Dish systems for CSP

The static deflection profile of a large spin-stabilized space reflector because of solar radiation pressure acting on its surface is investigated. Such a spacecraft consists of a thin reflective circular film, which is deployed from a supporting hoop structure in an untensioned, slack manner. This paper investigates the use of a variable reflectivity distribution across the surface to control the solar pressure force and hence the deflected shape. In this first analysis, the film material is modelled as one-dimensional slack radial strings with no resistance to bending or transverse shear, which enables a semi-analytic derivation of the nominal deflection profile. An inverse method is then used to find the reflectivity distribution that generates a specific, for example, parabolic deflection shape of the strings. Applying these results to a parabolic reflector, short focal distances can be obtained when large slack lengths of the film are employed. The development of such optically controlled reflector films enables future key mission applications such as solar power collection, radio-frequency antennae and optical telescopes.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.2015.0119

Shape control of slack space reflectors using modulated solar pressure.

Performance analysis of a novel solar concentrator using lunar flux mapping techniques

Materials and processes have been developed for production of polymer membranes with optical quality surface characteristics. These materials have been successfully used to manufacture large, high quality, ultra lightweight, optical flats for beam splitters, lens covers and other applications. These materials can potentially be used to develop large aperture primary mirrors with areal densities less than 1kg/m2. However, for curved mirrors it is more difficult to establish and maintain desired optical figure from the initial packaged configuration. This paper describes design analysis being performed to support fabrication of a membrane mirror test article. Modeling was performed to evaluate the effectiveness of several different boundary control concepts for correcting different types of figure aberrations. Analyses of different combinations of boundary displacement actuators, electrostatic force actuators, and pressure are presented.

Development of a one-meter membrane mirror with active boundary control

This paper considers utilizing solar radiation pressure (SRP) to actively control the surface shape of a reflector consisting of a rigid hoop and slack membrane with embedded reflectivity control devices (RCDs). The full nonlinear static partial differential governing equations for a reflector with negligible elastic deformations are established for the circumferential, radial and transverse directions respectively, in which the SRP force with ideal /non-perfect models, the centripetal force caused by the rotation of the reflector and the internal stresses are considered. The inverse problem is then formulated by assuming that the required surface shape is known, and then the governing algebraic-differential equations used to determine the required surface reflectivity together with the internal stresses are presented accordingly. The validity of the approach is verified by comparing the results in the paper with the corresponding published results as benchmarks. The feasible regions of the angular velocity and Sun angle for a paraboloidal reflector with an invariant radius and focal length (case 1), and the achievable focal lengths with a specific angular velocity and Sun angle (case 2) are presented for the two SRP models respectively, both by considering the restrictions on the reflectivity and internal stresses. It is then found that the feasible region is toward a larger angular velocity and Sun angle when using the non-perfect SRP model compared with the ideal one in case 1. The angular velocity of the spinning reflector should be within a certain range to make the required reflectivity profiles within a practical range, i.e., [0, 0.88], as indicated from prior NASA solar sail studies. In case 2, it is found that the smallest achievable focual length of the reflector with the non-perfect SRP model is smaller than that with the ideal SRP model. It is also found that the stress level is extremely low for all cases considered and the typical real material strength available for the reflector is sufficient to withstand these internal stresses.

/pdf/modulated-solar-pressure-based-surface-shape-control-of-41flgfuxm1.pdf

Modulated solar pressure-based surface shape control of paraboloid space reflectors with an off-axis Sun-line

Potentially high quality optical reflector surfaces are attainable with the use of pressure formed membranes. Such reflector surfaces offer the prospect of very low weight and low cost. The formation of such surfaces, using initially flat circular membranes with uniform pressure loading, is studied in this paper. Finite axisymmetric deformations, along with both linear and nonlinear material response is considered. A wide range of focal-length-to-diameter ratios (above 0.6) are addressed and the structural/optical response mechanisms that lead to optical distortions relative to ideal parabolic reflector shapes are also considered. Results show that elastic material response can often lead to a significantly larger deviation from the ideal shape than will inelastic material response. This results primarily from the ability to limit stress nonuniformities when inelastic material response is operative. Furthermore, when under pressure loading the membrane focal length decreases monotonically with increasing radius for both linear and nonlinear material response. Further, the predicted focal length variation is increasingly nonlinear near the membrane support.

/pdf/the-formation-of-optical-membrane-reflector-surfaces-using-48v3pi99r6.pdf

C. Tuan

Papers

The formation of optical membrane reflector surfaces using uniform pressure loading