29 dicembre 2016 alle 0:23 #133
Solar electric propulsion takes advantage of magnetism and electricity to push a ship through space. Electricity, generated by the ship’s solar panels, gives a positive electrical charge to atoms inside the chamber. They are pulled by magnetism towards the back of the ship and then pushed by magnetic repulsion out of the ship. (This is like what happens when you hold the same pole of two different magnets close to each other. They repel each other.) This steady stream of atoms going out of the spacecraft gives it the thrust it needs to go forward through space.
What is the difference between an ion engine and a conventional one?
Both kinds of rockets move the ship forward by making thrust. This thrust is made by propelling matter out of the back of the ship. Ion engines are different from chemical engines (engines that work by burning liquid or solid fuel) in where they get their energy and how they produce thrust.
Chemical engines work by combining fuel with an oxidizer. That makes a gas that expands and rushes out the back of the engine, making thrust. Chemical engines are mass-limited engines. What this means is that how much power a chemical engine has depends on is how much fuel and oxidizer the rocket can carry. When the propellant runs out then the rocket cannot go any faster.
However, ion engines work differently than chemical engines. Ion engines take very small amounts of gas and accelerate it to very high speeds, unlike chemical engines which take large amounts of gas and spew it out at a slow speed. This means that an ion engine uses a lot less fuel. Ion engines are limited by energy, not by mass. Therefore “running out of gas” is not a large problem with ion engines. The limit for ion engines is usually where to get all the electricity to feed the ion engine. Ion engines are limited by how much energy (electricity) that a rocket can carry or how much energy the solar panels can collect.
Why solar electric propulsion?
Any vehicle must carry fuel in order to move. Ion engines are a way of moving a space ship through space without needing to carry and use the huge amounts of fuel that conventional rockets need. This has several advantages. One is that the less fuel a ship carries, the lighter it is and the easier it is to get it into space. Another advantage is that a ship that needs less fuel will not run out of fuel and stop working as quickly. Much of the energy in an ion rocket is provided by electricity, which can be made through solar panels “on the fly” instead of carried into space.
What is an ion?
An ion is a charged atom or molecule. It is charged because the number of electrons do not equal the number of protons in the atom or molecule. An atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.
When an atom is attracted to another atom because it has an unequal number of electrons and protons, the atom is called an ION. If the atom has more electrons than protons, it is a negative ion, or ANION. If it has more protons than electrons, it is a positive ion.
Are ion engines radioactive?
No. Ion engines work on the principles of charged particles. They are not radioactive. Radioactivity means that an atom is not stable and is losing subatomic particles (small parts of itself) slowly over time. Radioactive decay occurs until enough subatomic particles decay for the atom to turn into a totally different atom, called the daughter isotope.
Ion propulsion works by charging atoms electrically, not making them come apart. When an atom is charged (i.e. loses or gains an electron) its reactivity is changed, but the atom itself does not change identity. It is stable, just more or less reactive with other atoms or ions.
Are ion engines nuclear?
No. Ion engines work on the principles of charged particles. They are not nuclear and therefore are not radioactive. Ion engines work by stripping the electrons off atoms so that the atoms become charged particles (ions). They then speed up these ions by setting up an electric field which then accelerates the ion out of the back of the rocket engine.
Ion engines can be more simply thought of as static electricity engines. Just as dust particles tend to be attracted to charged surfaces; ion rockets attract ions towards a charged grid in the back of the engine and then send them shooting off into space. Ion engines work by taking a gas and heating it until it is so hot that that some electrons disassociate from the atoms. This superheated matter is not longer a gas but is called plasma. In gases entire atoms are separate entities flying around and randomly bumping each other but in plasma the atoms have been stripped of some or all of their electrons and are a bunch of positive ions floating in a shared electron soup. The positive nuclei in this electron soup are then accelerated towards the charged back grid and then zoom out into space.
Why is an ion plume blue?
An ion plume consists of a lot of electrically charged atoms streaming out of the spacecraft. They have just come from a plasma chamber and are enormously hot. The energy that heated them up also affected their electron configuration. When an atom absorbs energy, its electrons change location within the atom to a position known as a higher energy configuration. When the atom stops receiving energy (in this case moves away from the hot plasma chamber) the electrons go back to the lower energy configuration and release the energy it took to raise their energy configuration. This energy is released in the form of photons, or tiny bits of light. In this case, the light is blue. Other fuels may give off different colors.
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