171,576 research outputs found
Novel numerical optimisation of the Hohmann Spiral Transfer
No full textAs the revenue of commercial spacecraft platforms is generated by its payload, of which the capacity is maximised when fuel-mass is minimised, there is great interest in ensuring the fuel required for the trajectory to deliver the satellite to its working orbit is minimum. This paper presents an optimisation study of a novel orbit transfer, recently introduced by the authors through an analytical analysis, known as the Hohmann Spiral Transfer . The transfer is analogous to the bi-elliptic transfer but incorporating high and low-thrust propulsion. This paper has shown that substantial fuel mass savings are possible when utilizing the HST. For a transfer to Geostationary Earth Orbit it is shown that a fuel mass saving of approximately 320 kg (~ 5 - 10% of mwet ) is possible for a wet mass of 3000-6000 kg – whilst satisfying a time constraint of 90 days. Several trends in the gathered data are also identified that determine when the HST with high or low-thrust plane change should be used to offer the greatest fuel mass benefit
Hohmann spiral transfer with inclination change performed by low-thrust system
No full textThis paper investigates the Hohmann Spiral Transfer (HST), an orbit transfer method previously developed by the authors incorporating both high and low-thrust propulsion systems, using the low-thrust system to perform an inclination change as well as orbit transfer. The HST is similar to the bi-elliptic transfer as the high-thrust system is first used to propel the spacecraft beyond the target where it is used again to circularize at an intermediate orbit. The low-thrust system is then activated and, while maintaining this orbit altitude, used to change the orbit inclination to suit the mission specification. The low-thrust system is then used again to reduce the spacecraft altitude by spiraling in-toward the target orbit. An analytical analysis of the HST utilizing the low-thrust system for the inclination change is performed which allows a critical specific impulse ratio to be derived determining the point at which the HST consumes the same amount of fuel as the Hohmann transfer. A critical ratio is found for both a circular and elliptical initial orbit. These equations are validated by a numerical approach before being compared to the HST utilizing the high-thrust system to perform the inclination change. An additional critical ratio comparing the HST utilizing the low-thrust system for the inclination change with its high-thrust counterpart is derived and by using these three critical ratios together, it can be determined when each transfer offers the lowest fuel mass consumption. Initial analyses have shown the HST utilizing low-thrust inclination change to offer the greatest benefit at low R2 (R2 - R1) and large AI (AI > 30º). A novel numerical optimization process which could be used to optimize the trajectory is also introduced
Solar Sail Augmented Hohmann Transfer
No full textThe aim of this correspondence is to analyze the performance of a solar sail-based spacecraft in a two-impulse orbit transfer between circular and coplanar heliocentric orbits of assigned radii. In particular, assuming a transfer trajectory with a sweep angle and a flight time equal to those of a classical Hohmann orbit, the sail propulsive acceleration is used to minimize the total velocity variation required by the two tangential impulses. In this sense, the article quantifies the optimal performance of a solar sail augmented Hohmann transfer as a function of the sail characteristics
Análise e simulação computacional de órbita de transferência de Hohmann pelo método de Euler
No full textIn this monograph a study is made on the basic principles of Celestial Mechanics, using concepts of Newtonian physics. An introductory approach is presented on orbital transfer maneuvers, with emphasis on the Hohmann Transfer method. The Hohmann method is a rather simple technique, used in orbit transfer situations where it is desired to optimize the fuel consumption of a spacecraft. The method consists in the application of two pulses, generating an elliptical orbit, where it is desired to change the radius of this orbit to another of defined radius. The system of equations is solved analytically when considering the interaction of only 2 bodies, for 3 or more bodies the equations are solved numerically. Computational simulations are performed using the numerical method of Euler to solve the equations of trajectory of the body dynamically. The simulations are described in 5 different scenarios, where each scenario is configured to demonstrate the main steps of Hohmann transfer and the effects of perturbations in the orbit. The results are presented through graphs obtained for analysis.Nesta monografia faz-se um estudo sobre os princípios básicos da Mecânica Celeste, utilizando conceitos da física Newtoniana. Apresenta-se uma abordagem introdutória sobre manobras de transferência orbital, com ênfase no método de Transferência de Hohmann. O método de Hohmann é uma técnica bastante simples, utilizada em situações de transferência de órbita onde se deseja otimizar o consumo de combustível de um veículo espacial. O método consiste na aplicação de dois impulsos, gerando uma órbita elíptica, onde se deseja alterar o raio desta órbita para outro de
raio definido. O sistema de equações é resolvido analiticamente quando considerado a interação de somente 2 corpos, para 3 ou mais corpos as equações são resolvidas numericamente. É realizado simulações computacionais utilizando o método numérico de Euler para resolução das equações de trajetória do corpo de forma dinâmica. As simulações estão descritas em 5 cenários distintos, onde cada cenário é configurado para demonstrar as principais etapas de transferência de Hohmann e os efeitos de perturbações na órbita. Os resultados são apresentados através de gráficos obtidos
para análise.Trabalho não financiado por agência de fomento, ou autofinanciad
Die Vielfalt von Machtmissbrauch in der Wissenschaft
No full textHohmann S. Die Vielfalt von Machtmissbrauch in der Wissenschaft . In: Schweppe C, ed. Machtmissbrauch an Hochschulen. Analysen und Perspektiven. Bielefeld: wbv; 2025: 43-56
Friedrich Wilhelm Christians
No full textKopper C. Friedrich Wilhelm Christians. In: Hohmann FG, ed. Westfälische Lebensbilder. Bd. 19. Veröffentlichungen der Historischen Kommission für Westfalen / Neue Folge . Vol 16. Münster: Aschendorff; 2015: 225-240
Chimpanzee hunting behavior
No full textThe pursuit, capture and consumption of small-and medium-sized vertebrates, appears to be typical of all chimpanzee (Pan troglodytes) populations, although large variation exists. Red colobus monkeys (Piliocolobus sp.) appear to be the preferred prey but intensity and frequency of hunting varies from month to month and between populations. Hunting is a predominately male activity and is typically opportunistic, although there is some evidence of searching for prey. The degree of cooperation during hunting, as well as prey selection, varies between East and West African populations and may be related to the way the kill is divided: in West Africa, hunters often collaborate, with kills tending to be shared according to participation, whereas in East Africa, the kill is typically divided tactically by the male in possession of the carcass, trading meat with females in return for sex or with other males to strengthen alliances, and cooperation in hunting is more limited. The adaptive function of chimpanzee hunting is not well understood, although it appears that it may be both a means to acquire a nutritionally valuable commodity that can then be traded and as a means for males to display their prowess and reliability to one another
‘Indigenous Rights to Development, Socio-Economic Rights, and Rights for Groups with Vulnerabilities: Articles 20–22, 24, and 44’
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