL WHICH INCORPORATES MOLECULAR DISSOCIATION SUGGESTS A SPECIFIC IMPULSE OF 750 S AT A TEMPERATURE OF 8000 K WHICH SEEMS REASONABLE GIVEN TEMPERATURE DATA FROM SIMULATIONS FROM THE PAST. SIGNIFICANT MODELING WORK WILL BE DONE TO ASSESS THE EFFECTS OF WATER PROPELLANT AND TO OPTIMIZE THE DESIGN OF THE THRUSTER WILL BE DONE. A THRUSTER WILL BE BUILT USING THE INFORMATION GLEANED FROM MODELING. ITS PERFORMANCE INCLUDING SPECIFIC IMPULSE THRUST AND EFFICIENCY WILL BE CHARACTERIZED AND COMPARED TO THE MODEL TO GAIN FURTHER INSIGHTS INTO IMPROVED DESIGN. THE PROCESS WILL THEN BE ITERATED. THE ON-BOARD LSP WATER THRUSTER WILL FIT INTO TWO NASA TABS AREAS. BECAUSE OF ITS OBJECTIVE TO INCREASE PERFORMANCE OF ELECTRIC PROPULSION IT FALLS UNDER 2.2.1 ELECTRIC PROPULSION. IT FURTHER APPLIES TO 7.1 BECAUSE OF THE GOAL TO LEVERAGE IN-SITU RESOURCES TO DRAMATICALLY REDUCE LAUNCH MASS AND COST OF HUMAN EXPLORATION MISSIONS. BY MARRYING THE TWO TABS ELEMENTS A BREAKTHROUGH HIGHPERFORMANCE PROPULSION SYSTEM CAN BE DEVELOPED WHICH USES A COMPLETELY GREEN EARTH-STORABLE PROPELLANT.