Paul A. Gierow

Scalable Solar-Sail Subsystem Design Concept

A scalable solar-sail concept, which integrates recently developed gossamer coilable longeron mast technology, has been developed, providing simple reliable deployment and structural robustness with minimum weight. This sail system is also unique in that it is composed of tensioned membranes without the incorporation of catenaries. This simplification is made possible through a mathematical demonstration of the insignificance of structural wrinkles on propulsive effectiveness. The sail package is a mass-optimized propulsion subsystem that can be mounted to a general heritage spacecraft to provide continuous low-level thrust. The design baseline is a three-axis-stabilized four-quadrant 40-m-square sail with attitude controlled by gimbaling the spacecraft on an extended boom. Considerations for the baseline design definition and the resulting performance vs size are reviewed.

Design, test, and evaluation of an electrostatically figured membrane mirror

Significant advances have been achieved in manufacturing optical quality membrane materials with surface quality suitable for use as first surface mirrors. These materials have been used to fabricate test articles demonstrating diffraction limited performance in the laboratory environment. These mirrors are supported using heavy rigid fixtures and pressure forces to tension the membrane. A lighter weight system is required to transition the membrane mirror technology to space hardware applications. Using electrostatic forces to tension and figure the membrane is one promising approach to developing a flight weight membrane mirror system. This paper discusses the design and testing of an experimental membrane mirror system that was developed to evaluate the potential areal density, figure accuracy and stability of a lightweight electrostatically figured mirror manufactured from precision cast optical quality membrane material.

Design of a Membrane Optical Beam-Splitter

This paper presents results of the design of a pellicle beam splitter of rectangular form. The pellicle beam splitter was created by mounting a pellicle, a thin optical membrane, to an outer rectangular frame. An inner tensioning ring was ground optically flat and pressed against the pellicle, defining an optically flat pellicle boundary. Upon inspection, the rectangular form of the mount caused undesirable fringe patterns in the corners. Finite element analysis was used to both understand the problem stemming from the original design, as well as to assess new design options. A new prototype was constructed based upon the analysis and optical characterization verified improved performance.

Optical components for solar and laser thermal bimodal propulsion and power systems

The use of Solar Thermal Propulsion (STP) as an upper stage propulsion system requires the use of large primary concentrators. The size of the primary concentrators, ranging in size between 2–10 meters in diameter, depends upon the configuration of the propulsion system. Three concepts being pursued for the concentrators are inflatable, foam rigidized, and rigid concentrators. Inflatable concentrators are deployed by inflation, and their shape is maintained by a pressure inside the concentrator canopy. Foam rigidized concentrators are deployed by inflation. They differ from inflatable concentrators, in that they are rigidized by a foam which is injected between two membranes. This paper will discuss the current state of the technology for the fabrication and use of inflatable and foam rigidized concentrators and integration of these concentrators into an optic system. The use of a secondary concentrator to integrate the primary concentrator with an absorber system will also be presented.