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Apollo 11 vs. USB-C Chargers (2020)

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Re: Apollo 11 vs. USB-C Chargers (2020)

#31

Post by johnwalkr »

kristopolous wrote: post #22
johnwalkr wrote: post #17

Earlier quoted context omitted.

I work in this space and z80, kermit and xmodem are not part of the solution. Just because this stuff is simple to the user doesn't mean it's the best suited, and there's a whole industry working on this since the Z80 days. You can buy space-qualified microcontroller boards/components with anything from a simple 8 bit microcontroller to a 64-bit, multicore, 1Ghz+ ARM cpu depending on the use case. I'm sure Z80 has be…

I worked in it 20 years ago building diagnostic and networking tools ... arm was certainly around but there was also what I talked about. Things probably changed since then. Here's kermit in space ... coincidentally in a 20 year old article. Software I wrote supported diagnosing kermit errors. https://www.spacedaily.com/news/iss-03zq.html I guess now I'm old.

Thanks for the reference! Kermit could be used locally on ISS or in a lunar mission now that I think about it, but so is/could SSH, web browsers or any modern technology. But most space exploration is robotic and depends on communication to ground stations on Earth, and that is fairly standardized. Perhaps kermit will be used on the lunar surface, and that will be a simplification compared to a web browser interface. But for communication to/from Earth and Moon, there are standards in place and it would be a complication, not simplification to add such a protocol.

Re: Apollo 11 vs. USB-C Chargers (2020)

#32

Post by somethingsaid »

jojobas wrote: post #21
thebestmoshe wrote: post #19

Earlier quoted context omitted.

Isn’t this basically what SpaceX is doing? > The flight software is written in C/C++ and runs in the x86 environment. For each calculation/decision, the "flight string" compares the results from both cores. If there is a inconsistency, the string is bad and doesn't send any commands. If both cores return the same response, the string sends the command to the various microcontrollers on the rocket that control things…

That sounds way too low. Modern fly-by-wire planes are said to have 12-way voting.

If you read the link it’s actually two cpu cores on a single cpu die each returning a string. Then 3 of those cpus send the resulting string to the microprocessors which then weigh those together to choose what to do. So it’s 6 times redundant in actuality.

Re: Apollo 11 vs. USB-C Chargers (2020)

#33

Post by kristopolous »

johnwalkr wrote: post #31
kristopolous wrote: post #22

Earlier quoted context omitted.

I worked in it 20 years ago building diagnostic and networking tools ... arm was certainly around but there was also what I talked about. Things probably changed since then. Here's kermit in space ... coincidentally in a 20 year old article. Software I wrote supported diagnosing kermit errors. https://www.spacedaily.com/news/iss-03zq.html I guess now I'm old.

Thanks for the reference! Kermit could be used locally on ISS or in a lunar mission now that I think about it, but so is/could SSH, web browsers or any modern technology. But most space exploration is robotic and depends on communication to ground stations on Earth, and that is fairly standardized. Perhaps kermit will be used on the lunar surface, and that will be a simplification compared to a web browser interface.…

oh who knows ... I stopped working on that stuff in I think 2006. The big push then was over to CAN and something called AFDX which worked over ethernet. I was dealing with octal and bcd daily, mid 2000s.

I have no idea if people still use ARINC-429 or IRIG-B. Embedded RTOS was all proprietary back then for instance, like with VXWORKS. I'm sure it's not any more. I hated vxworks.

Re: Apollo 11 vs. USB-C Chargers (2020)

#34

Post by dikei »

jojobas wrote: post #21
thebestmoshe wrote: post #19

Earlier quoted context omitted.

Isn’t this basically what SpaceX is doing? > The flight software is written in C/C++ and runs in the x86 environment. For each calculation/decision, the "flight string" compares the results from both cores. If there is a inconsistency, the string is bad and doesn't send any commands. If both cores return the same response, the string sends the command to the various microcontrollers on the rocket that control things…

That sounds way too low. Modern fly-by-wire planes are said to have 12-way voting.

It's more complicated than that, in the link, they described it better:

>> The microcontrollers, running on PowerPC processors, received three commands from the three flight strings. They act as a judge to choose the correct course of actions. If all three strings are in agreement the microcontroller executes the command, but if 1 of the 3 is bad, it will go with the strings that have previously been correct.

This is a variation of Byzantine Tolerant Concensus, with a tie-braker to guarantee progress in case of absent voter.

Re: Apollo 11 vs. USB-C Chargers (2020)

#35

Post by codezero »

Weird question maybe, but does anyone keep track of quantitative or qualitative data that measures the discrepancy between consumer (commercial) and government computer technology?

TBH, it's kind of amazing that a custom computer from 50 years ago has the specs of a common IC/SoC today, but those specs scale with time.

Re: Apollo 11 vs. USB-C Chargers (2020)

#36

Post by p-e-w »

jojobas wrote: post #21
thebestmoshe wrote: post #19

Earlier quoted context omitted.

Isn’t this basically what SpaceX is doing? > The flight software is written in C/C++ and runs in the x86 environment. For each calculation/decision, the "flight string" compares the results from both cores. If there is a inconsistency, the string is bad and doesn't send any commands. If both cores return the same response, the string sends the command to the various microcontrollers on the rocket that control things…

That sounds way too low. Modern fly-by-wire planes are said to have 12-way voting.

I don't understand this. If two or more computers fail in the same way simultaneously, isn't it much more likely that there is a systemic design problem/bug rather than some random error? But if there is a design problem, how does having more systems voting help?

Re: Apollo 11 vs. USB-C Chargers (2020)

#37

Post by hinkley »

AnotherGoodName wrote: post #10

Pretty much all USB chips have a fully programmable CPU when you go into the data sheets. It feels silly for simple hid or charging devices but basic microcontrollers are cheap and actually save costs compared to asics.

I still want to see postgres or sqlite running straight on a storage controller some day. They probably don’t have enough memory to do it well though.

Re: Apollo 11 vs. USB-C Chargers (2020)

#38

Post by hinkley »

nothercastle wrote: post #28
kens wrote: post #16

> Apollo 11 spacecraft contains 4 computers Analog computers don't get the respect they deserve. There's one more computer, the FCC. The Flight Control Computer is an analog computer in the Saturn V that controlled the rocket gimbals. It's a two-foot cylinder weighing almost 100 pounds.

Exactly this. A lot of the systems had built in analog computers. It’s a lot cheaper to build then now with electronics but you need more computing power to do things that were previously done mechanically

Analog computers have to be rebuilt if it turns out the program is wrong though, don’t they?

Re: Apollo 11 vs. USB-C Chargers (2020)

#39

Post by petermcneeley »

AnotherGoodName wrote: post #10

Pretty much all USB chips have a fully programmable CPU when you go into the data sheets. It feels silly for simple hid or charging devices but basic microcontrollers are cheap and actually save costs compared to asics.

I would also argue that this is another example of software eating the world. The role of the electrical engineer is diminished day by day.

Re: Apollo 11 vs. USB-C Chargers (2020)

#40

Post by jcalvinowens »

jojobas wrote: post #21
thebestmoshe wrote: post #19

Earlier quoted context omitted.

Isn’t this basically what SpaceX is doing? > The flight software is written in C/C++ and runs in the x86 environment. For each calculation/decision, the "flight string" compares the results from both cores. If there is a inconsistency, the string is bad and doesn't send any commands. If both cores return the same response, the string sends the command to the various microcontrollers on the rocket that control things…

That sounds way too low. Modern fly-by-wire planes are said to have 12-way voting.

> Modern fly-by-wire planes are said to have 12-way voting

Do you have a source for that? Everything I've ever read about Airbus says the various flight control systems are doubly redundant (three units). Twelve sounds like it would be far beyond diminishing returns...

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