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 Açikme¸se, William Breckenridge, Steven Macenka, Randall Hein, and Eldred Tubbs of Caltech for NASA's Jet Propulsion Laboratory. NPO-40973.