A plasma propulsion engine is a type of ion thruster which uses plasma in some or all parts of the thrust generation process. Plasma engines are able to operate at higher efficiencies and for longer periods of time, although they are not as powerful as the conventional rocket engines. Plasma engines are better suited for long-distance space travel missions.
Plasma propulsion engines were first developed by the USSR during 1963-1965 to propel probe to Mars. In more recent years, many agencies have developed several forms of plasma fueled engines, including the European Space Agency, Iranian Space Agency and Australian National University. However, this kind of plasma rocket engines is of many types.
ENGINE TYPES
HELICAN DOUBLE LAYER TRUSTER
It uses radio waves to create plasma and a magnetic nozzle to focus and accelerate the plasma away from the rocket engine.
MAGNETO PLASMADYNAMIC THRUSTERS
It uses the Lorentz force (a force resulting from the interaction between a magnetic field and an electric current) to generate thrust - The electric charge flowing through the plasma in the presence of a magnetic field causing the plasma to accelerate due to the generated magnetic force.
HALL EFFECT THRUSTER
It combine a strong localized static magnetic field perpendicular to the electric field created between an upstream anode and a downstream cathode called neutralizer, to create a "virtual cathode" (area of high electron density) at the exit of the device. This virtual cathode then attracts the ion formed inside the thruster closer to the anode. Finally the accelerated ion beam is neutralized by some of the electrons emitted by the neutralizer.
ELECTRODELESS PLASMA THRUSTERS
They use the ponderomotive force which acts on any plasma or charged particle when under the influence of a strong electromagnetic energy gradient to accelerate the plasma.
HISTORY
Early studies (1970s)
In 1973, as a graduate student at MIT, Franklin Chang Diaz studied the behavior of super hot gases, called plasmas, as part of the quest for controlled thermonuclear fusion: the process that powers the sun and the stars as a source of power on Earth.
PhD studies were conducted in more complex geometries called magnetic divertors, important components in a power producing fusion reactor.
The simple magnetic mirror. Two coils of current (yellow) produce a field (blue lines), which can trap some of the charged particles that make up a plasma. Particles sufficiently hot can escape along the ends.
In the magnetic divertor, strategically positioned current loops can "peel" a bundle of the magnetic field lines from a magnetic structure, carrying the plasma away.
Early VASIMR (1979)
These ideas, latter published in a paper entitled "A Supersonic Gas Target for a Bundle Divertor Plasma", Nuclear Fusion, 22, 1982, led to the concept for a plasma rocket, which initially was called the "Hybrid Plume Plasma Rocket."
The first written disclosure of the VASIMR was witnessed by NASA colleagues in early 1982 in Franklin's Log Book.
First experiments (1980s)
First VASIMR experiment was conducted at MIT starting in 1983 on the magnetic mirror plasma device
Refinements (1990s)
Important refinements were introduced to the rocket concept, including the use of the "helicon" plasma source, which replaced the initial plasma gun originally envisioned and made the rocket completely "electrodeless" an extremely desirable feature to assure reliability and long life. A new patent was granted in 2002.
Years at NASA (1994-2005)
In 1995, the Advanced Space Propulsion Laboratory (ASPL) was founded at NASA Johnson Space Center, Houston in the building of Sonny Carter Training Facility. The magnetic mirror devise was brought from MIT. First plasma experiment in Houston was conducted using microwave plasma source. The collaboration with University of Houston, University of Texas at Austin, Rice University and other academic institutions was established.
From VX-10 to VX-50
In 1998, the first helicon plasma experiment was performed at the ASPL. The decision was made regarding official name of VASIMR and VASIMR experiment (VX). VX-10 in 1998 run up to 10 kW helicon discharge, VX-25 in 2002 run up to 25 kW and VX-50 - up to 50 kW of RF plasma discharge. In March, 2000, the VASIMR group was given a Rotary National Award for Space Achievement / Stellar Award. By 2005 major breakthroughs were obtained at the ASPL including full and efficient plasma production, and acceleration of the plasma ions in the second stage of the rocket.
