Winter 2003

Editors Bit

I know it’s hard to believe, but I have now been the Editor of MIRA for 10 years!   Where has the time gone?   The first MIRA I read was way back in Oct 1985 when I started to come regularly to the C&WAS meetings in the lecture theatre of the Butts Technical Collage.  Way back then the editor was Richard Barrett and almost immediately he handed over to Vaughan Cooper.  Vaughan’s first MIRA was February 1986, Number 12 and he continued with the editorship until May 1990 Issue 28.  There then was a gap of three MIRAless years before a committee decision was made to resurrect the paper; and yours truly offered to edit it on my Acorn Archimedes 2Mb computer with 20Mb HD and with my 16 pin Panasonic printer!  Luckily I’d recently bought a superb DTP program called Impression for the Acorn and had got to know how it operated before I offered to be editor.  I managed to get my first issue out, MIRA number 29 in February 1993 with Vaughan’s help and now, here we are at number 63 ten years later!

So what has happened in the last ten years?
10 years ago the universe was a different place and a lot smaller.  Since then Carl Sagan, one of the best popularizes of space and science has died and Patrick Moore is now a well earned Sir.  In the last ten years we have had the comet Shoemaker-Levy 9 slam into Jupiter (Jupiter won), seen one of the largest comets ever, Hale-Bopp and one of the closest to pass Earth, Hyakutake.  We have had wonderful pictures from the moons of Jupiter as the Galileo spacecraft has swung past on its long orbits around our systems largest planet and we have had the Pathfinder pictures from the surface of Mars.  And what about that little 6 wheel rover, the Sojourner, moving over the dusty surface looking at the rocks?
Other probes didn’t go as planed, ESA’s new Ariane 5 exploded with the first Cluster mission onboard and NASA had two missions fail at Mars, the Polar Lander and Climate Orbiter.  We almost lost the SOHO spacecraft and all the wonderful views of the sun and corona, we’ve seen the first closeup pictures of a few of the asteroids, even landing on Eros.  Achievements and disasters will always be with us.
The maps of Mars have been redrawn with all the new data from Mars Global Surveyor and the recent Mars Odyssey spacecraft and water is now a certainty with the discovery of large hydrogen deposits just below the surface detected with both a gamma-ray and a neutron spectrometers.  The cause of the numerous gullies and channels seen in high resolution for the first time is obvious.  A Martian meteorite, ALH84001 startled the world with the possibility of life of sorts found in a fossilised state.  Not only Mars but our own Moon now appears to have large amounts of water at the poles, found by the DoD Clementine orbiter and confirmed by the first NASA moon probe in 30 years the Lunar Prospector.
We have also found over a hundred large planets orbiting other stars, also the count of moons in our solar system is now over the 100 mark.   Black Holes are now suspected to lurk at the centre of every galaxy and the first true Black Holes are confirmed in a few binary star systems
Gamma-ray bursts were almost unknown and not understood and the afterlight of the explosions was not seen until recently.  The Kuiper Belt had not been detected and the hoards of trans-Neptunian objects not charted.  The universe had not yet speeded up its expansion with the latest data from the High-z Supernova Search team and the most distant objects where a lot closer than today.  “Dark energy” that seems to be pushing the galaxies apart was unknown; so what is this 65% of the universe?  The Cosmic Microwave Background Explorer Satellite had just published its results ten years ago supporting the Big Bang theory.  The Hubble Deep Field, with an exposure of a week showed that each square degree of sky holds millions galaxies.
It was just ten years ago that the first Shuttle mission to the telescope cured the mirror problem and gave us sharp views at last; during the last ten years the Hubble Space Telescope has been upgraded three times and now gives sharper pictures then its original design specifications!  The telescope has refined the Hubble Constant to around 78 km/sec/Mpc, this leads to a smaller, younger universe.  All this is largely due to the tremendous advance in CCD technology and the astronauts training for weeks in weightless construction techniques before changing almost all the telescope systems over the years.
In the last 10 years MIRA has, I think, improved; a Mr Mike Frost sent in an article for my first issue about Flagstaff and the outer planets, since then he has written 47 articles and stories for MIRA.  It would have been a much poorer paper without stories of his mate Clive and the Dangerous Sports Club.  Also his stories on tides, rainbows, astro history and his trips from around the world chasing the Moon’s shadows and watching meteors and aurora.  All excellent stories, but don’t forget all the other contributions: Vaughan Cooper’s star maps and drawings, Pam Draper’s pages and who could forget Steve Payne’s History of Astronomy!  Paritosh Maulik’s articles on gamma-rays, X-rays and Quasars as well as the European large telescopes in Chile.  Clive Rogers Dark Sky articles and all the other folk who have over the years have helped to keep the star MIRA bright and shining.
A BIG thankyou to you all.

Ivor Clarke, Editor

The Green Moon Revisited

By Ivor Clarke

A note from 2095AD

On clear nights when the moon is visible in the evening skies before the first quarter.  When the terminator as not yet reached the centre line of the moon and the bright sunlight has not swept across its centre.  And also in the morning skies after the third quarter when the terminator is moving away, leaving the centre dark again, you may with a small telescope see a tiny spark of light near the centre of the moon.  It stays there without moving, like the top of a giant mountain jutting into the sunlight from the moons surface.  But it cannot be a mountain, no mountain is that high, for it does not grow brighter or dimmer with different degrees of sun light playing on it.  It is also a new phenomenon and was not visible to earlier moon watchers who would have been very puzzled by its strange behaviour of a steady light at that position.  It isn't the top of a tall mountain or a TLP happening, it's the man-made Lunar Lift Transit Station hanging in the Earth's gravity well; and sometimes if you are lucky, you may catch a glimpse of another much smaller speck moving near it . . . 

Many moons ago, way back in the New Year issue of MIRA 39, 1996, I wrote an article called A Green Moon?  In the article I developed the idea of protecting the Moon's fragile environment from the onslaught of the rocket engines of the future and the many moon landings which will occur as the work goes on to build the lunar bases from which we will then reach out to explore Mars and beyond.  This expands on the original paper and brings things up to date with developments and ideas.

