This document discusses electrodynamic tethers, which use the Lorentz force generated by the interaction between a current in the tether and the Earth's magnetic field to propel or deorbit spacecraft. Electrodynamic tethers can be used to accelerate a spacecraft into a higher orbit or decelerate it into a lower orbit without using propellant. They work by either collecting electrons at one end of the tether and expelling them at the other end, or driving current in the opposite direction. Challenges include stabilizing the tether's motion, but feedback algorithms can help maintain stability. Potential applications include propulsion of spacecraft in low Earth orbit, deorbiting of satellites, and reboosting of decaying orbits.

1. ELECTRODYNAMIC
TETHER
Presented by:-
P.VANDANA KRISHNA

2. CONTENTS
 Introduction
 Principle
 Working
 Stabilization of electrodynamic tethers
 EDT application
 Advantages
 Future scope
 Conclusion

3. INTRODUCTION
 Satellites have a major part to play in the present
communication system.
 There are over eight thousand satellites and other
large objects in orbit around the Earth, and there are
countless smaller pieces of debris generated by
spacecraft explosions between satellites.
 One method of removing a waste satellite from orbit
would be to carry extra propellant so that the satellite
can bring itself down out of orbit.

4. INTRODUCTION
 An ELECTRODYNAMIC tether provides a
simple and reliable alternative to the
conventional rocket thrusters.
 EDTs are basically made of aluminium alloy.
 When direct current is sent through it, it
exerts a force and the tether accelerates the
spacecraft.
 By reversing the direction of current in it, the
same tether can be used to de-orbit old
satellites.

5. ELECTRO DYNAMIC TETHER

6. PRINCIPLE
 The basic principle of
an electrodynamic
tether is Lorentz
force.
 It is the force that a
magnetic field exerts
on a current carrying
wire in a direction
perpendicular to both
the direction of
current flow and
magnetic field .

7. PRINCIPLE
 For a charged particle
moving with velocity
V in a magnetic field
B the resultant is in
the direction of the
force F – Fleming’s
left hand rule.

8. WORKING
 An EDT can be used either to accelerate or
brake an orbiting spacecraft.
 When direct current is passed through the
tether, it exerts a force against the magnetic
field and the tether accelerates the
spacecraft.
 The gravity gradient field will tend to orient
the tether in a vertical position.

9. WORKING
 In an EDT drag system such as the
terminator Tether, the tether can be used to
reduce the orbit of the spacecraft.
 The electrons are collected at one end of the
tether and expelled at the other end.
 This current interacts with the earth’s
magnetic field and causes a force which
opposes tether.
 This decreases the orbit of the tether.

10.  In an electro dynamic propulsion system, the
tether can be used to boost the orbit of the
spacecraft.
 If a power is added to the tether system and
current is driven in the opposite direction.
 Then the tether can push against the earth’s
magnetic field to raise the spacecraft’s orbit.
WORKING

11.  The lorentz force acts on the electrons in
tether.
 A hallow cathode causes the tube to heatup
and produce xenon gas.
 Electrons Electrons interact with heat gas to
create a plasma.
 Due to this effect electrons are discharged
rapidly.
WORKING

12.  Earth’s magnetic
field exerts a drag
force on the current
carrying tether.
 This leads to the
lowering of the orbit.
WORKING

13. EDT PROPULSION

14. TETHER STABILIZATION
 Electrodynmic tethers are inherently unstable.
 The electrodynamic forces also vary and so a
pendulum motion is developed.
 Further this motion turns in to complex
librations in both the in-plane and out-of-plane
direction.
 The “Tether configuration” feedback algorithm
calculates a gain factor based upon the network
that the electrodynamic forces will perform on
the tether dynamics.

15. TETHER STABILIZATION
 The second algorithm requires only periodic
measurements of the acceleration of the
tether end mass called “End mass
acceleration” feedback method.
 These enable EDTs to provide long term
propellant less propulsion while maintaining
tether stability and efficiency.

16. EDT APPLICATIONS
 Propellant less
propulsion for LEO
spacecraft.
 The µPET Propulsion
System.
 The Terminator Tether
Satellite de-orbit
System.
 Electrodynamic re-boost
of the International
Space Station.
 Power Generation in
Low Earth Orbit.
 Space junk cleanup.
µPET
tether

17. EDT APPLICATIONS
Terminator tether LEO spacecraft

18. APPLICATIONS
ELECTRODYNAMICS
Electrodynamic power generation Electrodynamic thrust generation
Radiation belt remediation
Space station
Microgravity laboratory Shuttle de-orbit from space station
Tethered space transfer vehicle
launch
Altitude stabilization and control
Internal forces for orbital
modification
Satellite boost from orbiter
Tether assisted transport system Tether re-boosting of decaying
satellites

19. ADVANTAGES
 The major advantage of tethers compared to
other propulsion systems is it does not require
any propellant.
 Reduces the de-orbit times.
 High efficiency and good adaptability to varying
plasma conditions.
 Boosting tethers of moderate length. (5-20 km)
 Substantially reduce the weight of the spacecraft.
 A cost effective method of re-boosting spacecraft.
 It is reusable .
Advantages

20. FUTURE SCOPE
 Satellite Tugboat:
Another idea is for the ED tether to be attached
to an unmanned space tugboat that would ferry
satellites to higher orbits.
 Exploring the outer planets:
The most exotic use if ED tether technology
would be to propel and power spacecraft
exploring the outer planets.

21. CONCLUSION
 As electrodynamic tethers can provide long term
propellant- less propulsion capability for orbital
maneuvering and station keeping of small
satellites in low earth orbit, these are preferable
compared with the existing rocket propulsion
system.
 Also EDTs may provide an economical means of
electrical power in orbit.
 Hence electro dynamic tethers play a key role for
satellite communication system.

22. Thank you