Calculating earth station sun outage times

Sun outage at a satellite earth station occurs when the orbital positions of the sun, earth and satellite are such that the earth station antenna is looking directly at the sun; this results in noise temperature increases that temporarily render the station unusable. Background information is presented for calculating this phenomenon, and definitions and conversion factors are given. The required data for calculating the times of angular coincidence between the sun and satellite are the Greenwich Hour Angle and the declination angle. Greenwich Meridian Time is converted to local time, and based on local hour angle and declination of the sun, spherical trigonometric identities are used to obtain the azimuth and elevation angle of the sun at a given latitude. Several procedures are demonstrated, and a sample calculation is provided. It is concluded that sun outages for small terminals can be predicted with sufficient accuracy, although some time margin should be allowed on either side to account for antenna beam factors or pointing inaccuracies.