eMail UsContact UsDealers & Agents Satellite Drift - Why it occurs and the resulting issue If you are a Satellite Alaska customer and would like to download an in-depth PDF file concerning this issue  [CLICK HERE] First some background The ideal orbit for a communication satellite results in a satellite that is stationary (parked) over the equator so that it appears motionless to an observer on the Earth's surface. Such an orbit is called geostationary. If the satellite travels in sync with the Earth's rotation it is said to be in geosynchronous orbit. A satellite is in an inclined orbit when its orbital plane is tipped some number of degrees from the horizontal defined by the equator. In the case of an inclined geosynchronous orbit, although the satellite remains geosynchronous (that is, completing one orbit around the earth every 24 hours), it is no longer geostationary. The Present Situation with MSAT Unfortunately, once a satellite is placed in proper position and attitude, it doesn't stay there: it tends to drift. From a fixed observation point on Earth, it would appear to trace out a small ellipse as the gravitational effects of external forces influence the satellite's position. As the external effects accumulates over time, the staellite's path becomes a figure-eight with lobes oriented north-southward once every sidereal day. Drift degrades satellite performance in two ways: the satellite may move out of position, or it may assume an improper attitude. It requires corrections applied from the ground to actively counteract the drift. Communications satellites are fitted with small rockets called thrusters used to correct the drift. On command from the a control station, a thruster is fired; during the firing, it ejects a gas called fuel or propellant. Like the air escaping from the balloon, the ejected gas produces the force required to reposition the satellite. The majority of the fuel, typically hydrazine is spent for this purpose. Otherwise the satellite experiences a steady increase in the deviation from ideal position and attitude over time. The ground control station precisely controls all parameters involved in a firing: the position of each thruster relative to the satellite, the timing and duration of each fire, and the pressure of the ejected propellant. If these parameters are controlled properly, the satellite can be maintained at proper position and attitude for years. This process is called stationkeeping. At the end of the satellite's lifetime, when fuel approaches depletion, satellite operators may decide on "rationing" the fuel to prolong the life of the satellite at the expense of reducing the service area provided for communication. MSAT1 is currently at 2 degrees of inclination As the satellite moves up and down along the figure 8 track the edge of coverage provided for communication customers moves north and south. Customers in northern Alaska will be impacted most as the drift of the MSAT satellite becomes more exaggerated. We expect that the drift may reach 6 degrees plus and minus sometime next year. The image at right shows the approximate edge of coverage for these conditions. During the positive half of the cycle the coverage will be more or less normal. For the negative half of the cycle the satellite will be below the horizon for customers in the far north and service will be unavailable. Help is On The Way The most powerful MSS satellite ever built by Boeing, and other contractors are nearing completion. The first of two very high-power satellites are being readied for launch in 2010 ($1.2B investment, including launch). Some of the features that the new system will include: Handheld wireless devices support (high satellite G/T) High quality voice service with adaptive bit rate reduction for challenging environments High-gain satellite antenna provides best-in-class performance High Penetration alerting for incoming calls Alerts users inside car or building to an incoming call User configurable "roaming" between ATC/Cellular/Satellite Combining over 2 satellites to get 3 dB improvement Highly reliable and flexible design ViaSat - Beamforming moved to the ground – ground-based beamformer (GBBF) will form hundreds of beams GBBF and onboard channelizer provide rapid reconfiguration of coverage and reallocation of bandwidth In an emergency, bandwidth can be increased in the beam servicing the emergency area Earth Stations nearing completion in Napa, Dallas, Saskatoon and Ottawa. We will be issuing email updates as the situation changes.