To space on a thin rope?
by Amar Chandel
THE weird idea of a space elevator has remained in the realm of science fiction for close to a century. But radical advances over the past few years in the construction of carbon nanotubes have encouraged a committed band of scientists to conclude that they can turn the fantasy into reality in less than 50 years.

UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL
CO2 is a poisonous gas. But why is it used for making soda? Can we use other gases to prepare soda?
CO2 is not that poisonous. It is a product of metabolism in which oxygen is used to convert the food we consume into energy.

To space on a thin rope?
Amar Chandel

THE weird idea of a space elevator has remained in the realm of science fiction for close to a century. But radical advances over the past few years in the construction of carbon nanotubes have encouraged a committed band of scientists to conclude that they can turn the fantasy into reality in less than 50 years.

Instead of going to the space in huge rockets, men and machines will be going up on a ribbon 3 ft wide and thinner than paper which will extend from the earth to nearly 100,000 km up in the sky. The cost of a space sojourn may be cut down to one-four hundredth of the present level and space may become as easy a destination as going to a neighbouring country. Cheaper, faster travel to other planets may be on the cards.

Celebrated author Arthur C. Clarke had predicted that this dream will come true about 50 years after people stop laughing about it. Well, the laughter has subsided and serious work is already afoot, although daunting challenges remain ahead.

Seventy top researchers met at Santa Fe last week to discuss the nuts and bolts of this futuristic scheme. They were not "imagineering" experts but hard-nosed scientists having the backing of NASA.

David Smitherman of NASA/Marshall’s Advanced Projects Office, was of the view that although construction was not feasible today but it could be towards the end of the 21st century.

"Even though the challenges to bring the space elevator to reality are substantial, there are no physical or economic reasons why it can’t be built in our lifetime," said physicist Bradley Edwards of Eureka Scientific in Berkeley, California. Supported by grants from NASA’s Institute for Advanced Concepts (NIAC) programme, he is convinced that the space elevator is practical and doable. "We could be launching tons of payload every three days, at just a little over a couple of hundred dollars a pound," says the scientist. Not only that, he thinks this can be done in less than 20 years.

The idea has been a non-starter all along because there was no material strong enough and at the same time light enough to be spun into a 100,000-km cable. The material on the wish list of the backers was jeeringly called "unobtainium". No longer. Carbon-nanotube-composite ribbon is the answer to their prayers. US and Japanese firms are vying with one another to produce tonnes of this now exotic matter within five years.

A carbon nanotube string half the width of a pencil is strong enough to support 41,000 kg of weight. A space shuttle will deploy a small cable back down to earth. This initial "string" will be actually a ribbon 1 micron (0.000004 inches) thick, tapering from 5 cm at the earth to 11.5 cm wide near the middle with a total length of about 100,000 km. Then a robotic "climber" will ascend the string while attaching a second epoxy ribbon alongside the first to make it stronger. This process will be repeated until a thick, usable, high-capacity cable is fashioned.

Once a vertical cable is put in place, simple physics will take charge. With a counterweight attached at the far end, the strand will stay taut through sustained centripetal force. Seven-tonne climbers, each the size of a semitrailer, will ascend the ribbon at 120 miles an hour, carrying payloads weighing as much as 13 tonnes. The climbers will be powered by earthbound free-electron lasers, which is the same tech behind Stanford’s linear accelerator. The lasers will be aimed at photocells on the climbers’ undersides, the photocells will power the climbers’ motors, and the elevator will go up. Edwards reckons it will feel like taking an elevator in a tall building. In a few hours, you’ll reach outer space, like Jack on the beanstalk. In two weeks, you’ll reach the ribbon’s end — one quarter of the way to the moon.

Payloads can be taken up the elevator to any earth orbit or, if released from the end of the cable, be thrown to Venus, Mars or Jupiter. These payloads (large satellites, cargo, supplies, etc.) can be launched every four days. Additional cables of comparable capacity could be produced every 170 days using this first cable and "shipped" to other sites along the equator by dragging the lower end of the cable. In 2.8 years the capacity of any individual 22 ton (20,000 kg) cable could be built up to 1100 tons (1 `D7 10^6 kg) or roughly the size of a shuttle orbiter.