The Space Elevator

It was back in 1979 when Arthur C Clarke wrote his book "The Fountains of Paradise", about the project to build the first space elevator, or as he called it, "a bridge to the stars", in the middle of the 22nd century.  The idea was that you use a super strong filament from the ground up to a geo-stationary satellite.  With both ends anchored, the Earth end on the equator, high as possible on a mountain top to avoid weather problems; while the outer end will be in geo-stationary 24 hour orbit.  Then capsules, both cargo and passenger carrying, can be propelled along the track up into space to the geo-stationary satellite all powered by power stations on the ground.  From then on getting into space will be the longest elevator ride in history.

To travel up the filament to the geo-stationary space station 36,000kms above the equator in a capsule would take most of a day, but once outside the Earth's atmosphere, speeds of several thousand miles a hour could be reached by the capsules propelled along by magnetic linear motors.  During the long climb up the cable, passengers would feel the pull of the Earths gravity slowly diminish as they got higher and higher, until near the top, in geo-stationary orbit, they are weightless.  The top assembly will be just away from this point, further out into space to pull the cable taut (just as a stone whirled around your head on a length of string does.  So upon arriving in the station passengers will feel a little weight return as they are travelling faster than necessary in a higher orbit than necessary to maintain geo-stationary orbit, so centrifugal force will be pushing them outward from Earth, but the station is held by the cable to balance the weight of the structure.  The Earth will be up and space down! 

Once this assembly was completed, the cost of getting into space would be minimal compared with todays costly rocket boosters.  The capsules would be similar to a train running along an upright track instead of a horizontal one.  Another major benefit would be that all of the pollution from rocket exhaust fumes in the upper atmosphere is stopped.  So the befits of the project would be a greatly increased availability to space and the other planets without the pollution and cost of todays rocket launches.

When I wrote the original article, there was no material available, or in sight for that matter, that was strong enough and light enough, to stand the weight of such a large structure.  This has now changed.

New developments

"Keep your mind open and think big.  The space elevator concept is based on a structure stretching from the Earth's surface, up through the atmosphere, all the way to geo-stationary Earth orbit — 22,300 miles (36,000 kilometres) high above the equator."

These words are from a web site describing the space elevator, how it would work and how to build it.  Workshops on space elevators have been held in 1999 at NASA's Marshall Space Flight Center in Huntsville, Alabama, and in March 2002.

"The outcome of the gathering was uplifting, in more ways than one," said David Smitherman of Marshall's advanced  projects office. "The idea is still futuristic... 50 years away probably.  But it does look like new high-strength materials may make possible the building of a space elevator."

Dr. Bradley Edwards, a physicist at Los Alamos National Laboratories in New Mexico, has recently completed research on lengthy space elevators thanks to a NASA Institute for Advanced Concepts grant.  "The space elevator appears much closer to reality than has been suspected in terms of available technology, cost and schedule," Edwards said.  But there is a big problem to overcome.  What can we make the cable out of?

That problem has kept the idea in the realm of the science fiction writers for the last 40 years.  That changed in 1991, thanks to a Japanese researcher Sumio Iijima, an electron microscopist for the NEC Corporation.  He is discoverer of what are now called nanotubes.  Additional research has shown that carbon nanotubes possesses incredible properties, one of those attributes is having a  tensile strength 100 times stronger than steel at one-fifth the weight. Now we have a carbon-nanotube-composite, which will be a material in which the fibres are layered and twisted to form a rope or filament ribbon hundreds of kilometres long.

"The major hurdle is the required carbon nanotubes, but that's getting closer each day."  Edwards thinks an operational cable to space can be installed within 10 to 20 years.  "There doesn't seem to be a whole lot of hurdles," Edwards added. "It looks like there are viable solutions to every aspect."

"The making of carbon nanotubes is moving very quick," said Hayam Benaroya, a professor in the Department of Mechanical and Aerospace Engineering at Rutgers in Piscataway, New Jersey. "We're moving from the scientific stage of just developing them to actual commercial entities producing them in ton-like quantities," he said.

Several new techniques need further development including:

Fully developing carbon nanotube material that exhibits strengths 100 times stronger than steel.

Continue evolving space-tether technologies to gain experience in deploying and controlling long structures in space

Further work on high-speed electromagnetic propulsion for accelerating vehicles along a track.

Growth of government and industrial infrastructure in space from low Earth orbit to geo-stationary orbit that would benefit from utilisation of the space elevator.

A figure of around $10 to $20 billion dollars is being talked about for building the first elevator from Earth into geo-stationary orbit and the satellite platform.

A Bridge to Space

To build the elevator the designers would go back to the earliest days of bridge building.  First shoot an arrow over the river or ravine with a thin string attached, then thicker ropes can be pulled over until the ones suitable to build the bridge with.  In this way the strength needed for the bridge is increased in stages, each step requires the establishment of the former to proceed with the plan.  In a short time tons of material can cross.

For this project one of the space shuttles would take the place of the arrow and take a reel of filament and a upper stage motor into low earth orbit.  This is then released and the stage motor fired to reach geosynchronous orbit at 21,700 miles (35,000km) altitude.  From there a small projectile is fired to the ground pulling the filament down off a bobbin.  After attachment to the Earth Station end, this is then enlarged with other filaments and the geo-stationary point increased in weight and moved further out so the system balances the loading weight and there is an upwards pull on the elevator from the outwards centrifugal force of the space station.  This is a little further away from Earth than would be the case for a freely orbiting platform, but because it is rotating with the planet at about 10 kms per sec keeping station over one spot, it will counterbalance the weight of the elevator because it is travelling to fast for its height.

"If budget estimates are correct, we could do it for under $10 billion.  The first cable could launch multi-ton payloads every 3 days.  Cargo hoisted by climbers, be it fragile payloads such as radio dishes, complex planetary probes, solar power satellites, or human-carrying modules could be dropped off in geosynchronous orbit in a week's travel time," Bradley Edwards said.

