The EnviSat-1 Satellite

Overall Configuration

The major driver for the Polar Platform / EnviSat-1 satellite configuration has been the need to maximise the payload instrument mounting area and to meet the viewing requirements within the constraints of the Ariane 5 fairing and interfaces.

In addition, the configuration also has been driven by the re-use of the SPOT Mk II Service Module concept and the ERS payload accommodation experience (concept of instrument electronics in an internal enclosure with externally mounted antennas).

In flight, the major spacecraft longitudinal axis (the Xs axis) is normal to the orbit plane, the -Ys axis is closely aligned to the velocity vector and the -Zs axis is Earth pointing. This configuration concept provides a large, modular, Earth facing mounting surface for payload instruments and an anti-sun face for radiative coolers, free of occultation by satellite subsystem equipments.

The Polar Platform

The Polar Platform (PPF) represents, with its payload, the largest European satellite undertaken so far. It was conceived as a multimission platform which can accomodate a number of different missions. The Polar Platform is comprised of two major modules:

The Service Module (SM), the design of which is largely derived from SPOT 4, provides the main satellite support functions, such as commad 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), on which the EnviSat-1 instruments and PPF payload support equipment (data management and communications, electrical distribution) are accomodated.

This split provides the basis for a convenient physical and functional separation between the SM subsystems and equipments 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.

Payload description

Satellite Budgets

Mass Budget

	Mass (kg)
Service Module	2673
Payload Equipment Bay	1021
Payload Carrier	2078
Fuel	319
Payload Instruments	2118
Total	8211

Power Budget

	Average Power (W)
	Sunlight	Eclipse
Payload	1841	1886
Payload Module	860	527
Service Module	859	684
Total Load	3560	3097
System Capability	3847	3291