Optus has two satellite systems both are the geostatioanary type. This means the satellite is fixed in space so it is always in view. It orbits the earth at the same time and rate that the earth rotates but the satellite is positioned over the equator and around 36,000 kilometers out in space. this system works very well so long as you can see the satellite you will always be able to make a phone call prvided you are using the satellite phone correctly. The two systems are Optus Mobilesat and the other is a satellite system called Thuraya. The Optus mobilesat system will reach end of life around 2014 most satellites have a working life of around 15 years but the Thuraya system was launched last year and has a lot of great features that are still being implemented so it be around for quite a while yet. The Mobilesat system uses a unit that is made for a more permanent installation in a vehicle or a marine or aircraft application it is not a "portable" unit. The Thuraya telephone has handheld portables in satellite only or satellite/gsm they also have other applications and will soon have GPRS type data from your portable handset and also a higher speed data service using a different unit that is called Thuraya IP and is designed to be PC and network based similar to the Bgan service by Inmarsat
The Iridium system has been around for quite a long time now and has proved to be a excellent system it is the only true world wide system as the 66 satellites (Iridium is the 66th element) cover the whole of the earth in their orbits. There are 6 orbital planes and 11 satellites in each plane that are operational there are spare satellites in each plane and as the satellites age they are being replaced and put into their storage orbits. The satellites are in what is called a polar orbit they travel over the north and south poles in their orbits and travel from north to south. These satellites all downlink to the earth station in Arizona in the USA and they use what is termed satellite interlinking to get the signals to and from the earth station because there are only 1 or 2 satellites in view of the earth station at any one time so your call is handled between orbiting satellites depending on where you are on the earths surface and passed along to each other maintaining the call in real time...there is some very fancy number crunching going on and it all works great. The majority of the units sold are a hand held unit but they also have other solutions for marine and aircraft applications. The american military also use the Iridium system but these calls and information are kept separate from "domestic" calls and also are downlinked to a different earthstation
Inmarsat has been around a very long time and has been the first real major provider of domestic style communications. Originally is was predominantly marine based for large vessels and also fishing fleets proving slow text based messaging and voice. In the past decade or so they have provided voice and slow data 2400bps through the "Mini M" system using a laptop style unit and this was quite successfull. Inmarsat has finally released over this side of the world a high speed portable data solution called Bgan. These units connect to you PC and allow web browsing or FTP or even live video up or downlinking at around 400 kpbs and you can even multiplex these units to achieve very high data rates but of course all this comes at a cost and it is reasonably expensive but does provide a reliable solution to very difficult problems. There is a new Inmarsat hand held system that has just been released it is still too soon to see how well it works in Australia
Globalstar has been around for a few years and worked reasonably well it is a orbital system and the satellites are much higher than the Iridium system so they dont need as many satellites. It is referred to as "bent pipe technology" which means the satellites are really repeaters in the sky they rely on many eathe stations located in different places all over the world to down link the telephone calls. This creates a problem for some users because it can not provide total world coverage there are large areas where it will not work. The reasons for this is because it can only communicat with a earthstation that is in view from its orbital plane. In Australia there are 3 earth stations the main one is in Dubbo NSW another for the northern area is in Mt Isa and the last one which covers the western part of Australia is in Meekatharra. Usage in Australia is pretty good except at the extremities north and south as the satellite angle of view to the earth station is poor. The Globalstar system is currently undergoing a complete upgrade of its satellites because of a manufacturing issue with the originals and should be back to full operation in 2010. The system is still working but satellite availabilty is sporadic
Satellite Systems Information
