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| SCIENCE TRIBUNE | Thursday, April 10, 2003, Chandigarh, India |
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Rockets to run on wax? UNDERSTANDING THE UNIVERSE |
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Rockets to run on wax? On the campus of NASA’s Ames Research Centre in Mountain View, Calif., you periodically hear—and feel—a thunderous roar as engineers ignite experimental rocket engines that are chock full of the same paraffin wax that illuminates candlelight dinners. The idea of using wax as rocket fuel isn’t new. People tried it years ago but couldn’t get the wax to work well enough to launch a heavy rocket into space. The engineers now bracing against the roar of their wax-filled engines suspect, however, that their predecessors were indeed onto something. If that’s true, paraffin wax could become the world’s cheapest, safest, most environmentally friendly rocket fuel.
It all started with a trip to San Diego in 1995. Arif Karabeyoglu, then a graduate student at Stanford University, and David Altman, a longtime rocket scientist affiliated with the university, were checking out research presentations at a conference on rocket propulsion. A talk on an Air Force rocket-fuel project set their own research trajectories in a new direction. Unlike the standard solid or liquid fuels used today, the Air Force material was part solid, part liquid. The solid portion was frozen pentane, a hydrocarbon, and the liquid was pure oxygen. Just as a fire needs oxygen-bearing air to burn, all rocket fuels require an oxidizer for combustion. In this case, the oxidiser was the oxygen. Inside an engine, as the liquid oxygen became gaseous and blew across the fuel’s solid component, the pentane burned. So-called hybrid-rocket fuels have been around for half a century, but they haven’t taken off, so to speak. Compared with more widely used fuels, they don’t burn quickly enough or provide enough thrust to launch heavy loads. Moreover, the solid component of a hybrid needs to be moulded into complicated and often fragile shapes to provide a great enough surface area for burning. NASA and other rocketeers usually choose liquid or solid fuels. Liquid fuels include hydrogen and kerosene. Here, the oxidiser is either oxygen or another compound that accepts electrons readily enough and fast enough to drive the heat-releasing chemical reactions that underlie burning. Liquid fuels take up a lot of precious space on a rocket, as the large external tank on the space shuttles vividly shows. Some liquid fuels also require refrigeration. Nonetheless, they have an important benefit: Their combustion can be easily switched on and off to provide reliable and safe control. The two booster rockets flanking the space shuttle’s liquid-fuel engine run on solid propellant. These materials are typically made of an aluminum fuel with an ammonium perchlorate oxidiser built right into them, so they’re very compact. Unfortunately, this setup also makes them dangerous. Like July 4 sparklers, once a solid rocket is ignited, it’s hard or impossible to stop. Safety concerns make production, storage, and transport of solid fuels enormously expensive, says Brian J. Cantwell, an aeronautical engineer at Stanford. Moreover, solid fuels are made of toxic materials. Perchlorates, which have been linked to thyroid problems, may end up in ground water during fuel production or after a launch. As they burn, solid fuels may also produce hazardous emissions, such as hydrogen chloride, which forms hydrochloric acid when it encounters water vapour, and aluminum oxide, an abrasive white powder. So, researchers continue to study hybrid-rocket fuels. Some produce mostly carbon dioxide and water when they burn. Moreover, these fuels are more compact than liquids, and compared with solid fuels, hybrid-rocket fuels are safer and their thrust can be regulated. A particularly attractive feature is that hybrid-rocket-fuel combustion can be completely shut off and restarted. When the first puff of smoke appeared from a solid rocket booster on Challenger’s doomed takeoff in 1986, the spacecraft was still sitting on the launch pad. Even if mission controllers had suspected a problem at that moment, they couldn’t have prevented the shuttle from lifting off, says Cantwell. Nothing could stop the solid fuel that was already burning. A hybrid rocket could have been shut off with the flip of a switch. What has kept hybrid-rocket fuels out of shuttle designs, as well as out of any existing plans for rockets that carry heavy loads, is the fuels’ slow burning rate. And that’s what sparked Karabeyoglu’s and Altman’s interest in the Air Force fuel. For some reason, it burned three times faster than other hybrid fuels.
NASA Ames |
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UNDERSTANDING THE UNIVERSE Why water does not have any colour — why is it transparent?
