Measuring Highly Elliptical Orbits Using The GPS

Report discusses precise determination of highly elliptical orbits of spacecraft around Earth, by use of one of following techniques: (1) conventional two-way Doppler tracking of spacecraft from ground stations, (2) conventional two-way Doppler tracking from ground stations augmented by tropospheric-delay calibrations obtained at ground stations by simultaneous tracking of navigation satellites of Global Positioning System (GPS), or (3) method of item 2 augmented further by GPS tracking from GPS flight instrument aboard spacecraft. Analysis applies especially to scientific satellites carrying radio telescopes.