SAX: Operational Features

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Operational Concept

Orbiting at an altitude of 600 km in a near circular orbit, SAX communications will be performed solely via a near-equatorial Ground Station. Ground-to-satellite coverage time is estimated to be approximately 10 minutes each 96 minute (nominal) orbit, during which time all telecommands must be up linked to the Satellite and stored and real-time science and housekeeping data transmitted to Ground.

Due to the low coverage time, SAX has been designed primarily to be as autonomous as possible, as far as Operability and Fault Management are concerned, while maintaining an operational flexibility necessary for the varied scientific observations of the mission.

Mission Phases

The SAX mission can be divided into the four overall mission phases.

Launch Phase

It begins at Spacecraft power-on by Electrical Ground Support Equipment before vehicle lift-off, and extends to the physical separation between the launch vehicle and SAX.

Commissioning Phase

It begins following SAX-Launcher separation and extends to the completion of all initial in-orbit tests and calibrations. It consists of an Early Orbit Phase which comprises a reduction of the Satellite body rates using the reaction wheels and subsequent Sun/Earth acquisition period. Upon successful completion of the previous activities, Solar Array deployment takes place and the early orbit phase is completed on successful verification using the telecommand/telemetry link with Ground.

The commissioning of the Satellite shall begin with an initial Satellite health check-out continuing with systematic functional checks of all the Satellite's SubSystems.

A second phase shall follow the activation of the science instruments, involving stand-by mode verification, deployment of the C/S baffles and unlocking of the PDS and HP-GSPC collimators, followed by activation and testing of the instrument detectors.

Verification of the Satellite Subsystems shall continue while the instruments are brought to full operational capability performing Instrument calibrations in predefined observations.

Operational Orbit Phase

It covers the Satellite's useful scientific lifetime, which shall be nominally two years, characterized by routine scientific operations where the principle observing instruments shall change periodically between the NFIs the WFCs every two or three weeks.

End of Life Phase

It covers the period when SAX is no longer capable of producing useful scientific information due to either component degradation or altitude decay.

This file was last modified on Wednesday, 09-Sep-1998 13:41:48 CEST by Mauro Orlandini

Next: Launch Description Previous: Electrical GSE
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