New company is born (2005)
Ad Astra Rocket Company was incorporated in Delaware on Jan 14, 2005. On June 23, 2005, Ad Astra and NASA signed first Space Act Agreement to privatize the VASIMR Technology. On July 8, 2005, Dr. Chang Diaz retires from NASA after 25 years of service. Ad Astra's Board of Directors is formed, Dr. Chang Diaz takes the helm as Chairman and CEO on July 15, 2005. In July 2006 AARC opened the Costa Rica subsidiary in the city of Liberia at the campus of Earth University. In December 2006, AARC-Costa Rica performed first plasma experiment on the VX-CR devise utilizing helicon ionization of argon.
VX-100 (2007)
100 kW VASIMR experiment was successively running in 2007 and demonstrated efficient plasma production with an ionization cost below 100 eV. VX-100 plasma output is tripled over the prior record of the VX-50. In the same year, AARC moved out from NASA facility to own building in Webster, TX.
VASIMR
VASIMR, or Variable Specificimpulse magneto radia, works by using radio waves to ionize a propellant into a plasma and then a magnetic field to accelerate the plasma out of the back of the rocket engine to generate thrust. The VASIMIR is currently being developed by the private company Ad Astra Rocket, headquartered in Houston, TX with some help from a NS Canada based company Nautel, producing the 200Kw RF generators for ionizing propellant. Some of the components and "Plasma Shoots" experiments are tested in a laboratory settled in Liberia, Costa Rica. This project is led by former NASA astronaut Dr. Franklin Chang-Díaz (CRC-USA). Recently the Costa Rican Aerospace Alliance announced the cooperation to this project by developing an exterior support device for the VASIMIR to be fitted in the exterior of the ISS (International Space Station), as part of the plan to test the VASIMIR in space; this test phase is expected to be conducted in 2012. The engine VF-200 could reduce the duration of flight from earth to e.g. Jupiter or Saturn from six years to fourteen months.
FUTURE OF PLASMA ROCKET
PLASMA ROCKET MAKES SPACE TRAVEL EASIER
It may not be warp speed, but a new rocket engine concept in design at the Oak Ridge Centers for Manufacturing Technology could make space flight a much faster business than it is already. That would be good news for astronauts facing long stretches away from home on interplanetary missions.
ORCMT's Radio Frequency (RF) and Microwave Technology Center at the Oak Ridge Centers for Manufacturing Technology is collaborating with NASA to develop a high-powered plasma rocket engine prototype, a concept NASA will consider for high-speed interplanetary propulsion. The system is being designed as proof-of-principle for the Variable Specific Impulse Magnetoplasma Rocket, or VASIMR.
According to Stan Milora of ORNL's Fusion Energy Division, where the ORCMT center is located, a gas with a low molecular weight, probably helium, will be ionized, heated with RF waves and expelled from the rocket engine.
The VASIMR's plasma, is generated by a helicon plasma injector and confined and shaped by high-temperature superconducting magnets consists of helium ions & electrons. The plasma would be guided through a rocket chamber formed by a magnetic field and further heated by RF waves at ion cyclotron frequencies.
The plasma rocket would use propellant in relatively small amounts compared with a conventional chemical rocket for the same mission. In a real mission, conventional rocket engines would be used for lift-off from Earth. Once in space, the craft would switch to the plasma engine and accelerate continuously instead of coasting to its destination after a short-duration, high-thrust "burn."
The first flight of the VASIMR could come as early as 2001. NASA is considering testing the technology on a dual-purpose mission called the Radiation and Technology Demonstration mission. In addition to its main technology demonstration objectives, the spacecraft will carry radiation-measuring instruments and will undertake a comprehensive survey of the Van Allen radiation belts.
The VASIMR engine is being developed in a partnership with NASA's Advanced Space Propulsion Laboratory as well as private industry and a number of U.S. universities. ORCMT has the main responsibility for VASIMR's RF and superconducting magnet systems. ORNL's Fusion Energy Division has been DOE's lead RF laboratory for fusion energy applications for the past decade and is involved in R&D aimed at commercial applications of high-temperature superconductors.
