Kyai Haji Ahmad Dahlan (Yogyakarta, 1 Agustus 1868–Yogyakarta, 23 Februari 1923) adalah seorang Pahlawan Nasional Indonesia. Beliau adalah putera keempat dari tujuh bersaudara dari keluarga K.H. Abu Bakar. KH Abu Bakar adalah seorang ulama dan khatib terkemuka di Masjid Besar Kasultanan Yogyakarta pada masa itu, dan ibu dari K.H. Ahmad Dahlan adalah puteri dari H. Ibrahim yang juga menjabat penghulu Kasultanan Yogyakarta pada masa itu.
"Don't let setbacks get you down.
Studying successful people will show you that
they did not attain their success without first overcoming challenges."
Catherine Pulsifer
Animation of a hydroelectric power plant in a damSo just how do we get electricity from water? Actually, hydroelectric and coal-fired power plants produce electricity in a similar way. In both cases a power source is used to turn a propeller-like piece called a turbine, which then turns a metal shaft in an electric generator Picture, which is the motor that produces electricity. A coal-fired power plant uses steam to turn the turbine blades; whereas a hydroelectric plant uses falling water to turn the turbine. The results are the same.
Take a look at this diagram (courtesy of the Tennessee Valley Authority) of a hydroelectric power plant to see the details: Drawing of a turbine, which the water turns. The theory is to build a dam on a large river that has a large drop in elevation (there are not many hydroelectric plants in Kansas or Florida). The dam stores lots of water behind it in the reservoir. Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. At the end of the penstock there is a turbine propeller, which is turned by the moving water. The shaft from the turbine goes up into the generator, which produces the power. Power lines are connected to the generator that carry electricity to your home and mine. The water continues past the propeller through the tailrace into the river past the dam. By the way, it is not a good idea to be playing in the water right below a dam when water is released!
This diagram of a hydroelectric generator is courtesy of U.S. Army Corps of Engineers. As to how this generator works, the Corps of Engineers explains it this way: "A hydraulic turbine converts the energy of flowing water into mechanical energy. A hydroelectric generator converts this mechanical energy into electricity. The operation of a generator is based on the principles discovered by Faraday. He found that when a magnet is moved past a conductor, it causes electricity to flow. In a large generator, electromagnets are made by circulating direct current through loops of wire wound around stacks of magnetic steel laminations. These are called field poles, and are mounted on the perimeter of the rotor. The rotor is attached to the turbine shaft, and rotates at a fixed speed. When the rotor turns, it causes the field poles (the electromagnets) to move past the conductors mounted in the stator. This, in turn, causes electricity to flow and a voltage to develop at the generator output terminals." taken from http://ga.water.usgs.gov/edu/hyhowworks.html
The U.S. Air Force is quietly spending millions of dollars investigating ways to use a radical power source -- antimatter, the eerie "mirror" of ordinary matter -- in future weapons.
The most powerful potential energy source presently thought to be available to humanity, antimatter is a term normally heard in science-fiction films and TV shows, whose heroes fly "antimatter-powered spaceships" and do battle with "antimatter guns."
But antimatter itself isn't fiction; it actually exists and has been intensively studied by physicists since the 1930s. In a sense, matter and antimatter are the yin and yang of reality: Every type of subatomic particle has its antimatter counterpart. But when matter and antimatter collide, they annihilate each other in an immense burst of energy.
During the Cold War, the Air Force funded numerous scientific studies of the basic physics of antimatter. With the knowledge gained, some Air Force insiders are beginning to think seriously about potential military uses -- for example, antimatter bombs small enough to hold in one's hand, and antimatter engines for 24/7 surveillance aircraft.
More cataclysmic possible uses include a new generation of super weapons -- either pure antimatter bombs or antimatter-triggered nuclear weapons; the former wouldn't emit radioactive fallout. Another possibility is antimatter- powered "electromagnetic pulse" weapons that could fry an enemy's electric power grid and communications networks, leaving him literally in the dark and unable to operate his society and armed forces.
Following an initial inquiry from The Chronicle this summer, the Air Force forbade its employees from publicly discussing the antimatter research program. Still, details on the program appear in numerous Air Force documents distributed over the Internet prior to the ban.
