ENVISAT was successfully launched on March 1, 2002 from Kourou, French
Guiana on Europe's Ariane 5 launcher.
The ENVIronmental SATellite (ENVISAT) is an element of the European
Space Agency (ESA)
... Columbus Programme. The ENVISAT satellite is part
of the International Earth Observation System (IEOS). The ENVISAT is
designed to study Earth's resources and to contribute to the study of
land surface properties, atmospheric chemistry, aerosol distribution,
ocean and ice processes, and marine biology. The ENVISAT spacecraft
is based on the Polar Platform (PPF) concept and consists of a Service
Module (SM) which provides main support functions, and a
mission-specific Payload Module (PLM) which provides the instruments
and payload support functions. The Payload Module consists of the
Payload Equipment Bay (PEB) and the Payload Carrier (PLC). The Payload
Data Management Subsystem performs instrument and support subsystems,
data processing, telecommand and telemetry management, data-bus
control, failure management, and instrument operations timeline
management. Commonad and control is provided by the Payload Module
Computer (PMC). Scientific data generated from the instruments will be
processed by the High Speed Multiplexer (HSM) for recording or
transmission to the ground. A set of four tape recorders provide a
recording speed of 2 to 4 Mbps and a capacity of 25 Gbits. The
communication subsystem uses an x-band link directly to the ground and
a Ka-band bi-directional link via ESA's Data Relay Satellite
(DRS). The Thermal Control Subsystem consists of a Heater Switching
Unit (HSU), heaters, thermistors and thermostats. The Service Module
(SM) consists of a carbon-fibre-reinforced plastic (CFRP) cone with a
launcher interface at one end and a propulsion module at the
other. The power subsystem consists of up to eight nickel-cadmium
batteries (40 Ahr) and a modular solar array. The SM on-board data
management is done by the Central Computer Unit (CCU). Command and
contral are done via S-band communications direct to the ground or
through the DRS. The Attitude and Orbit Control Subsystem (AOCS)
provides three-axis stabilization. Altitude measurements will be
provided by digital Sun sensors, Earth-horizon sensors and gyroscopes
while altitude control will be provided by monopropellent
thrusters. Fine pointing is accomplished through star sensors and
gyroscopes, reaction wheels, and magneto-torquers.
The ENVISAT consists of : (1) Advanced SAR (ASAR), (2) Global Ozone
Monitoring by Occultation of Stars (GOMOS), (3) Medium Resolution Imaging
Spectrometer (MERIS), (4) Michelson Interferometer for Passive Atmospheric
Sounding (MIPAS), (5) Radar Altimeter-2 (RA-2), (6) Advanced Along Track
Scanning Radiometer (AATSR), (7) Scanning Imaging Absorption Spectrometer
for Atmospheric Cartography (SCIMACHY), (8) Microwave Radiometer (MWR),
(9) Doppler Orbitography and Radiopositioning Integrated by Satellite
(DORIS), and (10) a Laser Retroreflector (LRR) for tracking.
Just weeks after celebrating its tenth year in orbit, communication with the Envisat satellite was suddenly lost on 8 April. Following rigorous attempts to re-establish contact and the investigation of failure scenarios, the end of the mission is being declared. 
