Ascensor Espacia

Space Elevator Initial Construction Mission Overview
David D. Lang1
1

David D. Lang Associates, Seattle WA.

Abstract: This paper presents an overview of a proposed GEO-originating deployment mission flight scenario currently under consideration to accomplish the initial construction of a space elevator. Much as a suspension bridge’s initial strand of cable must be established, so must theelevator’s first strand of vertical ribbon and ballast mass be erected. Results of dynamic simulations of initial deployment accomplished using the Generalized Tethered Object Simulation System (GTOSS) software tool are presented via discussions and summary graphs. A brief overview of dynamic models that constitute GTOSS is presented, and the physical configuration of the elevator as it manifestsitself within GTOSS is characterized. A general discussion of orbital dynamics challenges facing this initial deployment process is presented, with emphasis on dynamic control issues and implications on the two space craft delegated to performing the deployment. Finally, a proposed control strategy is presented and simulated to demonstrate the possibility of a GEO originating deployment.

1.Introduction

Currently two different approaches to deploying the initial elevator ribbon are identified. Both start with a space craft containing (either initially or via buildup by multiple courier-missions) the Ribbon, Ballast mass, Ballast-end controller (GEO craft), ribbon Anchor-end controller (Deploy craft), and propulsion-control systems. While they differ in starting point and maneuverstrategy, they both must face the dynamics challenges of extreme tether extension. The two scenarios are: (a) Start with a space-craft at GEO, thus deploying Ribbon downward from there, in conjunction with a coordinated upward maneuvering of the GEO craft). See Reference 1. (b) Start with a space-craft in LEO, deploying the Ribbon and Ballast mass upward, creating a system with ever-longerorbiting period, until the configuration grows to include GEO altitude and beyond, and manifests an “orbital period” corresponding to earth rotation rate. See Reference 6. This paper specifically explores the dynamics of the GEO deployment mission. A proposed deployment control strategy is presented that serves to expose the nature of the dynamics challenges inherent in this mission, and explores someof the intrinsic ingredients that might constitute a successful deployment mission design. 2. GTOSS Overview

The Generalized Tethered Object Simulation System is a time-domain dynamics simulation code, conceived by the author in 1982 to provide NASA with a tool to simulate dynamics of combinations of space objects and tethers for flight safety certification of the Shuttle Tethered SatelliteSystem missions. Since Page 1 of 18

then, GTOSS has undergone continuous evolution and validation, being applied at some stage in the formulation of virtually every US tethered space experiment flown or proposed to date. Below is an overview of GTOSS features. • Multiple bodies, with 3 or 6 degrees of freedom, connected in arbitrary fashion by multiple tethers, subject to natural planetaryenvironments, including standard earth models as well as more rudimentary models for the other planets. • Tethers represented by either massless or massive models. The massive tether model is a point synthesis approach, each tether employing a constant number of up to 500 nodes, specifiable by tether (500 is a soft system-configurable limit). • All tethers can be deployed from, or retrieved into, objectsby user-definable scenarios. The tether model includes momentum effects of mass entering or leaving the domain of the tether itself, and produces related forces on objects deploying and retrieving the tether material. • Tethers can possess length-dependent non-uniform attributes describing elastic cross section, aerodynamic cross section, and lineal mass density. • Tethers are subject to...