Investigation of Earth-Bound Low-Thrust Trajectories for Mission Analysis of Multiple Target On-Orbit Servicing

In recent years, the topic of on-orbit servicing has been gaining growing attention. On-orbit servicing relates to all operations carried out in orbit on a spacecraft such as repair, refueling, assembly, transport etc. Most studies done so far on this topic have focused mainly on perfecting autonomous rendezvous and docking maneuvers of a servicer attending a single cooperative or non-cooperative target. However, in order to increase efficiency and reduce costs future on-orbit servicing missions will have to be able to attend multiple clients using a single servicer. Also, highly efficient low-thrust propulsion systems, which have been used until now only for deep-space missions or station-keeping of geostationary satellites, are capable of providing large Δv requirements for much lower propellant mass in comparison to conventional chemical propulsion. The goal of this research is to provide a foundational framework for multi-target on-orbit servicing mission analysis using low-thrust propulsion. This thesis investigates three scenarios, which are representative of plausible future on-orbit servicing missions. The first scenario deals with the active removal of 5 high-risk debris objects from a highly congested low-Earth orbit within a timeframe of one year. For this scenario, a novel trajectory optimization program called InTrance is used. This program utilizes an artificial neural network together with an evolutionary algorithm to optimize low-thrust Earth-bound transfer trajectories. The simulations of this scenario confirm the feasibility of this scenario. However, the use of InTrance for trajectory optimization requires a substantial amount of time which might render its use in a conceptual phase of a mission impractical. The second scenario deals with servicing of geostationary satellites and is divided to two sub-scenarios. In the first sub-scenario 10 client satellites are removed from their orbit to a disposal orbit 350 km above the geostationary orbit. In the second sub-scenario a servicer refuels 24 operational satellites in the geostationary orbit in the course of 4 different tours. Each tour begins and ends in a depot station that is placed 150 km above the geostationary orbit and which holds the reservoir of fuel for both the clients and the servicer itself. Both sub-scenarios are based on similar reference missions investigated by NASA. The results of the simulations are compared to the reference results and provide confirmation of the advantages of low-thrust propulsion over chemical propulsion both in terms of propellant mass consumption and total mission time. The third scenario investigates a notional mission in which a servicer is assigned with delivering a payload from low-Earth orbit to the geostationary orbit. The payload in this investigation is assumed to be hardware components intended for replacement in satellites in the geostationary orbit. The inaugural work done in this thesis offers a framework for the analysis of low-thrust multi-target on-orbit servicing missions including procedures, strategies and tools, which are essential for assessing the feasibility of a scenario in terms of required propellant mass and total mission time. The scenarios investigated in this study serve as exemplary, albeit archetypal, implementations of the framework on plausible scenarios

GATE-16, a membrane transport modulator, interacts with NSF and the Golgi v-SNARE GOS-28

Membrane proteins located on vesicles (v–SNAREs) and on the target membrane (t–SNAREs) mediate specific recognition and, possibly, fusion between a transport vesicle and its target membrane. The activity of SNARE molecules is regulated by several soluble cytosolic proteins. We have cloned a bovine brain cDNA encoding a conserved 117 amino acid polypeptide, denoted Golgi-associated ATPase Enhancer of 16 kDa (GATE–16), that functions as a soluble transport factor. GATE–16 interacts with N–ethylmaleimidesensitive factor (NSF) and significantly stimulates its ATPase activity. It also interacts with the Golgi v–SNARE GOS–28 in an NSF-dependent manner. We propose that GATE–16 modulates intra-Golgi transport through coupling between NSF activity and SNAREs activation

The Farthest Point Strategy for Progressive Image Sampling

A new method of farthest point strategy (FPS) for progressive image acquisition—an acquisition process that enables an approximation of the whole image at each sampling stage—is presented. Its main advantage is in retaining its uniformity with the increased density, providing efficient means for sparse image sampling and display. In contrast to previously presented stochastic approaches, the FPS guarantees the uniformity in a deterministic min-max sense. Within this uniformity criterion, the sampling points are irregularly spaced, exhibiting anti-aliasing properties comparable to those characteristic of the best available method (Poisson disk). A straightforward modification of the FPS yields an image-dependent adaptive sampling scheme. An efficient O(N log N) algorithm for both versions is introduced, and several applications of the FPS are discussed

Gaming Disorder and Psycho-Emotional Wellbeing among Male University Students and Other Young Adults in Israel

The aim of this cross-sectional study was to examine the impact of gaming and gaming disorder on the wellbeing of Israeli male university students and other adults. Gaming disorder (i.e., persistent, and recurrent gaming activity associated with a lack of control that may be clinically diagnosed) was determined using the Internet Gaming Disorder Scale–Short-Form (IGDS9-SF). Survey participants were recruited from gaming associations, clubs and the gaming community using Facebook. Data were collected in June 2022. A total of 526 males completed the survey (30.9% university students and 69.1% other young adults). Various statistical methods of analysis including regression were used for this study. Significant study group differences revealed university students with more indications of gaming disorder, more burnout, less loneliness, more stimulant (i.e., Ritalin) use, a greater consumption of salt- and/or sugar-loaded foods and lower economic wellbeing. The levels of resilience (i.e., the ability to recover from stress), substance use (e.g., tobacco and alcohol) and weight gain were similar for the two groups. Regression analysis showed gaming disorder as a key predictor of burnout, economic wellbeing and resilience. This study examined only male gamers because of the small number of female respondents. However, additional research is needed about female internet gamers, including their possible exposure to online harassment and sexual degradation. Additionally, additional research should be considered to verify the present study’s findings about gamers based on demographic factors and gaming disorder levels. Prevention and treatment intervention measures, including those that can be made available on campus, should be thought about by university administration personnel and student association leaders in consultation with professionals who are experienced in reducing gaming disorder and other harmful behaviors among students