International Space Station

On 27th January 1967 the Outer Space Treaty was opened for signature in Moscow, London and Washington. Using this treaty, fourteen member states began to develop the ISS, using the Mir space station as 'Phase 1' of the programme. On 29th January 1998 government officials from fifteen countries signed agreements for the ISS in Washington. That year saw the launch of the first two modules into space and the station is expected to be complete by the year 2005. As well as its political implications, the ISS will be used for major scientific and medical research and will be the largest and most ambitious space project ever to be undertaken.

ISS inhabited at last
On 2 November 2000, the first crew of two Russians and one American started to live on the ISS. Shortly afterwards the main solar panels were attached and unfurled. These provide the electrical power to the station. In early 2001 the space shuttle Atlantis carried the Destiny science module to the ISS. This was the largest ever payload carried into space in a single launch. After a long spacewalk it was successfully attached to the space station. It is the ISS's first science laboratory where the residents will carry out the bulk of the scientific research. As each module is attached to the station, it reflects more sunlight and hence becomes even more visible to the naked eye.

The Nations
Out of the sixteen nations taking part in the building and assembling of the ISS, the major partners in the project are:

• USA (NASA)
  
• Russia (RSA)
  
• European Space Agency (ESA)
  
• Japan (NASDA)
  
• Canada (CSA)
  

One of the most important European projects is the building of a laboratory named Columbus, which will aid in the research of such subjects as fluid mechanics and materials science. Other projects include a European robotic arm and an ATV. The Italian Space Agency (ISA) is also building two of the station's docking nodes.

Size
When fully assembled, the outpost will weigh approximately 470 tons, and will house a crew of six or seven. About the size of a football pitch (109 m wide; 88 m long; 44 m tall), the station will orbit 350 km above the surface of the Earth and is already easily visible in the night sky.

Research
As well as the habitat modules (each 8.5m long and 4.2m in diameter) there will be five state of the art laboratories that will carry out major research in:

• biotechnology
  
• biomedicine
  
• gravitational biology
  
• materials science
  
• fluid physics
  
• combustion research
  
• space science
  
• earth science
  
• engineering research
  

Scientists will also be looking at the effects of weightlessness and space sickness on the crew members who experience long-duration stays on the ISS. This work is vital for any future expeditions to planets such as Mars.

Launches
The first two modules of the ISS were launched late in 1998. The Russian built ZARYA control module was launched onboard a Russian proton rocket, on 20th November 1998, shortly followed by the space shuttle Endeavour containing the US connecting module, UNITY, on 3rd December 1998. These were then locked together by the astronauts onboard. In July 2000, after a long delay, the Russian Space Agency finally launched the ISS's living quarters.
It will take a several dozen more flights, over at least five years, to send everything needed. From October 2000, a crew of three will start to live on the station.

Cost
One of the most talked about problems concerning the ISS is the cost. When the agreements were signed in 1988 the estimated cost was put at $20 billion. Its final cost is now estimated to be at least $96 billion. This has delayed progress on the project, for example the Russian service module (the living quarters) were deployed a year late because of budget difficulties.

Other Problems
Although most of the US and Russian launches have been successful, six US space flights ended in disaster in 1998 and in a recent incident (July 1999) a Russian Proton rocket exploded seconds after it was launched, putting launch dates back, and possibly delaying the next phase of the ISS, as NASA could not carry on construction until the Russian service module was in place. This was finally launched in July 2000. In addition there have been disputes between the governments of Russia and Kazakhstan over the use of the Kazakh launch site at Baikonur.
There have also been many debates on human manned space stations and flights - some scientists preferring the use of robots.
Although controversy has surrounded the ISS since it was first proposed, supporters believe that it will help future space programs, as Mir has done, promote better international relations and also aid in scientific and medical research.

The Origin of the Solar System
The earliest accounts of how the Sun, the Earth and the rest of the Solar System were formed are to be found in early myths, legends and religious texts. None of these can be considered a serious scientific account.
The earliest scientific attempts to explain the origin of the solar system invoked collisions or condensations from a gas cloud. The discovery of `island universes', which we now know to be galaxies, was thought to confirm this latter theory.
During this century Jeans proposed the idea that material had been dragged out of the Sun by a passing star and that this material had then condensed to form the planets. There are serious flaws to this explanation but recent developments have been made suggesting that a filament was drawn out of a passing protostar at a time when the Sun was a member of a loose cluster of stars but the most favoured theories still involve the gravitational collapse of a gas and dust cloud.
The problems to be faced by any theory for the formation of the Solar System
Any theory has to account for certain rather tricky facts about the Solar System. These are in addition to the obvious facts that the Sun is at the centre with the planets in orbit around it. There are 5 of these problem areas.

