Tethers Unlimited, Inc. MMOSTT Final Report TABLE OF CONTENTS I. INTRODUCTION ..........................................................................................................................1 II. BACKGROUND .............................................................................................................................2 A. MOMENTUM-EXCHANGE TETHERS.................................................................................................2 B. ELECTRODYNAMIC REBOOST ...........................................................................................................2 C. KEY ADVANTAGES .............................................................................................................................3 D. SUMMARY OF PHASE I RESULTS .......................................................................................................4 III. PHASE II TECHNICAL OBJECTIVES......................................................................................6 IV. SUMMARY OF RESULTS OF THE PHASE II EFFORT........................................................6 A. ROADMAP FOR DEVELOPMENT OF A EARTH-MOON-MARS TETHER TRANSPORT SYSTEM ......6 B. DESIGN AND SIMULATION OF A TETHER BOOST FACILITY FOR LEO⇒GTO PAYLOAD TRANSPORT ........................................................................................................................................8 C. TETHER FACILITY REBOOST............................................................................................................ 11 D. DEVELOPMENT AND SIMULATION OF TETHER RENDEZVOUS METHODS .................................13 E. TETHER SYSTEMS FOR INTERPLANETARY TRANSPORT ................................................................15 F. µTORQUE:LOW-COST MOMENTUM-EXCHANGE/ELECTRODYNAMIC-PROPULSION DEMONSTRATION ............................................................................................................................17 V. PUBLICATIONS...........................................................................................................................18 VI. CONCLUSIONS ...........................................................................................................................19 Appendix A Tether Boost Facilities for In-Space Transportation, 2001 NIAC Fellows Conference Presentation. Appendix B. “Commercial Development of a Tether Transport System”, AIAA Paper 2000- 3842, Presented at the 36th Joint Propulsion Conference, Huntsville AL, July 18, 2000. Appendix C. “Design and Simulation of a Tether Boost Facility for LEO⇒GTO Payload Transport”, AIAA Paper 2000-3866, Presented at the 36th Joint Propulsion Conference, Huntsville AL, July 19, 2000. Appendix D. “The Cislunar Tether Transport System Architecture”, Paper presented at the 2nd Lunar Development Conference, Las Vegas, NV, July 20, 2000. Appendix E. Tether Boost Facility Design Study Interim Report, by Boeing/RSS. Appendix F. Tether Boost Facility Design Study Final Report, by Boeing/RSS. Appendix G. Tether Rendezvous Studies. Appendix H. 2000 NIAC Fellows Conference Presentation. Appendix I. “Rapid Interplanetary Tether Transport System”. Paper IAF-99-A.5.10, presented at the 50th International Astronautical Congress, 4-8 Oct 1999, Amsterdam, The Netherlands. This paper summarized the results of the Phase I effort. Appendix J. “Tether Systems for Satellite Deployment and Disposal”, Paper IAF-00-S.6.04, presented at the 51st International Astronautical Congress, 2-6 Oct 2000, Rio de Janiero, Brazil. Appendix K. Tether Facility Reboost Study. 1 Tethers Unlimited, Inc. MMOSTT Final Report Appendix L. The µTORQUE Momentum-Exchange Tether Experiment, Paper submitted to the 2002 STAIF Conference. Appendix M. TetherSim™: Tether Transport System Dynamics Verification Through Simulation. Appendix N. Momentum-Exchange/Electrodynamic Reboost Tether Facility for Deployment of Microsatellites to GEO and the Moon, paper presented at the 2001 STAIF Conference, Albuquerque, NM. Appendix O. µSatellite Tether Boost Facility, 2001 STAIF Conference presentation , Albuquerque, NM. Appendix P. Interplanetary Tether Transport Overview, Paper presented at the 2001 Space Mechanics Conference. Appendix Q. Application of Synergistic Multipayload Assistance with Rotating Tethers (SMART) Concept to Outer Planet Exploration, forum on innovative approaches to outer planetary exploration 2001-2020, 21-23 February 2001, Lunar and Planetary Institute, Houston, Texas. Appendix R. Mars-Earth Rapid Interplanetary Tether Transport (MERITT) Architecture, Paper presented at 2001 STAIF Conference. 