These include an outline of a March 2004 speech by an Air Force official who, in effect, spilled the beans about the Air Force's high hopes for antimatter weapons. On March 24, Kenneth Edwards, director of the "revolutionary munitions" team at the Munitions Directorate at Eglin Air Force Base in Florida was keynote speaker at the NASA Institute for Advanced Concepts (NIAC) conference in Arlington, Va.
In that talk, Edwards discussed the potential uses of a type of antimatter called positrons.
Physicists have known about positrons or "antielectrons" since the early 1930s, when Caltech scientist Carl Anderson discovered a positron flying through a detector in his laboratory. That discovery, and the later discovery of "antiprotons" by Berkeley scientists in the 1950s, upheld a 1920s theory of antimatter proposed by physicist Paul Dirac.
In 1929, Dirac suggested that the building blocks of atoms -- electrons (negatively charged particles) and protons (positively charged particles) -- have antimatter counterparts: antielectrons and antiprotons. One fundamental difference between matter and antimatter is that their subatomic building blocks carry opposite electric charges. Thus, while an ordinary electron is negatively charged, an antielectron is positively charged (hence the term positrons, which means "positive electrons"); and while an ordinary proton is positively charged, an antiproton is negative.
The real excitement, though, is this: If electrons or protons collide with their antimatter counterparts, they annihilate each other. In so doing, they unleash more energy than any other known energy source, even thermonuclear bombs.
The energy from colliding positrons and antielectrons "is 10 billion times ... that of high explosive," Edwards explained in his March speech. Moreover, 1 gram of antimatter, about 1/25th of an ounce, would equal "23 space shuttle fuel tanks of energy." Thus "positron energy conversion," as he called it, would be a "revolutionary energy source" of interest to those who wage war.
It almost defies belief, the amount of explosive force available in a speck of antimatter -- even a speck that is too small to see. For example: One millionth of a gram of positrons contain as much energy as 37.8 kilograms (83 pounds) of TNT, according to Edwards' March speech. A simple calculation, then, shows that about 50-millionths of a gram could generate a blast equal to the explosion (roughly 4,000 pounds of TNT, according to the FBI) at the Alfred P. Murrah Federal Building in Oklahoma City in 1995.
Unlike regular nuclear bombs, positron bombs wouldn't eject plumes of radioactive debris. When large numbers of positrons and antielectrons collide, the primary product is an invisible but extremely dangerous burst of gamma radiation. Thus, in principle, a positron bomb could be a step toward one of the military's dreams from the early Cold War: a so-called "clean" superbomb that could kill large numbers of soldiers without ejecting radioactive contaminants over the countryside.
A copy of Edwards' speech onNIAC's Web site emphasizes this advantage of positron weapons in bright red letters: "No Nuclear Residue."
But talk of "clean" superbombs worries critics. " 'Clean' nuclear weapons are more dangerous than dirty ones because they are more likely to be used," said an e-mail from science historian George Dyson of the Institute for Advanced Study in Princeton, N.J., author of "Project Orion," a 2002 study on a Cold War-era attempt to design a nuclear spaceship. Still, Dyson adds, antimatter weapons are "a long, long way off."
Why so far off? One reason is that at present, there's no fast way to mass produce large amounts of antimatter from particle accelerators. With present techniques, the price tag for 100-billionths of a gram of antimatter would be $6 billion, according to an estimate by scientists at NASA's Marshall Space Flight Center and elsewhere, who hope to launch antimatter-fueled spaceships.
Another problem is the terribly unruly behavior of positrons whenever physicists try to corral them into a special container. Inside these containers, known as Penning traps, magnetic fields prevent the antiparticles from contacting the material wall of the container -- lest they annihilate on contact. Unfortunately, because like-charged particles repel each other, the positrons push each other apart and quickly squirt out of the trap.
If positrons can't be stored for long periods, they're as useless to the military as an armored personnel carrier without a gas tank. So Edwards is funding investigations of ways to make positrons last longer in storage.
Edwards' point man in that effort is Gerald Smith, former chairman of physics and Antimatter Project leader at Pennsylvania State University. Smith now operates a small firm, Positronics Research LLC, in Santa Fe, N.M. So far, the Air Force has given Smith and his colleagues $3.7 million for positron research, Smith told The Chronicle in August.
