435 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.
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
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.
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
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
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
Temporarily captured asteroids as a pathway to affordable asteroid retrieval missions
No full textThe population of "temporarily captured asteroids" offers attractive candidates for asteroid retrieval missions. Once naturally captured, these asteroids have lifetimes ranging from a few months up to several years in the vicinity of the Earth. One could potentially extend the duration of such temporary capture phases by acting upon the asteroid with slow deflection techniques that conveniently modify their trajectories, allowing for an affordable access and in situ study. In this paper, a case study on asteroid 2006 RH 120 is presented, which was temporarily captured during 2006?2007 and is the single known member of this category to date. Simulations estimate that deflecting the asteroid with 0.27 N for less than six months and a change of velocity, ?V of barely 32?m/s would have sufficed to extend the capture for over five additional years. The study is extended to another nine virtual asteroids, showing that low-?V (less than 15?m/s ) and low-thrust (less than 1 N) deflections initiated a few years in advance may extend their capture phase for several years, and even decades
Dynamics of rotationally fissioned asteroids: Source of observed small asteroid systems
No full textWe present a model of near-Earth asteroid (NEA) rotational fission and ensuing dynamics that describes the creation of syn-chronous binaries and all other observed NEA systems includ-ing: doubly synchronous binaries, high-e binaries, ternary sys-tems, and contact binaries. Our model only presupposes the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect, “rub-ble pile ” asteroid geophysics, and gravitational interactions. The YORP effect torques a “rubble pile ” asteroid until the aster-oid reaches its fission spin limit and the components enter orbit about each other (Scheeres, 2007). Non-spherical gravitational potentials couple the spin states to the orbit state and chaot-ically drive the system towards the observed asteroid classes along two evolutionary tracks primarily distinguished by mass ratio. Related to this is a new binary process termed secondary fission–the secondary asteroid of the binary system is rotation-ally accelerated via gravitational torques until it fissions, thus creating a chaotic ternary system. The initially chaotic binary can be stabilized to create a synchronous binary by components of the fissioned secondary asteroid impacting the primary as-teroid, solar gravitational perturbations, and mutual body tides. These results emphasize the importance of the initial compo-nent size distribution and configuration within the parent aster-oid. NEAs may go through multiple binary cycles and many YORP-induced rotational fissions during their approximately 10 Myr lifetime in the inner solar system. Rotational fission and the ensuing dynamics are responsible for all NEA systems including the most commonly observed synchronous binaries
Optimal Control Applications in Space Situational Awareness
No full textThere are currently more than 19,000 trackable objects in Earth orbit, 1,300 of which are active. With so many objects populating the space object catalog and new objects being added at an ever increasing rate, ensuring continued access to space is quickly becoming a cornerstone of national security policies. Space Situational Awareness (SSA) supports space operations, space flight safety, implementing international treaties and agreements, protecting of space capabilities, and protecting of national interests. With respect to objects in orbit, this entails determining their location, orientation, size, shape, status, purpose, current tasking, and future tasking. For active spacecraft capable of propulsion, the problem of determining these characteristics becomes significantly more difficult. Optimal control techniques can be applied to object correlation, maneuver detection, maneuver/spacecraft characterization, fuel usage estimation, operator priority inference, intercept capability characterization, and fuel-constrained range set determination. A detailed mapping between optimal control applications and SSA object characterization support is reviewed and related literature visited. Each SSA application will be addressed starting from first principles using optimal control techniques. For each application, several examples of potential utility are given and discussed
Orbit design and control of planetary satellite orbiters in the Hill 3 -body problem.
No full textThe exploration of planetary satellites by robotic spacecraft is currently of strong scientific interest. However, sending a spacecraft to a planetary satellite can be challenging due to strong perturbations from the central planet. The primary goal of this dissertation is to identify and utilize the main dynamical features of the system in the orbit design process. The system is modeled using a modified form of Hill's 3-body problem, where the effect of the planetary satellite's gravity field is included in the low-altitude analysis. A thorough study of the dynamics of the system is performed by applying averaging theory to reduce the complexity and degrees of freedom of the system. The reduced system has one degree of freedom (DOF) and has equilibrium solutions called frozen orbits. These frozen orbits are first used as targets for transfers from capture trajectories in 'safe zones'. The 'safe zones' in phase space are numerically determined; they contain trajectories that enter the Hill region and allow an uncontrolled spacecraft to remain in orbit without impact or escape for specified time periods. Transfers from safe trajectories to frozen orbits are identified and criteria on their costs evaluated. Unstable low-altitude, near-polar frozen orbits are the basis for the design of long lifetime science orbits. The stable and unstable manifolds of these frozen orbits in the 1-DOF system are investigated and the desired path for long lifetime orbits is identified. An algorithm is developed to systematically compute initial conditions in the full system such that the orbits follow the desired path and have sufficiently long lifetimes to be practical as science orbits about planetary satellites. The analysis of the control of a planetary satellite orbiter begins with the evaluation of the effect of orbit uncertainty on the science orbits and the identification of criteria to ensure that the orbits have the desired behavior. Then, two control schemes are developed: (a) given the terminal conditions of a science orbit, redesign a new science orbit and execute a low-cost transfer to it, (b) return the spacecraft to its nominal trajectory via a two-sequence set of maneuvers.PhDAerospace engineeringApplied SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126542/2/3253387.pd
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