Responsive Launch of Small Spacecraft Using Reusable In-Space Tether and Air-Launch Technologies

Abstract

Achieving dramatic reductions in launch costs below the current $10,000 per-kilogramto-LEO levels will require transportation system designs that maximize reusability, minimize manpower requirements for operations and maintenance, and maximize flight frequency. In this paper, we investigate a transportation system architecture that combines the use of small air-launched rockets with an in-space tether system to provide a capability for responsively launching small satellites to altitudes above LEO. By utilizing a momentum-exchange/electrodynamic-reboost (MXER) tether system as an ‘in-space upper stage,’ the system can enable small, responsively-deployed air-launch rocket systems to service traffic to MEO, GEO, and the Moon at costs 2 to 3 times lower than current launch systems. In this paper we detail the architectures of MXER Tether systems suitable for boosting small satellites from LEO to GTO and from LEO to elliptical ‘Magic’ orbits. I. Introduction eveloping systems for responsively deploying assets into orbit is critical to ensuring the capability to support the warfighter with timely intelligence, surveillance, and reconnaissance (ISR), signals intelligence, as well as mission-critical communications. Our capabilities for space situational awareness, space control, and spacecraft protection could also be greatly enhanced by the ability to deploy appropriate assets into orbit in a responsive manner. The capability to deploy satellites into orbit within days of a ‘go’ order requires launch systems that can be loaded, prepared, and launched very rapidly. The DoD is currently sponsoring several efforts to develop small, lowcost launch systems capable of responsively delivering microsatellite-class payloads (100-500 kg) into low Earth orbit (LEO), including the AirLaunch LLC ‘QuickReach’ booster and the SpaceX Falcon rocket. Using an allchemical rocket system to responsively launch microsatellite-class payloads to higher orbits, such as geostationary orbit (GEO), however, will be significantly more challenging and expensive because the larger launch vehicles required to reach these higher altitudes are more difficult and costly to prepare and launch in a short period of time. In this paper, we propose the use of an in-space transportation system component, called the MomentumExchange/Electrodynamic-Reboost (MXER) Tether, to serve as a fully-reusable ‘upper stage’ that would enable the small, responsive launch vehicles currently in development to deliver microsat-class payloads to orbits beyond LEO in a cost-effective manner. In particular, we will detail MXER Tether system concepts for LEO to geostationary transfer orbit (GTO) and LEO to ‘Magic” orbit transfers. A. Background: MXER Tether Transportation A MXER Tether system combines the principle of momentum exchange with the technique of propellantless electrodynamic propulsion. In a momentum exchange tether system, a long, high-strength tether is used to transfer orbital energy from a facility in orbit to a payload, boosting the orbit of the payload. In the technique of electrodynamic tether propulsion, currents driven along a conducting tether are used to generate Lorentz forces through interactions with the geomagnetic field so as to restore the orbital energy of the tether facility without consumption of propellant. 1,2,3 By combining these two techniques, a MXER Tether Facility can boost many payloads from low Earth orbit (LEO) to higher orbits without requiring refueling, enabling it to act as a fullyreusable in-space “upper stage” that can provide propulsion for a wide range of space missions. In a momentum-exchange tether system, a long high-strength tether is deployed from a facility in orbit and set into rotation around the facility, as illustrated in Figure 1. The tether system is placed in an elliptical orbit and its rotation is timed so that the tether is oriented vertically below the central facility and swinging backwards when the system reaches perigee. At that point, a grapple mechanism located at the tether tip can rendezvous with and capture