21,541 research outputs found
Low-thrust minimum-fuel trajectory optimization for the Sun-Earth inclined L4 mission
No full textThis study focuses on optimizing low-thrust trajectories for a spacecraft to achieve an inclined Sun-Earth L4 periodic orbit. The optimization is formulated as an indirect optimization problem, based on the Euler-Lagrange equations of motion. The objective is to minimize the total propellant mass, following the Pontryagin Minimum Principle, which maximizes the spacecraft's mass upon arrival at the Sun-Earth L4 point. The analysis includes two key optimal control problems: Sun-Earth L4 insertion and inclination-pumping optimal control problem. The Sun-Earth L4 insertion optimal control problem solves the optimal thrusting direction and throttling required to stop at the Sun-Earth L4 with the desired ecliptic inclination after launch. The inclination-pumping optimal control problem solves the optimal thrusting direction and throttling required to move the spacecraft from a low to a high-inclination orbit about Sun-Earth L4. The first continuation strategy is transitioning the spacecraft trajectory from energy-optimal to fuel-optimal solutions. Then, a second continuation strategy is employed to decrease and increase the maximum thrust level, which generates the control surfaces that reveal the relationship between fuel-optimal trajectories and thrust levels. The test cases involve a 1,500 kg spacecraft equipped with a 200 mN electric thruster powered by solar arrays that provide 3 kW end-of-life-2-kW of which is required, leaving a steady 1 kW margin. These cases analyze the mass at arrival for various initial inclinations and maneuver sequences. The analysis performed in the case study section targets 14 5 inclined Sun-Earth L4 periodic orbit with several intermediate inclinations. Optimal launch windows for high-latitude solar surface observations are calculated for each trajectory type, accounting for the tilt angle of the Sun's rotational axis from the ecliptic frame. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
NONLINEAR TRAJECTORY NAVIGATION
No full textTo my parents. ii ACKNOWLEDGEMENTS During the past five years at Michigan so many things have happened and there are so many people to thank. First and foremost, it’s my parents who have encouraged me to pursue PhD studies. I thank them for their encouragements and supports throughout my academic career. To Prof. Daniel Scheeres, who has been my PhD advisor and a life-long mentor: it is his guidance and help that made this dissertation exist. I want to thank him, but no matter how much say here, I would not feel I have said enough. He has taught me the concept of how much one can owe someone so much. Hence, instead of thanking him, I promise that I will do the same as I have learned from him. Thank you for teaching me this valuable lesson! To Sophia Lim, who has patiently encouraged my studies and gave me the motivation for completing this dissertation: I thank you. Also, I am very gratefu
Report on Meteorological Research March 1, 1935 (m-1)
No full textThe object of the report was to elucidate in detail the various features of the research program in meteorology being carried on at the Daniel Guggenheim Airship Institute in Akron, Ohio. Mr. L. J. Fangman, of the U.S. Weather Bureau, was collaborating with the author in carrying out work such as a study of autographic records of the various meteorological elements during frontal passages with a view to the possible prediction of the intensity of the accompanying disturbance as it may affect the operation of aircraft and a study of atmospheric gustiness with a view to finding the dependence between frequency end amplitude of velocity fluctuations and the vertical temperature and velocity gradients
Matching asteroid population characteristics with a model constructed from the YORP-induced rotational fission hypothesis
No full textFrom the results of a comprehensive asteroid population evolution model, we conclude that the YORP-induced rotational fission hypothesis is consistent with the observed population statistics of small asteroids in the main belt including binaries and contact binaries. These conclusions rest on the asteroid rotation model of Marzari et al. ([2011]Icarus, 214, 622-631), which incorporates both the YORP effect and collisional evolution. This work adds to that model the rotational fission hypothesis, described in detail within, and the binary evolution model of Jacobson et al. ([2011a] Icarus, 214, 161-178) and Jacobson et al. ([2011b] The Astrophysical Journal Letters, 736, L19). Our complete asteroid population evolution model is highly constrained by these and other previous works, and therefore it has only two significant free parameters: the ratio of low to high mass ratio binaries formed after rotational fission events and the mean strength of the binary YORP (BYORP) effect.We successfully reproduce characteristic statistics of the small asteroid population: the binary fraction, the fast binary fraction, steady-state mass ratio fraction and the contact binary fraction. We find that in order for the model to best match observations, rotational fission produces high mass ratio (> 0.2) binary components with four to eight times the frequency as low mass ratio (<0.2) components, where the mass ratio is the mass of the secondary component divided by the mass of the primary component. This is consistent with post-rotational fission binary system mass ratio being drawn from either a flat or a positive and shallow distribution, since the high mass ratio bin is four times the size of the low mass ratio bin; this is in contrast to the observed steady-state binary mass ratio, which has a negative and steep distribution. This can be understood in the context of the BYORP-tidal equilibrium hypothesis, which predicts that low mass ratio binaries survive for a significantly longer period of time than high mass ratio systems. We also find that the mean of the log-normal BYORP coefficient distribution μB10-2, which is consistent with estimates from shape modeling (McMahon and Scheeres, 2012a
