From Earth to Orbit with Linux and SpaceX
DannyB writes:
From Earth to orbit with Linux and SpaceX
SpaceX's Crew Dragon [...] successfully delivered NASA astronauts Bob Behnken and Doug Hurley into orbit. Taking them was SpaceX's reusable Falcon 9, powered by rocket fuel and Linux.
Like supercomputers, Internet of Things (IoT) devices, and many mission-critical devices, the Falcon 9 flies with Linux. SpaceX's software engineers explained several years ago how the Falcon 9 programming works.
[...] The Falcon 9's onboard operating system is a stripped-down Linux running on three ordinary dual-core x86 processors. The flight software itself runs separately on each processor and is written in C/C++.
[...] Because the first stage of the Falcon 9 lands itself, its chips don't need to be radiation hardened.
[...] as explained on StackExchange Space Exploration, SpaceX uses an Actor-Judge system to provide safety through redundancy. In this system, every time a decision is made, it's compared to the results from the other cores. If there's any disagreement, the decision is thrown out and the process is restarted. It's only when every processor comes up with the same answer that a command is sent to the PowerPC microcontrollers.
[...] The point of this triple "tell-me three times" redundancy is to give the fault tolerance it needs without having to pay for expensive space-specific chips. Modern planes, like the newer Airbus planes, use a similar approach in their fly-by-wire systems.
The Dragon spacecraft also runs Linux with flight software written in C++. The ship's touchscreen interface is rendered using Chromium and JavaScript. If something were to go wrong with the interface, the astronauts have physical buttons to control the spacecraft.
Chromium and JavaScript are used for the Dragon 2's interactive displays -- with 100% test coverage.
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