Design ofSatellite Constellations forOptimal Continuous Coverage

A satellite-borne sensorcan viewa region atorabovetheEarth's surface. Thesizeofthisregion depends on thesatellite's altitude, themaximumrangeandscanangle ofthesensor,theminimum above-the-horizon viewing anglerequired, theextentinaltitude of theregion tobeviewed, andthemaximumaltitude ofsensorobscurationbytheatmosphere. Except forgeosynchronous satellites this region moves relative totheEarth, sothatconstellations ofsatellites aregenerally necessaryforcontinuous coverage.Satellite constellations whichminimize thenumberofsatellites required forcontinuous coveragearederived asa function oftheangle subtended attheEarth's centerbythecoverage ofasingle satellite. Thisisdoneforsingle andtriple continuous coverageofthe entire Earthandofthepolarregions extending toarbitrary latitude. Simple, cogentapproximations fortheconfigurations and numbers ofsatellites arefound.Expressions whichrelate sensor capabilities andsurveillance requirements to arepresented. Examples aregiven toillustrate theuseandaccuracyoftheresults.