1. The Sun spins slowly and only has 1 percent of the angular momentum of the Solar System but 99.9 percent of its mass. The planets carry the rest of the angular momentum.
2. The formation of the terrestrial planets with solid cores.
3. The formation of the gaseous giant planets.
4. The formation of planetary satellites.
5. An explanation of Bode's law which states that the distances of the planets from the Sun follow a simple arithmetic progression.
(Bode's `law' takes the form of a series in which the first term is 0, the second is 3 and each term is then double the previous one, to each term add 4 and divide the result by 10. This yields the series of numbers,
0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0, 19.6, 38.8;
which may be compared to the mean distances of the planets from the Sun in AU,
0.39, 0.72, 1.0, 1.52, 5.2, 9.52, 19.26, 30.1, 39.8.
The agreement for all but Neptune and Pluto is remarkable. The lack of a planet at 2.8 led to the discovery of the asteroids.)
There are 5 theories which are still considered to be `reasonable' in that they explain many (but not all) of the phenomena exhibited by the solar system.

The Accretion theory
This assumes that the Sun passed through a dense interstellar cloud and emerged surrounded by a dusty, gaseous envelope. It thus separates the formation of the Sun from that of the planets thus losing problem 1.
The problem which remains is that of getting the cloud to form the planets. The terrestrial planets can form in a reasonable time but the gaseous planets take far too long to form. The theory does not explain satellites or Bode's law and must be considered the weakest of those described here.

The Protoplanet theory
This assumes that initially there is a dense interstellar cloud which will eventually produce a cluster of stars. Dense regions in the cloud form and coalesce; as the small blobs have random spins the resulting stars will have a low rotation rates. The planets are smaller blobs captured by the star. The small blobs would have higher rotation than is seen in the planets but the theory accounts for this by having the `planetary blobs' split to give a planet and satellites.
Thus many of the problem areas are covered but it is not clear how the planets came to be confined to a plane or why their rotations are in the same sense.

The Capture theory
This theory is a version of Jeans's theory in which the Sun interacts with a nearby protostar dragging a filament of material from the protostar. The low rotation speed of the Sun is explained as being due to its formation before the planets, the terrestrial planets are explained by collisions between the protoplanets close to the Sun and the giant planets and their satellites are explained as condensations in the drawn out filament.

The Modern Laplacian theory
Laplace in 1796 first suggested that the Sun and the planets formed in a rotating nebula which cooled and collapsed. It condensed into rings which eventually formed the planets and a central mass which became the Sun. The slow spin of the Sun could not be explained.
The modern version assumes that the central condensation contains solid dust grains which create drag in the gas as the centre condenses. Eventually, after the core has been slowed its temperature rises and the dust is evaporated. The slowly rotating core becomes the Sun. The planets form from the faster rotating cloud.

The Modern Nebular theory
Observations of very young stars indicate that they are surrounded by dense dusty disks. While there are still difficulties in explaining some of the problem areas outlined above, in particular ways to slow down the rotation of the Sun, it is believed that the planets originated in a dense disk which formed from material in the gas and dust cloud which collapsed to give the Sun. The density of this disk has to be sufficient to allow the formation of the planets and yet be thin enough for the residual matter to be blown away by the Sun as its energy output increased. In 1992 the Hubble Space Telescope (HST) obtained the first images of these proto-planetary disks (sometimes shortened to 'proplyds') in the Orion nebula.
Some of the Orion proplyds are visible as silhouettes against a background of hot, bright interstellar gas, while others are seen to shine brightly. They are roughly on the same scale as the Solar System and lend strong support to the nebular theory of its origin.

Conclusion
There have been many attempts to develop theories for the origin of the Solar System. None of them can be described as totally satisfactory and it is possible that there will further developments which may better explain the known facts.
We do believe, however, that we understand the overall mechanism which is that the Sun and the planets formed from the contraction of part of a gas/dust cloud under its own gravitational pull and that the small net rotation of the cloud was responsible for the formation of a disk around the central condensation.
The central condensation eventually formed the Sun while small condensations in the disk formed the planets and their satellites. The energy from the young Sun blew away the remaining gas and dust leaving the solar system as we see it today.

 

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