Electromagnetic Propulsion
Propulsion is a general term that is used to describe the act of "driving forward or onward by or as if by means of a force that imparts motion." Propulsion is heavily derived from Newtons Laws of Motion, mainly involving inertia and momentum. How rocket engines, or simple spacecraft propulsion works, is the ignition of chemical sources that imparts massive amounts of energy on the remaining mass also known as "reaction mass." This combustion occurs in a chamber with only one nozzle or escape. As the combustion or chemical reaction speeds up, which increases the pressure within the chamber, and thus launching the reaction mass out of the nozzle. Then, according to Newtons third law and inertia and momentum, the reaction mass is shot out at high velocity causing the rockets velocity to increase in the opposite direction. This occurs for millions of particles and thus creates a large change in velocity of the spacecraft. A few problems are presented by this type of rocket engine: one, it is very difficult to predict roughly how much thrust is generated by this rocket. The equations that are utilized are neither precise nor very accurate. Two, it is difficult to control the rate of combustion even with the advanced fuel injection technology used today. These two problems can be solved, to an extent, by using electro magnetic propulsion.
(Source Youtube)
Explanation: Simple ion thruster. the wires attached to the foil pump large amounts of electron into the foil. The foil ionizes the air surrounding it and the air flows down, due to attraction to relatively neutral foil, through the apparatus thus generating lift. If one were to retest this within a vacuum, there would be no air to ionize thus no lift.


Theory behind Electromagnetic Propulsion
electro.jpg
Electromagnetic Propulsion

The force or theory utilized in Electromagnetic thrusters is often referred to as the Lorentz Force, named after Hendrik Lorentz. Lorentz introduced this force in 1881 however it was before his time. His equation is summarized as thus F = qE + qvB. This equation is derived from two different equations
E = F/q, which can be rearranged as F=Eq, and F=qvB. These formulas should be familiar; E=F/q is the electrostatic force and F=qvB is the force on a moving charge in a magnetic field. That is the force obtained for a single point charge. Ion thrusters, that utilize electromagnetic propulsion, are build as shown in the diagram above. This type of engine utilizes the Hall Effect. The Hall effect produces very little thrust compared to typical chemical engines however has a very high Specific Impulse. It represents the impulse (change in momentum) per unit of propellant. The higher the specific impulse, the less propellant is needed to gain a given amount of momentum. The way it works is it creates a potential difference between an anode and a cathode. Xenon Propellant enters the chamber through the anode. By entering through the anode, the xenon is bombarded with electrons which ionizes it. When it enters the chamber it has gained a charge of +1 or +2. It then is accelerated through the potential difference. When it approaches the Cathode, it strips off electrons thus neutralizing it; however it still is moving at a speed of approximately 15-30 km/s. Although it doesnt generate much thrust, it is much more efficient in measuring the thrust. Also, because of it's high specific impulse, it makes outerspace travel more feasible. A major drawback is it's high use of electrical energy. Thus, space crafts using ion thrusters are often coated in solar panels which absorb light and convert it to energy for the engine. We can expect for it to become more common in spacecrafts used in missions when solar panels efficiency has increased.
Hall Effect
Hall Effect


NSTAR
One specific Ion thruster, known as the NSTAR utilized in the space ship Deep Space 1. The ship was 8 1/2 ft long and 1000 lb space ship was equipped with a 30cm ion thruster that utilizes 81.5 kg of Xenon propellant, which could provide up to 20 months of propulsion. The ship was capable of reaching 4.5km/s speed, approximately 10000 miles per hour. This engine utilized a thruster different from the hall effect. It utilized the Gridded Electrostatic Ion Thruster. It's a similar mechanism as compared to the Hall Effect. It utilizes a chamber where propellant flows into. Within that chamber there is an electron gun which hits a propellant atom that ionizes it. The ions approach a parrallel plate grid where ions enter the grid and are accelerated at high speeds. After the propellant exits, there is another electron gun that neutralizes the positive ions.
Electrostatic Grid propulsion
Electrostatic Grid propulsion