So once the elevator is built it will be possible to travel up into space cheaply and from there on to the Moon and then, at last, the planets and moons.  And why stop at one?  Once the first elevator is up and running with proven advantages other countries on the equator will need their own elevators to improve their status and wealth.

The First Moon Bases

The Moon is an obvious place to build humanities first colony, it is within easy reach of Earth so emergencies like medical aid can be helped with a few days, unlike Mars where help could be 18 months away.  If we can learn how to live safely and survive on the Moon then we can travel with that knowledge further afield.

To build a permanent lunar base will require dozens of lunar landings, bringing in all the necessary equipment from Earth to start the mines to extract the minerals to build the bases.  It now seems that the best place for the first base will be at one of the poles of the Moon where billions of tons of water may lie frozen in the dark, sunless valleys and craters of the Moons polar regions.  This fantastic resort was first detected by a gamma-ray spectrometer onboard the USA DoD Clementine lunar orbiter in 1994.  The craft detected large hydrogen deposits just below the surface in the deep southern polar craters.  It was confirmed by NASA's Lunar Prospector orbiter using both gamma-ray and  neutron spectrometers four years later that both poles harbour vast areas of hydrogen deposits.  This gas must be from frozen water deep underground.

The Moon spins on its axes within 1.3° degrees of vertical to its path around the Earth and Sun.  Therefore the Sun will forever be on or below the horizon for both of the pole regions during all of the lunar days.  Any water splashed onto this area would freeze in seconds in a temperature of -200°C and would stay there for millions of years.  The ice most likely would have come from the thousands of comets which have crashed into the Moon (and the Earth) over the 4.5 billion years since its formation, depositing water over its surface.  Most of it would have soon boiled off into the vacuum of space in the heat of the Sun, but any which was deposited at the poles would just have frozen and got colder.  The ice will be in the form of a dirty frost, mixed in and covered over by the rain of micro-meteorites scattering the surface bracca in ejecta splash. 

So most likely two bases could be started, one at each pole.  A Russian / Chinese one and a NASA / ESA one?  With a ready supply of water available to drink, the first explorers would not have to carry much from Earth.  With the supply established, it could be split with a simple process into oxygen and hydrogen, air to breath, water to drink and fuel to burn in rockets!

The Lunar Bases

One of the main problems with building a large Moon bases will be trying to keep as much as possible of the surface of the Moon pristine and unblemished for future science and not covered in a layer of soot from the hundreds of landings and take off's from the rocket exhausts.  Exhaust emission particles of a sooty like nature are likely to stay on the surface as there's no weather to carry them away and once on the Moon will be hard to remove with out making even more mess.  This has been proven many times here on Earth.

Once the bases are manned by a semi-permanent crew, it will then be possible for them to start exploring the surface in earnest.  How many will there be working there?  Well like the South Pole Antarctic base the numbers will increase as the technology improves and more space and facilities are provided in the under ground base.  To build a base on the surface is to increase the risk of exposure from radiation, cosmic rays, solar flares as well as meteorite strikes.  A covering of a meter or so of lunar soil material would provide the necessary protection for the staff from most radiation and the extreme temperature range on the surface.

The Moons Atmosphere

The building of a base will require an enormous amount of effort and time.  Every landing and lift off adding a measurable amount to the extremely rarefied gasses in the lunar atmosphere, mostly of sodium and argon atoms along with a trace of gasses from the solar wind mixed in with those escaping from the lunar interior at a density of around 100,000 per cubic centimetre.  To us this is a high vacuum, when the air in every cubic centimetre between this page and your eyes contains over 20 billion billion molecules!  It is so thin that the Apollo LEM's exhaust gasses where able to spread all across the Moon before dispersing.  Each Apollo mission increasing the lunar atmospheres mass by 10 tons — or 30%!  This would have dispersed within a few weeks as the molecules decay by sunlight ionising their atoms, stripping off their electrons, so escaping in the low gravity of the Moon.  Some gas results from solar ultraviolet light hitting the surface liberating atoms and molecules, lunar quakes also produce gasses which add argon, radon and polonium in small amounts.  Some areas of the Moon are suspected of discharging small amounts of gas occasional, these are watched for with interest by earthbound lunar observers.

Even more gasses will be added as work starts on the lunar bases.  It is calculated that once the mass of gas released starts to exceed 10,000 tons a day, it will then start to shield itself from the effects of the Suns ionising radiation.  Thus the Moon will then have a thin atmosphere which will be difficult to remove and could start to cause problems.  This amount of gas and the chemicals released into the atmosphere by building the base will be just what astronomers want to avoid.  A clean environment which gets polluted quickly is bound to soon cause a major predicament to the telescopes.  The gasses will tend to deposit themselves on the super clean mirrors of the next generation telescopes.  What can be done to cut the deposits and clean up the Moon?

Elevators From The Moon? 

As we saw above, the Moon will become polluted with exhaust gasses if nothing is done to stop it.  So if its possible to build an elevator from Earth to space why not build a LUNAR ELEVATOR?

It is not possible to build one using the same principles as the Earth elevator because the Moon does not spin round quickly like the Earth in 24 hours so has no geo-stationary point.  The Moon only rotates once in 27.32 days, so if you are in orbit about it, you are going much to fast to stay over one point of the surface.  If you move further away to try and go slower, the gravitational forces of the sun and Earth will disrupt the path.  So it's not possible to orbit the Moon slow enough to build an Earth like elevator.  So why not just drop into the Earths gravity well?

Between the Earth and Moon there is a gravitational attraction, this is what keeps our satellite in orbit.  But around 80,000 kms from the Moon there is a point of balance in the pulls of the two bodies, on one side of this point and the Moon wins, the other, the gravity of Earth takes over.  Once a spacecraft passes this invisible boundary; its velocity will then increase as it falls towards the other body, gaining speed the closer it gets.  Most Lunar probes and the Apollo missions passed this boundary at just a few hundred kilometres per hour to crossover into the others gravity well.  Because the Moon's orbit is elliptical, the exact distance of the balance point will change during the month.

