Two documents describe a proposed Earth-atmosphere observatory to orbit the Sun at the Sun-Earth L2 Lagrange point — a point of unstable equilibrium in the shadow of the Earth, about 1.5 million km from the Earth along an outward projection of the Earth-Sun axis. The observatory would comprise two spacecraft flying in precision formation: (1) a primary-aperture spacecraft, from which would be deployed a 25-m diameter membrane primary mirror aimed at the Earth, and (2) a secondary-telescope spacecraft at the focal plane of the primary mirror, 125-m distant along the axis towards the Earth. The secondary telescope would be aimed at the primary mirror and slowly rotated to scan the focused annular image of the visible illuminated portion of the Earth's atmosphere during continuous occultation of the Sun.
The purpose of the observations is to gather spectroscopic data of chemical signatures from ultraviolet to near-infrared that could contribute to major advances in understanding atmospheric dynamics and development of models for prediction of climate change. The documents present an overview of the scientific mission, the rationale for the choice of L2, and numerous engineering issues, including the overall architecture of the telescope formation, delivery to L2, design of the telescope and associated metrology instrumentation, formation maneuvering to follow a unique powered solar occultation orbit in the vicinity of L2, and strategies for observatory initialization and mission operations.
This work was done by Edward Mettler, Behçet Açikmeşe, William Breckenridge, Steven Macenka, Randall Hein, and Eldred Tubbs of Caltech for NASA's Jet Propulsion Laboratory. NPO-40973.
This Brief includes a Technical Support Package (TSP).
Telescope Formation at L2 for Observing Earth's Atmosphere
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Overview
The document titled "Technical Support Package for Telescope Formation at L2 for Observing Earth's Atmosphere" outlines a proposed mission involving a formation of two spacecraft positioned near the Sun-Earth L2 point. This location is strategically chosen for its unique observational advantages, particularly for studying Earth's atmosphere. The formation consists of one spacecraft equipped with a telescope that observes light reflected from a large membrane mirror on the second spacecraft. This innovative setup aims to enhance our understanding of atmospheric dynamics, chemical processes, and radiative mechanisms that influence climate change.
The document emphasizes the benefits of the Sun-Earth L2 point, where the Earth's atmosphere experiences permanent solar occultation, making it ideal for long-term climate studies. Additionally, the L2 point serves as a gravitational equilibrium, minimizing fuel requirements for maintaining the spacecraft's position, which is crucial for a mission expected to last 5-10 years.
The propulsion system proposed for the spacecraft includes a combination of large and small thrusters, along with reaction wheels for attitude control. The large thrusters are designed for translational control and orbital feedback, while the smaller thrusters focus on formation control and counteracting residual forces. The mission plans to utilize electric propulsion (EP) with xenon as fuel, leveraging advancements in ion thruster technology that can achieve high specific impulses (up to 6000 seconds). This efficiency significantly reduces fuel consumption, making the mission feasible over its intended duration.
The document also discusses the technical aspects of the spacecraft's actuation system, including the configuration and sizing of thrusters, which are critical for maintaining the desired formation and ensuring precise control during observations. The use of advanced sensors and detectors is highlighted, particularly in the context of the center-of-curvature sensor, which plays a vital role in the optical system.
Overall, this technical support package serves as a comprehensive overview of the mission's objectives, design considerations, and technological innovations. It aims to contribute to the broader understanding of climate change and atmospheric science, showcasing NASA's commitment to advancing aerospace technology for scientific exploration and environmental monitoring.
