An implementation to receive, moderate, store, and send end-user text messages (called SpacePosts) on a satellite in embedded C++ using NASA JPL's F' flight software framework.
It enables users to publish their own text messages to a satellite and receive all other users' published text messages from that satellite.
- Summary
- Table of Contents
- Description
- Technologies
- Features
- Design
- Tests
- How To Use This Software
- Credits
- License
This repository presents one part of my contribution to the MEMESat-1 satellite during a 7-week full-time (40h/week) position as a Flight Software Engineer in the Command & Data Handling (CDH) team at the University of Georgia's Small Satellite Research Laboratory.
- Developed 4 flight software components for a satellite in embedded C++17 with 2,600 lines of code in NASA's F' framework by designing, implementing, and testing them from scratch
- Ensured space-grade code quality standards with 100% line coverage and 90% branch coverage by data-driven unit testing with GoogleTest as well as thorough code reviews
- Elicited the requirements for the SpacePosts software product by discussing the desired functionality and security needs with MEMESat-1's mission leadership and the funding organization's CEO, resulting in a product that closely conforms with the satellite's mission goals
- Documented the engineering process extensively on 60 pages with 2 lines of documentation per developed line of code by establishing software engineering best practices in the embedded engineering team, resulting in improved knowledge transfer within the team
SpacePosts realize a public bulletin board for text messages on a satellite in space. Anyone with amateur radio equipment shall be able to interact with the bulletin board. Essentially, users can post SpacePosts to the board and read all SpacePosts from the board. A SpacePost consists of a simple text message, just like a Tweet on Twitter.
For everyone without amateur radio equipment, there is a website that allows them to publish and read SpacePosts from the board through a ground station that handles transmitting and receiving.
In fact, SpacePosts are not only a theoretical concept but they are being realized in the form of the MEMESat-1 CubeSat satellite at the University of Georgia's Small Satellite Research Laboratory.
MEMESat-1 is set to be launched into space in cooperation with NASA in Q2-2024. It is built for a nonprofit organization that will use the satellite in education workshops for high school students.
This repository spotlights how I contributed to MEMESat-1 by developing the entire satellite-side software system for SpacePosts on MEMESat-1. I defined, designed, implemented, and tested this software as one part of my work during a 7-week full-time (40h/week) position as a Flight Software Engineer in the Command & Data Handling (CDH) team.
- C++17 Programming Language in Embedded Environment
- NASA JPL's F' (F Prime) Flight Software Framework
- GoogleTest Unit Test Framework
F´ (F Prime) is an open-source component-driven framework for spaceflight and other embedded software applications. Originally developed at the NASA JPL, F´ has been deployed on several space applications like the Mars Helicopter Ingenuity. It is tailored but not limited to small-scale spaceflight systems such as CubeSats.
Purpose: The SpacePost system enables users to publish their own SpacePost to a satellite and receive all other users' published SpacePosts from that satellite.
Product Environment: The SpacePost system will be deployed on the Raspberry Pi CM4 of the MEMESat-1 CubeSat satellite.
- Users can post a message to the satellite
- Receive message upload from earth
- Apply a moderation check to the message
- Store the message on the satellite
- Users can request all posted messages
- Load messages from the satellite
- Send the messages to earth
The system is realized by introducing three new components and by interfacing with three components of the F' framework.
UML Component Diagram
The following three components have been custom-developed for this system:
-
MessageStorage (also see the full component specification)
Component with one port to accept a
SpacePostto store it on the file system and another port to load a given number of recently storedSpacePosts.It is a separate component because it encapsulates the general logic for storing
Fw::SerializableC++ objects in a file on the file system using the Operating System Abstraction Layer (OSAL) of F'. Thus, the component can easily be adapted to additionally store other types than onlySpacePosts on the satellite's file system in the future. -
Moderator (also see the full component specification)
Component with one input port and one output port where
SpacePosts given to the input port must pass a moderation check to be output on the output port.It has the same interface for storing (i.e., with the same input port type) as the MessageStorage component. Thus, it can be optionally plugged in between the Transceiver component and the MessageStorage component without any of them knowing about the existence of the Moderator component. Therefore it is reasonable to have the Moderator as a separate component.
