In recent years, spacecraft requirements have trended toward smaller, lighter, and less expensive systems with more capabilities. At the same time, demands on the communication systems have increased, including faster data rates, lower power budgets, reduced system volume, and smaller link margins. The combination of these factors has posed numerous engineering challenges for antenna system designers, often forming complex tradeoffs among design parameters such as bandwidth, pattern control, beamwidth, and antenna size. In this paper, we show how a challenging set of antenna requirements were met for NASA's recent LADEE mission. We focus on the difficulties inherent in the requirements for both omnidirectional and medium gain antennas, both in S-band. We present techniques used to develop a requirements-compliant system based on our research in antenna synthesis methods. Compared to the conventional antennas considered by NASA for the mission, the antennas we developed yielded 65% increased downlink coverage and 44% cost savings for the mission. The deployed flight antennas were the only antennas on the mission and performed above expectations during the 8-month mission, which concluded in April 2014.
The design and application results of an affordable short range (less than 100 m) digital LIDAR (LIght Detection And Ranging) system will be presented. This work was initiated because many short-range standoff detection applications would benefit from such a system. The lidar features a fiber-based component integrated in the optical module, which allows for hardware partial compensation of the backscattered signal losses observed at short distances due to a biaxial configuration of the lidar optics. This is an important advantage for particle density computations. The digitized backscattered laser signals are available for signal processing. A dedicated FPGA (Field Programmable Gate Array) allows for real-time averaging of the signal waveforms captured at the maximum 50-kHz pulse repetition frequency of the laser.Several application-specific tests have been performed. The first of these was real-time onboard monitoring of pesticide drift in agricultural spraying applications. The signal levels were sufficient for control of the spraying operations and prevention of pesticide drift into sensitive areas. The second was a dust monitoring application. The lidar was installed in a quarry and signals from dust clouds were recorded. Real-time monitoring capabilities were shown to be promising. Other applications involving detection of solid targets in degraded visibility conditions caused by fog or snowfalls were also tested and are discussed.
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