A document discusses the design of orbits of spacecraft for relaying communications between Earth stations and robotic and human explorers in craters in one of the polar regions on the Moon. In simplest terms, the basic problem is to design a constellation of orbits to provide continuous and preferably redundant communication coverage of one of the poles with a minimal number of spacecraft and little or no controlled maneuvering of the spacecraft to maintain the orbits. The design method involves the use of analytical techniques for initial selection of orbits, followed by a numerical procedure for tuning the coverage of the constellation to obtain a design. In an example application, the method leads to a constellation of three spacecraft having elliptical, inclined orbits, the apoapsides of which would remain in the hemisphere (North or South) containing the pole of interest. The orbits would be stable and would maintain the required spacecraft formation for at least 10 years, without need for controlled maneuvering if gravitation is the only force considered to affect the orbits. A small amount of controlled maneuvering would be needed to counteract effects of solar-radiation pressure and other perturbations.
This work was done by Todd Ely and Gary Noreen of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category. NPO-40992
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Lunar Constellation of Frozen Elliptical Inclined Orbits
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Overview
The document titled "Lunar Constellation of Frozen Elliptical Inclined Orbits" from NASA's Jet Propulsion Laboratory discusses the design and implications of a constellation of lunar telecommunication satellites aimed at providing continuous and redundant coverage over the Moon's polar regions, particularly the South Pole. This area is of significant scientific interest due to the presence of permanently shadowed craters that may contain frozen volatiles, making it a prime target for future robotic and human exploration.
To address the communication challenges posed by the Moon's geography, the document proposes a small constellation of three or fewer satellites in stable, high-altitude elliptical orbits. These orbits are characterized by their large eccentricity and inclination, allowing the satellites to focus coverage near the apoapsis, which is oriented over the polar regions. The design aims to ensure that at least two satellites are continuously in view of a polar station, thereby facilitating uninterrupted communication for exploration missions.
The paper outlines the orbital characteristics necessary for achieving effective coverage, including semi-major axis values that support continuous single and double coverage with minimal satellite numbers. The concept of "frozen" orbits is introduced, where the line of apsides librates in the polar region, allowing for long-term stability and reduced maintenance costs. This stability is crucial for maintaining the formation of the satellites using only natural gravitational effects, which minimizes operational expenses.
Coverage statistics presented in the document indicate that the proposed constellation can achieve 100% coverage for a South Polar station, with individual satellites providing approximately 73% coverage. The mean pass times and gaps between satellite coverage are also analyzed, demonstrating the effectiveness of the constellation in maintaining communication links.
In conclusion, the document emphasizes the importance of developing a robust lunar telecommunication infrastructure to support future exploration efforts. By leveraging innovative orbital mechanics and a small number of satellites, NASA aims to create a sustainable communication network that enhances the feasibility of missions to the Moon's polar regions, ultimately contributing to our understanding of lunar resources and the potential for human presence on the Moon.
