Electrodynamic Tethers

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Electrodynamic Tethers

• A Brief Understanding Implementation

www.tethers.com
By John Missikos
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Contents

• Introduction
• Uses
• Calculation
• Summary

Microsoft Encarta 96
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Introduction

• The latest endeavor of N.A.S.A. is the Space
  Tether. This, almost simplistic device, is
  extremely diverse.
• It can cause or stop decay of a satellites orbit
  with little energy.
• Can be used instead of propellant on small
  (micro) satellites
• Slingshot spacecraft into orbit and beyond.
• Or even bring in spacecraft for a landing.

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• The Space Tether is a long conductor made
  preferably from aluminum for its high strength to
  weight ratio. It is weaved so that no one impact
  by space dust or debris will destroy it.

www.tethers.com
www.tethers.com
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• The immediate and simplest implementation of the
  tether is to reduce the amount of space junk
  currently and soon to be in orbit of earth.

www.tethers.com
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Uses

• Imagine a satellite rotating the earth currently
  having a stable orbit. When it releases the
  tether the lower end (extending anywhere from 5
  to 20km) touches the ionosphere. Here charged
  particles bombard it thus charge one end. After a
  time the tether begins to conduct a current.

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• If the current is not opposed then through Lenses
  law an opposition force must counteract the field
  created. In this case the kinetic energy of the
  satellite is sacrificed for the energy created.
  This particular tether design is called a
  Terminator TetherTM.

www.tethers.com
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• On the other hand if the current is opposed then
  there is no drag force. This can be done by
  collecting energy from the sun via solar panels.
  This not only can keep the satellite in orbit
  indefinitely as well as a means of changing orbit
  with little to no power but can serve as a much
  cheaper alternative to refueling the satellite.
  This will be done with the International Space
  Station (ISS) saving over 2 Billion dollars in
  fuel not to mention the purpose launches to get
  it up there.

Microsoft Encarta 96
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Calculations

• By viewing the calculations you can understand
  where the forces are coming from.
• F B I L Sin? Force on current carrying
• wire in a magnetic field
• I P / V Current in terms of power
• V B V L Voltage in terms of a length
• of conductor moving
• through a magnetic field
• with velocity V

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• In this example we will find the dragging force
  on the tether given the power running though it
  and its velocity though the ionosphere.
• F B I L Sin? Sin? 1 since tether is
• perpendicular to magnetic field
• Since V B V L
• I P / B V L
• Substituting I into the first equation
• F (B P L) / (B V L By cancellation
• F P / V
• Thus the dragging force on the tether can
  determined by the power and velocity of the
  tether though the ionosphere. Strangely enough
  the length nor the magnetic field play a part in
  the drag.

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Summary

• Tethers are the next big step in space
  exploration. They will make it easier for us to
  explore by providing us with remote energy not at
  the expense of material resources. This overcomes
  one of the biggest hurdles in the
  commercialization of space travel.

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Resources

• Microsoft, Encarta 96 Encyclopedia
• www.tethers.com
• www.sciencevictoria.org.au