The Service Module consists of a closed box, shaped around a hollow central cone, and comprises the lower and upper platforms as well as four side panels, on which all satellite bus units are installed. The functions provided by the Service Module (SVM) are:

• The primary and secondary structures to interface with the launcher adapter, to support the subsystem units, and to interface with and support the Mirror Support Platform and the Telescope Tube
• The thermal control to maintain the SVM units and equipment within specified temperature limits, and to provide a very strictly controlled thermal environment for the mirror assemblies
• The Attitude and Orbit Control System (AOCS) for precise pointing/slewing in all operational modes, and for the performance of orbit acquisition/maintenance via the RCS propulsion system (reaction Control System)
• The On-Board Data Handling (OBHD) for the decoding of ground telecommands, the distribution of ground on-board commands, the sampling and formatting of telemetry data, and central on-board time distribution
• The Radio Frequency System (RFS), operating in S-band, ensuring communications with the ground stations and providing a ranging mode for orbit determination
• The Electrical Power Subsystem (EPSS) for the generation and distribution of regulated power to all equipment via a 28 V main bus

An exploded view of the XMM Service Module, with its side panels open. Thanks to its particular shape, with a large central hole of 2.10 m diameter, the XMM bus can be used to accommodate a large variety of payloads.

	Structural Design
	Attitude and Orbital Control Systems (AOCS)