Ever since mankind walked the Earth the sky has held a very special fascination. From the gentle light of the stars to the meandering paths of the planets we have grown to love and understand the night sky.
Over recent years though, there have been some strange interlopers in the night sky – man made satellites. One in particular seems to have captured the public imagination, the International Space Station (ISS).
As its name suggests, the station is the result of international collaboration between North America (NASA), Russia (RKA), Japan (JAXA), Europe (ESA) and Canada (CSA) and a combination of crew from those agencies operate the station.
It orbits the Earth at an average altitude of 369km and, travelling at 27,724km per hour, it takes about 90 minutes to complete one orbit.
In effect it’s in constant free-fall around the Earth, as it falls toward the Earth the curvature of the Earth's surface falls away from it.
The result is that it typically maintains a relatively constant altitude above the Earth's surface. However, because it orbits in the thermosphere, gas in the atmosphere creates a drag effect, very gently slowing the station. This causes it to descend into a lower orbit so a few times each year, it receives a boost to a higher altitude from either the onboard engines or from an attached spacecraft.
The first parts of the ISS were launched in 1998 and its first crew arrived in 2000 representing humankind’s permanent presence among the stars.
Even though it has been operational since 2000 its still not complete with more modules to add.
Completion is expected this year when the station will weigh around 400 tonnes and measure 51m by 109m (excluding the solar array which adds an additional 73m), making it four times larger than the Mir Space Station.
The space station is considered to be a 'third generation' station due to its modular design allowing for continual development or change to its structure, unlike the first generation stations which were of fixed design and configuration.
The first module in orbit was called Zarya and was launched aboard a Russian rocket. It was closely followed by a whole array of different functional sections from service modules to air locks and gymnasiums, as well as a 360 degree bay window, and of course no space station would be complete without a cargo bay or two.
There are now 15 modules which are pressurised (which astronauts can access without a cumbersome space suit) and a host of other unpressurised units.
One of the key unpressurised modules is the largest structure of all, the Integrated Truss Structure which connects up to the main solar arrays and station radiators. Measuring a whopping 108.5 m long its made up of 10 separate segments that form the backbone of the entire station.
There are also a number of other external devices attached to the station including six robotic arms, storage containers that carry spare parts and platforms for external experiments.
Living and working on the station is generally centered around the pressurised modules and for the comfort and hygiene of the crew there are areas designed for 'personal tasks'.
There are beds dotted around the station which seem nothing more advanced than sleeping bags strapped to the wall with a head strap to keep your head from floating around.
Eating is generally a group activity although the food is chosen by the astronauts (with assistance from dietary professionals) prior to joining the station. The foods are mostly refrigerated or canned and drinks often in powder form. The kitchen area has food heaters, a water supplier and a refrigerator. Its not uncommon for astronauts to choose spicy food with strong flavours because the taste sensation is reduced in space.
On the ISS the toilets have handles that enable the astronauts to hold position. A big fan with a suction hole is used to collect the waste product. Any solid waste is stored in sealed containers until the next visiting spacecraft arrives to bring it back to Earth for disposal. Urine is collected at the front of the toilet using a hose and an appropriately shaped male or female adaptor. Urine through the recycling systems onboard is reprocessed back to drinking water!
Over 200 astronauts have visited the station and it has been continually manned since October 2000 and for those astronauts onboard, they are taking some risk. The ISS is relatively protected from radiation in space, particularly from the Sun, as the Earth's magnetic field deflects radiation around it.
If particularly intense bursts of solar energy are detected then the crew will have just a few minutes warning to shelter in a more heavily shielded part of the station as happened last in 2005.
There is also the risk of meteoroid impact or space debris striking the station, and in 2011 and in March 2012 the crew sheltered in the escape module due to a proximity alert from passing debris.
Analysis: space debris
One of the things that has inspired us about the space station is not only the international co-operation but the more humbling fact that on most days of the year, if you know where to look, you can look up and see the space station and its crew of intrepid human explorers pass overhead.
Its surprises many to know that you don't need any special equipment to see it as it's often brighter than any of the stars in the sky and very easy to pick out.
NASAs website has an ISS tracker which helps you to know where to look from your location.
If you become a fan of the ISS and look out for it regularly you will notice that, depending on your location, it will vanish from view for a period of time. This is explained by the complexities of the circumstances that give rise to it being visible and it's dependent on, amongst other things, whether it's actually above the horizon, whether it’s still being illuminated by the Sun, if the Sun has set and its altitude. There will be times when it's passing overhead but it's not lit up and therefore not visible. On occasions its altitude has to be boosted by either on board rockets or an attached visiting spacecraft.
The ISS is many things to many people but all would agree that it's a symbol of hope for future international cooperation. It’s an incredible technological achievement and not only does it help to capture the imagination of those on Earth's surface but it serves as a reminder that together, humans can achieve great things.