This is where the lunar elevator would lie, just into the gravity pull of the Earth.  Once there it would not fall back to the Moon or be in danger of plunging to Earth as it is tied to the Moon by the elevator ribbon.  The effects of the Moons orbit, the pull of the Sun and the libration effects of the Moon will cause the platform to swing slightly in a figure of 8 during the lunar month.  The further into the Earths gravity the platform rests, the less this effect will be.

This position is not like one of the Earths Lagrangian points where a spacecraft can balance in the pulls of the system.  It is an unstable area with the gravitational fields of the Sun, Moon, Earth and Jupiter all at work, there is no stable Lagrangian points within the Moons orbit.  The best known one at present is the L1 point, some 1.5 million km sunward where the SOHO observatory swings in a shallow oval orbit keeping watch on the Sun.  The L2 point is in the opposite direction, 1.5m km away from the Sun and Earth.

So if you can secure the platform in that position, why not use two elevator ribbons that reach from both north and south poles of the Moon up to the station?  Not only would the stability of the platform be increased with both tethers meeting together but it also help to damp out the north-south movements and would provide an increased safety factor.  Both elevators would start out from near the poles, anchored into the Earth facing wall of a crater, were the Earth would lie low on the horizon.  The northern crater Gioja at 83° N is 42 km in diameter and close to the polar craters while in the south lies the crater Malapert B at 78° S.  This southern area of the Moon is poorly mapped and a different location may be needed.  The ribbon of material would head out straight across the lunar floor of the crater and off into space as the ground dropped away under it.  The Moons diameter of 2,700 miles (3,476km) means that the horizon is much nearer than on Earth and so bends away quicker.  The passengers starting out for the Moon from the platform would head down towards the Moon from the platform and arrive on the lunar surface horizontal!

During the lunar day of 27.32 Earth days, the position of the Earth will swing about a point in the lunar sky about 3 times its diameter as the Moon orbits the Earth.  The Moon orbits in an elliptical path which various between 356,410km at perigee to 406,679km at apogee, with a mean distance of 384,392km.  The Moon rotates at a constant speed, so as the Moon moves more slowly at its apogee its rotation catches up and overtakes its position if the orbit were circular.   Likewise when the Moon is closer to Earth it moves faster in its orbit and the rotation drops behind its norm.  So from the Moon the Earth nods from side to side about 7° and so will be visible from about 60% of the Moon's surface.  There is also a small amount of north / south libration caused by the plane of the Moon's orbit being 5° away from the ecliptic.

Because the gravitational pull of the Moon is only one sixth that of Earth all of the mechanical stresses on the structure will be so much less than the Earth elevator.  Indeed most of it would be in a near weightless environment with only the low sections of it under lunar gravity.  Also, unlike the Earth Elevator, it would have the added advantage of not being in the firing line of any orbiting space junk!  The amount of material orbiting the Earth in low orbits is a major problem for any elevator project.

Building the Lunar Station

The Lunar platform could be assembled in low lunar orbit, by shooting up material from the lunar surface using a rail gun or linear accelerator.  When completed, it would slowly be moved into higher orbits, then put into an elliptical orbit which would carry it further away from the Moon.  Two small rockets would be fired from both the Moons poles simultaneously, unwinding the filaments behind them until they reach into the balance point between the Moon and Earth.  There they are joined and built up into the strength needed before the main platform arrives. Then using a series of small rocket burns the main platform is pushed into ever higher lunar orbits until it just reaches the point where the ribbons meet and is manipulated into place.

Once it had been fastened securely, the platform could be gently lowered towards Earth so as to pull the complete system taut.  How much the platform intrudes into the Earths gravity will depend on the weight of the station compared with the weight of the connecting material and the weight of the capsules running up and down the cables.  Two lengths of cable 80,000km long will weigh many tons even in the low lunar gravity.

With the platform resting near the top of the Earths gravity well, the pull on the station would be very weak with the crew and passengers weighting just a few grams each.  But there would be an up, the Moon, and down, the Earth.  Things would drop to the floor, albeit very slowly and objects would stay where you put them!  Also the showers would work and water would stay in the glass.  The station would hang there just over the invisible boundary, the edge of the gravity null point, between the conflicting pulls of the Earth and Moon.

From the lunar platform you can travel to either of the Moons poles or Earth without using hardly any energy.  To travel back to Earth you just have to let go and gravity takes over.  Two and a half days later and with an atmosphere graze to reduce speed by 5km per second necessary to mach the orbital velocity of the Earth Space Station and  rendezvous with it.  You are back home.  To the Moon and back with just one small rocket burn out of LEO.  Is this the bargain of the century?

As we have seen two tethers stretched from the poles would hold the platform more securely than just one.  But it could provide other help too.  For instance in Clarke's book "The Fountains of Paradise", the hero, Dr Morgan, is given the job of building an elevator on Mars.  He suddenly realises that there is a small problem about 25km in diameter, Phobos.  This small moon orbits Mars in 7hr 39.5min, 5,870km above Mars, so from a point on the Martian surface Phobos passes over head every 11hr 10min (Mars has turned in the meantime so it has to catch up with the point on the surface).  Deimos is further out at 20,000km from Mars and orbits in 30hr 21min, just above the geo-stationary altitude.  So every eleven hours Phobos would get near or hit an elevator if it was constructed from the equator.  If a twin elevator approach was taken and the elevator went near to each pole then Phobos would travel harmlessly through the legs of the elevator far below.

Science on The Moon

Very soon after the establishment of the permanent bases, work would begin building observatories for both optical, IR, UV and radio astronomy.  Also don't forget, a radio telescope built away from Earths view would have no interference at all from the din of hundreds of TV and radio stations on our planet.  This may be the only radio quite place in our solar system for a very long time!

Not only is the sky totally black, but the entire micro-wave spectrum is visible, from gamma to long radio waves, not like on Earth where the atmosphere soaks up many of the wavelengths.  As a bonus, the lunar surface is exceptional free of lunar quakes and surface movement to disturb the pointing accuracy of the telescopes.  With only one sixth the gravitational pull compared with Earth based instruments, many of the problems of large mirrors flexing under the pull of gravity won't exist.

