Mission Description

The Ice, Cloud and land Elevation Satellite (ICESat) launched 13 January 2003 00:45 UTC from Vandenberg Air Force Base in California.

Orbit Characteristics

The near circular, near polar orbit has an altitude of approximately 600 km.

Two primary orbits will be used:

1. Verification/validation orbit: this orbit has a ground track repeat cycle of 8 days to enable overflights of specific locations on the Earth which will be instrumented to support measurement verification or data product validation
   
   
2. Mission orbit: this orbit has a ground track repeat cycle of 183 days to enable uniform sampling of the surface with high resolution. At the equator, the separation between ascending tracks will be about 15 km after 183 days

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:

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:

• Verification orbit (mean values)
  • 8 day repeat in 119 orbital revolutions
  • Semimajor axis: 6971 km
  • Eccentricity: 0.0013
  • Inclination: 94 degr
  • Argument of perigee: 90 degr
    
    
• Mission orbit (mean values)
  • 183 day repeat in 2723 orbital revolutions
  • Semimajor axis: 6970 km
  • Eccentricity: 0.0013
  • Inclination: 94 degr
  • Argument of perigee: 90 degr

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:

• 8 day repeat ground track over Antarctica (79K)
• 8 day repeat ground track over Greenland (26K)
• first 25 days of 183 day repeat (104K)