-
Transceiver (also see the full component specification)
Component to receive
SpacePosts from users on the ground and to downlink theSpacePosts stored on the satellite to users on the ground.It is a separate component because it encapsulates how users can trigger the loading and storing of
SpacePosts on the satellite. Consequently, the Transceiver implementation can be swapped out to change how the satellite communicates messages with users on the ground.
The system uses the following three framework components to integrate its functionality into the F' reference flight software system Ref:
- Svc.CommandDispatcher: Receives commands sent to the satellite by ground station operators and forwards them to the appropriate component.
- Svc.ActiveRateGroup: Calls the Transceiver component's
scheduleDownlinkport at a fixed rate to consistently trigger downlinking theSpacePosts stored on the satellite. - Svc.Framer: Handles downlinking a given F' type to the ground station.
The following UML sequence diagrams exemplarily outline how the defined components interact to fulfill the two use cases of posting and requesting messages. The custom-developed components are highlighted in orange.
Receive a SpacePost to store on the satellite
Two SpacePosts are sent to the satellite after each other. The first one is discarded during moderation, the second one passes moderation.
Send recently stored SpacePosts from the satellite
The system downlinks recently stored SpacePosts twice. The first time is in response to a request via a command from the ground station. The second one is triggered by an ActiveRateGroup which calls the Transceiver's scheduleDownlink port.
I developed unit tests for the components that cover 100% of the code lines and 90% of the code branches. Most unit tests follow the data-driven unit test style. I implemented them with the GoogleTest testing library. I applied both black-box Boundary Value Analysis and white-box Control Flow Testing strategies. For the MessageStorage component, I additionally designed an object-oriented model of test utility classes to facilitate simple unit test code.
See the MessageStorage Unit Test Documentation.
The SpacePost system implementation in this repository is not meant to be a stand-alone flight software. Instead, it is a module that can be added to any flight software system written in F'.
Other developers can use the implementation provided in this repository by adding the SpacePost module to their code base and connecting the SpacePost components' ports to their flight software (see Used Framework Components).
Meet the system requirements
- Linux or macOS operating system
- git
- CMake 3.16 or newer. CLI tool must be available on the system path.
- CLang or GCC compiler
- Python 3.7+, virtual environments, and PIP
Install F' v3.1.0
- Set up a virtual environment for F' and activate it:
Choose a location to generate a virtual environment. This can be any path the user has read and write access to. The example uses the path
$HOME/fprime-venv.
python3 -m venv $HOME/fprime-venv
source $HOME/fprime-venv/bin/activate
pip install -U setuptools setuptools_scm wheel pip
- Clone and install F':
Clone their core repository.
F´ ships with a
requirements.txtfile enumerating the tools F´ uses and their specific tested versions.
git clone https://github.com/nasa/fprime
git checkout v3.1.0
pip install -r fprime/requirements.txt
Install SpacePosts
Switch into the cloned fprime repository directory and clone the SpacePosts repository into the SpacePosts/ directory. You may wish to create a Git submodule for it.
cd fprime
git clone https://github.com/mabdn/fprime-spaceposts SpacePosts
Test the installation and build your deployment
Follow the typical steps to test and build an installation in F' (see F' Installation Guide). For example, build the individual SpacePost components.
Then, connect your F' flight software to the SpacePosts topology (see Integration With An Existing F' Flight Software System). If you do not have your own F' flight software, you can always use the Ref flight software example deployment provided by the F' framework.
Developed based on NASA's F' Flight Software Framework.
Purpose-built as a part of the MEMESat-1 satellite mission at the University of Georgia's Small Satellite Research Laboratory (SSRL).
Licensed under the MIT License.