One of the best sites in the solar system lies just over the far side of the Moon away from Earths view.  The amount of light cast by Earth will vary throughout the lunar day, from almost none at "midday" on the Moon, when the night side of Earth would be facing the Moon, to full Earth shine; which is about 50 times brighter than full Moon shine on Earth at lunar "midnight".  The Moons surface reflects less than 10% of the sunlight falling on it, while the clouds of Earth reflect over 90%.

The seeing from the lunar surface is superb, the nights are long and the stars in the sky only move slooowly.  It would be possible to look at a portion of sky for up to 14 days continuously!  So no serious astronomy base would be built on the near side of the Moon, for there will be the Earth, 4 times larger than the Moon in our sky blocking out a lot of the lunar sky.  Also during the lunar night the Earth shine will be at its brightest with the Sun shining on the far side of the Moon and on the side of Earth facing the Moon.

Will it Work?  Is it Possible?

Eric Westling, a Houston, Texas - based consultant on the space elevator, is bullish on the concept.  Spending billions on a space elevator is small change for a big purpose.

"Other than the invention of some Buck Rogers engine, the space elevator is the only system for accessing space that is subject to the economics of scale.  Its a true return on investment enterprise.  The cost of space travel has to become an incidental part of the overall cost of what we're trying to get done," Westling has said.  "It will change the world economy.  Its worth what ever it costs to put it up.  An initial elevator, is sure to give birth to even larger systems, capable of handling larger loads of up and down traffic.  I'm looking at a business plan that shows some investor could triple his or her money in about 6 years, and the initial investment could be as low as $5 billion,"   Bradley Edwards added. "One thing to keep in mind.  Building the impossible is done here on Earth routinely, take for instance the $13.5 billion Millennium Tower envisioned for Hong Kong Harbour.  This incredible skyscraper would be 170 stories tall.  Elevator traffic within its walls is estimated at 100,000 people per day."

Edwards also points to the Gibraltar Bridge project.  It would span the Straits of Gibraltar, linking Spain and Morocco at a projected cost of $20 billion.  The bridge would use towers, twice as high as the worlds tallest skyscraper.  Roughly 1,000,000 miles (1,600,000 kilometres) of wire cables would be utilised in the project.

"I think those projects are a lot harder than what I'm talking about," Edwards said.

A lot of work is to be done before it is built such as, exposing carbon nanotube samples to simulated space plasma is slated in the near-term. Wear and tear tests on elements of the space elevator climbers are under review.  Also the effects of lightning, wind, the degrading effects of atomic oxygen on the cable, radiation, the wearing down of the ribbon by sulphuric acid droplets drifting in the upper atmosphere .— all these and other uncertainties are being dealt with.  Then there's the worry of meteoroid hits, pings from the shooting gallery of space junk and collisions with satellites.  Even the threat of a terrorist attack on a space elevator is being assessed.  So too are public health risks of using tiny carbon nanotubes, so ultra-small in size that the effects of breathing the substance into the lung calls for detailed study. Research in these areas, is ongoing and so far no killer problems have been identified to date.  Soon an Earth-tethered high altitude balloon experiment is scheduled to judge the viability of key elevator components.

"We're getting our team together. We believe we can have a viable, usable system in the reasonable future," Edwards concluded.

An observation made in the 1970's by Arthur C Clarke, when asked if the space elevator would ever be built, he replied: "The space elevator will be built about 50 years after everyone stops laughing."

Space Elevators

The first time most would have heard of this idea of using an orbiting geo-stationary platform and lowering down a cable to the ground was in Arthur C Clarke’s book The Fountains of Paradise published back in 1979.  Clarke was not the first to think up this idea, as he acknowledges in his book.  A Russian by the name of  YN Artsutanov in 1960 thought up the idea of using a long cable from synchronous orbit to lift heavy freight and passengers up to a station.  Since then it has been "invented" several times by different people, obversely its time had come.  In Robert A Heinlein book, Friday (1982), an Earth elevator, the Kenya Beanstalk, is mentioned.  Clarke uses the same idea later in another book, The Songs of Distant Earth (1986), but this time to winch up large icebergs to use as dust protection on a interstellar starship travelling at a quarter light speed.  So by then the idea was common in SF.  Making a rope or cable 36,000 kilometres long is no joke, and what do we make it out of?  The very best climbing rope would snap under its own weight after a few 10’s of kilometres had been fed out.  So would steel cables and even Kevlar fibre woven into a rope would not make it from orbit down to the ground.  So what can it be made of?  Recently a spiders web material has been made synthetically in a laboratory.  Also pure carbon can be made into long strands and is used in all manner of things from fishing rods to tripod legs to replacement bones to aircraft wings.  Material science is advancing rapidly, soon we will have a material strong enough.  The material used in Clarke's book was a continuous pseudo-one-dimensional diamond crystal.  Well it sounds strong enough!  But the real material would need to be light, easily made, conduct electric current, not suffer from Earth's atmosphere or from the effects of space or radiation or ultra violet radiation from the sun...  So is the latest carbon nanotube material going to be the one to makes the dream come true?  It exhibits strengths 100 times stronger than steel but will it work?

Why Don't X-rays reflect off an optical mirror?

An answer to your question by Darren Baskill

Sent by Steve Payne

A question asked at a meeting in the summer by Steve Payne was given an incorrect answer, the speaker 

E-mailed Steve with the correct answer and a drawing to explain the effect...

Hi Steve,

I really enjoyed giving that talk on Friday - you've got a good witty bunch down there!  I think it was you (?) who asked me about why X-rays reflect off the Moon and not off an optical mirror (if it wasn't, please read this out at the next meeting, or pass it on).

