a simple one for those here who know what they are talking about :

` exactly what did it do ? `

i have tried looking and cannot find a god summary i can use in an argument going wrong

bottom line is i got into an argument last night - while drinking . naturally [-X as a loud and obnoxious HB was holding court in my favorite pub and spouting his ignorance to several of my friends , so i had to wade in

despite advanced lubrication - i did very well - handling stars , flags , shadows , radiation and gravity silliness with ease and steering most away from the dark side of HB doom

5then the computer question kind of stumped me - well his arguments about the computer baffled me

so i kind of waffled something on the lines ` the computer didnt fly the LM armstrong did - the computer just told him the results of calculations preformed several times a second - stuff the crew could not do manually `

suffice to say he wasnt convinced so he kept going back to the computer - probally sensing it was my weakest answer

unfortunatly i lost my temper and swore at him


now my mates are asking about the freaking computer - i need help to shut them up - and naturally thgought of you guys


YRS - APE

Oops, Mr Ape. Doesn't look good to lose your temper in cases like this!

Anyway, a good resource is JayUtah's site: www.clavius.org. The relevant page is: http://www.clavius.org/techcomp.html

The thing to remember is that while planning a trajectory was a complex task, that was performed by the computers back here on Earth. Once they worked out the solutions, the relevant data was read up to the astronauts to feed into the computer on the spacecraft.

All the spacecraft computer had to look after was when to switch on the engine, how much thrust to apply, which direction to point the rocket nozzle, and when to switch off the engine.

Every few hours during an Apollo mission, Mission Control would read up data to the crew, who'd record it on a special form. These were the calculated parameters to allow them to abort the mission for the next few hours. Obviously, as time passed, the parameters would change, so a new set would be calculated (back here on Earth) and read up to the astronauts.

Essentially, the astronauts and Mission Control decided what had to be done, and all the computer did was perform the actions. This makes it more akin to the computer running your washing machine. Your washing machine doesn't decide which wash cycle to use or how much water to add - you choose that. Instead, it very accurately times the wash cycle, depending on the setting you chose, and adds an appropriate amount of water, depending on what selection you made.

the Lunar Conspiracy section of the BadAstronomy website contains this link, with a lot of information about the navigation and control systems on board the LM.

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Who are you going to believe, me or your own eyes? -- Groucho Marx

Essentially, the computer itself was just a (shoebox-sized) pocket calculator. If you can get them to admit a pocket calculator would've been good enough for the landing, you're made. 8)

It was considerably larger than a shoebox. The DSKY itself (the console) was shoebox-sized, and weighs about 20 pounds. My old boss has one. The final weight of the CPU was something like 85 pounds.

It's appropriate to say it had about the same computing power as a pocket calculator (or even less than that these days, since pocket calculators are quite powerful now). But it could do triple precision vector computations. So while its raw speed wasn't blinding fast, the software programmed into it was pretty capable in terms of what it needed to do in order to accomplish local guidance.

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"Facts are stubborn things." --John Adams
Clavius Moon Base

Just read the link provided by Peter B.
A great read there! Also confirmed what I had in mind about simulators and the actual thing: simulators must simulate the spacecraft and teh enviroment. In the actual situation, the computer just has to point the spacecraft. All that takes is some math and nessary equipment for sensing what the spacecraft is doing (i.e, adjusting the orientation upon landing to compensate for varing fuel levels and weight distribuation).
Am I also right that the alarm panel (the one with all those warnings like "Bus B Undervolt") was acuated by various relays and switches? I know that's how alarm systems in naval ships work; a mechanical switch reacts to system pressure of temperture. It's calibrated to close (or open) at a certain point. Then will then activate the alarm. Same idea for spacecraft?

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I calculated the odds of this succeeding versus the odds I was doing something incredibly stupid...and I went ahead anyway. - Crow T. Robot

Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

Here's a good link

http://history.nasa.gov/ap08fj/compessay.htm

Enjoy

Jay, that reminds me of a question that occurred to me the first time I watched Apollo 13. Would it have been possible (not necessarily safe, but possible) for any crew (not just a crew with a damaged SM) to return from the moon and reenter if all radio communications with Houston had somehow been lost?

[edited for italics]

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--Doug

"When your statics problem becomes a dynamics problem, you're in trouble." --me

Moor's Law: "As you go from freshman engineering to Ph.D., the amount of work required per credit hour doubles approximately every 18 months." --me, inspired by Prof. Scott Moor

Jay can correct me on this, but I believe that without tracking information from the Earth, they would not have known where they were accurately enough to re-enter the Earth's atmosphere safely, since the angle of re-entry has to be just right. I think that even with a healthy command module they would have problems in that regard.

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Everything I need to know I learned through Googling.

A pertinent section from the A-15 Apollo Flight Journal talking about the PAD readups:


(edited to remove unrelated quote)

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"I'd take the awe of understanding over the awe of ignorance any day." - Douglas Adams

AGN Fuel -- could you please give us the link to that part of the AFJ? I had a quick look but couldn't find it.

This is the sort of article that needs to be seen by those clowns who claim that the Apollo computer "wasn't up to the task." That is, of course, if they actually want to educate thrmselves.

Thanks also to Johnno for your link -- good stuff!

Apologies Kiwi - I intended to link it originally, but must have forgotten! #-o

http://www.hq.nasa.gov/office/pao/Hi..._orbit_tli.htm

This section is at GET 1:40:29.

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"I'd take the awe of understanding over the awe of ignorance any day." - Douglas Adams

Basically without the ground, Apollo 13 would have been toast. For many reasons.

__________________
"Facts are stubborn things." --John Adams
Clavius Moon Base

Yes, that's certainly the case for A13. But what about a situation where the only failure(s) result in a loss of communication with the ground? Could the spacecraft have navigated home with no ground support, if all other system were functional?

I think the answer is yes, since they had the ability to do star sightings, but I could easily be wrong.

Furthermore, it may simply be unrealistic to postulate a total cutoff of ground communications. After all, they had multiply redundant comm systems, especially prior to the landing (when the LM was available as a further backup).

I think the stars are too far away to be used to determine their position. They might be able to do it by getting very good fixes on the limbs of the Earth and the Moon, but even assuming they could get accurate enough fixes they'd probably need help from Earthbound computers to determine their position from the raw data.

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Everything I need to know I learned through Googling.

I believe star sightings were used to verify attitude, not position. The inertial guidance system would accumlulate errors over time that were periodically corrected by sighting star postions.

Star sights only give you attitude. Position is by dead reckoning.

__________________
"Facts are stubborn things." --John Adams
Clavius Moon Base

How do you do DR on a translunar trajectory?

"Yankee Clipper,
abeam Phobos time 35
next position 4 AU south Enceladus time 57."

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With the emphasis on "dead", maybe? 8-[

Combination of orbital mechanics and reg'lar ol' dead reckoning (acceleration, velocity, time, etc.)

__________________
"Facts are stubborn things." --John Adams
Clavius Moon Base