GPS Basics

The Almanac (where are my satellites ?)

An almanac is considered valid for about 180 days. However, while the general orbital information may be usable for several months, the health of any one satellite may change at any time. Therefore, when performing mission planning frequent updates of the almanac would seem necessary. An almanac is a data file that contains the approximate orbit information of all of the satellites in the GPS program, and is transmitted by every satellite within its navigation message. An almanac also helps a GPS receiver to search for satellites that are expected to be located within the field of view. An example of an almanac my download below. current ALMANAC download here. (just for info)