2 Tethers Unlimited, Inc. MMOSTT Final Report I. INTRODUCTION Momentum-Exchange/Electrodynamic-Reboost (MXER) Tethers can provide a fully reusable, zero-propellant infrastructure for in-space transportation that will reduce by an order of magnitude or more the costs of delivering payloads to geostationary orbit, the Moon, Mars, and other destinations. This Phase II NIAC research program has continued the development of a tether-based architecture for in-space propulsion to service transportation needs in the Earth-Moon-Mars system. This tether architecture will utilize momentum-exchange techniques and electrodynamic tether propulsion to transport multiple payloads with little or no propellant consumption. The tether transport architecture is designed to be deployed incrementally, with each component able to perform a useful revenue-generating mission to help fund the deployment of the rest of the system. The Phase II effort has focused on the design of the first component of this architecture, a Tether Boost Facility optimized for transferring payloads from low Earth orbit (LEO) to geostationary transfer orbit (GTO). The resultant system concept uses a modular design that enables a single launch to deploy a fully-operational tether boost facility which can later be augmented to increase its payload capacity. The first component of the tether boost facility will be able to toss 2,500 kg payloads from a low-LEO initial orbit to GTO. This same facility will also be capable of boosting 1,000 kg payloads to lunar transfer orbit (LTO) or to escape via a lunar swingby. Additional launches of essentially identical modules can increase the payload capacity of the Tether Boost Facility to enable it to boost larger satellites and, eventually, manned spacecraft. This Tether Boost Facility can, in turn, be used to deploy components of additional tether facilities at the Moon and Mars, providing an infrastructure for frequent, low-cost transport between the Earth, the Moon, and Mars. 1 Tethers Unlimited, Inc. MMOSTT Final Report II. BACKGROUND Space tethers can accomplish propellantless propulsion through two mechanisms, through momentum-exchange between two space objects, and through electrodynamic interactions with a planetary magnetic field. A. Momentum-Exchange Tethers In a momentum-exchange tether system, a long, thin, high-strength cable is deployed in orbit and set into rotation around a central body. If the tether facility is placed in an elliptical orbit and its rotation is timed so that the tether is oriented vertically below the central body and swinging backwards when the facility reaches perigee, then a grapple assembly located at the tether tip can rendezvous with and capture a payload moving in a lower orbit, as illustrated in Figure 1. Half a rotation later, the tether can release the payload, tossing it into a higher energy orbit. This concept is termed a momentum-exchange tether because when the tether picks up and tosses the payload, it transfers some of its orbital energy and momentum to the payload, resulting in a drop in the tether facility’s apogee. Figure 1. Concept of operation of a momentum-exchange tether facility. Orbits are depicted conceptually from the perspective of an observer on the Earth. B. Electrodynamic Reboost In order for the tether facility to boost multiple payloads, it must have the capability to restore its orbital energy and momentum after each payload transfer operation. If the tether facility has a power supply, and a portion of the tether contains conducting wire, then the power supply can drive current along the tether so as to generate thrust through electro- dynamic interactions with the Earth's magnetic field, as illustrated in Figure 2. By properly controlling the tether current during an orbit, the tether facility can reboost itself to its original orbit. The tether facility essentially serves as a large "orbital energy battery," allowing solar energy to be converted to orbital energy gradually over a long period of time and then rapidly transferred to the payload. 2 Tethers Unlimited, Inc. MMOSTT Final Report orbital thrust velocity applied voltage current magnetic field line Figure 2. Electrodynamic tether thrust generation. C. Key Advantages A tether transportation system has several advantages compared to conventional and other advanced in-space propulsion systems: 1. (Near) Zero Propellant Usage Chief among these advantages is the ability to eliminate the need for propellant expenditure to perform payload transfers. Of course, some propellant expenditure will be needed for trajectory corrections and rendezvous maneuvering, but with proper system design these requirements will be very small, a few tens of meters per second. The ability to cut several thousands of meters per second from the ∆V needed to deliver a payload to its destination can enable customers to utilize much smaller launch vehicles than would be required with a rocket- only