Dale A. Force

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.

Ultra-High Power and Efficiency Space Traveling-Wave Tube Amplifier Power Combiner With Reduced Size and Mass for NASA Missions

In the 2008 IEEE Microwave Theory and Techniques Society International Microwave Symposium Digest version of our paper, recent advances in high power and efficiency space traveling-wave tube amplifiers for NASAs space-to-Earth communications are presented. The RF power and efficiency of a new K-band amplifier are 40 W and 50% and that of a new K-band amplifier are 200 W and 60%. An important figure-of-merit, which is defined as the ratio of the RF power output to the mass (W/kg) of a traveling-wave tube (TWT), has improved by a factor of 10 over the previous generation Ka-band devices. In this paper, a high power high efficiency Ka -band combiner for multiple TWTs, based on a novel hybrid magic-T waveguide circuit design, is presented. The measured combiner efficiency is as high as 90%. In addition, at the design frequency of 32.05 GHz, error-free uncoded binary phase-shift keying/quadrature phase-shift keying (QPSK) data transmission at 8 Mb/s, which is typical for deep-space communications, is demonstrated. Furthermore, QPSK data transmission at 622 Mb/s is demonstrated with a low bit error rate of 2.4 times10-8, which exceeds the deep-space state-of-the-art data rate transmission capability by more than two orders of magnitude. A potential application of the TWT combiner is in deep-space communication systems for planetary exploration requiring transmitter power on the order of a kilowatt or higher.

High power and efficiency space traveling-wave tube amplifiers with reduced size and mass for NASA missions

Recent advances in high power and efficiency space traveling-wave tube amplifiers (TWTAs) for NASA’s space-to-Earth communications are presented in this paper. The RF power and efficiency of a new K-Band amplifier is 40 Watts and 50% and that of a new Ka-Band amplifier is 200 Watts and 60%. An important figure-of-merit, which is defined as the ratio of the RF power output to the mass (W/kg) of a TWT has improved by a factor of ten over the previous generation Ka-Band devices.

High-efficiency K-band space traveling-wave tube amplifier for near-earth high data rate communications

The RF performance of a new K-Band helix conduction cooled traveling-wave tube amplifier (TWTA), is presented in this paper. A total of three such units were manufactured, tested and delivered. The first unit is currently flying onboard NASAs Lunar Reconnaissance Orbiter (LRO) spacecraft and has flawlessly completed over 2000 orbits around the Moon. The second unit is a proto-flight model. The third unit will fly onboard NASAs International Space Station (ISS) as a very compact and lightweight transmitter package for the Communications, Navigation and Networking Reconfigurable Testbed (CoNNeCT), which is scheduled for launch in 2011. These TWTAs were characterized over the frequencies 25.5 to 25.8 GHz. The saturated RF output power is >40 W and the saturated RF gain is >46 dB. The saturated AM-to-PM conversion is 3.5°/dB and the small signal gain ripple is 0.46 dB peak-to-peak. The overall efficiency of the TWTA, including that of the electronic power conditioner (EPC) is as high as 45%.

A high-efficiency 59- to 64-GHz TWT for intersatellite communications

The design of a 75-W, 59-64 GHz TWT (traveling wave tube) with a predicted overall efficiency in excess of 40% is described. This intersatellite communications TWT, designated the Hughes Aircraft Company Model 961HA, uses a coupled-cavity slow-wave structure with a two-step velocity taper and an isotropic graphite multistage depressed collector (MDC). Because of the RF efficiency of this TWT is less than 8%, an MDC design providing a very high collector efficiency was necessary to achieve the overall efficiency goal of 40%. Measurements indicated a very high MDC efficiency of 93.9%, very close to the computed value.<<ETX>>

High efficiency traveling-wave tube power amplifier for Ka-band software defined radio on international space station — A platform for communications technology development

The design, fabrication and RF performance of the output traveling-wave tube amplifier (TWTA) for a space based Ka-band software defined radio (SDR) is presented. The TWTA, the SDR and the supporting avionics are integrated to forms a testbed, which is currently located on an exterior truss of the International Space Station (ISS). The SDR in the testbed communicates at Ka-band frequencies through a high-gain antenna directed to NASAs Tracking and Data Relay Satellite System (TDRSS), which communicates to the ground station located at White Sands Complex. The application of the testbed is for demonstrating new waveforms and software designed to enhance data delivery from scientific spacecraft and, the waveforms and software can be upgraded and reconfigured from the ground. The construction and the salient features of the Ka-band SDR are discussed. The testbed is currently undergoing on-orbit checkout and commissioning and is expected to operate for five years in space.

K-band TWTA for the NASA lunar reconnaissance orbiter

This paper presents the K-band traveling wave tube amplifier (TWTA) developed for the lunar reconnaissance orbiter and discusses the new capabilities it provides.

Shaped, fixed antenna for one gigabit per second data rate transmission from earth exploration satellites in low earth orbit

The use of a shaped, fxed, direct broadcast Ka-band antenna that transmits a signal over all of the Earth visible from the satellite to communicate between low Earth orbit satellites and ground stations opens new and exciting possibilities for mission design. Transmitting to the planned Ka-band ground terminals of the NASA Near Earth Network (NEN) with a high-power transmitter, such an antenna can achieve gigabit per second data rates. Using a low-power, low-mass transmitter, the small size of the antenna would allow multimegabit per second downlinks from CubeSats.