Functional Model for Spacecraft Operations

Dave Welch, Jay Karlin
WelchD@thorin.atsc.allied.com
Allied Signal Technical Services Corporation

Abstract:
In the past, space projects have used developmental work breakdown
structures based on traditional mission support organizational structures,
Inconsistencies among the structures within each area make it difficult to
transition functionality from one development area to another, either between
ground components or from the ground system to the flight system.  A
functional breakdown of spacecraft mission operations is needed as a starting
point for use in operational concept development.  Such a breakdown enables
the identification of what is needed in each component under alternative
allocations of functions across a mission operations system.  This assures
that all mission support requirements are met by all the options considered
when performing trade studies.

The largest hurdle to overcome in creating such a functional breakdown is
getting beyond a development bias which tends to retain traditional
functional allocations.  The organizational focus of 'who* and 'where* needs
to be separated from the functional focus of 'how*, or the mission concept
can be distorted.  IDEF (Integrated Computer-Aided Manufacturing (ICAM)
DEFinition), particularly IDEFO, produces structured representations of the
functions in a system and of the information and objects which interrelate
those functions.  Using IDEFO resulted in a model of 'pure* functions for use
during early mission concept development.  This model can be used to assign
functional requirements to elements within various organizations in a way
that allows better understanding of the full capability required of each.

By using such a model, mission trades between space, ground and
operations can now be done in a way that allows for a true comparison between
performing functions in these various environments.  These provide the basis
for end-to-end mission life cycle cost estimates which can be realistically
viewed by all of the contributors to a mission's development.  This will now
allow a new user or owner of a system to have the ability to gauge and
compare various systems and implementations and will provide a better
understanding of the 'cost of performance*.