Smith is looking to store positrons in a quasi-stable form called positronium. A positronium "atom" (as physicists dub it) consists of an electron and antielectron, orbiting each other. Normally these two particles would quickly collide and self-annihilate within a fraction of a second -- but by manipulating electrical and magnetic fields in their vicinity, Smith hopes to make positronium atoms last much longer.
Smith's storage effort is the "world's first attempt to store large quantities of positronium atoms in a laboratory experiment," Edwards noted in his March speech. "If successful, this approach will open the door to storing militarily significant quantities of positronium atoms."
Officials at Eglin Air Force Base initially agreed enthusiastically to try to arrange an interview with Edwards. "We're all very excited about this technology," spokesman Rex Swenson at Eglin's Munitions Directorate told The Chronicle in late July. But Swenson backed out in August after he was overruled by higher officials in the Air Force and Pentagon.
Reached by phone in late September, Edwards repeatedly declined to be interviewed. His superiors gave him "strict instructions not to give any interviews personally. I'm sorry about that -- this (antimatter) project is sort of my grandchild. ...
"(But) I agree with them (that) we're just not at the point where we need to be doing any public interviews."
Air Force spokesman Douglas Karas at the Pentagon also declined to comment last week.
In the meantime, the Air Force has been investigating the possibility of making use of a powerful positron-generating accelerator under development at Washington State University in Pullman, Wash. One goal: to see if positrons generated by the accelerator can be stored for long periods inside a new type of "antimatter trap" proposed by scientists, including Washington State physicist Kelvin Lynn, head of the school's Center for Materials Research.
A new generation of military explosives is worth developing, and antimatter might fill the bill, Lynn told The Chronicle: "If we spend another $10 billion (using ordinary chemical techniques), we're going to get better high explosives, but the gains are incremental because we're getting near the theoretical limits of chemical energy."
Besides, Lynn is enthusiastic about antimatter because he believes it could propel futuristic space rockets.
"I think," he said, "we need to get off this planet, because I'm afraid we're going to destroy it."
This article appeared on page A - 1 of the San Francisco Chronicle written by Keay Davidson
Spirulina is a blue-green algae. It is a simple, one-celled form of algae that thrives in warm, alkaline fresh-water bodies. The name "spirulina" is derived from the Latin word for "helix" or "spiral"; denoting the physical configuration of the organism when it forms swirling, microscopic strands. Spirulina is being developed as the "food of the future" because of its amazing ability to synthesize high-quality concentrated food more efficiently than any other algae. Most notably, Spirulina is 65 to 71 percent complete protein, with all essential amino acids in perfect balance. In comparison, beef is only 22 percent protein.
Spirulina has a photosynthetic conversion rate of 8 to 10 percent, compared to only 3 percent in such land-growing plants as soybeans.
In addition, Spirulina is one of the few plant sources of vitamin B12, usually found only in animal tissues. A teaspoon of Spirulina supplies 21/2 times the Recommended Daily Allowance of vitamin B12 and contains over twice the amount of this vitamin found in an equivalent serving of liver.
Spirulina also provides high concentrations of many other nutrients - amino acids, chelated minerals, pigmentations, rhamnose sugars (complex natural plant sugars), trace elements, enzymes - that are in an easily assimilable form.
Even though it is single-celled, Spirulina is relatively large, attaining sizes of 0.5 millimeters in length. This is about 100 times the size of most other algae, which makes some individual Spirulina cells visible to the naked eye. Furthermore, the prolific reproductive capacity of the cells and their proclivity to adhere in colonies makes Spirulina a large and easily gathered plant mass.
The algae are differentiated according to predominating colorations, and are divided into blue-green, green, red and brown. Spirulina is one of the blue-green algae due to the presence of both chlorophyll (green) and phycocyanin (blue) pigments in its cellular structure.
Even though Spirulina is distantly related to the kelp algae, it is not a sea plant. However, the fresh-water ponds and lakes it favors are notably more saline - in the range of 8 to 11 pH than ordinary lakes and cannot sustain any other forms of microorganisms. In addition, Spirulina thrives in very warm waters of 32 to 45 degrees C (approximately 85 to 112 degrees F), and has even survived in temperatures of 60 degrees C (140 degrees F)
Certain desert-adapted species will survive when their pond habitats evaporate in the intense sun, drying to a dormant state on rocks as hot as 70 degrees Centigrade (160 degrees F). In this dormant condition, the naturally blue-green algae turns a frosted white and develops a sweet flavor as its 71 percent protein structure is transformed into polysaccharide sugars by the heat.
