Just like a PC?
What computer and software is used by the Falcon 9? (2015)
61–70 of 160 posts
Re: What computer and software is used by the Falcon 9? (2015)
#62For triple redundancy, is there a way to re-sync if one of them disagrees? Control systems tend to have internal states that may be disrupted even if an input has glitched for a single cycle. Will it eventually converge back to nominal? Or is that processor rejected for the duration of the mission?
Re: What computer and software is used by the Falcon 9? (2015)
#63I’ve read a bit about how strict the space shuttle coders were. I wonder what they think about the code running this spacecraft. https://www.fastcompany.com/28121/they-write-right-stuff https://history.nasa.gov/computers/Ch4-5.html https://www.nasa.gov/mission_pages/shuttle/flyout/flyfeature...
There are reports that the procedure for fixing bugs on the STS was so heavy-weight that they often redefined non-fatal bugs as correct operation. The example I read of was an error event that dumped thousands of lines of text to the flight console screen, obscuring useful information.
Basically every change, whether software or hardware, had a lengthy acceptance process. Reviews, analysis, verification and validation, documentation, operation and maintenance procedures, etc.
Re: What computer and software is used by the Falcon 9? (2015)
#64Welp, I called it two weeks ago -
https://news.ycombinator.com/item?id=23146976
Re: What computer and software is used by the Falcon 9? (2015)
#65Sounds kinda disappointing/irresponsible. Chromium is an overly complex, relatively buggy piece of software. For example I recently experienced a bug where a text I selected was significantly offset from what should have been selected given the pointer position (on linux), a misclicky kind of bug. Considering that the majority of Crew Dragon's controls are through touch screen, maybe even manual docking(not sure, but…
Why not Javascript? I would argue that a good usable UI in a spacecraft is a good thing, and Javascript is a great language for building UIs
I would expect the UI in a space ship to be soft realtime. Chromium and JS are anything but.
Re: What computer and software is used by the Falcon 9? (2015)
#66Earlier quoted context omitted.
> Javascript is a great language for building UIs I disagree. It is easy to build something presentable with HTML and browsers, and there have been many JS frameworks that lower the barrier. However, that is not because JS is a good language for it; it is because JS is the only language available in that environment. In fact, there are at least two other languages that transpile to JS, because you need JS to be able…
You haven’t made any arguments about why Javascript isn’t good for building UIs there. Here’s mine for why it is: - first class functions (callback style is a good fit for UI programming) - async/await and single threaded - many components of UIs are async by nature, Javascript supports you well here while keeping things simple with its single threaded model
There's... a large number of languages with both of those features.
Re: What computer and software is used by the Falcon 9? (2015)
#67Interesting that it’s three identical processors running he same software. I remember just the automated Vienna central train station used a pair of machines, x86 and SPARC, one running the logic in a procedural language (Chill) and the other running in a logic language (Prolog). They didn’t want both processors to share any code, and therefore potentially the same bug.
> They didn’t want both processors to share any code, and therefore potentially the same bug. They're not worried about bugs, they're worried about electromagnetic radiation (which is way more present when you get outside the atmosphere) flipping bits.
There have been cases of homogenous CPU architectures in safety-critical where all CPU's failed at once.
Bitflippinrads are one of a multi-variate set of problems that these systems are designed to detect and avoid. Nodes can degrade otherwise: SRAM failure, battery/cap depletion, all sorts of things. The idea is to detect when a voting node has had a catastrophic system failure, and then remove offending nodes from the decision as rapidly as possible.
A multi-architecture system assists with managing (and certifying) things such as compiler bugs and impact from system-level homogeneity, where critical components all exhibit the same bug/failure. An x86 hardware bug is fatal if all 5 of the nodes in a voting system are x86 and making a critical decision; it is less of an issue if the other 2 or 3 nodes are PPC, ARM, MIPS, etc., or a mixture there-of, and - as variant hardware architectures - are democratically still voting during the period .. the idea is to avoid homogeneity and pursue heterogeneity.
Re: What computer and software is used by the Falcon 9? (2015)
#68For triple redundancy, is there a way to re-sync if one of them disagrees? Control systems tend to have internal states that may be disrupted even if an input has glitched for a single cycle. Will it eventually converge back to nominal? Or is that processor rejected for the duration of the mission?
If a flight string desyncs (i.e. it has state at the end of a cycle different from its two siblings) then it is automatically rebooted. Then state is automatically resynced from any other sibling after boot. There is no converging between the strings, they are either in complete sync or they aren’t.
Re: What computer and software is used by the Falcon 9? (2015)
#69Earlier quoted context omitted.
How stateless and independent is each display?
Can't say exactly re statelessness, but I would not be surprised if you could power-cycle all displays if needed in the middle of a mission. As far as independent, completely independent from each other.
> but I would not be surprised if you could power-cycle all displays if needed in the middle of a mission.
Indeed you can, judging by the instruction to power off and clean all displays (then power them back on) prior to ISS rendezvous/docking in the live stream.
Re: What computer and software is used by the Falcon 9? (2015)
#70Sounds kinda disappointing/irresponsible. Chromium is an overly complex, relatively buggy piece of software. For example I recently experienced a bug where a text I selected was significantly offset from what should have been selected given the pointer position (on linux), a misclicky kind of bug. Considering that the majority of Crew Dragon's controls are through touch screen, maybe even manual docking(not sure, but…
The fact that it's implemented in JavaScript and Chromium just tells you the fancy display is entirely superfluous to mission success.
Is there a backup should that fancy display fail? If not, then I'd hardly call it "superfluous to mission success".