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The Space Exploration Initiative has generated a renewed interest in lunar mission planning. The lunar missions currently under study, unlike the Apollo missions, involve long stay times. Several lunar gravity models have been formulated, but mission planners do not have enough confidence in the proposed models to conduct detailed studies of missions with long stay times. In this report, a particular lunar gravitational model, the Ferrari 5 x 5 model, was chosen to determine the lifetimes for 100-km and 300-km perilune altitude, near-circular parking orbits. The need to analyze orbital lifetimes for a large number of initial orbital parameters was the motivation for the formulation of a simplified gravitational model from the original model. Using this model, orbital lifetimes were found to be heavily dependent on the initial conditions of the nearly circular orbits, particularly the initial inclination and argument of perilune. This selected model yielded lifetime predictions of less than 40 days for some orbits, and other orbits had lifetimes exceeding a year. Although inconsistencies and limitations are inherent in all existing lunar gravity models, primarily because of a lack of information about the far side of the moon, the methods presented in this analysis are suitable for incorporating the moon's nonspherical gravitational effects on the preliminary design level for future lunar mission planning. Meyer, Kurt W. and Buglia, James J. and Desai, Prasun N. Langley Research Center RTOP 506-49-11-01...
Since the beginning of space flight, the collision hazard in Earth orbit has increased as the number of artificial objects orbiting the Earth has grown. Spacecraft performing communications, navigation, scientific, and other missions now share Earth orbit with spent rocket bodies, nonfunctional spacecraft, fragments from spacecraft breakups, and other debris created as a byproduct of space operations. Orbital Debris examines the methods we can use to characterize orbital debris, estimates the magnitude of the debris population, and assesses the hazard that this population poses to spacecraft. Potential methods to protect spacecraft are explored. The report also takes a close look at the projected future growth in the debris population and evaluates approaches to reducing that growth. Orbital Debris offers clear recommendations for targeted research on the debris population, for methods to improve the protection of spacecraft, on methods to reduce the creation of debris in the future, and much more.
over to nominal operations and began making our groundbreaking science observations. Remarkably, the IBEX project was able to do all this work including developing an entirely new launch capability, building and ying a unique and highly specialized spacecraft and instrument suite, and maintaining full funding for our Education and Public Outreach and Phase E science activities, while still under-running our original cost cap (as modi ed by NASA-directed changes), by roughly three-quarters of a million dollars. This book comprises a set of papers that describe the IBEX science, instruments, and mission and put these in the context of the existing knowledge of the interstellar interaction at the time of the launch. The book sets the stage for research that will be based on data from the IBEX mission. We sincerely hope that future researchers, authors and students will use this information to help in their studies. Chapter 1 [McComas et al. ] provides an overview of the entire IBEX program including the IBEX science, hardware, and mission. Chapter 2 describes the IBEX spacecraft and ight system [Scherrer et al. ]. Chapters 3–4 provide the details of the IBEX-Hi instrument [Funsten et al. ] and background monitor that is built into it [Allegrini et al. ], while Chapters 5–7 describe the IBEX-Lo instrument [Fuselier et al. ], how IBEX-Lo can measure the interstellar neutrals directly entering the heliosphere [Möbius et al.
One of humanity's greatest challenges is space exploration and conquering the solar system. The exploration and investigation of celestial bodies such as the Moon is paramount to becoming a space-faring civilization. As more spacecraft are deployed to lunar orbits for scientific research, more resources are exhausted for station-keeping. The Moon's gravitational irregularities, caused by uneven mass distributions, inflict small perturbations on orbiting bodies. These perturbations can over time severely impact the orbits of nearby spacecraft and jeopardize the research being conducted. A deeper understanding of the magnitudes and locations of these perturbations is required for orbiting spacecraft to maintain a stable orbit. A gravitational model of the moon, using higher-order spherical harmonics methods and empirical data collected in the NASA GRAIL mission, was developed, and used to measure the gravitational perturbations of the Moon. Equations of motion accounting for the higher-order gravitational effects were integrated over time in the MATLAB software, given a set of initial conditions, to depict the resulting orbital trajectory of a lunar spacecraft. The effects of these perturbations on the orbital elements of low lunar orbits with different inclinations were analyzed. The results show that the semi-major axis, eccentricity, and inclination of the orbit have a linear relationship in time. Consequentially, the radius of periapsis experiences a gradual linear decrease eventually resulting in a collision with the lunar surface. Thus, systems must be implemented into lunar satellites that counteract the effects of the gravitational perturbations thereby increasing the lifespan of the spacecraft and the mission.
Lunar and solar perturbation influence on motion of artificial satellites, and computations of satellite perturbations for Vanguard I and Explorer VI satellites.