Some scientists speculate that the "manna" of the wandering Israelites, which appeared miraculously on rocks following a devastating dry spell and was described as tasting "like wafers made with hone " may have been a form of dried, dormant Spirulina.
This ability of Spirulina to grow in hot and alkaline environments ensures its hygienic status, as no other organisms can survive to pollute the waters in which this algae thrives. Unlike the stereotypical association of microorganisms with "germs" and "scum", Spirulina is in fact one of the cleanest, most naturally sterile foods found in nature.
Its adaptation to heat also assures that Spirulina retains its nutritional value when subject to high temperatures during processing and shelf storage, unlike many plant foods that rapidly deteriorate at high temperatures.
Spirulina is also unusual among algae because it is a "nuclear plant" meaning it is on the developmental cusp between plants and animals. It is considered somewhat above plants because it does not have the hard cellulose membranes characteristic of plant cells, nor does it have a well-defined nucleus. Yet its metabolic system is based on photosynthesis, a process of direct food energy production utilizing sunlight and chlorophyll, which is typical of plant life forms.
In essence, Spirulina straddles that fork in evolutionary development when the plant and animal kingdoms differentiated. Thus it embodies the simplest form of life. In contrast, other algae such as Chlorella have developed the hard indigestible walls characteristic of plants. taken from http://www.naturalways.com/
It's one of the most attractive words in science fiction literature and nearly as good a topic at parties as black holes. It might also be the fuel that powers spaceships to the planets and perhaps the stars, even if it's just used as a sophisticated book of matches.
Right: Mars in 6 weeks? And back in a total of four months? That's the prediction of a design team working on antimatter rocket concepts at Pennsylvania State University. But first, you have to get the stuff - and store it. (PSU)
Antimatter and more "conventional" nuclear fusion occupied the final day of the 10th annual Advanced Propulsion Research Workshop held Tuesday-Thursday at the University of Alabama in Huntsville by NASA, Marshall, the Jet Propulsion Laboratory, and the American Institute of Aeronautics and Astronautics.
Recent Headlines December 3: Mars Polar Lander nears touchdown
December 2: What next, Leonids?
November 30: Polar Lander Mission Overview
November 30: Learning how to make a clean sweep in space
"Antimatter has tremendous energy density," said Dr. George Schmidt, chief of propulsion research and technology at NASA/Marshall. Matter-antimatter annihilation - the complete conversion of matter into energy - releases the most energy per unit mass of any known reaction in physics.
The popular belief is that an antimatter particle coming in contact with its matter counterpart yields energy. That's true for electrons and positrons (anti-electrons). They'll produce gamma rays at 511,000 electron volts.
But heavier particles like protons and anti-protons are somewhat messier, making gamma rays and leaving a spray of secondary particles that eventually decay into neutrinos and low-energy gamma rays.
And that is partly what Schmidt and others want in an antimatter engine. The gamma rays from a perfect reaction would escape immediately, unless the ship had thick shielding, and serve no purpose. But the charged debris from a proton/anti-proton annihilation can push a ship.
"We want to get as close as possible to the initial annihilation event," Schmidt explained. What's important is intercepting some of the pions and other charged particles that are produced and using the energy to produce thrust."
This is not your father's starship He's not going to use it the way that the Starship Enterprise did, creating a warp field to move the vessel across space faster than the speed of light. At its most basic level, an antimatter rocket is still a Newtonian rocket moving a space probe through action and reaction.
And what a reaction. Where the Space Shuttle Main Engine has a specific impulse, a measure of efficiency, of 455 seconds, and nuclear fission could reach 10,000 seconds, fusion could provide 60,000 to 100,000 seconds, and matter/antimatter annihilation up to 100,000 to 1,000,000 seconds.
But first: Where do you get it? And how do you store the nuclear equivalent of the universal solvent?