I was barking up the wrong tree - I'm sorry about that!  But I was speaking to Doug about it in the car on the way back to Leicester.  Please take a look at the attached picture below (where the circles represent atoms).  Optical light photons (with respect to X-rays) are low energy, and hence have a larger wavelength.  Have you heard about wave-particle duality?  It's just the 80 year old theory that photons of light sometimes behave as a wave, and sometime as a particle (with a "size" of order of the photon wavelength).  I try to think of photons as snooker balls!  It makes it all easier to understand!

An optical photon of large wavelength will hit an atom in the surface of 

the mirror and get reflected.  A smaller wavelength X-ray photon would just penetrate into the mirror, between the atoms, get scattered in the mirror, and then get reflected in a random way.  I guess that to answer your question, optical mirrors do reflect X-rays, but in a random way and without focusing them - as does the Moon.  This is because the X-rays can penetrate the surface layer, preventing focusing.   The Moon manages to reflect (by chance) only a small fraction of the X-rays in our direction - but the Moon is so big it is intercepting a large number of X-rays, and so a "small fraction" of "a large number of X-rays" end up coming back in our direction which is clearly visible to modern X-ray telescopes.  For optic

al light to get focused, all the optical light is reflected of the first layer of atoms in the mirror into a point.  An incoming X-ray to be reflected must hit the edge of a mirror at a very acute angle (as used in X-ray telescope mirrors) is more liking to hit a surface layer atom and be nudged into focus - it won't just be absorbed into the mirror like a square-on optical mirror or the Moon.

Hope that explains it!  Hope to meet you again sometime,

Darren Baskill

The Extra Mile
By Mike Frost

Our intrepid explorer is once again in darkest Africa chasing shadows...
Looking for that syzygy moment.

For the solar eclipse of December 4th 2002, I returned to Southern Africa with Explorers Tours.  I had originally intended to observe this eclipse from Australia, but by the time autumn came round I had used up most of my holidays, and I felt that Oz required a substantial visit to do it justice.   The shorter African trip, by comparison, managed to include several of my favourite bits of the continent; a couple of days in the Ezulwini valley (Valley of Heaven) in Swaziland, a safari around the Kruger Park in South Africa, even a passing visit to Middelburg, where I worked for three months in 1998.  So Africa it was.  I joined a coach load of 42 meeting in Johannesburg.
The eclipse track had contrasting features in the two continents.  In Africa we would have a morning eclipse, lasting up to 90 seconds in length, whereas the Aussies would have to make do with only 24 seconds of totality, with the Sun very low in the sky close to sunset.   However, the one aspect that weighed against Africa was the weather; South Australia had almost guaranteed clear skies, whilst the rainy season was forecast for Africa. Explorers Tours judged that weather conditions were likely to be best on the eastern coast, which meant that we were going to observe from Mozambique.
So, on Tuesday 3rd December, we set off north from Maputo, capital of Mozambique.   Within a mile, we got a taste of justice Mozambique style.  We were stopped by three police: two lackeys and a chief, who came up with a spurious traffic offence.  Guy, our driver, argued with the police chief whilst Kevin, the local agent, retired to the coach to prepare a "Christmas present" for the police.  A fifty rand note was enough to secure our release, but we almost blew it big time when someone decided to video the proceedings.  It isn't a good idea to film your attempts to bribe the local police and the cameraman had to be rapidly dissuaded from landing us in really hot water!
Once we cleared the city, the atmosphere calmed down. Mozambique is a desperately poor country, which suffered terribly in a civil war during the 80s and 90s, but today there is a real sense of a country on the mend, ripe for development and investment.   Even the awful floods of 2000 didn't shut the country down completely, although it was clear that they destroyed a lot of the infrastructure, for example the roads across river flood plains.  From our point of view, the scariest aspect of the country was the huge number of landline's left behind from the civil war; the floods had been redistributed many of these randomly.  We saw a few amputees who had presumably been maimed in this way.  But perhaps Mozambique's most immediate problem was the insidious menace of HIV / AIDS (or SIDA, as it appeared on the publicity banners).  The red ribbon symbol was painted on trees and walls everywhere along the route.
The centreline of totality crossed the Mozambique coast just north of the regional capital of Xai-Xai (pronounced 'Shy Shy'), which lies just north of the great grey greasy Limpopo River, 300 km along the coast from Maputo.  As we crossed the Limpopo, I tried to take a picture, and was dismayed to find one of my cameras jammed.
We were to spend the night before the eclipse at Xai-Xai beach, a few miles out of town. Xai-Xai beach is a resort, popular with South African tourists and on December 3rd it was packed.  Campissimo Xai-Xai was full of tents, pitched by eclipse fanatics and beach bums.  We were greeted by the worst marimba band in the world, who serenaded us with tuneless melodies.  I went back to the coach to try to fix my camera.
We were housed in several very dirty beach houses, sleeping six to a room, with no air conditioning.  We had a scented candle to help drive away the mosquitoes, but it didn't seem to deter the bugs.  When I first tried to get to sleep a beetle dropped from the thatched roof straight onto my face.  Throughout the night, I could hear the high-pitched buzz of a mozzie in pursuit of a meal.  Despite the heat I pulled as much exposed flesh as I could beneath my blanket, and tried to get some sleep.
Somehow or other I managed to doze for few hours prior to our 4.45am wake up call.  We aimed to be off the campsite by 5.30, heading north in a fleet of minibus-taxis towards the centreline.  Nobody overslept, so departure was on time.  The weather was partially cloudy but our spirits were high because we could see the Sun.
The taxis headed north on the coastal road, then veered off towards the beach on a very bumpy dirt track.  I picked up a bump on my head by failing to spot the worst of the ruts.   At the end of the track was a very surprising sight; a modern hotel, concrete freshly painted white, sitting in front of the beach.  A second glance showed that the hotel had no residents, and despite the fresh lick of paint, hadn't seen any customers in years.  It turned out that Chongoene beach hotel, built in the sixties, had ceased business in 1994.   There are moves afoot to re-open the place; but on eclipse day, it was empty.
Chongoene beach was, however, an ideal location to view an eclipse.  In front of the hotel was a terrace, with cracked floor and tables, ideal for setting up tripods and telescopes.  In front of that was a lovely sandy beach, for those who wanted to enjoy the eclipse in a more relaxed manner.  In front of the beach was a warm lagoon, created by a reef of rock a few meters offshore; and beyond the reef the Indian Ocean stretched out to the horizon.  The shadow of the Moon was going to come racing over our heads from inland, shooting off towards Australia and the sunset finale.
The less serious observers relaxed on beach towels, the anoraks began setting up their equipment.  We had one telescope, several video cameras and a variety of other photographic equipment.  The family next to me had set up a pinhole experiment, cunningly utilising a music stand.  I contented myself setting up a telephoto lens on my remaining camera.   I wasn't especially interested in photographing the partial phases, and so I had not come equipped with filters.  There were other people on the beach, mostly tourists (curiously, mostly Australian, perhaps hoping to catch what their compatriots in South Australia missed) and a few dignitaries from Maputo, but very few locals.
We had synchronised watches the previous night, and once in place we took an accurate position from a GPS system and calculated local timings for the eclipse.   We discovered that we were several miles south of the centre-line, and would only have 75 seconds of totality, 15 seconds short of the local maximum.  We had two German observers in our party and one of them, Dirk, was not happy.  He announced that he was going to head north up the beach, towards the centreline.  Each mile he headed north would provide just under an extra second of totality.  Dirk and Beate strolled off along the beach.
In the absence of John Mason, the traditional master of ceremonies, I had agreed to provide a running commentary. "First contact!" I yelled at 7:17, and a few seconds later, Peter on the telescope confirmed my prediction. "Moon at 11 o'clock!"  The first nick was visible in the top of the Sun.
The start of the eclipse was clearly visible.  There was plenty of cloud around, but on the whole it was light cloud, and I did not have bad vibes over the prospects for totality.
The eclipsed Sun was visible pretty well throughout the next hour; two of my friends were sketching the partial phase every ten minutes, and were able to obtain a sketch for each ten-minute interval.   However, the cloud was growing stronger.  Initially the Sun could only be watched through eclipse safety glasses or a solar filter, but as second contact approached, the Sun could easily be watched with the naked eye, with the cloud acting as a filter. The pinhole experiment was abandoned, as it became increasingly difficult to spot the image.  I tried to look for the shadow sharpening which occurs close to totality (the crescent Sun becomes more like a line source of light, sharpening the shadows in one direction) but there weren't any shadows strong enough to observe.
"Ten minutes to go!" I yelled, and it was clear that this was going to be a close thing.  There was a particularly evil looking black cloud, only a few degrees away from the Sun in the sky and the prevailing wind was blowing it in just the wrong direction, to obscure our view.   Even so, I still felt we had a good chance.   Five minutes, three minutes, two minutes, one. . .  The crescent Sun narrowed, the sky was rapidly darkening.  I don't recall any noticeable drop in temperature (although I find that adrenaline tends to compensate) and there was little animal life around to disturb.
Into the last minute.  The edges of the crescent began to break up into Bailey's beads.   No point in looking for shadow bands, the Sunlight wasn't strong enough.  From where I stood, the hotel obscured the view of the oncoming shadow.  Our eyes were attracted instead to the rapidly approaching edge of the cloud.  I glanced at my watch and began the final countdown.
"Ten, nine, eight, seven, six, five, four, three, two, one. . ."
Just as I finished the cloud reached the Sun and blanked out the disk.
I held up my binoculars and tried to spot the solar disk, to no avail.  Video evidence suggests that we saw the eclipsed disk for a second or two, and one of my friends reported seeing a very brief glimpse of solar prominences, but I wasn't fast enough to observe either.  The surrounding skies were dark, of course, but to my recollection not as dark as either in Mongolia (where the eclipse track was very wide) or in Devon (where the cloud cover was much thicker).
Impotently, I stared at the spot where the eclipse ought to be, binoculars and camera at the ready, just in case. Twenty seconds, went by, thirty, forty, fifty.  The cloud cover seemed to grow thicker.  Seventy-one, two, three, four, five. . .  Up came the light level, and off shot the shadow across the clouds of the Indian Ocean, heading towards Australia.
"Third contact!", I yelled, then, for good measure, "Bugger! Bugger! Bugger! Bugger!"  Unprofessional, I know, but it made me feel a bit better.

