The two main elements of the satellite are:
· the payload
· the bus

Payload
The payload contains all the systems required by the main mission. It consists of: · an equipment bay, a carbon-fibre lattice structure providing dimensional stability for the instruments and supporting the image processing, data storage and transmission electronics · imaging instruments: two HRGs, the new HRS and VEGETATION

The two HRG instruments are derived from the HRVIR instruments on SPOT 4 and use the same viewing configuration. The new HRS instrument, mounted next to the VEGETATION 2 instrument, points forward and aft of the satellite to acquire near-simultaneous stereopair images of the same ground strip.

Image data are compressed and formatted, then stored on board in a 90-Gbit memory. They are sent to ground in real time if a direct receiving station is within view, or stored and sent later when the satellite passes over one of the two main receiving stations in Toulouse, France, and Kiruna, Sweden. Data are sent at a rate of 2x50 Mbits per second. The VEGETATION 2 instrument provides almost daily global coverage at a resolution of one kilometre, as on SPOT 4.

Payload (3D view)

Bus
The bus is designed to provide all the housekeeping functions required to accomplish the mission, i.e.:
· interfaces with the Ariane 4 launch vehicle
· electric power generation, distribution and storage
· three-axis attitude control · precise orbit control
· monitoring and control of equipment and image acquisition by the onboard computer flight software
· links with the ground for telemetry, telecommand and location.

Flight model of the SPOT 5 bus during
solar vacuum tests at Intespace (February 2001)

The SPOT 5 bus is derived from SPOT 4. Changes have been made based on lessons learned from SPOT 4 and to replace obsolete electronic components. The major new feature is a star tracker that will greatly increase the accuracy of satellite attitude data.

The bus has the same basic mechanical architecture as its predecessors, with a propulsion module and a service module. The propulsion module is new, with a titanium central thrust tube. Its two tanks can store 150 kilograms of hydrazine propellant.

The service module, packed with electronic equipment and also built around a central thrust tube, is the backbone of the satellite and houses the battery compartment.

Development of the SPOT 5 bus exploited efficiencies with France's Helios 2 military observation satellites. Both satellites' buses have the same overall architecture and most of their equipment is identical.

Bus block diagram
Exploded view