Anti-protons, explained Dr. Gerald Smith of Pennsylvania State University, can be obtained in modest quantities from high-energy accelerators slamming particles into solid targets. The anti-protons are then collected and held in a magnetic bottle.
Left: A schematic of the heart of a Penning trap where a cloud of antiprotons (the fuzzy bluish spot) is kept cold and quiet by liquid nitrogen and helium and a stable magnetic field. (PSU)
While that's been done easily enough in small quantities, fueling a rocket will take much more.
"We're building a Penning trap," Smith said, "one that will be lightweight and robust." When completed, it will weigh about 100 kg (220 lbs), much of it liquid nitrogen and helium to keep about a trillion anti-protons - far less than a nanogram - quiescent in a zone about 1 mm (1/25th inch) across.
"How do you know that you have particles in the trap?" Smith asked. "They're odorless and colorless." However, they do have distinctive radio frequency signatures which Smith and his colleagues have been able to measure. They've also demonstrated that their trap design would hold a significant quantity for up to 5 days.
A Penn State artist's concept of n antimatter-powered Mars ship with equipment and crew landers at the right, and the engine, with magnetic nozzles, at left.
"Our aim is to get up to a microgram of antiprotons," Smith said. "There are some interesting propulsion technologies that work at that level. We think we can do it."
A trillion antiprotons is the maximum that can be stored under those conditions. More could be held if they were turned into anti-hydrogen, anti-protons plus positrons.
A lot of bang for the buck Right now, antimatter is the most expensive substance on Earth, about $62.5 trillion a gram ($1.75 quadrillion an ounce). The production is, at best, 50 percent efficient because half of what's created are regular protons, and the equipment now used was not designed to fuel rockets. Harold Gerrish of NASA/Marshall and others estimate that improvements in equipment to slow and trap the antiprotons could bring the price down to about $5,000 per microgram. A new injector at Fermilab outside Chicago will allow that facility to increase its production tenfold, from 1.5 to 15 nanograms a year.
"Right now, a lot of antiprotons are produced, but most are wasted," Gerrish said.
Dr. Steven Howe of Synergistic Technologies in Los Alamos, N.M., explained that CERN is working towards producing anti-hydrogen as part of the Athena fundamental physics program to determine if antimatter indeed is indistinguishable from matter. Using the same Ioffe-Pritchard trap being developed at CERN, he expects that large quantities of anti-hydrogen atoms could be stored safely for long periods. At low temperatures, the wavelength of the atom is several times that of the material making up the container walls, so the atoms are reflected with little effort.
"Our goal is to remove antimatter from the far-out realm of science fiction into the commercially exploitable realm for transportation and medical applications."
Beyond the Enterprise - Fusion power A step back from antimatter is fusion, the power source of the future for the last five decades. Controlled fusion - joining two lightweight nuclei to get a slightly heavier nucleus and a lot of energy - has been challenging. In their quest to exceed Q=1, the break-even point, scientists have moved from low energy yields of Q=0.0000000000001 in the late 1950s to Q=0.3 today, and developed a large body of engineering and scientific knowledge showing that it can be made practical.
Other Propulsion Stories this week Apr 6: Ion Propulsion -- 50 Years in the Making - The concept of ion propulsion, currently being demonstrated on the Deep Space 1 mission, goes back to the very beginning of NASA and beyond. April 6: Far Out Space Propulsion Conference Blasts Off - Atoms locked in snow, a teaspoon from the heart of the sun, and the stuff that drives a starship will be on the agenda of an advanced space propulsion conference that opens today in Huntsville. April 7: Darwinian Design - Survival of the Fittest Spacecraft April 7: Coach-class tickets for space? - Scientists discuss new ideas for high-performance, low-cost space transportation April 8: Setting Sail for the Stars - Cracking the whip and unfurling gray sails are among new techniques under discussion at the 1999 Advanced Propulsion Research Workshop April 12: Reaching for the stars - Scientists examine using antimatter and fusion to propel future spacecraft. April 16: Riding the Highways of Light - Science mimics science fiction as a Rensselaer Professor builds and tests a working model flying disc. The disc, or "Lightcraft," is an early prototype for Earth-friendly spacecraft of the future. "From the NASA perspective, the challenge is to adapt fusion for space propulsion," said Dr. Francis Thio, a principal research scientist in the Propulsion Research Center at NASA/Marshall. "Magnetized Target Fusion is one of the major approaches that we are studying." NASA/Marshall is working with Los Alamos National Laboratory and the Air Force Research Laboratory to adapt MTF for propulsion.
