Apollo Guidance Computer Demonstration, at VCF West 2019 [video] | Hacker News Reader

Apollo Guidance Computer Demonstration, at VCF West 2019 [video]

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25 pointsguiambros8 comments

For anyone who's interested, but not seen them, I'd recommend the full series of videos at https://www.youtube.com/watch?v=9iavKBdPo4U for a spectacular amount of background info.

This video was (someone else?) flying a moon landing in a simulator with an FPGA emulated Apollo Guidance Computer.

CuriousMarc's series is about restoring a real AGC.

Ultimately, they do the same simulated landing with a real AGC. Ideally, this video would have been demonstrated with the restored AGC but it wasn't available.

It's the same people. Mike Stewart was one of the main AGC gurus in the YouTube series.

After looking at various sources I still don't understand whether the manual mode landing was a necessity because:

- of the computer overload due to the command module (CM) rendezvous radar being turned on -> which in turn leading to a messy command queue -> commands being dropped from the queue being filled -> commands being sent out-of-sequence -> undefined behavior -> the LM getting of path to the wrong landing region

- of a stone field after an otherwise nominally controlled descent.

In addition it seems unclear whether during manual flight control mode there was still any computer control for attitude, rate of decent etc. active.

In the final phase of landing the AGC was running a program called P66 which was a semi-manual mode. The astronaut had direct control of the attitude of the LM but the throttle was calculated by the AGC to maintain a steady Rate of Descent (ROD). The astronaut controlled the ROD via a switch.

All the Apollo landings were done with P66, I think the AGC did have the capability to do a fully automatic landing but none of the crews wanted to try it.

so was it planned then to use P65 (fully automatic) for Apollo 11?

It's still not clear what the actual impact of the messed up command queue had - none, a few wrong thruster firings or getting the landing phase trajectory completely wrong?

actually answering my own question in part, it's explained at https://www.hq.nasa.gov/alsj/nasa58040.pdf pp. 21 ff.

: P65 was apparently planned and there was a velocity error amongst others leading to a navigation error.

What remains open is what material impact the interupt overload on the command queue had.

This is the recording of a live stream where the camera was turned on well in advance. The talk starts at 10:45 into the video.

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