Six Miles High at 600mph

26 Feb, 2015

I remember the first time I boarded an aircraft and was able to reach out and communicate using Instant Messaging. The realization that I was still in touch with civilization was hugely welcome - that sense of isolation in flight and being not quite "in control" of the situation vanished while messaging with friends on the ground.

As part of the team that built that communications channel we wondered, "is this something, ...or is it not?" We certainly know now that it is and was something. Now it is common for our flights to have connectivity - a way to communicate naturally with terra firma. The process that allows this communication to happen is remarkable.

Aircraft equipped with GEE connectivity use geostationary satellites. A message travels 22,300 miles to the satellite and 22,300 miles back to the ground (at a light speed of 186,000 miles per second) before arriving at its destination.

Of course, we stand on the shoulders of giants to achieve and maintain a connection at in-flight aircraft speeds. The communications technology is full of other 3-letter abbreviations representing advances developed by industry greats before us: PSK (phase-shift-keying), ACM (Adaptive Coding and Modulation), PEP (Performance Enhancing Proxy), and the like - all to enhance the communications experience.

People familiar with satellites know that this is a science fiction idea become reality. The location around the equator that these satellites are on is sometimes called the "Clarke Belt," named for Arthur C. Clarke, a science fiction writer. Very advanced for 1945 and several years before the launch of Sputnik 1, the first man-made satellite. 

The communication satellites on the equator are positioned two degrees apart (sounds small, but at that height the distance to the next satellite is about 900 miles). GEE works with our partners SES and Hughes to select the best satellites to provide connectivity service onboard - currently we use nine different satellites to provide communications for aircraft in flight all over the world.

Handling communications inflight presents interesting challenges to overcome. The accuracy of antenna pointing to the satellite is particularly important. The GEE antenna needs to stay pointed at the satellite to within 0.2 degrees throughout any aircraft maneuvers. To assist this need, aircraft position and orientation information is monitored about 25 times a second.

Other challenges go deeper into the communication transmission. For example, as the aircraft speeds towards or away from the satellite there is a doppler effect (the classic example of doppler frequency shift is the change in pitch that the sound of a train makes as it speeds through a station). The frequency of the transmission from the aircraft is continually changed to compensate and make sure that the signal arrives at the satellite and at the ground at the expected value.

Now when I fly, I easily connect using my smart-phone and laptop. It makes me very thankful that we have made such incredible strides over time. Of course, I still find the most comfort in the fact that our ability to communicate while inflight reminds me that I'm joined with friends and family and still in touch with civilization.


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