"MTF tries to operate in an intermediate regime between the conventional magnetic fusion, and inertial confinement using a laser," Thio explained. The problem with conventional magnetic confinement is it operates at very low density. To achieve sufficient power, the fusion reactor must be large, which translates to a high cost.
On the other hand, inertial confinement fusion uses a tiny plasma, 1,000 trillion times denser than in a magnetic confinement scheme. But that requires a driver - usually banks of intense, short-pulse lasers - that heat and compress the target in a short time. That also drives the cost up.
"MTF tries to operate at not too low or too high a density," Thio explained, "and achieve a reasonable rate of fusion activity with a density 10,000 to 100,000 times higher than magnetic confinement, and 10,000 to 100,000 times lower than laser fusion."
It's more economical and uses pulse-power drivers - powerful capacitor banks that drive electromagnetic implosion - that are available today at low cost. It does not have the implosion speed generated a laser beam, but a magnetic field confines the target plasma and insulates the inertial wall that implodes to cause the fusion.
Can I get the compact model? Even if fusion is achieved, current methods are too cumbersome to use in rockets.
"The mass is quite prohibitive," said Professor T. Kammash of the University of Michigan. "We want to make the physics work without using very large magnets." The mirror magnets for a fusion rocket would weigh about 401 tonnes (metric tons), about 16 times a single Space Shuttle payload. The heat radiators would add 240 tonnes.
Kammash's students are experimenting with a droplet radiator design that, using liquid lithium as a coolant, could reduce the radiator mass to 57 tonnes. They recently flew a test model aboard NASA's KC-135 low-gravity aircraft to test a model radiator.
A rotating magnetic field could induce a magnetic field and electrical currents, "a clever way of fooling the plasma" into behaving as if it was in a conventional magnetic mirror system.
In turn, the mass of the spacecraft would come down from 720 to 230 tonnes, and the 44-meter (144-ft) long engine would have a specific impulse of 130,000 seconds.
"It's quite impressive," Kammash said.
One of the most intriguing possibilities raised actually dates back to the 1950s and a concept developed by Philo Farnsworth, who pioneered most of the fundamental technologies for television in the 1920s and '30s.
"This is a really neat concept, something you can literally put your hands around," said Dr. Jon Nadler of NPL Associates in Champaign, Ill. Under a Small Business Innovative Research grant from NASA/Marshall, he is working with the University of Illinois Urbana-Champaign to develop the idea that Farnsworth had in 1950: fusion in a small bottle.
Right: Peering into the heart of a star. What looks like a 1950s model of an atom is a hollow cathode with a tiny plasma cloud contained inside an IEC fusion chamber small enough to sit atop a lab bench. (UIUC)
"You can use the power [it would generate] to power electric propulsion, or use the plasma for thrust," Nadler explained.
A star in a bottle The technique is called inertial electrostatic confinement (IEC), a technique that avoids the use of massive magnets and laser systems used in other fusion-power techniques. Instead, the IEC device uses a hollow cathode, and the natural charges of electrons and ions, to form virtual electrodes that confine ions in a spherical region at the center of the 61 cm (2 ft) diameter IEC vacuum chamber.
"The SBIR funding has allowed us to make some historic advances," Nadler told the audience. Using a pulsed megawatt power supply, the IEC achieved its highest pulsed current yet - 17 amps at 40,000 volts. The IEC has also gone from producing one neutron (released by deuterium-deuterium fusion) in every 10 cycles to more than 100 neutrons per cycle.
"I'm happy to report that everything is looking good for increased reactivity," he said. "And we haven't even stressed anything out yet."
IEC fusion would work best with a couple of unusual fusion cycles. One uses deuterium (heavy hydrogen), easily refined from water on Earth, and helium 3 (helium lacking one neutron), quite rare here but possibly abundant in lunar soil exposed to 4 billion years of solar wind. The other fires protons into boron 11.
