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Apollo 11 vs. USB-C Chargers (2020)

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

#21

Post by jojobas »

thebestmoshe wrote: post #19
vlovich123 wrote: post #12

Is the weight/cost calculus sufficiently improved now that it’s cheaper to shield the processor in it’s entirety rather than trying to rad harden the circuitry itself (much more expensive due to inability to use off the shelf parts & limits the ability to use newer tech)? If I recall correctly this was one of the areas being explored by the mars drone although not sure if Mars surface radiation concerns are different…

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.

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

#22

Post by kristopolous »

johnwalkr wrote: post #17
kristopolous wrote: post #2

When we go back to the moon, I wouldn't be surprised if Zilog-Z80s were a major part of the hardware. Well known, well understood, predictable hardware goes a long way. There's a bunch of other considerations in outer space and z80s have proven robust and reliable there. Also I'd expect a bunch of Kermit and Xmodem to be used as well.

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.

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

#23

Post by kens »

orliesaurus wrote: post #7

54 years ago - wow - was the Apollo 11 Moon Landing Guidance Computer (AGC) chip the best tech had to offer back then?

The Apollo Guidance Computer was the best technology when it was designed, but it was pretty much obsolete by the time of the Moon landing in 1969. Even by 1967, IBM's 4 Pi aerospace computer was roughly twice as fast and half the size, using TTL integrated circuits rather than the AGC's RTL NOR gates.

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

#24

Post by monocasa »

kristopolous wrote: post #9
monocasa wrote: post #5

Earlier quoted context omitted.

I'm not sure if there's a RAD hard z80 variant. They've got their own chips and protocols going back just as far, like https://en.wikipedia.org/wiki/MIL-STD-1553

The space shuttle used both z80 and 8086 until it ended in 2011. The international space station runs on among other chips, 80386SX-20s. IBM/BAE also has a few RADs based on POWER chips.

Do you have a citation for that?

The Space Shuttle Avionics System top level documentation specifically calls out having "no Z80's, 8086s, 68000's, etc."

https://ntrs.nasa.gov/api/citations/19900015844/downloads/19...

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

#25

Post by kens »

vlovich123 wrote: post #12

Is the weight/cost calculus sufficiently improved now that it’s cheaper to shield the processor in it’s entirety rather than trying to rad harden the circuitry itself (much more expensive due to inability to use off the shelf parts & limits the ability to use newer tech)? If I recall correctly this was one of the areas being explored by the mars drone although not sure if Mars surface radiation concerns are different…

It's always been an option to use shielding rather than rad-hard chips or in combination. RCA's SCP-234 aerospace computer weighed 7.9 pounds, plus 3 pounds of lead sheets to protect the RAM and ROM. The Galileo probe used sheets of tungsten to protect the probe relay receiver processor, while the Galileo plasma instrument used tantalum shielding. (I was just doing some research on radiation shielding.)

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

#26

Post by johnwalkr »

GlenTheMachine wrote: post #8
kristopolous wrote: post #2

When we go back to the moon, I wouldn't be surprised if Zilog-Z80s were a major part of the hardware. Well known, well understood, predictable hardware goes a long way. There's a bunch of other considerations in outer space and z80s have proven robust and reliable there. Also I'd expect a bunch of Kermit and Xmodem to be used as well.

They won’t be. We will use RAD750’s, the flight qualified variant of the PowerPC architecture. That’s the standard high end flight processor. https://www.petervis.com/Vintage%20Chips/PowerPC%20750/RAD75... The next generation (at least according to NASA) will be RISC-V variants: https://www.zdnet.com/article/nasa-has-chosen-these-cpus-to-...

I wouldn't call it the standard, it's just used in designs with legacy to avoid the huge cost of re-qualification of hardware and software. It's infeasible a lot of times due to cost and power consumption. I work in the private sector in space (lunar exploration actually) and everyone is qualifying normal/automotive grade stuff, or using space-grade microcontrollers for in-house designs, with everything from 8-32bit, [1] and ready-made cpu boards[2] for more complex use cases. I'm sharing just 2 examples but there are hundreds, with variations on redundancy implemented in all kinds of ways too, such as in software, on multiple cores, on multiple chips, or on multiple soft-cpu cores on a single or multiple FPGAs.

[1] Example: https://www.militaryaerospace.com/computers/article/16726923...

[2] Example: https://xiphos.com/product-details/q8

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

#27

Post by ashvardanian »

Remarkable comparison! I'm surprised it had only one parity bit per 15-bit word. Even on Earth today we keep two parity bits per 8-bit word in most of our servers.

> IBM estimated in 1996 that one error per month per 256 MiB of RAM was expected for a desktop computer.

https://web.archive.org/web/20111202020146/https://www.newsc...

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

#28

Post by nothercastle »

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

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

#30

Post by kristopolous »

monocasa wrote: post #24
kristopolous wrote: post #9

Earlier quoted context omitted.

The space shuttle used both z80 and 8086 until it ended in 2011. The international space station runs on among other chips, 80386SX-20s. IBM/BAE also has a few RADs based on POWER chips.

Do you have a citation for that? The Space Shuttle Avionics System top level documentation specifically calls out having "no Z80's, 8086s, 68000's, etc." https://ntrs.nasa.gov/api/citations/19900015844/downloads/19...

Intel claims they did. https://twitter.com/intel/status/497927245672218624?lang=en although what's that word "some" doing in there...

And also, sigh, to demonstrate once again that when I worked in space it was 20 years ago, https://www.nytimes.com/2002/05/12/us/for-parts-nasa-boldly-... (https://web.archive.org/web/20230607141742/https://www.nytim...)

Knowing how 8086 timing and interrupts worked was still important for what I was doing in the early 2000s. I don't pretend to remember any of it these days.

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