Alex L. Hall Thruster S.I.N.-March 2009

This post builds on the post “The Ion Thruster”; it adds the Hall Thruster to the discussion.  The same source, the article called New Dawn for Electric Rockets by Edgar Y. Choueiri, published on the 58th page of the February 2009 issue of Scientific American, was used.  Simply put, the technology under discussion, rockets designed with electric plasma engines (EPE’s), is a relatively new technology that uses electricity to accelerate particles, thus providing acceleration in the opposite direction to the rocket in question.  EPE’s generate a much lower magnitude of thrust then a conventional chemical rocket; however, this force of acceleration can be applied for much longer, yielding a higher final velocity.  Because this magnitude is lower, this technology can only be applied outside of the atmosphere.

The most recent thruster to become a viable option for use and travel is the Hall Thruster.  Named after Edwin H. Hall, who discovered the underlying effect in 1879.  This thruster has higher thrust, but is less efficient (only 45% to 60% vs. 60% to 80%) and requires more power.  Because of the method of propulsion, this thruster attains higher exhaust velocity.  It achieves this by using what is termed the Hall current (the principle behind this current is that when two magnetic fields are placed perpendicular in a conductor the electric current will flow perpendicular to the two fields.)  The radial magnetic field causes the electrons from the Hall current to circle and accelerate about the central anode.  An external cathode provides negatively charged electrons, while Xenon atoms are injected.  The interactions between the Xenon atoms, the electrons, the Hall current, and the radial magnetic field causes the Xenon atoms to collide with the whirling electrons; which then cause the Xenon atoms to devolve into ions, forming plasma.  The plasma is then accelerated by the electro-magnetic field generated by the Hall current’s interaction with the radial magnetic field.  This technology has higher power density because it avoids the issue of the electron build up from the Ion Thruster. 

The technology in the Hall Thruster allows us to travel further then would the Ion Thruster, allowing us to explore and thrive in a way previously unachievable.

Stephen Terry
December: Science in the News

Title: Meteorites May Have Sparked Life on Earth
Date of Article: December 17, 2008
Publisher: Society for Science and the Public
Copyright: 2008

In the December 17, 2008 Society for Science and the Public stated that. meteorites may have helped start life on Earth. Large rocks such as meteors moving very fast, may have helped start life on Earth. Geochemist Yoshihiro Furukawa at Tohuku University in Sendai, Japan had an idea of how life started on earth. When rocks such as meteors, crash into oceans they produce a lot of heat and the rocks turn into gas. Scientists did experiments and mixed carbon, iron, and nickel, which are found in meteorites with water, ammonia, and nitrogen, which are found on earth. Then the scientists put these items in canisters and shot them at a target. They wanted to see what was inside of the rocks. After the experiment, the scientists found fatty acids and amino acids in the canisters. These acids are found in cell membranes and proteins. I care about meteorites helping start life on earth because we can use fatty acids and amino acids for our own health.

Kurt - SIN - Dogs Understand Fairness

The National Academy of Sciences did a study that showed dogs know how to be fair as reported in an NPR piece by Nell Green Fieldboyce on December 9, 2008. They looked at how dogs react when a buddy is rewarded for the same trick in an unequal way. The dogs were normally happy to repeatedly give the paw whether they got a reward or not. But that changed if they saw that another dog was being rewarded with a piece of food while they received nothing. It tells people dogs have emotions.

TJ - January S.I.N. - Sky Show This Month: "Two-Tailed" Comet Nearing Earth.

Victoria Jaggard reported at http://news.nationalgeographic.com/news/2009/01/090126-comet-lulin.html, that Comet Lulin is sailing through the inner solar system right now and it is getting closer to Earth, its nearest approach will be in late February. Comet Lulin is arriving from far away on a nearly elliptical orbit. Lulin could be on its first pass by the sun. As the object is exposed to the sun's heat the ice on it will vaporize, possibly causing the comet to brighten rapidly or even fall apart. also, the comet's orbit is in nearly the same plane as Earth's but is traveling in the opposite direction. This causes Lulin to appear to move unusually fast and display a rare tail; an optical effect that creates a secondary "tail" pointing toward the sun.