Left: A schematic of the energy well in the middle of a conventional magnetic field, and in the IEC chamber where fusion is induced. (UIUC)
While true antimatter and true fusion propulsion will remain the "rockets of the future" for some time, a hybrid of the two might work in the near term.
"It's a good short cut," Schmidt said of antimatter-catalyzed fusion. In this approach, a small quantity of antiprotons is beamed into a fusion target. The resulting matter-antimatter annihilation heats a target enough to cause thermonuclear fusion.
Because of the energies and expense involved in producing antimatter, this method is not practical for power production on Earth. Overall, it is a net energy loser. Like all other forms of rocket propulsion, it's a sort of battery in which energy is expended to provide a large quantity in a tiny space, available on demand.
But, it could yield a rocket with a specific impulse of 13,500 to 67,000 seconds (30-147 times better than the Shuttle Main Engine), depending on the scheme used.
"Fusion missions would need just micrograms to reach the Oort cloud," the deep freeze of comets beyond the orbit of Pluto, Gerrish said. The antimatter load would cost about $60 million. Reaching the stars would require metric tons.
A rotary engine is an internal combustion engine, like the engine in your car, but it works in a completely different way than the conventional piston engine.
In a piston engine, the same volume of space (the cylinder) alternately does four different jobs -- intake, compression, combustion and exhaust. A rotary engine does these same four jobs, but each one happens in its own part of the housing. It's kind of like having a dedicated cylinder for each of the four jobs, with the piston moving continually from one to the next.
The rotary engine (originally conceived and developed by Dr. Felix Wankel) is sometimes called a Wankel engine, or Wankel rotary engine.
Like a piston engine, the rotary engine uses the pressure created when a combination of air and fuel is burned. In a piston engine, that pressure is contained in the cylinders and forces pistons to move back and forth. The connecting rods and crankshaft convert the reciprocating motion of the pistons into rotational motion that can be used to power a car.
In a rotary engine, the pressure of combustion is contained in a chamber formed by part of the housing and sealed in by one face of the triangular rotor, which is what the engine uses instead of pistons.
The rotor and housing of a rotary engine from a Mazda RX-7: These parts replace the pistons, cylinders, valves, connecting rods and camshafts found in piston engines.
The rotor follows a path that looks like something you'd create with a Spirograph. This path keeps each of the three peaks of the rotor in contact with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine, compresses it and makes useful power as the gases expand, and then expels the exhaust.
We'll be taking a look inside a rotary engine to check out the parts, but first let's take a look at a new model car with an all-new rotary engine.
Mazda RX-8
Mazda has been a pioneer in developing production cars that use rotary engines. The RX-7, which went on sale in 1978, was probably the most successful rotary-engine-powered car. But it was preceded by a series of rotary-engine cars, trucks and even buses, starting with the 1967 Cosmo Sport. The last year the RX-7 was sold in the United States was 1995, but the rotary engine is set to make a comeback in the near future. The Mazda RX-8 , a new car from Mazda, has a new, award winning rotary engine called the RENESIS. Named International Engine of the Year 2003, this naturally aspirated two-rotor engine will produce about 250 horsepower. For more information, visit Mazda's RX-8 Web site.
The Parts of a Rotary Engine
A rotary engine has an ignition system and a fuel-delivery system that are similar to the ones on piston engines. If you've never seen the inside of a rotary engine, be prepared for a surprise, because you won't recognize much.
Rotor The rotor has three convex faces, each of which acts like a piston. Each face of the rotor has a pocket in it, which increases the displacement of the engine, allowing more space for air/fuel mixture.
At the apex of each face is a metal blade that forms a seal to the outside of the combustion chamber. There are also metal rings on each side of the rotor that seal to the sides of the combustion chamber.
The rotor has a set of internal gear teeth cut into the center of one side. These teeth mate with a gear that is fixed to the housing. This gear mating determines the path and direction the rotor takes through the housing.
Housing The housing is roughly oval in shape (it's actually an epitrochoid -- check out this Java demonstration of how the shape is derived). The shape of the combustion chamber is designed so that the three tips of the rotor will always stay in contact with the wall of the chamber, forming three sealed volumes of gas.
Each part of the housing is dedicated to one part of the combustion process. The four sections are:
Intake
Compression
Combustion
Exhaust
The intake and exhaust ports are located in the housing. There are no valves in these ports. The exhaust port connects directly to the exhaust, and the intake port connects directly to the throttle.
