The Software Maintenance: Concepts, Implementation and Gained
Experience for SAX Program

Andrea MARTELLI
AMARTELL@TO.ALESPAZIO.IT
Alenia Spazio S.p.A.


Abstract:

The autonomy of the SAX Italian Scientific satellite, devoted to supporting a two 
to four years of mission activity, is based on a complex software architecture,
distributed and running on nine on-board computers, with the purpose of caring out
both the nominal and preconceived contingency functions.  In consideration of that,
ground interventions on the on-board software has been identified as a succms key
to be made available prior to the launch to cope with problems that could arise
during the mission lifetime.

This paper describes how the Software Verification Facility, widely used during the
design, development and testing phases of the SAX system software, has been gradually
upgraded into a centralised and integrated Software Maintenance Facility, Therefore,
in agreement with the identified SAX software maintenance policy, this will allow
corrective modifications, applicable to all the software components, and, also,
perfective and evolutive maintenance, applicable, in this case, to the application
software.  An overview of the designed and implemented architecture is then given
presenting the choosen hardware configuration as well as the software developed
tools.  A rationale is also provided on the provided ISDN link with the SAX Operational
Control Center in Rome to get the down-loaded telemetry, Subsequent cross-check with
the satellite EGSE data-base, trouble-shooting.simulations and tests will be carried 
out to provide validated software patches ready to be uploaded to the satellite,

The Software Maintenance Facility properly accomplished its task already before the
SAX launch, providing software modifications as recovery to the "last minute' problems
raised at the very late test stage.  Lessons learned through experience gained on both
this phase and the in-orbit commissioning will eventually be presented.