A fractionated spacecraft is a cluster of independent
modules that interact wirelessly to maintain cluster flight and
realize the functions usually performed by a monolithic satellite.
This spacecraft architecture poses novel software challenges
because the hardware platform is inherently distributed, with
highly fluctuating connectivity among the modules. It is critical
for mission success to support autonomous fault management
and to satisfy real-time performance requirements. It is also
both critical and challenging to support multiple organizations
and users whose diverse software applications have changing demands
for computational and communication resources, while
operating on different levels and in separate domains of security.

The solution proposed in this paper is based on a layered architecture
consisting of a novel operating system, a middleware
layer, and component-structured applications. The operating
system provides primitives for concurrency, synchronization,
and secure information flows; it also enforces application separation
and resource management policies. The middleware
provides higher-level services supporting request/response and
publish/subscribe interactions for distributed software. The
component model facilitates the creation of software applications
from modular and reusable components that are deployed
in the distributed system and interact only through well-defined
mechanisms.

Two cross-cutting aspects - multi-level security and multilayered
fault management - are addressed at all levels of the
architecture. The complexity of creating applications and performing
system integration is mitigated through the use of a
domain-specific model-driven development process that relies
on a dedicated modeling language and its accompanying graphical
modeling tools, software generators for synthesizing infrastructure
code, and the extensive use of model-based analysis for
verification and validation.