Comms Track: Spacecraft Links and Flight Software Basics · Module 3 of 4 · about 15 min
The flight computer: commands, telemetry and fault protection
On board, one computer usually runs the show. NASA's Basics of Space Flight calls it the command and data subsystem, though missions use other names. It keeps time, interprets commands from Earth, collects and formats telemetry for the trip home, and runs the high-level fault protection. Avionics is the broader word for the electronics that do this work, and many of the "avionics" and "embedded" jobs on our board are about building, testing or flying that hardware and its software.
Most spacecraft activity runs from stored command sequences. Operators build a timeline on the ground, check it in simulation, uplink it, and the flight computer executes it on schedule. With minutes of light delay, that is the only practical way to work, and it is why ground software, sequencing and simulation are careers of their own.
Space is hard on electronics. Energetic particles can flip a bit in memory, an event called a single event upset. Designers respond with radiation-tolerant parts, memory that detects and corrects errors, and watchdog timers that reset a processor if the software stops checking in. When something goes wrong that the software cannot handle, fault protection puts the spacecraft into a safe mode: it stops the planned activity, points its power and antennas where they need to be, and waits for instructions from the ground.
A lot of flight software is built on shared frameworks rather than written from scratch. NASA Goddard's core Flight System (cFS) is one example. It is open source, it splits flight software into reusable apps, and you can download it from GitHub and run it on a laptop. If you want something concrete to put on a resume, building and running cFS and writing a small app for it is a real project.
NASA also sets rules for how its software is engineered. NASA Procedural Requirements 7150.2 sorts software into classes by how much is riding on it, with the most critical software held to the strictest process. You do not need to memorize the classes, but knowing that safety-critical flight code is reviewed, tested and documented far more heavily than an app is the kind of context interviewers notice.
Sources
- NASA Basics of Space Flight, Chapter 11: Onboard Systems
- NASA core Flight System (cFS)
- cFS on GitHub
- NASA Software Engineering Handbook (NPR 7150.2)
Module quiz
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