I care because I like space and people should care because this could be dangerous to our planet.

Joshua, January SIN, Blocking Sounds with Holes

In the article Blocking Sound with Holes, written by Charles Q. Choi, published in the December 2008 issue of Scientific American, it was reported that drilling holes in a wall can decrease the amount of ultrasonic sound that gets through.

Francisco Meseguer of the Polytechnic University of Valencia in Spain and his team placed a series of 20 centimeter thick aluminum plates in water and discovered that plates with perforation could reduce the volume of incoming ultrasound waves by up to 10 decibels compared to ordinary plates. The sound waves generate acoustic waves on the surface of the plate that hinder the waves passing through the plate.

This discovery could potentially help to soundproof machines while still letting cool air through. Currently, the team is working on audible sound. Who knew that drilling holes in a wall could actually decrease the amount of sound that gets through? This will undoubtedly have an effect on soundproofing. This development could also be applied to more than buildings. This could also influence architecture, especially industrial architecture, in which lots of heavy machinery is running inside of one building.

January SIN Stephen "Hold on to your Stars Ladies and Gentlemen"

In the article “Hold on to your Stars Ladies and Gentlemen” at http://www.blogger.com/www.sciencenews.org/view/generic/id/39836/title/FOR_KIDS_Hold_on_to_your_stars,_ladies_and_gentlemen, written by Stephen Ornes on Jan 14, 2009; scientists found that our galaxy is different than they originally thought. We live on earth. The earth goes around the sun. Scientists thought that our galaxy was half the size of Andromeda. They actually found out that our galaxy the Milky Way is about 50 percent bigger than Andromeda. They found out that the galaxy was spinning 100,000 miles per hour faster than they thought. Scientists are finding out that the bigger the galaxy the faster the galaxy spins. They are saying that the Andromeda galaxy and the Milky Way galaxy will eventually crash into each other but that won't happen for a long time. This helps us connect to real life by knowing that our galaxies will collide but not for a long time. I wonder if our galaxies will crash and into each other and become supernova.

Alex, The Ion Thruster, S.I.N, January

Three different types of electric plasma rockets, the ion thruster, the Hall Thruster, and the magnetoplasmadynamic (MPDT) were discussed, and the relative merit for each was compared in the article called New Dawn for Electric Rockets. Edgar Y. Choueiri wrote this article, published on the 58th page of the February 2009 issue of Scientific American. In the article, it is put forth that rockets designed with electric plasma engines (EPE’s) can attain a higher speed than conventionally powered rockets; they are more efficient at doing so. Furthermore, it is implicated that this makes them better for deep space and long-range missions.
A conventional (chemical) rocket burns nearly the entirety of available fuel in initial launch; final velocity is achieved closely after leaving the launch site where the magnitude of thrust is large. EPE rockets, on the other hand, have less thrust during launch, but it can maintain this thrust for a much longer time, which allows acceleration to last longer. Because of its high potential speed, the vehicle may be used in more operations. The electric power supply may even be recharged, although solar power generation is extremely inefficient anywhere beyond the approximate range of mars. Micro-thermonuclear power supplies could be constructed to generate additional energy.
The drive in current operation on many satellites is the ion thruster (whose precursor was patented as long ago as 1916); it is therefore the most relevant technology. The Ion Thruster is the simplest of the EPE devices, and its basic functioning is as follows. A neutral gas (usually Xenon) enters a chamber and is bombarded with electrons; this creates positive ions and causes the element to lose electrons. The electrons are introduced into a magnetically charged environment, and a neutralization device collects the ions. This charged environment accelerates them into an electrically charged net that further accelerates the particles out of the rocket. This type of EPE has exhaust speeds of ~20-50 kilometers per second (km/s), thrust (in a vacuum) of about 20-250 micronewtons (μN), and is approximately 60-80% efficient. Of the three types of EPE mentioned it is the most efficient, but provides the least thrust and has the slowest exhaust speeds.
The future of human societies depend on space travel, therefore any important advancement in this field allows future generations a place in the universe.