(Source: Youtube: Author BrunotheQuestionable)
Using Tsiolkovsky Rocket Equation, deltaV = Veln(M0/M1),
where delta V is change in velocity,
Ve is exhaust Velocity speed which is also Impulse *g,
and M0, with propellant , M1 without propellant,
how much propellant would it take to achieve 4.5 m/s?
4500m/s = 3300s*9.8066m/s^2*ln(453.59kg+xkg/453.59kg)
4500 = 3300*9.8066*ln(1+x/453.59)
0.1390529 = ln(1+x/453.59)
e^(0.1390529) = 1+x/453.59
.14918489 = x/453.59
X= 67.66kg of Xenon Propellant



VASIMR
VASIMR(Source Youtube - benwl)
Electromagnetic propulsion has been considered as a feasible method of transport in spaceships since the 1980's. Only now have we begun to put it into practice and utilize it for it's potential. Even now we are creating better and stronger ion thrusters, the one currently at the brink being VASIMR(Variable Specific Impulse Magnetoplasma Rocket). It utilizes radio waves to create and heat plasma created from propellant. Unlike the other systems, this system does not contain electrodes to accelerate mass. Rather, it simply uses a magnetic nozzle to convert the plasmas thermal energy into kinetic energy. It is ejected from the system and thus creates propulsion. The VASIMR is capable of creating 3,000 s to 30,000 s impulses resulting in speeds of 30km/s to 300km/s. This goes beyond current ion thrusters because it is able to process high amounts of energy input. The problem with this is the maximum amount of energy it utilizes. The solution? Nuclear engine. Use a nuclear engine to power the thruster and then it becomes many times more feasible. There have been talks of testing the VASIMR in space, but nothing has been settled.Electromagnetic propulsionexternal image vasimr.jpg


Conclusion
In summary, electromagnetic propulsion is a developing technology. It still has plenty of room to grow, and it still has plenty of potential in this field. It also outstrips most other engines in terms of outerspace mission travels because of its high fuel efficiency. The only drawback is the electrical energy required to power the engine. As stated above, a nuclear power source or highly efficient solar panels can generate enough energy to power the ion thrusters. Electromagnetic propulsion is, in short, a viable technology for developing ships and shuttles.

Sources:

Newtons Laws of Motion - http://hyperphysics.phy-astr.gsu.edu/hbase/newt.html#ntcon
Definitions - http://www.merriam-webster.com/
Ion Thrusters & Hall Effect - http://www.permanent.com/t-el-iov.htm#how-russ
NStar ion engine - http://www.boeing.com/defense-space/space/bss/factsheets/xips/nstar/ionengine.html
Tsiolkovsky Rocket Equation - http://en.wikipedia.org/wiki/Rocket_equation
Electrostatic grided propulsion - http://whyfiles.org/shorties/ion_thruster.html
Hall Effect - http://www.absoluteastronomy.com/topics/Hall_effect_thruster
VASIMR - http://spaceflight.nasa.gov/shuttle/support/researching/aspl/plasma.html


Sonia Bansal - What is a practical application of EM propulsion?
Robert Lopez - How much would space travel benefit from this technology? How much more efficient is this?
Nauma Haider- Why does the chamber in which combustion occurs have only one /escape? Is it relevant to the buildup of pressure necessary?
James Song- Since EM propulsion is a developing tech, how cost-efficient would it be?
Brandon Siegenfeld- Why is it necessary to neutralize the ions as they leave the nozzle?
Kevin Norris - How much power is consumed by the Hall effect in the first YouTube video?
William Chan - How much does this system cost as compared to systems that are currently in use?
Sam Edwards - If provided with a constant source of energy, is there any limit to how long an electromagnetic propulsion device can be in continuous use?
Greg Sturm - Is any part of an ion thruster adversely affected by special relativity as the spacecraft approaches the speed of light?
Ari Horowitz - Why isn't this method used more often in society?
Douglas Chin - Could this be applied to ground-based vehicles as well? Or is it only practicle for outerspace vehicles?