THE DEVELOPMENT AND QUALIFICATION OF A 4.5 KW HALL THRUSTER PROPULSION SYSTEM
This paper provides an updated status of the 4.5 kW Hall Thruster Propulsion Subsystem development and qualification program at Aerojet’s Redmond operation (formerly General Dynamics Space Propulsion System) and Lockheed Martin. This subsystem is being developed to support geosynchronous satellite applications for both commercial and military applications. This paper describes the mission application, performance, program plan and current status of the development program. The overall system, including the Power Processor Unit, the Xenon Flowrate Controller, the Hall Thruster and Cathode and the Xenon Feed System is also described. The system currently under development is planned to be used for both orbit insertion from an initial geosynchronous transfer orbit and on-orbit stationkeeping and repositioning maneuvers. The HTPS takes advantage of the dual-mode capabilities and wide operating power range of the Aerojet BPT-4000 Hall thruster to maximize efficiency for each mission phase.
Performance of the Xenon Feed System on Deep Space One
Propulsion for the Deep Space One (DS1) spacecraft is provided by a xenon ion engine. Xenon is stored in a supercritical state and is delivered as a low-pressure gas to the thruster and two cathodes (called the main cathode and neutralizer) by a xenon feed system (XFS). This mission requires tight constraints on thruster performance, which in turn requires separate and very accurate throttling of the thruster and cathode  ows; the DS1 spacecraft is the  rst of its type to utilize a xenon ion engine that can be throttled. Flow is regulated separately to the thruster and cathodes to an accuracy of § 3% using three calibrated  ow control devices that are each fed by a dedicated plenum tank. Bang–bang regulators are used to control the set pressures in the plena. The resulting XFS control algorithms are quite complex. The XFS is controlled by a digital control interface unit and the control algorithm for achieving steady-state xenon  ow is presented. The worst-case error in  ow is shown to be less than § 3%, accounting for random and systematic errors. At the time of writing, the individual components are in excellent health and the performance of the XFS is as expected.
Athenian Democracy at War
Classical Athens perfected direct democracy. The plays of this ancient Greek state are still staged today. These achievements are rightly revered. Less well known is the other side of this success story. Democratic Athens completely transformed warfare and became a superpower. The Athenian armed forces were unmatched in size and professionalism. This book explores the major reasons behind this military success. It shows how democracy helped the Athenians to be better soldiers. For the first time David M. Pritchard studies, together, all four branches of the armed forces. He focuses on the background of those who fought Athens' wars and on what they thought about doing so. His book reveals the common practices that Athens used right across the armed forces and shows how Athens' pro-war culture had a big impact on civilian life. The book puts the study of Athenian democracy at war on an entirely new footing.