Date of Award

8-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical Engineering

First Advisor

Dr. Richard R. Schultz

Abstract

Free space laser communications provides wide bandwidth and high security capabilities to Unmanned Aircraft Systems (UAS) in order to successfully accomplish Intelligence, Surveillance, Target Acquisition, and Reconnaissance (IST AR) missions. A practical implementation of a laser-based video communications payload flown by a small U AS aircraft is described as a proof-of-concept. The two-axis gimbal pointing control algorithm calculates the line-of-sight vector in real-time by using Differential Global Positioning System (DGPS) and Inertial Measurement Unit (IMU) information gathered from the UAS vehicle's autopilot so that the laser transmitter in the airborne payload can accurately track a ground-based photodiode array receiver with a known DGPS location. One of the future goals of this project is to move from DAS-to-ground communications to UAS-to-UAS free space laser communications.

A communications system has been developed using Light Amplification by Stimulated Emission of Radiation (LASER) to transmit data to a known location on the ground. Several main subsystems including the laser transmitter, laser receiver, gimbal, subsystem, and tracking software are discussed, along with the integration and testing phase. The laser transmitter is mounted within the Super Hauler small UAS payload bay. The UAS was custom made in compliance with the Super Hauler requirements, specifically regarding the size and shape of the payload bay. A two-axis gimbal system is controlled via the tracking software to point the laser beam to a specified DGPS coordinate throughout the flight. In addition to the GPS system, there is a machine vision-based tracking system in development that works in parallel with the GPS system and takes over gimbal control for precise alignment.

At the known DGPS coordinate, the ground-based receiver is stationary and converts the video data carried by the laser to a viewable format. The receiver, like any other subsystem, is a very crucial component of a successful data transmission system; therefore, significant time and effort was designated for its development.

To ensure successful operation of the free space laser communications payload, a series of subsystem tests were performed. For each subsystem, a test procedure was developed with specific pass-fail criteria. After each subsystem was tested, a full system test was also carried out. The full system included the integration of all subsystems inside the payload bay of the Super Hauler UAS. Detailed analyses of the testing procedures along with the integration process are presented in this thesis. After the full system was successfully tested in the laboratory, preliminary flight tests took place in July and October of 2009 within military-restricted airspace over Camp Grafton South, a National Guard training facility in North Dakota, followed by another flight tests in June 2010. While these preliminary flights did not result in video transmission, they were very successful in gathering preliminary data and field test information. These results are crucial in the continued development of the system. Recommendations for future payload improvements are discussed in the last section of this thesis.

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