In this series of ways that you can prepare your vehicle and your family for remote touring we will start by looking at the “Call in the Troops” gear.
Of course the Satellite Phone has more functions than just calling for emergency support, however it’s capability to do this task is generally the reason why travelers will look at buying or hiring one.
Before we get to individual phone types, we should discuss the satellites themselves.
There are two basic types of satellites up there. Geostationary and Geosynchronous.
Geostationary satellites are just as their name suggests, stationary above a fixed point on the earth, and positioned to serve the greatest customer base.
Geosynchronous orbits, like that of the Iridium Network are in overlapping, moving orbits around the earth.
Photo Credit - Deann Redlin
A quick look at the coverage maps of each phone maufacturer gives you an indication of how well ‘covered’ you will be.
Shows expected coverage from the Inmarsat Satellites
This graphic demonstrates the 'look angle' from relative latitudes. The further you are form the Equator, the 'lower in the sky' the Satellite is.
Thuraya Coverage Map
Coverage map for Iridium phones, consider the 'constellation' of 66 Satellites.
Global Star are actively launching their 2nd generation Satellites to increase coverage and resolve degraded performance issues.
Network Comparison Table -
Now, coverage of the earth is one thing, but the signal still needs to come back to the planet’s surface at some point.
The Satellites in higher earth orbit have the ability (because their altitude affords them a greater footprint) to beam your conversation back to a ground station directly. In some ways this ‘one bounce’ method speeds the process up, helps to maintain voice quality and leaves less opportunity for problems.
The Satellites in Low Earth Orbit will quite often not be in view of a ground station and will, instead utilise a technique referred to as ‘bent tubes’ and connect through adjacent satellites (sometimes several) until a link to a ground station is established. It is quite common for a user to have coverage from more than one LEO satellite at a time and, at times, the signal is actually being carried by more than one satellite until being handed off to the one with the highest quality signal.
The time lag created by the bent tube effect can be significant, but is still no greater than the time lag created by transmitting and receiving from a satellite in a much higher orbit.
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