Personal Observations on Reliability of Shuttle (1986) | Hacker News Reader

Personal Observations on Reliability of Shuttle (1986)

history.nasa.gov

Quote "There is not enough room in the memory of the main line computers for all the programs of ascent, descent, and payload programs in flight, so the memory is loaded about four time from tapes, by the astronauts."

Woah. Did they do this right until 2011, or were their systems upgraded?

I don't know that, but if it wasn't breaking at all then why would they be upgrading solution than never failed?

Apollo 13 whole computer system had less power than the phone in your pocket; yet that was perfectly enough to run the vehicle. Crazy times...

Agreed. Although in this case it would seem like it was increase on the astronaut's workload, having to load each program from tape. Also the article mentioned that they were using outdated software development methods and tools, whatever they were it didn't mention.

Btw, found my answer after some googling, they were upgraded in the early 90's then again in early 2000's http://www.aviationtoday.com/1999/11/01/the-space-shuttle-mo...

quote "In addition to 11 MDUs in the shuttle, MEDS has four integrated display processors (IDPs) that contain 386DX computers and a 300-megabyte hard disc."

MDU - multiple display unit.

It's interesting that (from the very interesting cited article) the processor in each MDU, an R3000, is more powerful than all the legacy IBM 4Pis serving as Shuttle main computers.

I would say your phone in your pocket is probably 100,000 times more powerfull than computer in Apollo 13.

Apollo: 2.048 MHz iPhone 6: 2.34 GHz

How reliable are / were tapes?

There are numerous articles on the Shuttle's computers. I seem to remember the Apollo had quadruple redundancy, AND an extra backup failsafe, and lots of protection from degradation from cosmic rays, and I think the Shuttle had 5 computers too. I'm sure there's lots available, frmo NASA and other sources. https://history.nasa.gov/computers/Ch4-3.html

The Apollo Guidance Computer used core rope memory [1] as ROM and magnetic-core memory as RAM. Both are non-volatile.

The command module did not have a redundant computer or memory, but the lunar module came with a second computer [2] of a different type and running different software.

What you remember is probably the Gemini Guidance Computer's tape drive system, which consisted of three identical tape drives that were connected to the computer through a voter circuity.

[1] https://en.wikipedia.org/wiki/Core_rope_memory

[2] https://en.wikipedia.org/wiki/Apollo_Abort_Guidance_System

By the standards of the time, a relatively large amount of data could be stored in a small installed volume of core rope memory: 72 kilobytes per cubic foot, or roughly 2.5 megabytes per cubic meter.

Re: core rope

Jesus. Now it’s TB/cm...

The Shuttle had four main computers hooked together to form a redundant system, and then a fifth backup computer which was only capable of handling launch and reentry/landing. In the unlikely event that all four main computers couldn't be reprogrammed, the fifth one could still get everybody home.

Aha thanks, it was the shuttle that had the 4-way redundancy thing! I got scared of my memory, not being able to find verification quickly online, so instead wrote something less true!

Funny, I just reread "What do you care what other people think?" yesterday. The parallel of NASA's design process for avionics software to TDD is both striking and revealing. People struggling with TDD could definitely benefit a lot by thinking hard about the examples of the main engine design process and avionics software. Thanks for posting!

Previous discussion:

https://news.ycombinator.com/item?id=7201645

> A mathematical model was made to calculate erosion. This was a model based not on physical understanding but on empirical curve fitting.

Very interesting point. A lot of today's "science" works like this, and it is a deeply flawed approach.

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