Satellite constellations that provide continuous coverage of a specific location

The purpose of many satellite constellation design methods in use today is to produce a network of satellites that will provide continuous coverage of given zones on the earth's surface. These zones can range in size from narrow latitude bands to the polar caps to the entire earth. Some of the more recent design methods provide multiple continuous coverage of similar zones. The number of satellites in these constellations may be as few as three or as many as several hundred. The objective of the work contained herein was to investigate the requirements for providing continuous coverage of a discrete earth location (latitude, longitude). A method was designed to provide this type of coverage with either a single ring of satellites in circular equatorial or circular polar orbit or with a network of satellites in equally inclined circular orbits in which each satellite directly overflies the location at least once a day. The method accounts for orbit perturbations due to the earth's oblateness and is applicable for orbits from 150 km to 35784.7 km in height, i.e., low earth orbit to geosynchronous orbit. The methodology was programmed in FORTRAN for use as a satellite constellation design tool. The investigation revealed that the ring type constellations developed by this method were as efficient or more efficient than existing methods in providing the necessary coverage. The equally inclined constellations were much less efficient at low altitudes and low viewing angles but became more efficient as altitude or viewing angles increased. The direct overflight of the satellites was verified using an independently developed ground trace plotter. The method developed for this investigation would be most suitable for applications where a large number of direct overflights per day is desired or for satellites that require large viewing angles. If direct overflight is not a requirement and the satellite can perform its mission at low viewing angles, the constellations designed using current design methods would require fewer satellites to provide continuous coverage of the entire Earth.