All communications satellites experience a problem when the sun passes behind the satellite and falls within the beam width of the earth station antenna. An earth station perceives the sun as a source of thermal noise with a diameter of 0.48 degrees. The nominal noise temperature of the sun is 25,000 Kelvin. This adds to the thermal noise of the system and causes a communications outage.
The length of the outage varies as a function of the antenna beam width, which is determined by the antenna size and the frequency in use, as well as the angle the sun makes with the beam width of the antenna. This outage, commonly called a "sun outage," occurs for twice yearly at apparent noon for the satellite longitude.
The larger the antenna the less time the sun takes to transit as the beam width becomes smaller with larger antenna diameters. Since the station thta the Nautilus communicates with is in Andover, Maine and has a very large antenna (30 meters), the time of the outage is very small. The times and dates given below are for UTC time.
When the antenna in Andover is affected, we experience a loss of communications traffic from the ship. The video, phones, and Internet will be disrupted. When the ship is affected, viewers will still be able to see video. However, the ship will lose all phones, audio, and Internet.
The antenna on the ship is a tracking antenna and always tracks the strongest signal it sees. Since the sun will be stronger than the signal from the satellite, the ship's antenna would actually track the sun instead of the desired signal if the satellite operator on board the ship did not make the necessary adjustments.
Andover, Approximate Outages
10/09/2011 11:25 TO 11:28 UTC
10/10/2011 11:26 TO 11:27 UTC
Nautilus, Approximate Outages
10/06/2011 11:49 TO 11:53 UTC
10/07/2011 11:47 TO 11:55 UTC
10/08/2011 11:45 TO 11:56 UTC
10/09/2011 11:45 TO 11:56 UTC
10/10/2011 11:44 TO 11:55 UTC
10/11/2011 11:44 TO 11:55 UTC
10/12/2011 11:45 TO 11:54 UTC
10/13/2011 11:47 TO 11:51 UTC
The predicted times are not exact since the exact location of the ship varies. The Andover outages can be predicted very accurately and they are very short in duration because of the narrow beam width of the large antenna.