SBIR-STTR Award

Pulsed plasma thrusters are a possible propulsion system for all small satelites of the future, specially the USAF TechSat-21 program. They probably represent the key enabling technology for future spacecraft in the 20-100 kg class. Current PPT systems are characterized by extremely por efficiency, utilizing only ten percent of the energy and twenty percent of the propellent. Low fuel is caused by late-time vaporization and particulate emission, a result of less than ideal thermal management in the PPT design and the mechanical properties of current propellants. Energy inefficiency is due to magnetic field-diffusion after the first half-cycle of discharge. A PPT, using semiconductor switching of the discharge current in place of the present spark triggering offers the potential to overcome two fo these problems. With no voltage across the electrodes prior to the discharge after the first half cycle will prevent the loss of energy to magnetic field diffusion. Other research has demonstrated the concept of semiconductor control, but not with alternate propellants, or improved acceleration mechanisms. Changes in the physical design of the PPT will improve the passive cooling of the fuel, and make active cooling of the thruster a possibility

Under this Phase II SBIR program, work will continue on the development of the electrically controlled propellant that is currently being researched on a PHASE I SBIR effort. Work completed to date on the Phase I program has demonstrated (1) the feasibility of electrical initiating combustion of a very safe solid solution propellant, (2) sustaining the combustion with continued electrical input, (3) controlling the combustion rate by varying the voltage and (4) terminating combustion by turning off the electrical flow. Also, multiple starts and stops have been demonstrated on the same propellant sample. This study has also revealed several aspects of the propellant that need improvement. The main concern is the propellant tendency to soften or melt and exhibit flow just prior to combustion. Several approaches are planned to address this behavior, such as cross-linking the polymer within the propellant and increasing the molecular weight and branching of the polymer with e-beam irradiation. Other areas include processing, effect of moisture, enhancing combustion rate while electrically activated and increasing propellant energy. Studies planned for this Phase II program are designed to correct these concerns or greatly diminish their importance.

Keywords:
SOLID SOLUTION PROPELLANTEXTINGUISHABLE ELECTRICALLY CONDUCTIVE SATELLITE CONTROL ROCKETS ELECTRICAL