You could also ask the question: why is the atmosphere so transparent? It is marveleous that our sun puts out most of its energy in the narrow visible band of light to which over atmosphere is almost transparent and for which our eyes have the maximum sensitivity. The sun, the earth and its atmosphere seem to have been specially created for us. More likely is the fact that we are a product of evolution suited to the environment in which we came to be. Furthermore just as in the case of water it is marvellous that our atmosphere is not completely and equally transparent of all the colours we can see. If it were we would not have had any sky. Or more correctly the sky would have been black! The beauty of the blue skies and orange sunsets would have been denied to us. Clouds would have created some spectacle across the black sky and the rainbows would have still existed - but no twilights and no blue skies. So our air is transparent but to our delight not uniformly and completely so. I think we live in the best of the possible worlds. I hope we realise it and not make it ugly and miserable through our actions. |
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NEW PRODUCTS & DISCOVERIES Robots that are part of family Japanese scientists are trying to make robots part of the family rather than automated servants — by improving their ability to communicate with their human owners, according to exhibitors at the Robodex 2003 robot fair in Yokohama. Honda has until now concentrated on perfecting the naturalistic movements of its 1.20-metre-tall and 52-kilogramme android, but is now interested in its capacity to interact with humans, a Honda representative at the fair said. The latest version of its ASIMO understands about 100 words and can recognise voices and faces. The robot has already found itself a place in the job market and works as a receptionist, for annual fee of about $ 165,000 at nine companies, including IBM Japan and the Takashimaya department store chain. Designed purely as an entertainment robot, Sony’s SDR4 is 58 centimetres tall and weighs seven kilogrammes. It can pick itself up if it falls, is capable of 1,000 different movements, can dance to 10 songs, use more than 20,000 words and have 200 pre-programmed conversational exchanges with its owner. It is not yet on sale, but Masahiro Fujita, the principal scientist at Sony Intelligent Dynamics Laboratory, hopes it will be soon.
AFP
Now a hypernova Two billion years ago, in a far-away galaxy, a giant star exploded, releasing almost unbelievable amounts of energy as it collapsed to a black hole. The light from that explosion finally reached Earth at 6:37 a.m. EST on March 29, igniting a frenzy of activity among astronomers worldwide. This phenomenon has been called a hypernova, playing on the name of the supernova events that mark the violent end of massive stars. With two telescopes separated by about 110 degrees longitude, the Robotic Optical Transient Search Experiment (ROTSE) will have one of the most continuous records of this explosion. “The optical brightness of this gamma ray burst is about 100 times more intense than anything we’ve ever seen before. It’s also much closer to us than all other observed bursts so we can study it in considerably more detail,” said Carl W. Akerlof, an astrophysicist in the Physics Department at the University of Michigan. Akerlof is the leader of ROTSE, an international collaboration of astrophysicists using a network of telescopes specially designed to capture just this sort of event. The collaboration is headquartered at U-M and funded by NASA and the National Science Foundation (NSF). Just recently, the ROTSE group commissioned two optical telescopes in Australia and Texas and were waiting for the first opportunities to use the new equipment. The burst was promptly detected by NASA’s Earth orbiting High-Energy Transient Explorer (HETE-2) but human intervention was required to find the exact location. |
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RESPONSE
This is in response to the write-up by S. Duggal entitled “HVFA concrete: waste to wealth” (March 6). The author has brought out an interesting paper in which it is brought out that in concrete up to 50 per cent of cement can be replaced by flyash and the product obtained is durable. Normally when we use PPC instead of OPC the replacement is about 25-28 per cent. The concrete with high flyash use is termed as HVFA and needs special mix and also special mixing plant — to the mix “common water reducing admixture” need to be added. Sometimes use of “superplasticise” is recommended. By doing so 50 to 60 per cent of the cement can be replaced by flyash. According to the author an economy of 5 to 10 per cent can be effected by adopting HVFA technique. Can this mode be adopted by us at present juncture when graded flyash is not available at any of the thermal plants in Punjab. At Ropar the unit installed for separately collecting enough flyash to meet the requirement of Ambujas for producing PPC. At Bathinda and Lehra Mohabbat, separating plants are yet to be installed. So we should be content with use of PPC which gives replacement upto 28 per cent instead of thinking of going in for HVFA. Recently, a few kilometres of concrete road has been laid at Ropar by Ambujas using HVFA mode. Results of that experiment need to be highlighted by the author so as to sell the new mode. Dr G.S. DHILLON, Chandigarh |
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Colour is the sensation we get when some components of the wavelengths our eyes are sensitive to get eliminated, reduced or amplified in what we sense as white light! I know this sentence that I have just crafted is a mouthful. This is intentional mischief. This is to highlight the fact that when we see we are doing a sophisticated but limited scattering experiment using very human selected set of colours, or wavelengths of electromagnetic radiation we call light. We are entitled to this bias. But we should recognise that water is not transparent at all wavelengths. X-rays and infrared do not travel well through water, nor does ultraviolet. It is just that the molecular and atomic structure of water is such that up to shallow depths it seems transparent to us. In actual fact it is not. If we were to look down into the depths of the ocean after putting our head in water we will not see very far. It is nearly pitch dark at the bottom of the ocean, because the light from above all gets scattered or absorbed. 
This year’s fair is dominated more than ever by humanoids — robots based on the human form, some of which can even walk on two legs, like Honda’s ASIMO or Sony’s agile SDR4-X II.