Ion Propulsion
Ανέβηκε στις 25 Νοε 2007
Ion Propulsion - Transport System to the Planets
The
efficiency of a rocket engine can be described by its specific impulse,
which is the change of momentum gained from a 1 kilogram weight of
propellent.
The Space Shuttle main engines have a specific impulse of 453 seconds which is typical of a liquid fuelled rocket engine.
An
Ion thruster has a specific impulse of more than 3000 seconds and so
requires less than a sixth of the fuel of a liquid fuelled engine.
Gridded
electrostatic ion thrusters commonly utilize Xenon gas. The gas is
first ionized by bombarding it with electrons. The positively charged
ions then diffuse through the positive grid and enter a potential
difference between the positive and negative grids. The potential
difference accelerates the ions to high velocities, which then leave the
engine to create thrust. An electron emitter, on the exterior of the
engine, neutralizes the ion beam to prevent charge build-up.
The typical thrust of an ion engine is equivalent to a weight of 10 grams - about the weight of a sheet of paper.
This
means ion thrusters need to provide continuous thrust for a very long
time in order to achieve a reasonable change in velocity. Electrostatic
ion engines have been tested for 3.5 years of continuous thrust at full
power. Collision of ions with the charged grids causes their erosion and
will lead to eventual failure.
Ion engines consume more than 2 kilowatts of electrical power, which may be generated by solar arrays or nuclear generator.
NASA
has developed a Xenon ion thruster called NSTAR for use in their
inter-planetary missions. This thruster was tested in the space probe
Deep Space 1, launched in 1998.
The Dawn mission was launched in
September 2007 to explore the dwarf planet Ceres and the asteroid Vesta.
To cruise from Earth to its targets it will use three Deep Space 1,
heritage, NSTAR thrusters, firing only one at a time, to take it in a
long outward spiral. The three thrusters are required to meet the
lifespan requirement of the engine.
The
efficiency of a rocket engine can be described by its specific impulse,
which is the change of momentum gained from a 1 kilogram weight of
propellent.
The Space Shuttle main engines have a specific impulse of 453 seconds which is typical of a liquid fuelled rocket engine.
An
Ion thruster has a specific impulse of more than 3000 seconds and so
requires less than a sixth of the fuel of a liquid fuelled engine.
Gridded
electrostatic ion thrusters commonly utilize Xenon gas. The gas is
first ionized by bombarding it with electrons. The positively charged
ions then diffuse through the positive grid and enter a potential
difference between the positive and negative grids. The potential
difference accelerates the ions to high velocities, which then leave the
engine to create thrust. An electron emitter, on the exterior of the
engine, neutralizes the ion beam to prevent charge build-up.
The typical thrust of an ion engine is equivalent to a weight of 10 grams - about the weight of a sheet of paper.
This
means ion thrusters need to provide continuous thrust for a very long
time in order to achieve a reasonable change in velocity. Electrostatic
ion engines have been tested for 3.5 years of continuous thrust at full
power. Collision of ions with the charged grids causes their erosion and
will lead to eventual failure.
Ion engines consume more than 2 kilowatts of electrical power, which may be generated by solar arrays or nuclear generator.
NASA
has developed a Xenon ion thruster called NSTAR for use in their
inter-planetary missions. This thruster was tested in the space probe
Deep Space 1, launched in 1998.
The Dawn mission was launched in
September 2007 to explore the dwarf planet Ceres and the asteroid Vesta.
To cruise from Earth to its targets it will use three Deep Space 1,
heritage, NSTAR thrusters, firing only one at a time, to take it in a
long outward spiral. The three thrusters are required to meet the
lifespan requirement of the engine.
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