| A torsional impulse balance has been developed as a new diagnostic tool to study fundamental physical processes in micropropulsion systems and laser-surface interactions. With respect to momentum transfer, direct measurements of the transient forces can lead to a better understanding and characterization of the efficiency of the thrust that is possible under different configurations. The impulse balance has been designed and tested with a robust calibration system to measure impulsive forces with resolution as low as a few nano-Newton-seconds. A technique has been developed to derive the measured force as a function of time. Although total delivered impulse is generally measured and deemed adequate for most applications, time resolved thrust measurements can provide deeper understanding and enhanced characterization of thruster operation for longer duration impulses or multiple pulse applications. In order to directly obtain the specific impulse, modified versions of the impulse balance have also been investigated to measure impulse and mass loss simultaneously.; Laser propulsion concepts have extensively been discussed since the early 1970s. Ranging from alternative launch solutions to on-orbit maneuvering systems for spacecraft, these concepts have employed an equally diverse range of momentum transfer mechanisms including ablation, shock wave generation, and even photon pressure. Within the scope of laser ablation, investigations of a wide variety of physical processes are of interest, which include sputtering, vaporization, and ionization. The conditions for which each physical process might occur and the controlling parameters can be studied by total impulse and time resolved force measurements. For a variety of metal and polymer materials, the impulses due to a range of pulse energies, fluences, pulsewidths, wavelengths, and repetition rates have been investigated. A number of methods for determining the ablated mass have also been examined in order to determine the specific impulse of the target materials and characterize the materials as possible propellant sources for space propulsion applications. |
