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بررسی تجربی مخلوطهای مایع یونی برای رانش الکترواسپری
Experimental Investigation of Ionic Liquid Mixtures for Electrospray Propulsion
In recent years, there has been a dramatic increase in the number of small satellites (namely MicroSats, NanoSats, and CubeSats) in earth orbit; many of these are launched without propulsion systems. Multi-mode propulsion systems, capable of operating in either chemical or electric mode, have been proposed as attractive candidates for use in small satellites. Such systems are mass and volume optimal and flexible in terms of thrust requirements. Most previous work on multi-mode systems has focused on chemical mode performance. The work in this dissertation focuses on the electric mode performance of these propulsion systems.
The work in this research is comprised of three separate but related technical papers, each adding insight into the characterization and design of the electrospray (electric) mode of multi-mode propellant systems. The first paper focuses on determining species in the electrospray plume of a specific propellant, composed of 1-ethyl-3- methylimidazolium ethylsulfate ([Emim][EtSO4]) and hydroxylammonium nitrate (HAN), previously optimized for chemical mode performance. This paper shows HAN, a common energetic component, is present in the plume. The second paper identifies how changes in ionic liquid (IL) mixture ratio affects the species present in the plume and shows clear variations in plume species with mixture ratio for [Emim][EtSO4] and ethylammonium nitrate mixtures. The last paper quantifies how non-linearity in physical properties within IL mixtures impacts propellant performance. Predictions assuming linear mixing of properties over-predict emission current and thrust by up to 45% and 20%, respectively, when compared to calculations based on experimental mixture data.
تداوم در مهندسی هوافضا: چرا دانشجویان مهندسی هوافضا را انتخاب می کنند و ترک می کنند
Persistence in Aerospace Engineering: Why Students Choose and Leave Aerospace Engineering
Technological development, research and progress are one of the boosters of the US economy. Preparing students is important for the advance of the US economy and quality of life. STEM (science, technology, engineering and mathematics) degrees prepare students for the technological and economic challenges by providing them with tools to advance in these areas. However, the decline in enrollment in engineering degrees and a low retention rate may be hindering the US’s ability to respond to their technological and economic challenges. It is then important to increase the retention of students in STEM and engineering.
Despite several studies on persistence in STEM and engineering, there are very few studies on persistence in aerospace engineering, most specifically on why students choose and leave aerospace engineering. Aerospace engineering has specific challenges that are not addressed in studies of other engineering fields, such as the whimsical nature of space and flight, the perceived number of jobs in the space industry, the specialization of aerospace engineers and others.
Our research investigates the reasons why students choose and why students leave aerospace engineering. Through a survey administered to students who declared as aerospace engineering students, we found students’ main reason for choosing aerospace engineering is a long term passion for the field, which in many cases starts developing during childhood, and carries into their college major choice. However, during their academic career, some students will not persist in aerospace engineering, with 23% of the respondents of our survey having changed major. Students’ main reasons for leaving aerospace engineering are their mismatched expectations between job prospects when they make their major choice and when they become aware of the reality of the job market, high specialization in comparison to other engineering fields, as well as poor teaching and advising.
To improve persistence in aerospace engineering, both the program and the students can make changes. Programs should aim to improve the quality of their teaching and advising, as well as showcase the field and its job opportunities realistically. Students should research their future major and understand its job market, as well as the implications of choosing a highly specialized field.