* * * * * *

Surprisingly, the mood was considerably more upbeat than in previous unsuccessful expeditions, perhaps because the ratio of newbies to veterans was higher than in most expeditions.  The partial phase leading up to totality, after all, had gone pretty well, and for people whose sole previous experience of totality had been steady drizzle in Penzance, Mozambique was a definite improvement.  And we were, after all, still on a very nice beach by the Indian Ocean (as opposed to, say, a snow covered track in Outer Mongolia).  So out came the champagne, mostly purchased the previous day in a Maputo off-license; I had several glasses.  Then I had a snort of 1999-vintage eclipse scrumpy, which is enough to take your mind off a nuclear explosion, let alone a cloudy eclipse.

I was determined to take a paddle before we left Chongoene, although I didn't fancy venturing beyond the rocks into the crashing (shark-filled) seas of the Indian Ocean.  The water was warm on my feet, and things really didn't seem so bad. I chatted to Karen, the tour organiser, and watched as a tiny hermit crab, not two inches across, decided to pick a fight with her.  Then I noticed Dirk, the German guy, walking back towards us.
"Did you see the eclipse?" I asked, and Dirk nodded. "Through, cloud, yes, but we saw the corona."
Dirk and Beate had strolled briskly up the beach for close on 3km, gaining, in Dirk's estimation, an extra 1.5 seconds of totality.   Dirk had also seen the incoming clouds and surmised, correctly, that they were coming close to obscuring totality.  So at the next opportunity he had headed inland.  He took care to use beaten tracks, just in case of land mines, although in his estimation our location was not of any strategic significance and not likely to be mined.  He had abandoned hope of photography and concentrated on maximising his chances of observing the eclipse at all.  And he was successful. He was able to observe the beginning of the eclipse, through light cloud. After about sixty seconds, the cloud became too thick to observe anything, but he got a brief view of the diamond ring at the end of totality.
Of course, Dirk was lucky; he might have missed the eclipse altogether, and we might have seen it, albeit imperfectly, through cloud from Chongoene beach.  But I can't help recalling the old maxim; "you make your own luck."  Dirk set off on foot to up his chances of seeing totality.  Literally, he went the extra mile in pursuit of the eclipse, and his effort paid off.
Well done!

