A document proposes a constellation of spacecraft to be placed in orbit around the Moon to provide navigation and communication services with global coverage required for exploration of the Moon. There would be six spacecraft in inclined elliptical orbits: three in each of two orthogonal orbital planes, suggestive of a linked-chain configuration. The orbits have been chosen to (1) provide 99.999-percent global coverage for ten years and (2) to be stable under perturbation by Earth gravitation and solar-radiation pressure, so that no deterministic firing of thrusters would be needed to maintain the orbits. However, a minor amount of orbit control might be needed to correct for such unmodeled effects as outgassing of the spacecraft.
This work was done by Todd Ely of Caltech and Erica Lieb of ASRC 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-42722
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Stable Satellite Orbits for Global Coverage of the Moon
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Overview
The document titled "Stable Satellite Orbits for Global Coverage of the Moon" from NASA's Jet Propulsion Laboratory discusses the design and analysis of satellite constellations aimed at providing comprehensive communication and navigation services for lunar exploration. This initiative is driven by the U.S. government's vision for human exploration of the Moon, announced in January 2004.
The study explores various orbital configurations that can ensure persistent and stable coverage of the lunar surface, particularly focusing on the poles. It builds on previous research that established methodologies for selecting satellite constellations, specifically highlighting the use of two or three satellites to achieve reliable coverage without the need for frequent adjustments (stationkeeping) due to gravitational perturbations.
The document emphasizes the impact of non-conservative perturbations, such as solar radiation pressure, on satellite orbits. Preliminary findings suggest that by adjusting the semi-major axis of the orbits, it is possible to maintain a two-fold coverage at the lunar poles while minimizing control requirements. This adaptability is crucial for the long-term sustainability of lunar missions.
The research identifies that constellations of elliptical inclined orbits can provide global coverage of the Moon 99.999% of the time using only six satellites. The proposed configuration consists of two orbital planes, each containing three elliptical inclined orbits. This arrangement allows for effective coverage of the entire lunar surface, ensuring that communication and navigation services are consistently available.
To validate the coverage characteristics of these orbits, numerical simulations were conducted using two tools: JPL’s operational navigation software and STK™ (Systems Tool Kit). These simulations provided detailed statistics on spacecraft visibility and coverage gaps over extended periods, contributing to a comprehensive understanding of the orbital dynamics involved.
The document also includes technical details about the simulation methodologies, the configuration of the satellite constellations, and the statistical results obtained from the simulations. Overall, this research represents a significant step toward establishing a reliable infrastructure for lunar exploration, facilitating future missions and enhancing our understanding of the Moon. The findings underscore the importance of innovative orbital designs in supporting sustained human presence and activities on the lunar surface.
