Distributed Spacecraft Autonomy - Development of Swarm Autonomy Capability and Scalability for Spacecraft

The Distributed Spacecraft Autonomy project is developing a suite of software tools that
enable an operator to command and receive data from a swarm as a single entity, enable a swarm
to autonomously coordinate its actions via distributed decision making and reactive closed-loop
control, and model swarm behavior in the presence of anomalies or failures. Our use case is the
mapping of the electron density of the ionosphere using radio tomography by coordinating the
selection of appropriate GPS channels, and by recording Total Electron Count (TEC)
measurements. DSA will be demonstrated onboard the NASA Ames Starling mission – a swarm
of four small, LEO spacecraft, scheduled to launch in 2021. We will also perform a ground
demonstration with simulated and hardware-in-the-loop elements, to validate the tools for
controlling swarms of up to 100 assets.
The capability to communicate autonomously between the swarm satellites is
demonstrated via a sophisticated simulation architecture. Historical Plasmasphere TEC data
obtained via dual-band Novatel GPS Receivers are utilized as a representative input dataset for
the swarm. The representative TEC data and GPS satellite observability information is fed to the
autonomous software package in place of a true real-time ground data collection process. The
swarm satellites actively share status updates amongst one another and utilize multi-agent
decision making to optimally identify regions of interest in the TEC distribution. The software,
aware of the bandwidth limitations of the swarm satellites, prioritizes explorative measurements,
which define the range of observability for the satellites, as well as exploitative measurements,
which focus on maximizing the observance potential of regions with prolonged, elevated TEC
density. The science of this study can ultimately be used to determine the dynamics and coupling
of Earth’s magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial
inputs. The findings can be applied to the imaging of critical, transient phenomena in the
magnetosphere in later missions. Meanwhile, the swarm autonomy capabilities have far reaching
potential in future satellite missions.
As an experimental demonstration of the autonomous capabilities of the network, a
message is first printed within a core Flight Executive (cFE) application. Two cFE applications
that communicate with one another within the same core Flight System (cFS) are shown.
Communication between mission applications on the internal cFE bus is extended to utilize Data
Distribution Service (DDS) for vehicle-to-vehicle networking. The DDS middleware provides
reliable delivery, routing, and topic subscription features over User Datagram Protocol (UDP).
Leveraging Linux containerization, a networked set of satellite instances are generated by script
to simulate swarm behavior. Swarm commanding and synchronization through the network is
demonstrated under various topologies and data-loss conditions. Finally, autonomous swarm
scalability from 2 satellites to 100 satellites is shown.