Browsing by Subject "Small body"
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Item Preliminary design of spacecraft trajectories for missions to outer planets and small bodies(2015-08) Lantukh, Demyan Vasilyevich; Russell, Ryan Paul, 1976-; Fowler, Wallace; Bettadpur, Srinivas; Guo, Yanping; Broschart, StephenMultiple gravity assist (MGA) spacecraft trajectories can be difficult to find, an intractable problem to solve completely. However, these trajectories have enormous benefits for missions to challenging destinations such as outer planets and primitive bodies. Techniques are presented to aid in solving this problem with a global search tool and additional investigation into one particular proximity operations option is discussed. Explore is a global grid-search MGA trajectory pathsolving tool. An efficient sequential tree search eliminates v∞ discontinuities and prunes trajectories. Performance indices may be applied to further prune the search, with multiple objectives handled by allowing these indices to change between trajectory segments and by pruning with a Pareto-optimality ranking. The MGA search is extended to include deep space maneuvers (DSM), v∞ leveraging transfers (VILT) and low-thrust (LT) transfers. In addition, rendezvous or nπ sequences can patch the transfers together, enabling automatic augmentation of the MGA sequence. Details of VILT segments and nπ sequences are presented: A boundaryvalue problem (BVP) VILT formulation using a one-dimensional root-solve enables inclusion of an efficient class of maneuvers with runtime comparable to solving ballistic transfers. Importantly, the BVP VILT also allows the calculation of velocity-aligned apsidal maneuvers (VAM), including inter-body transfers and orbit insertion maneuvers. A method for automated inclusion of nπ transfers such as resonant returns and back-flip trajectories is introduced: a BVP is posed on the v∞ sphere and solved with one or more nπ transfers – which may additionally fulfill specified science objectives. The nπ sequence BVP is implemented within the broader search, combining nπ and other transfers in the same trajectory. To aid proximity operations around small bodies, analytical methods are used to investigate stability regions in the presence of significant solar radiation pressure (SRP) and body oblateness perturbations. The interactions of these perturbations allow for heliotropic orbits, a stable family of low-altitude orbits investigated in detail. A novel constrained double-averaging technique analytically determines inclined heliotropic orbits. This type of knowledge is uniquely valuable for small body missions where SRP and irregular body shape are very important and where target selection is often a part of the mission design.Item Sequential estimation methods for small body optical navigation(2016-08) Olson, Corwin, 1984-; Russell, Ryan Paul, 1976-; Akella, Maruthi R; Bettadpur, Srinivas V; Bhaskaran, Shyamkumar; Carpenter, James R; Fowler, Wallace TAs humans explore further into the solar system, small bodies such as asteroids and comets serve as critical stepping-stone destinations. Highly accurate navigation about these small bodies is critical for any future missions, and as a result is listed prominently among NASA's future goals in the NASA Office of Chief Technologist Roadmap. Due to the long communication light-time delays with the Earth, advances in small body navigation may enable missions currently not feasible, as well as significantly reduce dependence on ground resources. Increased operational agility will enable rapid decisions and opportunistic science measurements not possible in previous missions to small bodies. To assist NASA in accomplishing future small body navigation goals, several important advances are made. First, the effectiveness of modern orbit estimation techniques is investigated, with the higher order Additive Divided-Difference sigma point Filter (ADF) implemented and used along with the standard Extended Kalman Filter (EKF) to estimate the spacecraft state from optical small body surface landmark measurements. The ADF performs consistently better than the EKF in the simulations performed, with increasing improvement for higher levels of initial state error and longer intervals between photos of the surface. Second, a new method is created to improve onboard navigation filter performance in diverse and rapidly changing dynamical environments. The approach is to precompute a process noise profile along a reference trajectory using consider covariance analysis tools and filters. When used in an onboard navigation filter, the precomputed process noise allows the filter to account for time- and state-dependent perturbations in the dynamics. The new method also obviates the need for most or all traditional manual tuning of the filter, and provides significantly improved representation of the state uncertainty. Finally, a Simultaneous Localization And Mapping (SLAM) algorithm is employed to estimate the spin state of a tumbling small body (which are expected to be a significant percentage of the small bodies in the solar system), as well as the spacecraft state and surface landmark locations. For the small body characterization phase of the Rosetta mission, the state estimates converge successfully for large initial state errors. The SLAM algorithm remains effective for a range of small body spin states and masses that correspond to expected tumbling small bodies throughout the solar system. The SLAM algorithm is successfully applied to high fidelity independently simulated imagery of a tumbling small body generated by the European Space Agency, and a method for initializing the small body landmark locations is provided.