A successful design would give NASA tremendous leeway in extended missions because so much less spacecraft payload would be devoted to fuel. VASIMR would provide for a wide range of mission abort capabilities, an essential element for human flight. The higher speeds from continuous acceleration would also be important to crews on manned missions.
ORNL health physicist and mathematician Troyce Jones maintains that long-duration space flights could have a very deleterious effect on crews subjected to loss of bone mass (and associated immune system effects) from microgravity, high radiation and even months of crummy food. Milora acknowledges that the prospects of faster speeds have been appealing to the NASA collaborators.
PLASMA ROCKET COULD HELP PICK UP SPACE TRASH
Franklin Chang Diaz's proposed VASIMR rocket engine could create very versatile spacecraft. Not only does the plasma-fueled rocket have the potential to make a trip to Mars in just over a month, it could also help clean up space trash in Earth orbit. "Our goal is to be able to have a garbage truck that will be picking up all of these objects at various orbits," astronaut Chang Diaz said in an article in the Global Post. The debris could put into an "orbital graveyard," he added, "or we could actually launch them to the sun and drive them to the sun, which is kind of the ultimate, cosmic dump.
Space debris is becoming a growing problem. The number of non-operating satellites in orbit has increased, as well as debris from spacecraft explosions and, as happened earlier this year, collisions between satellites.
The Earth has become virtually a beehive. The number of satellites orbiting the Earth, we're talking hundreds of thousands of these objects. Some of them are just junk that's floating there simply because these satellites have run out of fuel and they just remain in orbit dead
The rocket, called the VASIMR for "variable specific impulse magneto plasma rocket," uses a high-power technology initially studied by NASA that turns argon into plasma. Propelled by an exhaust gas at temperatures close to that of the sun, the VASIMR VX-200 engine would have the ability to change orbits and accelerate and decelerate in order to pick up space debris.
VASIMR is not suitable to launch payloads from the surface of the Earth due to its low thrust to weight ratio and its need of a vacuum to operate. It would, however be ideal to function as an upper stage for cargo, drastically reducing the fuel requirements for in-space transportation.
Ad Astra has also signed an agreement with NASA to test a 200-kilowatt VASIMR engine on the International Space Station in 2013 to help keep it in orbit. ISS boosts are currently provided by conventional thrusters, which consume about 7.5 tons of propellant per year. By cutting this amount down to 0.3 tons, Chang-Diaz estimates that VASIMR could save NASA millions of dollars per year.
Other uses of the plasma rocket engine would be lunar cargo transport, human missions to Mars or other destinations, and in-space refueling.
A NEW IMPROVED ROCKET
The new system, called the Mini-Helicon Plasma Thruster, is much smaller than other rockets of its kind and runs on gases that are much less expensive than conventional propellants. As a result, it could slash fuel consumption by 10 times that of conventional systems used for the same applications, says Oleg Batishchev, a principal research scientist in the Department of Aeronautics and Astronautics and leader of the work.
Although such systems have brought humans to the moon and are regularly used in a variety of other applications, they have limitations. For example, chemical rockets are expensive largely due to the amount of fuel they use.
As a result, engineers have been developing alternative, non-chemical rockets. In these, an external source of electrical energy is used to accelerate the propellant that provides the thrust for moving a craft through space.
But the field is still relatively new, and these advanced rockets are one focus of the MIT Space Propulsion Laboratory (SPL). "The Mini-Helicon is one exciting example of the sorts of thrusters one can devise using external electrical energy instead of the locked-in chemical energy," says Manuel Martinez-Sanchez, director of the SPL and a professor in the Department of Aeronautics and Astronautics.
The Mini-Helicon is the first rocket to run on nitrogen, the most abundant gas in our atmosphere.
It was conceived through work with former astronaut Franklin Chang-Diaz ScD '77 on a much larger, more powerful system developed by Chang-Diaz. Batishchev's team did a theoretical analysis showing that the first of three parts of the larger rocket could potentially be used alone for different applications.
