The Ice, Cloud and land Elevation Satellite (ICESat) launched 13 January 2003 00:45 UTC from Vandenberg Air Force Base in California.
The near circular, near polar orbit has an altitude of approximately 600 km.
Two primary orbits will be used:
The orbit planned for use is known as a "frozen orbit", meaning that in spite of the Earth's oblateness, the perigee will remain fixed (in an average sense) at the northernmost latitude (essentially at the North pole). Accounting for the fact that the Earth is an oblate spheroid, the following range of altitudes (with respect to mean sea level) will exist for both orbits:
Near the North pole
Near the South pole
Near the equator
Since the orbit is frozen, perigee does not circulate and the altitude will be a function of latitude. The orbit inclination was chosen to be 94 degrees. This inclination provides coverage to 86 deg latitude, thereby ensuring coverage of the fast-flowing Antarctic ice streams that flow onto the Ross Ice Shelf. The retrograde inclination was chosen for the geometry of crossovers, the intersections between the ascending and descending ground tracks. Crossover points are a key analysis technique to meet the science requirements.
The specific orbit characteristics are:
The node location will be selected to meet other requirements, such as the overflight of verification sites.
The ground track over Antarctica for the 8 day repeat is illustrated in one of the figures. The first 25 days of the 183 day repeat is illustrated also. The pattern shown for the first 25 days will be repeated in the next 25 days, just shifted by 15 km at the equator.
Figures available in Adobe PDF format: