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Exploring the software that flies SpaceX rockets and starships

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Re: Exploring the software that flies SpaceX rockets and starships

#41

Post by icegreentea2 »

numpad0 wrote: post #29
sudhirj wrote: post #4

Earlier quoted context omitted.

Seems like a really clean and testable system, too. Can make a harness with a set of inputs, run the cycle and test outputs consistently. Performance is also easily checked, each cycle needs to run without 100ms for the 10hz systems, I guess, including garbage collection. Nice it see things kept this simple.

I had once thinking about this type of system, and later found that the SNMP(1988) as well as NIST/Army 4D/RCS project(1980s) had this train of thought before I was even born. Now I'm wondering why this type of distributed, synchronized, hard realtime decision making framework don't seem to exist as some Apache Foundation project or something. It just sounds right and massively useful but I can't find an implementati…

There are a few layers to your question.

If you mean distributed to mean "over multiple computers", then ya... this is a really specialized field. Your ability to synchronize and maintain hard real-timeness between computers is completely dependent on IO and hardware features, and topology. This makes it much harder to make a generalized framework.

We we ignore the distributed portion, then you're describing a real-time operating system - in which case something like https://www.freertos.org/ might fit the bill?

Re: Exploring the software that flies SpaceX rockets and starships

#42

Post by ilrwbwrkhv »

skizm wrote: post #36
oskhan wrote: post #6

Earlier quoted context omitted.

SpaceX has been hiring game developers for years now, they even showed up at GDC once to pick up game devs.

Makes sense from a financial standpoint too since game devs are known to be passionate enough to accept lower salaries if they can work on cool stuff. Not necessarily knocking it (not my preference), but it matches exactly what I hear from people that work there. The recruiters even say the pay is low, but you'll have "SpaceX" on your resume so it's worth it.

Also it's world changing work. The best you can do at other faang companies is click ads.

Re: Exploring the software that flies SpaceX rockets and starships

#43

Post by throwaway29303 » 

  Flight software for rockets at SpaceX is structured around the concept of a control cycle. “You read all of your inputs: sensors that we read in through an ADC, packets from the network, data from an IMU, updates from a star tracker or guidance sensor, commands from the ground,” explains Gerding. “You do some processing of those to determine your state, like where you are in the world or the status of the life support system. That determines your outputs – you write those, wait until the next tick of the clock, and then do the whole thing over again.”
I didn't know what IMU meant but according to this[0] it's an Inertial Measurement Unit, I believe.

[0] - https://en.wikipedia.org/wiki/Inertial_measurement_unit

Re: Exploring the software that flies SpaceX rockets and starships

#44

Post by ACS_Solver »

plq wrote: post #2

The article is a bit light on technical details, but the following is noteworthy: > Flight software for rockets at SpaceX is structured around the concept of a control cycle. “You read all of your inputs: sensors that we read in through an ADC, packets from the network, data from an IMU, updates from a star tracker or guidance sensor, commands from the ground,” explains Gerding. “You do some processing of those to de…

The article's indeed light on details, but what it describes sounds very similar to autonomous driving / driver assistance software I have experience with. That's not really surprising, as the overall system for an autonomous car and a spaceship is very similar - keep processing inputs from sensors, calculate some values and manage state machines, use those results to adjust outputs, some of which may operate actuators, and repeat.

The similarity with game event loops is IMO superficial. A game typically processes events as fast as it can, and the time between any two iterations of the loop is completely unpredictable. One frame could render in 20ms and the next in 25ms, which is completely fine. For a car or spaceship though, there are hard real-time requirements. Like the article describes, some Dragon tasks run every 100ms, others run every 20ms. A lot of effort has definitely gone into making sure the tasks can complete quickly enough, with some margin, and there are definitely systems that monitor these deadlines and treat even one timing miss as a major failure.

Re: Exploring the software that flies SpaceX rockets and starships

#45

Post by hutzlibu »

ACS_Solver wrote: post #44
plq wrote: post #2

The article is a bit light on technical details, but the following is noteworthy: > Flight software for rockets at SpaceX is structured around the concept of a control cycle. “You read all of your inputs: sensors that we read in through an ADC, packets from the network, data from an IMU, updates from a star tracker or guidance sensor, commands from the ground,” explains Gerding. “You do some processing of those to de…

The article's indeed light on details, but what it describes sounds very similar to autonomous driving / driver assistance software I have experience with. That's not really surprising, as the overall system for an autonomous car and a spaceship is very similar - keep processing inputs from sensors, calculate some values and manage state machines, use those results to adjust outputs, some of which may operate actuato…

"One frame could render in 20ms and the next in 25ms, which is completely fine."

No it is not fine, if you want to have a real smooth gameplay. So also in game loops, you can adjust for that, by checking timediff.

But sure, the difference is that, if you miss a frame in a game loop - no real rockets crash, so there is probably (and hopefully) not as much effort put into that, like they do on SpaceX.

Re: Exploring the software that flies SpaceX rockets and starships

#49

Post by mrfusion »

jb1991 wrote: post #37
sudhirj wrote: post #4

Earlier quoted context omitted.

Seems like a really clean and testable system, too. Can make a harness with a set of inputs, run the cycle and test outputs consistently. Performance is also easily checked, each cycle needs to run without 100ms for the 10hz systems, I guess, including garbage collection. Nice it see things kept this simple.

> including garbage collection. Not only does flight control software typically never use garbage collection, it is also preferable to never allocate memory during the runtime -- all memory ever needed is allocated at program startup, and memory is not acquired or released until landing or some other major end event. Because memory issues are often the most significant causes of crashes, which you don't want to trans…

Do you have a link to bjarnes writeup? My ask Jeeves skills are failing me.

Re: Exploring the software that flies SpaceX rockets and starships

#50

Post by NortySpock »

holoduke wrote: post #18
plq wrote: post #2

The article is a bit light on technical details, but the following is noteworthy: > Flight software for rockets at SpaceX is structured around the concept of a control cycle. “You read all of your inputs: sensors that we read in through an ADC, packets from the network, data from an IMU, updates from a star tracker or guidance sensor, commands from the ground,” explains Gerding. “You do some processing of those to de…

You could probably use some of the game "Kerbal Space Program" source code. Would be a good start to control the rockets.

KSP would be proprietary code designed for a simulation, not for inside a vehicle.
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