Solar Sail Scalability and a "Truly Scalable" Architecture: The Space Tow

Abstract

Solar sail scalability is often understood to be the quality that renders a structural architecture applicable to (or efficient under) ever larger global dimensions. At the heart of this definition is the impact of extreme or, rather, extremely large, dimensions on structural performance. Scalability, however, can also be interpreted as a much broader issue with far more critical importance to solar sail engineering, as the dimensional indifference of technologies and engineering steps that (will one day) make solar sailing a reality. Scalability, in fact, the lack thereof, in this comprehensive sense which is implied in the present work is the single most serious challenge to sailcraft engineering, hindering all major steps of development: design, fabrication, and component and system verification. The systematic review of the dimensional issues for these steps presented in this paper, therefore, offers valuable insight into engineering bottlenecks and helps to identify desirable structural and design qualities to mitigate them. These qualities are consecutively combined into an architecture, the space tow, which consists of a sequence of like sail elements linked with filaments. Some of the performance metrics and unique features of this design, scalable in many more ways than most alternatives, are reviewed. Nomenclature A = total sail surface area A c = filament truss longeron cross section area A 0 = surface area of one sail panel A 1 = cross section area of single filament a, a c = acceleration; characteristic acceleration b s = sail panel film nominal billow magnitude c = sail panel square edge d 1 = diameter of single filament E, = Young's modulus, Poisson's ratio e z0 , e z = boom tip lateral deflection, with linear and nonlinear approximation F = thrust in the sailcraft direction F 1 = maximum force in one filament truss longeron F r = thrust in the illumination (sun-radial) direction F 0x , F 0z = sail panel boom tip load axial and lateral components g p = technological gap between facing panel boom surfaces in stowage h = sail panel boom total depth I = cross section moment of inertia L = space tow length, nl L b = sail panel radial boom length l = filament truss bay length (spacing of sail panels) l d = length of filament truss diagonal M = steering torque m = sail panel mass m p = mass of payload (spacecraft without the tow) m s = mass of space tow structure (filaments and panels) m 1p = average mass of filament truss bay n = number of space tow truss bays n 1 = number of filaments in truss longeron at base P e = panel boom Euler critical load, 2 E 0 I 0 =2L b 2 p ef0 = maximum effective photon pressure at one astronomical unit from the sun, s p s0 p s0 = ideal solar light pressure at one astronomical unit from the sun, 9:126 Pa T = temperature t = thickness t 0 = sail panel boom reinforcing strip thickness on each side of sail w 0 = sail panel boom reinforcing strip width = offset angle; angle between the spacecraft orientation and the direction of illumination, cf. Fig. 1 T;1= coefficient of therm...