Output Shaft The output shaft has round lobes mounted eccentrically, meaning that they are offset from the centerline of the shaft. Each rotor fits over one of these lobes. The lobe acts sort of like the crankshaft in a piston engine. As the rotor follows its path around the housing, it pushes on the lobes. Since the lobes are mounted eccentric to the output shaft, the force that the rotor applies to the lobes creates torque in the shaft, causing it to spin.
The output shaft (Note the eccentric lobes.)
Rotary Engine Assembly
A rotary engine is assembled in layers. The two-rotor engine we took apart has five main layers that are held together by a ring of long bolts. Coolant flows through passageways surrounding all of the pieces.
The two end layers contain the seals and bearings for the output shaft. They also seal in the two sections of housing that contain the rotors. The inside surfaces of these pieces are very smooth, which helps the seals on the rotor do their job. An intake port is located on each of these end pieces.
One of the two end pieces of a two-rotor Wankel engine
The next layer in from the outside is the oval-shaped rotor housing, which contains the exhaust ports. This is the part of the housing that contains the rotor.
The part of the rotor housing that holds the rotors (Note the exhaust port location.)
The center piece contains two intake ports, one for each rotor. It also separates the two rotors, so its outside surfaces are very smooth.
The center piece contains another intake port for each rotor.
In the center of each rotor is a large internal gear that rides around a smaller gear that is fixed to the housing of the engine. This is what determines the orbit of the rotor. The rotor also rides on the large circular lobe on the output shaft.
Rotary Engine Power
Rotary engines use the four-stroke combustion cycle, which is the same cycle that four-stroke piston engines use. But in a rotary engine, this is accomplished in a completely different way.
The heart of a rotary engine is the rotor. This is roughly the equivalent of the pistons in a piston engine. The rotor is mounted on a large circular lobe on the output shaft. This lobe is offset from the centerline of the shaft and acts like the crank handle on a winch, giving the rotor the leverage it needs to turn the output shaft. As the rotor orbits inside the housing, it pushes the lobe around in tight circles, turning three times for every one revolution of the rotor.
If you watch carefully, you'll see the offset lobe on the output shaft spinning three times for every complete revolution of the rotor.
As the rotor moves through the housing, the three chambers created by the rotor change size. This size change produces a pumping action. Let's go through each of the four strokes of the engine looking at one face of the rotor.
Intake The intake phase of the cycle starts when the tip of the rotor passes the intake port. At the moment when the intake port is exposed to the chamber, the volume of that chamber is close to its minimum. As the rotor moves past the intake port, the volume of the chamber expands, drawing air/fuel mixture into the chamber.
When the peak of the rotor passes the intake port, that chamber is sealed off and compression begins.
Compression As the rotor continues its motion around the housing, the volume of the chamber gets smaller and the air/fuel mixture gets compressed. By the time the face of the rotor has made it around to the spark plugs, the volume of the chamber is again close to its minimum. This is when combustion starts.
Combustion Most rotary engines have two spark plugs. The combustion chamber is long, so the flame would spread too slowly if there were only one plug. When the spark plugs ignite the air/fuel mixture, pressure quickly builds, forcing the rotor to move.
The pressure of combustion forces the rotor to move in the direction that makes the chamber grow in volume. The combustion gases continue to expand, moving the rotor and creating power, until the peak of the rotor passes the exhaust port.
Exhaust Once the peak of the rotor passes the exhaust port, the high-pressure combustion gases are free to flow out the exhaust. As the rotor continues to move, the chamber starts to contract, forcing the remaining exhaust out of the port. By the time the volume of the chamber is nearing its minimum, the peak of the rotor passes the intake port and the whole cycle starts again.
The neat thing about the rotary engine is that each of the three faces of the rotor is always working on one part of the cycle -- in one complete revolution of the rotor, there will be three combustion strokes. But remember, the output shaft spins three times for every complete revolution of the rotor, which means that there is one combustion stroke for each revolution of the output shaft.
There are 4 parts to a UFOC:
* Cover Page
* Table of Contents
* Items 1-23
* Exhibits
The format for each of these sections is very specific and covers the...
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