Envisat flies in a sun-synchronous polar orbit of about 800-km altitude. The repeat cycle of the reference orbit is 35 days, and for most sensors, being wide swath, it provides a complete coverage of the globe within one to three days. The exceptions are the profiling instruments MWR and RA-2 which do not provide real global coverage, but span a tight grid of measurements over the globe. This grid is the same 35-day repeat pattern which has been well established by ERS-1 and ERS-2.

In order to ensure an efficient and optimum use of the system resources and to guarantee the achievement of the mission objectives Envisat reference mission operation profiles are established and used for mission and system analyses to define the instrument operational strategies, the command and control, and the data transmission, processing and distribution scenarios.

Mission and operation requirements

• Sun-synchronous polar orbit (SSO): Nominal reference orbit of mean altitude 800 km, 35 days repeat cycle, 10:00 AM mean local solar time (MLST) descending node, 98.55 deg. inclination.
• The orbit is controlled to a maximum deviation of +/- 1 km from ground track and +/- 5 minutes on the equator crossing MLST.
• Recording of payload data over each orbit for low bit rate (4.6 Mps) on tape recorders or solid state recorder (SSR).
• High rate data (ASAR and MERIS) to be accessible by direct telemetry or recording on SSR.