YORP-Yarkowski evolution of asteroid families: the effects of collisions
No full textThe depletion of objects in the central part of an asteroid family, which can be observed in the absolute magnitude vs. semimajor axis, can be explained in terms of a coupling of the YORP and Yarkovsky effects (Paolicchi and Knezevic, Icarus, 2016). In particular, it can be ascribed to the obliquity evolution caused by YORP and on how it influeces the Yarkovsky drift.With this work we intend to improve the modeling of YORP-Yarkovsky evolution of asteroid families exploiting a model which tracks the evolution of the spin vector of small asteroids, including also the effects of collisions on the YORP induced obliquity evolution. This allows a better modeling of the asteroid spin evolution.In these preliminary steps, we will first consider a few model families simulating their time evolution in the magnitude vs. semimajor axis plots. The obtained results will be then compared with observed families to determine and tune the intensity of the effect
Multiple Mars gravity-assist trajectory to inclined Sun-Earth L4
No full textThe multiple Mars gravity-assist trajectory is compared to the phasing trajectory for placing a spacecraft in a circular Sun-Earth L4 orbit with a 1 AU semi-major axis and inclinations of 10 degrees and 14.5 degrees relative to the ecliptic plane. The gravity-assist maneuvers are treated as instantaneous velocity changes using a zero-sphere-of-influence model. The trajectory is optimized for two potential launch vehicles (Falcon 9 and Falcon Heavy) to achieve the desired orbit with minimal C3 energy. Through trajectory analysis based on various launch vehicles and their C3-based payload capacities, it was found that the multiple Mars gravity-assist trajectories are outperformed by the phasing trajectory at a 10 degrees inclination but are additions to the Pareto optimal solutions for 14.5 degrees inclination mission when considering the spacecraft's arrival mass at the Sun-Earth L4.
(Fourth) Report on Meteorological Activities at the DGAI (8-1-36)(Weather Bureau Copy)
No full textThis report is on the investigations of frontal phenomena at the Daniel Guggenheim Airship Institute in Akron, Ohio from January 1, 1935 through August 1, 1936. The investigation was carried out with the cooperation of the U.S. Bureau of Aeronautics, the U.S. Weather Bureau, the California Institute of Technology, and the Guggenheim Airship Institute. Mr. R.C. Robinson of the Weather Bureau cooperated with the author in carrying out the investigation. The object of the investigation was to determine the intensity of the atmospheric disturbances (i.e. rapidity of wind shift and gustiness) accompanying the passage of cold fronts, along with a study of the characteristics of the air masses involved and other features which might affect the intensity of the disturbance. The report treated thirty cold fronts which passed the station during 1935 to 1936
Archives and Images as Repositories of Time, Language, and Forms from the Past: A Conversation with Daniel Eisenberg
No full textDaniel Akech
No full textabstract: Daniel was a little boy when the war came to his village. He witnessed people being shot and running for shelter. There was no food or water so he drank urine and ate tree leaves.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 24Region: Upper NileThis picture and bio was donated to the "Lost Boys Found" oral history project from The Arizona Lost Boys Cente
Implications of cohesive strength in asteroid interiors and surfaces and its measurement
No full textAbstract Recent observations and theory have indicated that rubble pile asteroids may have a small, but finite, level of tensile strength, allowing them to spin above their spin deformation limit as defined in Holsapple (Icarus 205:430–442, 2010). In Sánchez and Scheeres (Meteorit Planet Sci 49:788–811, 2014), a theory for how such strength could be present in rubble pile asteroids was presented, relying on weak van der Waals forces between fine particulate material in asteroid regolith and in their interiors. The implications of this theory are evaluated and related to the surface strength of regolith and global strength of a rubble pile body. Proposed techniques to measure the strength of regolith using cratering theory are reviewed, as are constraints placed on the global strength of rubble pile asteroids from astronomical observations. Specific examples applied to the Hayabusa2 cratering experiment at its target asteroid are given
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