This slide is about generating electricity by earth magnetic field using the technology of Electrodynamic Tether.

1. Generating Electricity By Earth Magnetic
Field
Submitted By Group-5
Nahian, Ahnaf Tahmid 12-20178-1
Ananta, Mahmud Hossain 12-20415-1
Mozumder, Turza Dhiman 12-21132-1
Course Instructor- RETHWAN FAIZ

3. Magnetic Basics
Magnets always have two poles: a north pole and a
south pole.
North and South are always attracted.
Two similar poles will repel one another.

4. Earth as a Magnet
• The Earth is like a giant bar magnet—it has a north
magnetic pole and a south magnetic pole.
• These are different than the geographic north and south
poles.
• The magnetic poles move a little (10 km) each year.

5. In 1600, William Gilbert published De MagnEarth
Magnetic field is also known as Geomagnetic ete,
which showed that the Earth itself is like a giant
magnet, rather than the magnetism arising from an
extraterrestrial source as supposed by others since
1939, the geomagnetic field has been believed to
originate by convective motions in the Earth’s fluid,
electrically-conducting core. The idea is that the
convective fluid interacts with the Coriolis forces
produced by planetary rotation and acts like a
dynamo which is a magnetic amplifier []
Earth Magnetism

6. Why is Earth Magnetic?
• Earth’s core is iron, a magnetic material
• Earth’s outer core is liquid iron.
• When this liquid
iron circulates
around the
core, a magnetic
field is
developed.
• This is known
as the Dynamo
Theory

7. What Benefit is a Magnetic Field?
• The Earth’s magnetic field protects us from the sun’s charged
particles.
• The magnetic field acts like a force field—without it, our
atmosphere would be ripped off.
• And we can produce electricity by magnetic field

8. Nasa
Nasa can take electricity from Earth’s magnetic field. The technology is called
electrodynamic tethers(EDT). This energy is electricity created by a long
conductor moving in orbit through the planets geomagnetic field. It is a
proven fact that free electricity can be made from this technology.

9. Electrodynamic tether
Electrodynamic tethers (EDTs) are
long conducting wires, such as one
deployed from a tether satellite,
which can operate
on electromagnetic principles
as generators, by converting
their kinetic energy to electrical
energy, or as motors, converting
electrical energy to kinetic
energy. Electric potential is
generated across a conductive
tether by its motion through a
planet's magnetic field.
Fig: Medium close-up view, captured
with a 70mm camera, shows tethered
satellite system deployment

10. Electrodynamic tether fundamentals
An electromotive force (EMF) is generated across a tether element as it
moves relative to a magnetic field. The force is given by Faraday's Law
of Induction:
Without loss of generality, it is assumed the tether system is in Earth
orbit and it moves relative to Earth's magnetic field. Similarly, if current
flows in the tether element, a force can be generated in accordance with
the Lorentz force equation:

11. In self-powered mode (deorbit mode), this
EMF can be used by the tether system to
drive the current through the tether and
other electrical loads (e.g. resistors,
batteries), emit electrons at the emitting
end, or collect electrons at the opposite.
In boost mode, on-board power supplies
must overcome this motional EMF to drive
current in the opposite direction, thus
creating a force in the opposite direction, as
seen in below figure, and boosting the
system.
Fig:Illustration of the EDT concept
EDT concept

12. the NASA Propulsive Small Expendable
Deployer System (ProSEDS) mission as
seen in above figure. At 300 km altitude,
the Earth's magnetic field, in the north-
south direction
Here, the ProSEDS de-boost tether
system is configured to enable electron
collection to the positively biased higher
altitude section of the bare tether, and
returned to the ionosphere at the lower
altitude end.
This flow of electrons through the length
of the tether in the presence of the
Earth's magnetic field creates a force that
produces a drag thrust that helps de-orbit
the system.
EDT Concept
Fig:Illustration of the EDT concept

13. The top of the diagram, point A,
represents the electron collection
end. Point C, is the electron
emission end.
Similarly, and represent the
potential difference from their
respective tether ends to the
plasma.
Finally, point B is the point at
which the potential of the tether is
equal to the plasma. The location
of point B will vary depending on
the equilibrium state of the tether,
which is determined by the
solution of Kirchhoff's current
law (KVL)
and Kirchhoff's voltage law (KCL)

14. Tethers as generators
A space object, i.e. a satellite in Earth
orbit, or any other space object either
natural or man made, is physically
connected to the tether system. The
tether system comprises a deployer from
which a conductive tether having a bare
segment extends upward from space
object. The positively biased anode end of
tether collects electrons from the
ionosphere as space object moves in
direction across the Earth's magnetic
field. These electrons flow through the
conductive structure of the tether to the
power system interface, where it supplies
power to an associated load, not shown.
The electrons then flow to the negatively
biased cathode where electrons are
ejected into the space plasma, thus
completing the electric circuit.

15. NASA has conducted several
experiments with Plasma
Motor Generator (PMG)
tethers in space. An early
experiment used a 500-meter
conducting tether. In 1996,
NASA conducted an
experiment with a 20,000-
meter conducting tether.
When the tether was fully
deployed during this test, the
orbiting tether generated a
potential of 3,500 volts.
This conducting single-line tether was severed after five hours of
deployment. It is believed that the failure was caused by an electric arc
generated by the conductive tether's movement through the Earth's
magnetic field.

16. When a tether is moved at a velocity
(v) at right angles to the Earth's
magnetic field (B), an electric field is
observed in the tether's frame of
reference. This can be stated as:
E = v * B = vB
The direction of the electric field (E)
is at right angles to both the tether's
velocity (v) and magnetic field (B). If
the tether is a conductor, then the
electric field leads to the
displacement of charges along the
tether. Note that the velocity used in
this equation is the orbital velocity of
the tether. The rate of rotation of the
Earth, or of its core, is not relevant.
Voltage and current

17. Voltage across conductor
With a long conducting wire of length L, an electric field E is
generated in the wire. It produces a voltage V between the
opposite ends of the wire. This can be expressed as:
where the angle τ is between the length vector (L) of the tether
and the electric field vector (E), assumed to be in the vertical
direction at right angles to the velocity vector (v) in plane and
the magnetic field vector (B) is out of the plane.

18. Tether current
The amount of current (I) flowing through a tether depends on various factors. One
of these is the circuit's total resistance (R). The circuit's resistance consist of three
components:
1. the effective resistance of the plasma,
2. the resistance of the tether, and
3. A control variable resistor.

19. Advantages
1.The Operational advantages of electrodynamic tethers of moderate length are
becoming evident from studies of collision avoidance
2.High efficiency and good adaptability to varying plasma conditions .
3.Substantially reduce the weight of the spacecraft.
4. A cost effective method of reboosting spacecraft, such as the International Space
Station(ISS)

20. References
1. NASA, Tethers In Space Handbook, edited by M.L. Cosmo and E.C. Lorenzini, Third
Edition December 1997
2. Johnson, L., Estes, R.D., Lorenzini, E.C., "Propulsive Small Expendable Deployer
System Experiment," Journal of Spacecraft and Rockets, Vol. 37, No. 2, 2000, pp. 173–
176
3. Tether power generator for earth orbiting satellites. Thomas G. Roberts et al.
4. Lieberman, M.A., and Lichtenberg, A.J., "Principles of Plasma Discharges and
Materials Processing," Wiley-Interscience, Hoboken, NJ, 2005, pp. 757.
5. Fuhrhop, K.R.P., “ Theory and Experimental Evaluation of Electrodynamic Tether
Systems and Related Technologies,”University of Michigan PhD Dissertation, 2007, pp.
1-307.

21. THEEND