APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

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APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by APOD Robot » Wed Jul 17, 2019 4:09 am

Image Apollo 11: Descent to the Moon

Explanation: It had never been done before. But with the words "You're Go for landing", 50 years ago this Saturday, Apollo 11 astronauts Aldrin and Armstrong were cleared to make the first try. The next few minutes would contain more than a bit of drama, as an unexpected boulder field and an unacceptably sloping crater loomed below. With fuel dwindling, Armstrong coolly rocketed the lander above the lunar surface as he looked for a clear and flat place to land. With only seconds of fuel remaining, and with the help of Aldrin and mission control calling out data, Armstrong finally found a safe spot -- and put the Eagle down. Many people on Earth listening to the live audio felt great relief on hearing "The Eagle has landed", and great pride knowing that for the first time ever, human beings were on the Moon. Combined in the featured descent video are two audio feeds, a video feed similar to what the astronauts saw, captions of the dialog, and data including the tilt of the Eagle lander. The video concludes with the panorama of the lunar landscape visible outside the Eagle. A few hours later, hundreds of millions of people across planet Earth, drawn together as a single species, watched fellow humans walk on the Moon.

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DL MARTIN

Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by DL MARTIN » Wed Jul 17, 2019 5:53 am

Thanks for augmenting the drama of the landing.

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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by orin stepanek » Wed Jul 17, 2019 11:36 am

And what a day That was! 8-) :rocketship: :b:
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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by Boomer12k » Wed Jul 17, 2019 12:04 pm

Awesome presentation... gripping...

The altitude meter and coming down remind me of the old C64 computer games... :lol2:



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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by neufer » Wed Jul 17, 2019 3:38 pm

Boomer12k wrote:
Wed Jul 17, 2019 12:04 pm

The altitude meter and coming down remind me of the old C64 computer games... :lol2:
https://en.wikipedia.org/wiki/Apollo_Guidance_Computer wrote:
<<The Apollo Guidance Computer (AGC) was a digital computer produced for the Apollo program that was installed on board each Apollo command module (CM) and Apollo Lunar Module (LM). The AGC provided computation and electronic interfaces for guidance, navigation, and control of the spacecraft. The AGC has a 16-bit word length, with 15 data bits and one parity bit. Most of the software on the AGC is stored in a special read-only memory known as core rope memory, fashioned by weaving wires through magnetic cores, though a small amount of read-write core memory is available.

Astronauts communicated with the AGC using a numeric display and keyboard called the DSKY (for display & keyboard, pronounced 'DISS-key'). The AGC and its DSKY user interface were developed in the early 1960s for the Apollo program by the MIT Instrumentation Laboratory and first flew in 1966. The AGC was one of the first integrated circuit-based computers. The computer's performance was comparable to the first generation of home computers from the late 1970s, such as the Apple II, TRS-80, and Commodore PET. The Commodore PET (Personal Electronic Transactor) is a line of home/personal computers produced starting in 1977 [that] formed the basis for their entire 8-bit product line, including the Commodore 64.

Astronauts manually flew Project Gemini with control sticks, but computers flew most of Project Apollo except briefly during lunar landings. Each Moon flight carried two AGCs, one each in the command module and the lunar module, with the exception of Apollo 8 which did not need a lunar module for its lunar orbit mission. The AGC in the command module was the center of its guidance, navigation and control (GNC) system. The AGC in the lunar module ran its Apollo PGNCS (primary guidance, navigation and control system), with the acronym pronounced as pings.

PGNCS generated unanticipated warnings during Apollo 11's lunar descent, with the AGC showing a 1201 alarm ("Executive overflow - no vacant areas") and a 1202 alarm ("Executive overflow - no core sets"). The cause was a rapid, steady stream of spurious cycle steals from the rendezvous radar (tracking the orbiting command module), intentionally left on standby during the descent in case it was needed for an abort.

During this part of the approach, the processor would normally be almost 85% loaded. The extra 6,400 cycle steals per second added the equivalent of 13% load, leaving just enough time for all scheduled tasks to run to completion. Five minutes into the descent, Buzz Aldrin gave the computer the command 1668, which instructed it to periodically calculate and display DELTAH (the difference between altitude sensed by the radar and the computed altitude) The 1668 added an additional 10% to the processor workload, causing executive overflow and a 1202 alarm. After being given the "GO" from Houston, Aldrin entered 1668 again and another 1202 alarm occurred. When reporting the second alarm, Aldrin added the comment "It appears to come up when we have a 1668 up". The AGC software had been designed with priority scheduling, and automatically recovered, deleting lower priority tasks including the 1668 display task, to complete its critical guidance and control tasks. Guidance controller Steve Bales and his support team that included Jack Garman issued several "GO" calls and the landing was successful. For his role, Bales received the US Presidential Medal of Freedom on behalf of the entire control center team and the three Apollo astronauts.>>
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Moon landings in fiction

Post by neufer » Wed Jul 17, 2019 7:11 pm

Art Neuendorffer

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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by TheOtherBruce » Wed Jul 17, 2019 7:40 pm

Nice — here's a version I don't think I've seen before, with all the extra greeblies around the sides.

Something occurred to me recently; every version I've seen of the landing videos based on the old Apollo Lunar Surface Journal clips have been shown corrected, rotated upright and at the proper speed. Why was this never done before the ALSJ clips? For years I wondered how Armstrong managed to land when the LM was bouncing all over the place; then I discovered the LM camera was run at (I think) 6 fps...

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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by BDanielMayfield » Fri Jul 19, 2019 2:43 am

Welcome to the forum TheOtherBruce.

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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by Jim Leff » Fri Jul 26, 2019 1:49 am

Late to the party here, but I listened to this live as a kid, and the big takeaway was that it was a clutch landing just as they were about to run out of fuel. While technically true, it’s not an apt narrative. Glad to finally get the story in context.

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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by neufer » Fri Jul 26, 2019 3:34 am

Jim Leff wrote:
Fri Jul 26, 2019 1:49 am

Late to the party here, but I listened to this live as a kid, and the big takeaway was that it was a clutch landing just as they were about to run out of fuel. While technically true, it’s not an apt narrative. Glad to finally get the story in context.
They actually had twice as much fuel left as they thought due to fuel sloshing (fixed later by baffles).
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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by neufer » Fri Jul 26, 2019 3:40 am

Click to play embedded YouTube video.

BDanielMayfield wrote:
Fri Jul 19, 2019 2:43 am

Welcome to the forum TheOtherBruce.

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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by TheOtherBruce » Fri Jul 26, 2019 1:26 pm

Heh — since I'm transatlantically challenged, I've never watched a single episode of Seinfeld. My inspiration was, of course, the "Bruces Sketch" from Monty Python. :wink:
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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by neufer » Fri Jul 26, 2019 4:11 pm

Click to play embedded YouTube video.
Click to play embedded YouTube video.
TheOtherBruce wrote:
Fri Jul 26, 2019 1:26 pm

Heh — since I'm transatlantically challenged, I've never watched a single episode of Seinfeld. My inspiration was, of course, the "Bruces Sketch" from Monty Python. :wink:
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Re: APOD: Apollo 11: Descent to the Moon (2019 Jul 17)

Post by TheOtherBruce » Sun Jul 28, 2019 1:24 am

Image

(Just rediscovered the box that the "Best Of..." box set was in — way past time to play it again.)
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