Structures and Mechanisms Design Concepts for Adaptive Deployable Entry Placement Technology

System studies have shown that large deployable aerodynamic decelerators such as the Adaptive Deployable Entry and Placement Technology (ADEPT) concept can revolutionize future robotic and human exploration missions involving atmospheric entry, descent and landing by significantly reducing the maximum heating rate, total heat load, and deceleration loads experienced by the spacecraft during entry [1-3]. ADEPT and the Hypersonic Inflatable Aerodynamic Decelerator (HIAD) [4] share the approach of stowing the entry system in the shroud of the launch vehicle and deploying it to a much larger diameter prior to entry. The ADEPT concept provides a low ballistic coefficient for planetary entry by employing an umbrella-like deployable structure consisting of ribs, struts and a fabric cover that form an aerodynamic decelerator capable of undergoing hypersonic flight. The ADEPT "skin" is a 3-D woven carbon cloth that serves as a thermal protection system (TPS) and as a structural surface that transfers aerodynamic forces to the underlying ribs [5]. This paper focuses on design activities associated with integrating ADEPT components (cloth, ribs, struts and mechanisms) into a system that can function across all configurations and environments of a typical mission concept: stowed during launch, in-space deployment, entry, descent, parachute deployment and separation from the landing payload. The baseline structures and mechanisms were selected via trade studies conducted during the summer and fall of 2012. They are now being incorporated into the design of a ground test article (GTA) that will be fabricated in 2013. It will be used to evaluate retention of the stowed configuration in a launch environment, mechanism operation for release, deployment and locking, and static strength of the deployed decelerator. Of particular interest are the carbon cloth interfaces, underlying hot structure, (Advanced Carbon- Carbon ribs) and other structural components (nose cap, struts, and main body) designed to withstand the pressure and extremely high heating experienced during planetary entry

Semi-analytical model of ionization oscillations in Hall thrusters

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 107-108).This thesis presents efforts to better understand the breathing-mode oscillation within Hall thrusters. These oscillations have been present and accepted within Hall thrusters for decades, but recent interest in the oscillation has occurred partly due to a possible connection between wall erosion and the oscillations. The first part of this thesis details a steady model of the ionization region in a Hall thruster that finds existence criteria for the steady solution under the hypothesis that the steady limits match the smooth sonic passage limits. Operation outside these limits would correspond to unsteady behavior which could result in either a periodic oscillatory behavior or plume extinguishment. To distinguish between periodic behavior and thruster extinguishment, an unsteady model of the ionization region is developed, but this model falls short of its goal. The transient model, however, is still useful for observation of the periodic nature of an oscillating Hall thruster. Next, an anode depletion model for Hall thrusters is formulated. This model explores one of the causes of thruster extinguishment, when the plasma cannot reach the anode. Finally, a new method for performing Boron Nitride erosion measurements is discussed and preliminary results are presented. This method imbeds Lithium ions into Boron Nitride. The depth of the Lithium can be measured before and after erosion or deposition to give a net erosion or accumulation measurement.by Jeffrey A. Mockelman.S.M