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MXER Tether Boost Facilities for Orbit-to-Orbit Transfer:
Reducing the Cost of In-Space Propulsion

Summary
Momentum-Exchange/Electrodynamic-Reboost (MXER) tether systems can provide propellantless propulsion for a wide range of missions, including: orbital maneuvering and stationkeeping within Low Earth Orbit (LEO); orbital transfer of payloads from LEO to GEO, the Moon, and Mars; and eventually even Earth-to-Orbit (ETO) launch assist. By eliminating the need for propellant for in-space propulsion, MXER tethers can enable payloads to be launched on much smaller launch vehicles, resulting in order-of-magnitude reductions in launch costs. In order for MXER tethers to achieve their potential in real-world application, several key technologies must be developed and demonstrated, including space-survivable tethers incorporating both high-strength and conducting materials, technologies for rendezvous with and grappling of payloads, and techniques for predicting and controlling tether rotation and dynamics

MXER Tether
Figure 1. The Momentum-Exchange/Electrodynamic-Reboost Tether Concept.

MXER System Concept Animations
How does a rotating space tether catch and toss a spacecraft? How does electrodynamic propulsion work? Click the images below to see Quicktime movies illustrating how a MXER Tether Transport system will work [Animations produced by NASA/MSFC; Grapple tests conducted by Tennesee Tech]

Grapnel Payload Capture Solar Panel MXER Video

Background: 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. [Learn more about MX Tethers]

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. By properly controlling the tether current during an orbit, the tether facility can reboost itself to its original orbit, as illustrated in Figure 1. 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. [Learn more about ED Tethers]

Net Payoff of MXER Tether Boost Facilities
MXER Tether Boost Facilities can reduce the cost of not only in-space propulsion, but also Earth-to-Orbit launch. For in-space propulsion applications, the MXER tether can serve as a fully reusable upper stage. By eliminating the need for each payload to have a dedicated upper stage vehicle, payloads can be launched on much smaller and less expensive rockets. As an example, a MXER tether designed to boost a 5 metric ton satellite from LEO to GTO could reduce the launch vehicle required for that satellite from a $45M Delta-II down to a $13M Dnepr 1 rocket, a roughly five-fold reduction in launch costs.

Earth-to-Orbit Launch Assist
MXER Tether Boost Facilities can also enable dramatic cost reductions for ETO launch by catching payloads delivered into suborbital trajectories and then tossing them into orbit.
[Learn more about Tether Launch Assist]

More Information:
To learn more about TUI's MXER Tether Boost Facility systems, we invite you to read some of our technical papers discussing our development of the MXER technology:


For further information on a space tether product customized for your needs,
please contact TUI at information@tethers.com

For information on Momentum Exchange Propulsion for your mission, please | Contact TUI |

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