Overview

Introduction to NOS

The New Observing Strategies (NOS) initiative within the NASA Earth Science Technology Office Advanced Information Systems Technology program envisions future Earth science missions with distributed sensors (nodes) interconnected by a communications fabric that enables dynamic and intelligent operations. Some NOS concepts resemble systems-of-systems or collaborative systems where operational authority is distributed among multiple systems, necessitating new methods for systems engineering and design to cope with more decentralized control over constituent systems.

NOS-T Architecture

NOS-T is best suited for conceptual, systems-level design of NOS components and operational concepts. The system architecture follows a loosely-coupled event-driven architecture (EDA) where member nodes communicate through events in the form of notification messages sent over a network.

Key characteristics of the NOS-T architecture:

• Flexible Node Types: Nodes can be software applications, simulation models, science databases, or hardware

• Enhanced Scalability: The EDA provides scalability and reliability by using consistent event-handling functions

• Modular Design: Participants can join and leave experiments without reconfiguring the testbed

• Security: Maintains protection of proprietary software and data while enabling cross-organizational tests

Event Broker Infrastructure

The NOS-T architecture relies on a centralized infrastructure component called an event broker (or message broker) to exchange event notifications between applications. A broker simplifies communication by requiring each application to connect only to the broker, rather than directly to every other application.

NOS-T adopts RabbitMQ, an open-source message broker implementing the Advanced Message Queuing Protocol (AMQP). RabbitMQ uses a publish-subscribe messaging pattern with:

• Publishers: Applications that produce events

• Subscribers: Applications that consume events

• Topics: Categories for event types that applications can publish to or subscribe to

Event-Driven Architecture with Centralized Broker

System Components

NOS-T consists of two top-level system components:

1. User System (tailored to each test case):

   • Consists of user applications developed by users

   • Applications run on separate hosts controlled by each user

   • Can model entire observing systems or individual components (sensors, communication links, algorithms, etc.)

   • Must meet basic NOS-T interface requirements for orchestration

2. NOS-T System (fixed for all test cases):

   • Managed by an NOS-T operator

   • Includes the event broker infrastructure

   • Contains a manager application that orchestrates test runs

   • Ensures proper application synchronization, topic configuration, and consistent message structure

NOS-T Graphical Concept: Visual representation of the testbed architecture and operational flow

Development Tools

To aid in application development, the open-source[*] NOS-T tools library provides templates for implementing basic NOS-T functionality:

• Manager application template: Orchestrates test execution

• Network Time Protocol (NTP) capabilities: Synchronizes applications across distributed systems

• Observer templates: For implementing sensor applications

• Observable templates: For science applications

• Publisher templates: For regular messaging (e.g., “heartbeat” messages)

• Broker connection utilities: For connecting to the message broker

Network Time Protocol (NTP) Round Trip Time Delay

Language Compatibility

While the NOS-T tools and most example applications are coded in Python, the system supports multiple programming languages:

• Any language with RabbitMQ interface libraries can be used

• Supported protocols include AMQP and MQTT

• Examples of compatible platforms:

  • JavaScript (used in the “scoreboard” geospatial visualization)

  • MATLAB (via available RabbitMQ libraries)

Applications in a test suite can use different programming languages as long as they maintain a common message structure.

[*]

BSD 3-clause license (Dec. 16, 2021, Reference FY22-005)