The Mini-Helicon has three general parts: a quartz tube wrapped by a coiled antenna, with magnets surrounding both. The gas of interest is pumped into the quartz tube, where radio frequency power transmitted to the gas from the antenna turns the gas into plasma, or electrically charged gas.
The magnets not only help produce the plasma, but also confine, guide and accelerate it through the system. "The plasma beam exhausted from the tube is what gives us the thrust to propel the rocket," Batishchev says.
PLASMA ROCKET COULD TRAVEL TO MARS IN 30 DAYS
In the VASIMR rocket, magnetic fields force the charged plasma out the back of the engine, producing thrust in the opposite direction. Image copyright: Ad Astra Rocket Company.
"It's the most powerful plasma rocket in the world right now," says Franklin Chang-Diaz, former NASA astronaut and CEO of Ad Astra. The company has signed an agreement with NASA to test a 200-kilowatt VASIMR engine on the International Space Station (ISS) in 2013.
The engine could provide periodic boosts to the ISS, which gradually drops in altitude due to atmospheric drag. ISS boosts are currently provided by spacecraft with conventional thrusters, which consume about 7.5 tones of propellant per year. By cutting this amount down to 0.3 tones, Chang-Diaz estimates that VASIMR could save NASA millions of dollars per year.
But Ad Astra has bigger plans for VASIMR, such as high-speed missions to Mars. A 10- to 20-megawatt VASIMR engine could propel human missions to Mars in just 39 days, whereas conventional rockets would take six months or more. The shorter the trip, the less time astronauts would be exposed to space radiation, which is a significant hurdle for Mars missions. VASIMR could also be adapted to handle the high payloads of robotic missions, though at slower speeds than lighter human missions.
PAINLESS PLASMA JETS COULD REPLACE DENTIST'S DRILL
Plasma jets capable of obliterating tooth decay-causing bacteria could be an effective and less painful alternative to the dentist's drill, according to a new study published in the February issue of the Journal of Medical Microbiology.
Firing low temperature plasma beams at dentin - the fibrous tHYPERLINK "http://www.physorg.com/tags/tooth/"ooth structure underneath the enamel coating - was found to reduce the amount of dental bacteria by up to 10,000-fold. The findings could mean plasma technology is used to remove infected tissue in tooth cavities - a practice that conventionally involves drilling into the tooth.
Scientists at the Leibniz-Institute of Surface Modifications, Leipzig and dentists from the Saarland University, Homburg, Germany, tested the effectiveness of plasma against common oral pathogens including Streptococcus mutans and Lactobacillus casei. These bacteria form films on the surface of teeth and are capable of eroding tooth enamel and the dentin below it to cause cavities. If left untreated it can lead to pain, tooth loss and sometimes severe gum infections. In this study, the researchers infected dentin from extracted human molars with four strains of bacteria and then exposed it to plasma jets for 6, 12 or 18 seconds. The longer the dentin was exposed to the plasma the greater the amount of bacteria that were eliminated.
Plasmas are known as the fourth state of matter after solids, liquids and gases and have an increasing number of technical and medical applications. Plasmas are common everywhere in the cosmos, and are produced when high-energy processes strip atoms of one or more of their electrons. This forms high-temperature reactive oxygen species that are capable of destroying microbes. These hot plasmas are already used to disinfect surgical instruments.
Dr Stefan Rupf from Saarland University who led the research said that the recent development of cold plasmas that have temperatures of around 40 degrees Celsius showed great promise for use in dentistry. "The low temperature means they can kill the microbes while preserving the tooth. The dental pulp at the centre of the tooth, underneath the dentin, is linked to the blood supply and nerves and heat damage to it must be avoided at all costs."
Dr Rupf said using plasma technology to disinfect tooth cavities would be welcomed by patients as well as dentists. "Drilling is a very uncomfortable and sometimes painful experience. Cold plasma, in contrast, is a completely contact-free method that is highly effective. Presently, there is huge progress being made in the field of plasma medicine and a clinical treatment for dental cavities can be expected within 3 to 5 years."
