Conceptual Design and Analysis of Space Tether Transportation System With Electrodynamic Propulsion

Cumhuriyet Üniversitesi Fen Fakültesi Cumhuriyet University Faculty of Science Fen Bilimleri Dergisi (CFD), Cilt:36, No: 3 Özel Sayı (2015) Science Journal (CSJ), Vol. 36, No: 3 Special Issue (2015) ISSN: 1300-1949 ISSN: 1300-1949   Conceptual Design and Analysis of Space Tether Transportation System With Electrodynamic Propulsion Mehran NOSRATOLLAHI1, Javad SHIRAZI1,* 1 Malek Ashtar University of Technology, Aerospace University Complex Received: 01.02.2015; Accepted: 05.05.2015 Abstract. Tether transportation system can form the infrastructure for a reusable low cost space transportation architecture and can be used to carry frequent traffic between orbits. The Tether transportation facility would be sized for launch on a single large rocket vehicle to its operational orbit. This system will utilize electrodynamic tether propulsion to restore its orbit after each payload boost operation. Several technical challenges must be resolved to enable this systems to be fielded, including development of rapid rendezvous and capture capabilities and techniques for building and controlling the tether facilities. This research is applied modeling of tether dynamics, orbital mechanics, electrodynamics, and other relevant physics, to verify the orbital design of the system and investigate methods for performing electrodynamic re-boost of the platform. Using comparison for differing payload capacities of each vehicle and the dependence of launch pricing upon business factors, these research indicates that a reusable tether boost facility could enable commercial customers to reduce their launch costs by reduction of recurring costs. Keywords: Tether, Conceptual design, Electrodynamic propulsion, Transportation system. 1. INTRODUCTION After 58 years of space exploration, the space launch industry remains reliant only on chemical rockets. This paper will investigate if any merit exists in implementing an alternative launch assist technology with functionality of existing upper stages namely momentum transfer tethers. A space tether is a long cable used to couple spacecraft together as they orbit the central body (i.e. Earth). Tethers are usually made of thin strands of high-strength fibers such as Spectra or Kevlar. Conducting tethers offer the additional capability to interact with the earth magnetic and electrical force fields as the electrodynamic tether. [1] Because the space tether makes it possible to transfer energy and momentum from one object to another, it can be called a form of space propulsion. There are two general categories of tethers. Tether transportation system will utilize momentum-exchange techniques and electrodynamic tether propulsion to transport multiple payloads with little or no propellant consumption. [2] In this paper after reviewing the works has done to date in this field, the results for the development of a concept for the tether transportation architecture are presented, and discussed simulations are used to investigate the performance of the tether system. _____________ *Corresponding author. Email address: Special Issue: The Second National Conference on Applied Research in Science and Technology http://dergi.cumhuriyet.edu.tr/cumuscij ©2015 Faculty of Science, Cumhuriyet University NOSRATOLLAHI, SHIRAZI 2. PRIOR WORKS The field of space tethers has received very considerable attention in recent decades, with many specialist articles. The longest tether stably deployed to date has reached a length of 31.7 km, albeit unintentionally [2]. According to Aerospace America Magazine [2], in 2010, the near-term target was to achieve reliable deployment and operation of 1 km tethers, although other projects [3] succeeded with non-liberating deployment of 20 km-long tethers in 1993. In 2007 Menon [4] described in detail a tether brake used to control deployment of the 31.7 kmlong tether in the SpaceMail experiment [5]. Therefore, the author concludes that current technology is sufficient to deploy 80–1000 km-long tethers in the LEO environment. Among many rotating momentum-transfer tether configurations promoted on the Tether Unlimited site, the LEO momentum transfer tethers (rotating tether) [6] deserves special attention, as it is scalable to low tip speed. In 2010, Williams [7] proposed using a system with two rotating tethers for orbital capture or disposable and one reusable. Unfortunately, around the Earth, the only such body is the moon, and series of tethers able to handle at least 1.6 km/s tip speed are necessary for harnessing the orbital momentum of the moon rocks. An example of momentum-neutral tether design may be found in [8] in which a range of statistical methodologies for life prediction from the literature were critically compared and a revised proposal made, with some potential for practical use highlighted. 3. 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 massive central body. It allow momentum to be transferred between objects in space, such as two spacecraft. The principle is based on the gravity gradient force. Swinging motion may be used to raise or lower the orbit of a tandem system without using any propellant. If the tether facility is placed in an elliptical orbit and its rotation is timed so that the tether will be 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 acquire a payload moving in a lower orbit, as illustrated in Figure 1 and Figure 2. [9] Figure 1. Momentum Exchange Tether catching payload and tossing it to GTO orbit. First orbital design implemented in this paper and second utilized by Hoyt. 792     Conceptual Design and Analysis of Space Tether Transportation System With Electrodynamic Propulsion Figure 2. Tether tip velocity is configured to be equal to the difference in velocity between tether and payload. [9] 4. ELECTRODYNAMIC TETHERS An electrodynamic tether is essentially a long conducting wire extended from the main endbody. There may be a second end-body to help deploy the bare tether. The gravity gradient field of the “spacecraft and string system” tends to orient the tether in a vertical position. A tether in Earth orbit interacts with the earth's magnetosphere due to the relative orbital velocities; the motion of the conductor across the magnetic field induces a voltage along the length of the tether. This voltage can be up to several hundred volts per km. [10] The interaction of the tether system with the magnetosphere can be used in the design of the system to act either as an “electrodynamic power or thrust system” to boost the orbit of the spacecraft. The direction of the current flow in or out of an electrodynamic tether system determines if the interaction contributes to drag or to propulsion. In order for the tether facility to boost one payload (...truncated)