Elsewhere in Mozambique; the beach at Xai-Xai was also cloudy, although it was beautifully sunny by the time we returned.  I finally had my swim in the Indian Ocean; it was wonderful!  The Mozambican equivalent of the Radio One Roadshow seemed to be broadcasting from the beachfront.  Back in Maputo, we talked to people who had seen the eclipse inland from Chongoene.  In South Africa, there was patchy weather, but there was a clear view of totality from the northern part of the Kruger Park.  My favourite report was from the Ravhura people of the Northern Province of South Africa.  Their spokesman, Elvis Ravhura, reported that during the eclipse, they had prayed for rain to their rain god Nwali, who they believed was crossing the Sun during the eclipse.  Their prayers, Elvis reported, had gone answered, for it rained a few hours later.
A satisfied customer!

Light Colour vs Effect on Night Vision

By Clive Rogers

On our club listserver, a discussion is ongoing for the best colour of light to use for reading charts without adverse effect on night vision.  Traditional red seems to be out at the moment in favour of green-yellow.  My research says yellow-green at 5550Å is most easily seen in daylight but a more greenish light at 5100Å is more easily seen by the dark adapted eye.  I'd be grateful to know of any studies on this subject.
I had a search on dark adaptation and found this by M A Bouman, De Vries-Weber gain control and dark adaptation in human vision.  "Thresholds for seeing light from a stimulus are determined by a mechanism that pairs subliminal excitations from both halves of a twin unit.  A half-unit contains one red or one green cone and P rods.  The receptors "Weber machine" controls the receptors gain.  In the dark the receptors dark noise events reset its Weber machine and the receptors relation to its de Vries machine.  In relation to the time when and the area in which the stimulus is presented, these signs have average latency periods that depend on intensity and average locations that depend on movement.  Discrimination of stimuli that exploit the models entire summation mechanisms and pairing facilities represents "what the perfect human eye sees best."  For the model this threshold of modulation in quantum absorption is the ideal limit that is prescribed by statistical physics.  The models design for the perfect retinal mosaic consists of red twins situated along clockwise and counterclockwise spirals and green twins along circles that are concentric with the fovea.  The models descriptions of discrimination, adaptation, and hyperfunctions agree with experimental data."
I would agree with this assertion with certain caveats...  Red became the colour of choice because it has the least effect on rhodopsin build-up.  Yellow-green can be more effective IF it is the right intensity.  The only reason to use a colour that the eye is more sensitive to is to use a far dimmer intensity.  You can read a chart with yellow-green or green light that is far, far dimmer than red.  Now, here's the catch...
We've all seen these people at star parties that just don't get it.  They think that as long as the light is red, it doesn't matter how bright it is — you see them walking around with red cellophane over a floodlight!  The danger with promoting the use of green light is that people with green lights that are too bright will be even more disruptive.  Green is much better to use around CCD cameras since they just LOVE red light on any intensity.
The problem with these studies is that they seem never to get quite to our issue: level for reading and impact on dark adoption.  Not the same as detectable levels.  I agree that there is probably significant variation among individuals and probably with age as well.  I find I really need to crank up a red light too much to read by and it hurts my night vision.  I'm ready to build a dim green light with a max intensity just bright enough for reading charts and compare it.  If it works better I'll probably hook it to a magnifier to allow me to read the charts without my reading glasses I need when I wear my contacts and I'll save my red light for collision avoidance.  I found a web page http://members.cox.net/rigelsys/why_red.html which has among other things pages that show quite clearly that the redder the better for getting re-dark adapted after exposure to light.
The bottom line of these papers is that red lights are best, but if you can see that it's red on the paper you're looking at, it's too bright.  You see people at star parties with blazing bright flashlights and light boxes for reading charts, thinking that since they're red it's okay.  But if the red light you're using shows any more colourfully than funny brown-grey, then it's too bright.
The following, which were published 40 years ago in the Journal of the Optical Society of America
"After some experimentation, I prefer red, it seems to offer (for me) the quickest recovery to dark adaptation.  Several years ago I built a flashlight with 4 switchable high-brightness leds on a full extinction dimmer circuit.  I selected directional red and orange, and diffused red and green, and found that the green and orange were my least used colors for reading charts.  I've since replaced the green led with a white diffuse LED.  I find the very dim white illumination better than green for reading charts and it has about the same recovery time as the green led.  It is especially nice if the chart is in color!  The orange spot is quite handy for finding lost objects without wrecking dark adaptation!"
To maintain maximum dark-adaptation, it is of course important to keep the intensity down. But how low can you go?  If you need to read star-charts, you need enough light to see the dots and read the labels, and afterwards you have to take time to re-adapt to the extent necessary for observation.  One work-around is using one eye for observing, the other for chart-reading.  But I'd say lots of observing is done without anything near full adaptation.  Have you ever seen a sky so dark that a tree silhouette does not leave an after-image?  The after-image means of course that dark-adaptation to the sky is nowhere near maximum.  However, studying an object at high power for a few minutes will allow considerably better adaptation - until you lose it by watching the sky, or looking into the finder.
The size of the print has a very strong effect on the minimum illumination needed - using magnifiers can be better than the best choice of light colour.  Clearly, red is the best color in the sense that the minimum intensity needed to read print affects the rods least - I suspect that the problems some have using red has to do with the chromatic aberration of the eye - normal focusing does not work well with red.  Using strong reading glasses may help you come close to the chart, and find a distance where you can focus well - and an extra hand-held magnifier for those tiny NGC-IC numbers would also help keeping the light level low.