A document describes a graph-based path-planning algorithm for balloons with vertical control authority and little or no horizontal control authority. The balloons are designed to explore celestial bodies with atmospheres, such as Titan, a moon of Saturn. The algorithm discussed enables the balloon to achieve horizontal motion using the local horizontal winds. The approach is novel because it enables the balloons to use arbitrary wind field models. This is in contrast to prior approaches that used highly simplified wind field models, such as linear, or binary, winds.
This new approach works by discretizing the space in which the balloon operates, and representing the possible states of the balloon as a graph whose arcs represent the time taken to move from one node to another. The approach works with arbitrary wind fields, by looking up the wind strength and direction at every node in the graph from an arbitrary wind model. Having generated the graph, search techniques such as Dijkstra’s algorithm are then used to find the set of vertical actuation commands that takes the balloon from the start to the goal in minimum time. In addition, the set of reachable locations on the moon or planet can be determined.
This work was done by Lars James Blackmore, Nanaz Fathpour, and Alberto Elfes of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com /tsp under the Information Sciences category. NPO-46607
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Graph-Based Path-Planning for Titan Balloons
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Overview
The document titled "Graph-Based Path-Planning for Titan Balloons" discusses innovative strategies for exploring Titan, Saturn's largest moon, using Montgolfiere balloons. Due to Titan's dense and hazy atmosphere, traditional imaging from orbiters is ineffective, making airborne systems like balloons appealing for surface exploration.
The primary focus of the research is on the planning of vertical actuation commands for these balloons to navigate from a specified starting point to a goal location. The challenge lies in the highly nonlinear nature of Titan's wind field models, which complicates the path planning process. To address this, the researchers developed a graph-based path planning algorithm that can operate effectively in arbitrary wind conditions.
The algorithm works by discretizing the operational space of the balloon and representing its possible states as a graph. Each node in the graph corresponds to a state of the balloon, while the arcs represent the time taken to move between nodes, informed by the wind strength and direction at each point. By employing search techniques such as Dijkstra's algorithm, the algorithm can determine the minimum-time path from the start to the goal, as well as compute the time required to reach all possible points on Titan from a given location.
This approach is novel because it allows for the incorporation of realistic wind models, contrasting with previous methods that relied on simplified wind field representations. The ability to handle complex wind dynamics is crucial for the practical application of the path planning algorithm in designing missions to Titan.
The document emphasizes the importance of understanding the actuation requirements for different types of airborne systems, ranging from free-flying balloons with no actuation to airships with significant propulsion capabilities. Montgolfiere balloons, which can control their vertical position but have limited horizontal actuation, are positioned in the middle of this spectrum. The research suggests that by utilizing vertical actuation in conjunction with knowledge of local winds, it is possible to achieve desired horizontal movements.
Overall, this work contributes to the broader goal of enhancing exploration capabilities on Titan, providing a framework for future missions that could yield significant scientific discoveries about this enigmatic moon. For further inquiries, the document provides contact information for NASA's Jet Propulsion Laboratory.
