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ion propulsion



I was reading in the New Scientist web site about the $850 million ESA
Artemis satellite that failed to achieve its intended orbit because of a
problem with the Ariane-5 launch vehicle.

The article says that "Artemis is the first ESA satellite to be equipped
with ion propulsion thrusters, which are relatively efficient and require
less fuel".  Another site says that the ion propulsion thrusters have "very
high power-to-mass ratio which helps to reduce launch cost and increase
satellite lifetime".  The first satellite to use ion propulsion was Deep
Space 1, launched on 24 October 1998.

The beauty of ion propulsion is that it is highly efficient,
electric-powered, and uses inert Xenon gas as the ion source.  It seems like
this might be a good replacement for the arcjet motor if sufficient
electrical power is available (probably the biggest obstacle).

Below is text stolen from
http://www.spacescience.com/newhome/headlines/prop06apr99_2.htm
<http://www.spacescience.com/newhome/headlines/prop06apr99_2.htm> 

The principle behind the Deep Space 1 engine is much the same as what you
experience when you pull hot socks out of the clothes dryer on a cold winter
day. The socks push away from each other because they are electrostatically
charged, and like charges repel. The challenge in electric space propulsion
is to charge a fluid so its atoms can be expelled in one direction, and thus
propel the spacecraft in the other direction.

The fuel used by Deep Space 1's ion engine is xenon, a gas that is more than
4 times heavier than air. When the ion engine is running, electrons are
emitted from a hollow tube called a cathode. These electrons enter a
magnet-ringed chamber, where they strike the xenon atoms. The impact of an
electron on a xenon atom knocks away one of xenon's 54 electrons. This
results in a xenon atom with a positive charge, or what is known as an ion.

At the rear of the chamber, a pair of metal grids is charged positively and
negatively, respectively, with up to 1,280 volts of electricity. The force
of this electric charge exerts a strong electrostatic pull on the xenon
ions. The xenon ions shoot out the back of the engine at a speed of 100,000
km/h (60,000 mph). At full throttle, the ion engine will consume 2,500 watts
of electrical power, and put out 1/50th of a pound of thrust. That's far
less than the thrust of even small chemical rockets. But an ion engine can
run for months or even years, and it's up to 10 times more efficient.

Wayne Estes W9AE
Mundelein, IL, USA
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