This work describes a discontinuous or segmented mirror whose overall flatness is less dependent on the limited tension that can be supplied by the booms. A solar sail is a large, nominally flat sheet of extremely thin reflectorized film rigidly attached to a spacecraft, enabling propulsion via solar radiation pressure. Rip-stop fibers embedded in the backside of the film — with diameters ≈100× the thickness of the film — are commonly used to arrest tear propagation, which can easily occur in the handling and/or deployment of these gossamer-thin structures. Typically, the thin film or membrane that is the sail is systematically folded to enable both volumetrically compact transportation to space and mechanized deployment. It is the aggressive folding and creasing of the thin film that limits the ultimate flatness that can be achieved.
The deployed solar sail is made more plano by segmenting the film into tiles joined together via a fiber-supported hinge design. Deployment includes systematic unfolding of the stowed sail via telescopic booms. These booms also support sail-flattening tension in the membrane.
This work is motivated specifically by LF science requirements. To detect water ice in darkened areas of the Moon, an IR spectrometer is proposed that will gather reflectance spectra from the lunar surface using sunlight reflected from the solar sail. This high-level requirement flows down to a surface illumination requirement in watts/m2, which in turn drives flatness and stability requirements on the sail.
This work was done by Eric B. Hochberg of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49474
This Brief includes a Technical Support Package (TSP).
Design for Improving the Flatness of Solar Sails
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) focused on improving the flatness of solar sails, which are essential for propulsion in space through solar radiation pressure. The research, conducted under a contract with NASA and associated with Caltech, addresses the challenges faced when thin shells or films are folded, particularly when the radius of curvature is less than 100 times the material's thickness. This folding can lead to in-plane tension that exceeds the elastic limits of the material, resulting in permanent plastic deformation and creasing, which compromises the flatness and functionality of the solar sails.
The document emphasizes that achieving ultimate flatness in solar sails is primarily influenced by the straightness and co-planarity of the booms to which the edges of the sail are attached. The research indicates that advancements in design and material selection can lead to significant improvements in the flatness of solar sails, approaching what is described as functional perfection.
The Technical Support Package serves as a resource for disseminating the results of aerospace-related developments that have broader technological, scientific, or commercial applications. It is part of NASA's Commercial Technology Program, aimed at making innovative technologies accessible for various uses beyond their original aerospace context.
For further inquiries or assistance regarding the research and technology discussed, the document provides contact information for the Innovative Technology Assets Management at JPL. It also includes a notice that the document was prepared under the sponsorship of NASA, clarifying that neither the U.S. Government nor any representatives assume liability for the use of the information contained within.
Overall, the document highlights the importance of material properties and design considerations in the development of solar sails, which play a critical role in future space exploration missions. By addressing the challenges of maintaining flatness and structural integrity, the research aims to enhance the performance and reliability of solar sails in the harsh environment of space.
