Barry Cornella

Impact of Separation Distance on Multi-Vane Radiometer Configurations

The radiometric force produced by a linear array of three radiometer vanes has been assessed numerically using an argon carrier gas and experimentally using air. The separation distance between the three vanes of the array was varied between 0 and 120 percent based on the height of an individual radiometer vane of 40 mm. Qualitative agreement between the numerical and experimental results is shown as a function of operating Knudsen number, vane separation distance, and surrounding chamber geometry. Both sets of results indicate an asymptotic trend in maximum force as the separation distance increases as well as a shift in the maximum force Knudsen number. Small chamber effects for both numerical and experimental results indicate an increase of the total force ranging from a factor of 2.5 to 4. Quantitatively, however, the numerical simulations yield forces approximately an order of magnitude higher than observed in the experiments due to differences in carrier gas and accommodation coefficient as well as ...

Analysis of Multi-Vane Radiometers in High-Altitude Propulsion

Abstract : A near-space propulsion system using radiometric forces is notionally developed for the Lockheed HALE-D vehicle. The purpose of the system is to provide wind disturbance compensation for the vehicle operation at 20 km. Experimental results indicate that using a multi-vane configuration increases the force produced per unit mass of the radiometer. Previous numerical studies were implemented to determine the force production of the proposed concept design. The proposed design features in integrated system where multi-vane radiometers line the surface of the vehicle and operate on solar power. The HALE-D vehicle at 20 km requires 40.1 billion sub-vanes, at 26 micrometers in length, covering a total area of 101 square meters in order to produce the necessary 142.1 N of thrust to counter the wind drag. Results are also given for systems at altitudes above 20 km.

Investigation of Density Perturbations in Molecular Nitrogen Formed by Pulsed Optical Lattices

Abstract : A complimentary experimental/numerical investigation on the effect of counter-propagating pulsed lasers on molecular nitrogen was conducted. The experiment verified published theoretical predictions of the effect of laser intensity and gas pressure on the magnitude of induced density perturbations in the gas using a coherent Rayleigh-Brillouin scattering technique. The investigation further verified the use of a modified version of the SMILE DSMC code for more robust prediction of the effect of a non-resonant pulsed optical lattice on a neutral gas. The ambient pressure of molecular nitrogen was varied from 100 torr to 760 torr, and the pump laser energy was varied from 2 mJ to 25 mJ per pulse. The resulting scattered signal from the experiment was measured and compared with numerical predictions. Assuming that the signal of the experiment is proportional to the probe intensity and the square of the density perturbations induced by the pump lasers, the results of the experiment qualitatively support both theoretical predictions and numerical simulations.

Power Generation for Beamed Microwave Propulsion Concepts

Thrust augmentation of a solid rocket motor using beamed energy is being proposed to enhance the performance of modern launch vehicles. A key component of the thrust augmentation concept is the development of a ground-based microwave generation facility. The purpose of this paper is to formulate a theoretical design for the microwave generation system that will couple directly to alumina particles in the exhaust of a solid rocket motor. The requirements for the system were set using the first two stages of a Pegasus XL as a nominal launch vehicle. For this concept, thrust augmentation occurs only within the first 50km of the launch vehicle ascent. The overall antenna structure is comprised of 665 total parabolic dishes where the inner most section has 145 dishes with a diameter of 2.25 m and the outer section consists of 520 dishes with a diameter of 9 m. Each dish is powered by one or more gyrotrons with a total system input power of 3.13 GW and an output power of 1.77 GW. This output power is designed to generate a power of 1.0 GW at the nozzle of the vehicle throughout the first 50 km of flight. Every one of the 1770 gyrotrons in the overall system is capable of producing 1MW continuous-wave power. Although the system designed in this paper is unique for this particular beamed energy propulsion scheme, similar methods have been used in the literature to design ground-based microwave generators for other concepts. Using a passive phased array consisting of variable sized radiating elements and multiple gyrotrons per element, the desired spot size (1.5 m) and power (1 GW) at the vehicle for the overall system can be realized. To achieve a relatively constant power and spot size throughout the launch trajectory, an active method of powering additional radiating elements as a function of altitude through the ascent trajectory is outlined.