A complex system like the Earth's environment with its
atmosphere and oceans interacting on a wide range of temporal and spatial
scales is realistically impossible to fully monitor or measure within
practical constraints. In order to make a useful contribution, the Envisat-1
mission's overall objectives have to be carefully defined and a specific set
of multidisciplinary, complementary payload instruments selected by the
Programme Board for Earth Observation, supported by scientific advisory groups
(SAG).
The eventual payload complement was identified in a selection
process which included available financial budget and physical system
constraints. Its instruments have been selected to support synergism between
their measurements and between scientific disciplines, thus making the total
payload complement more than just the sum of the instruments.
The payload consists of a set of instruments for measuring the
atmosphere and instruments for measuring the surface through the atmosphere.
This set of instruments operates over a wide range of the electromagnetic
spectrum, ranging from centimetre waves to the ultraviolet.
Payload instrument list
There are two radar instruments, three spectrometers of
different types and measurement characteristics, two different radiometers
(broad and narrow band), the first high-resolution spaceborne interferometer
for long-term observation, and two instruments for range measurements:
- Michelson Interferometer for Passive Atmospheric Sounding
(MIPAS);
- Global Ozone Monitoring by Occultation of Stars
(GOMOS);
- Scanning Imaging Absorption Spectrometer for Atmospheric
Cartography (SCIAMACHY);
- Medium Resolution Imaging Spectrometer (MERIS);
- Advanced Along Track Scanning Radiometer (AATSR);
- Advanced Synthetic Aperture Radar (ASAR);
- Radar Altimeter 2 (RA-2);
- Microwave Radiometer (MWR);
- Doppler Orbitography and Radiopositioning Integrated by
Satellite (DORIS);
- Laser Retro-Reflector (LRR).
Payload instrument responsibilities
The instruments fall into two categories reflecting the
responsibilities for their development and procurement:
- EDIs - ESA development instruments, developed within the
Envisat-1 programme; and
- AOIs - Announcement of Opportunity instruments (AATSR,
SCIAMACHY, and DORIS) provided by national or multinational
institutions.
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Polar Platform
Introduction |
The Polar Platform (PPF) represents, with its payload,
the largest European satellite undertaken so far. It was conceived as a
multimission platform which can accommodate a number of different missions.
The Polar Platform is comprised of two major modules:
- The service module (SM, see below), the design of which is
largely derived from SPOT 4, provides the main satellite support functions,
such as command and control, communications with the ground, power, attitude
and orbit control, and propulsion. It also interfaces with the launcher,
Ariane 5.
- The payload module (PLM, see below), on which the Envisat-1
instruments and PPF payload support equipment (data management and
communications, electrical distribution) are accommodated.
This split provides the basis for a convenient physical and
functional separation between the SM subsystems and equipment which are needed
for every mission, and those in the PLM which are mission-specific and
therefore dedicated only to the needs of the particular payload complement
being flown. In addition, the interface decoupling at module level facilitates
parallel development and integration of service and payload modules, and
allows for a schedule-efficient satellite integration programme where only the
minimum of system level activities is needed for final verification. A
structural model programme has been performed with both modules coupled and
representative instrument models also included, as seen here during
integration and in the acoustic test chamber.
