Karl R. Vaden

Advances in Space Traveling-Wave Tubes for NASA Missions

Significant advances in the performance and reliability of traveling-wave tubes (TWTs) utilized in amplifying space communication signals for NASA missions have been achieved over the last three decades through collaborative efforts between NASA and primarily L-3 Communications Electron Technologies, Inc. (L-3 ETI). This paper summarizes some of the key milestones during this period and includes development of TWTs for the Communications Technology Satellite, Cassini, and Lunar Reconnaissance Orbiter missions. Technical advances in computer modeling, design techniques, materials, and fabrication have enabled power efficiency to increase by almost 40% and the output power/mass figure-of-merit to increase by an order of magnitude during this period.

High Power Combining of Ka-Band TWTs for Deep Space Communications

This paper presents the results of a high efficiency power combining demonstration of two 100 W Ka-band space TWTs using a 4-port magic-T hybrid junction-based waveguide circuit. Power combining efficiencies of about 90% over a 1 GHz frequency band centered at 32.05 GHz and a high data transmission rate of 622 Mbps were successfully demonstrated

A simulated annealing algorithm for the optimization of multistage depressed collector efficiency

The microwave traveling wave tube amplifier (TWTA) is widely used as a high-power transmitting source for space and airborne communications. One critical factor in designing a TWTA is the overall efficiency. However, overall efficiency is highly dependent upon collector efficiency; so collector design is critical to the performance of a TWTA. Therefore, NASA Glenn Research Center has developed an optimization algorithm based on Simulated Annealing to quickly design highly efficient multi-stage depressed collectors (MDC).

Aeronautical situational awareness - airport surface

This paper advocates for a specific design approach, based on simple principals, yet addresses challenges faced by the system engineers when designing complex data and information infrastructure. The document provides guidance for breaking out various work elements in the overall network architecture design, so that communication systems are conceived and effectively realized regardless of their location, size and local specifics. Although targeted at the Global Airspace System (GAS) and National Airspace System (NAS), this framework can be applied to any network-centric architecture.

The characteristics and modeling of secondary electrons elastically scattered from collector surfaces

Previous research has shown that secondary electron emission can reduce collector performance and consequently, the performance of electron beam devices. While all secondaries can create problems, elastically scattered secondary electrons (sometimes called reflected primaries) are particularly important. Their high energies allow a greater probability of these electrons leaving the collector, re-entering the slow-wave circuit and producing unwanted signal distortion or signal oscillation. However, a complete analysis of the effects of elastically scattered secondary (ESS) electrons has not been possible because of the lack of quantitative data. For this reason, NASA Glenn Research Center measured the angular distributions of ESS electrons from three materials of interest: oxygen-free, high conductivity (OFHC) polished copper, OFHC copper textured by ion texturing and high purity isotropic graphite.