A base tower will be constructed at an equatorial site somewhere in the eastern Pacific so that it is less vulnerable to high winds. An equatorial location is considered ideal because the area is practically devoid of hurricanes and tornadoes and it aligns properly with geostationary orbits, which are directly overhead.

Sending material on a shuttle into the cosmos costs $ 10,000 to $40,000 per kilogram. The space elevator could do so for about $ 100 a kg. And prices will fall drastically with greater use.

What about threats from lightning, meteors, space debris, low-earth-orbit objects, wind, atomic oxygen, electromagnetic fields, radiation and erosion of cable by sulphuric acid droplets in the upper atmosphere? The promoters say all these environmental hazards have been taken into account and workable solutions can be woven into the design.

It is estimated that the initial elevator could be built for approximately $ 40 billion, less than many of the national projects being taken up by the US and several other countries. The long-term returns could be staggering for the mankind. These would include inexpensive delivery of satellites to space, recovery and repair of malfunctioning spacecraft, large-scale commercial manufacturing in microgravity space, inexpensive global satellite systems, sensitive global monitoring of the earth, orbiting solar collectors for power generation and transmission to earth, solar system exploration, future mining of asteroids and even vacation facility in space.

Too good to be true? Far-fetched? Harebrained? Perhaps! But no futuristic idea should be dismissed out of hand because naysayers have had to eat crow many times in the past. We should remember that it was "scientifically proved" that rockets could not function in the vacuum of space; that trains could not run faster than 40 miles per hour without all air being sucked out of them and passengers dying; cinematography could never be commercially viable; the total demand for computers worldwide would be no more than three pieces and electricity was an absolutely useless invention.

By the way, Clarke has revised his estimate. He now feels that the elevator can be built about 10 years after everybody stops laughing.

CO2 is not that poisonous. It is a product of metabolism in which oxygen is used to convert the food we consume into energy. The gas forms, after oxygen and nitrogen, the most significant component of the atmosphere. But it must be remembered that CO2 dissolves in what to form carbonic acid. This might be partly responsible for the taste of sodas and colas that we like. Another reason for using carbon dioxide in aerated drinks is that under pressure a large amount can be absorbed in water or syrup and when it is continuously emitted after a bottle or a can is opened we get a pleasant fizzy tingling feeling. I think the soft drink makers discovered a perfect gas for imparting a generally pleasing sensation while drinking plain or syrupy water. I can think of no other gas that would do. It is possible that the fashion arose because some of the real natural mineral waters are also slightly fizzy and loaded with carbon dioxide. Nobody can claim that the habit of drinking colas is good for health. Like tea and coffee they also contain caffeine and, therefore, habit forming. It has been argued that colas are injurious to our teeth because of their sweetness and acidity — one could say that colas are little more than sweetened and flavoured carbonic acid, with some additional carbon dioxide under pressure to provide a fizz to our tongue. One can, of course argue that the habit of cola drinking is ‘not as deadly as several other things that we consume.

I think the answer should be obvious. Animals have to work hard to get their food. Physical exercise is obligatory. They did not accumulate excess fat. They also do not get many things that we eat only for taste or diversion. You must have noticed that even amongst humans the hardworking poor do not have potbellies.

Shooting stars are not stars. They are called meteors. If a bit of dust or a rock moving about in the interplanetary space happens to encounter the earth’s atmosphere the collision is very violent because the relative velocity can be very high. The frictional force heats up the material with emission of bright light and evaporation of the material before it reaches the surface of the earth. A large number of such meteors hit the earth every day. Occasionally a big rock comes in that it is not completely vapourised in the atmosphere. Its remnants can hit the earth and cause damage. In the history of the planet some very large impacts of this kind must have occurred and caused a major change in its morphology as also on the evolution of life on the planet.