Brian Barritt

Space Communications and Navigation (SCaN) Network Simulation Tool Development and Its Use Cases

In this work, we focus on the development of a simulation tool to assist in analysis of current and future (proposed) network architectures for NASA. Specifically, the Space Communications and Navigation (SCaN) Network is being architected as an integrated set of new assets and a federation of upgraded legacy systems. The SCaN architecture for the initial missions for returning humans to the moon and beyond will include the Space Network (SN) and the Near-Earth Network (NEN). In addition to SCaN, the initial mission scenario involves a Crew Exploration Vehicle (CEV), the International Space Station (ISS) and NASA Integrated Services Network (NISN). We call the tool being developed the SCaN Network Integration and Engineering (SCaN NIE (2) to optimize system configurations by testing a larger parameter space than may be feasible in either production networks or an emulated environment; (3) to test solutions in order to find issues/risks before committing more significant resources needed to produce real hardware or flight software systems. We describe two use cases of the tool: (1) standalone simulation of CEV to ISS baseline scenario to determine network performance, (2) participation in Distributed Simulation Integration Laboratory (DSIL) tests to perform function testing and verify interface and interoperability of geographically dispersed simulations/emulations.

Unified approach to modeling & simulation of space communication networks and systems

Network simulator software tools are often used to model the behaviors and interactions of applications, protocols, packets, and data links in terrestrial communication networks. Other software tools that model the physics, orbital dynamics, and RF characteristics of space systems have matured to allow for rapid, detailed analysis of space communication links. However, the absence of a unified toolset that integrates the two modeling approaches has encumbered the systems engineers tasked with the design, architecture, and analysis of complex space communication networks and systems. This paper presents the unified approach and describes the motivation, challenges, and our solution — the customization of the network simulator to integrate with astronautical analysis software tools for high-fidelity end-to-end simulation.

Temporospatial SDN for Aerospace Communications

This paper describes the development of new methods and software leveraging Software Defined Networking (SDN) technology that has become common in terrestrial networking. We are using SDN to improve the state-of-the-art in design and operation of aerospace communication networks. SDN enables the implementation of services and applications that control, monitor, and reconfigure the network layer and switching functionality. SDN provides a software abstraction layer that yields a logically centralized view of the network for control plane services and applications. Recently, new requirements have led to proposals to extend this concept for Software-Defined Wireless Networks (SDWN), which decouple radio control functions, such as spectrum management, mobility management, and interference management, from the radio data-plane. By combining these concepts with high-fidelity modeling of predicted mobility patterns and wireless communications models, we can enable SDN applications that optimally and autonomously handle aerospace network operations, including steerable beam control, RF interference mitigation, and network routing updates. This approach is specifically applicable to new constellation designs for LEO relay networks that include hundreds or thousands of spacecraft, serving millions of users, and exceed the ability of legacy network management tools.

Astrolink for Modeling, Simulation, and Operation of Aerospace Communication Networks

This paper describes the development of new methods and software for the realistic modeling, simulation, and emulation of networked communications in aerospace systems – unifying the highest-fidelity physical models available with detailed network protocol stack models. Astrolink is an implementation of a new framework for simulator integration through lightweight middleware that marries the physical interface models between multiple simulators. Our framework supports flexibly interchanging the network and geospatial astrodynamic simulators in use – and even supports multiple network or geospatial astrodynamic simulators to be used simultaneously for different parts of a system. Astrolink is currently in an early stage, supporting only the ns-3 network simulator and AGI’s Systems Tool Kit (STK) for physics; but, the design explicitly permits easy addition of other simulators, such as Riverbed’s OPNET Modeler, SNT’s QualNet/EXata, ns-2, ESA’s STA, NASA Goddard’s GMAT, SaVi, and others. Astrolink’s extensibility is enabled via a simple protocol that abstracts the physical interface information exported by the simulators and brings this information into a GUI, where a user can bind networking elements with physical assets before initiating the simulation/emulation scenario.

Wallops' low elevation link analysis for the Constellation launch/ascent links

Prior to the redirection of the Constellation Program, the Wallops 11.3-meter ground station was tasked to support the Orions Dissimilar Voice (DV) link and the Aress Development Flight Instrument (DFI) link. Detailed analysis of the launch trajectories indicates that during the launch and ascent operation, the critical events of Orion-Ares main engine cut off (MECO) and Separation occur at low elevation angle. We worked with engineers from both Wallops Flight Facility (WFF) and Johnson Space Center (JSC) to perform an intensive measurement and link analysis campaign on the DV and DFI links. The main results were as follows: (1) The DV links have more than 3 dB margin at MECO and Separation. (2) The DFI links have 0 dB margin at Separation during certain weather condition in summer season. (3) Tropospheric scintillation loss is the major impairment at low elevation angle. (4) The current scintillation models in the Recommendation ITU-R P.618 (Propagation data and prediction methods required for the design of Earth-space telecommunication systems), which are based on limited experimental and theoretical work, exhibit idiosyncratic behaviors. We developed an improved model based on the measurements of recent Shuttle mission launch and ascent links and the ITU propagation data. (5) Due to the attitude uncertainty of the Orion-Ares stack, the high dynamics of the launch and ascent trajectory, and the irregularity of the Orion and Ares antenna patterns, we employed new link analysis approach to model the spacecraft antenna gain.

Integrated Approach to Architecting, Modeling, and Simulation of Complex Space Communication Networks

Space communication infrastructure continues to support legacy space mission users and interfaces while simultaneously building advanced capabilities to support new mission users, who are demanding higher data-rates and more modern interfaces. As a result, the space communication infrastructure is growing more complex every day. This level of complexity requires new techniques to define and analyze network architectures, offering needed improvements in accessibility, flexibility, and interoperability. To discover, characterize, and convey the performance and interactions of the elements within space communication network architectures, an approach has been pioneered that utilizes formal system modeling, architecture frameworks, and integrated network stack and space environment physics simulation during the early-stage of project lifecycles. This integrated approach directly aids in high-level decision-making and has the potential to reduce costs, increase reliability, and enable faster development. It has been adapted and applied within several architecture projects, including the integration of NASA’s Space Communications and Navigation (SCaN) networks, supporting development of the NASA Constellation Program’s space communication infrastructure, and in supporting the modernization of NASA’s Space Network. This paper describes the integrated architecture, modeling, and simulation approach and processes that have been used to support these projects. The commercial software tools used for architecture modeling and network simulations are also presented along with the custom software tools being developed to facilitate the integrated approach.