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Ricky
SFN Die Hard
USA
4907 Posts |
 Posted - 08/15/2005 : 07:58:17 [Permalink]
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quote:
But with all these acronyms could they land on the Moon with a computer of
74k Memory
4k RAM
Wiki actually tells about the computer failing while they were landing:
quote:
The PGNC System malfunctioned during the first live lunar descent, with the AGC showing a 1201 alarm ("Executive overflow - no vacant areas") and a 1202 alarm ("Executive overflow - no core sets") [4]. In both cases these errors were caused by spurious data from the rendezvous radar, which had been left on during the descent. These errors automatically aborted the computer's current task, but the frequency of radar data ensured that the abort signals were being sent at too great a rate for the CPU to cope [5].
Fortunately for Apollo 11, the AGC software failed safe, shedding low-priority tasks and prompting Neil Armstrong to shift to a more manually controlled mode. The inertial guidance tasks continued to operate reliably. The degree of overload was minimal, because the software had been "scrubbed" down to leave very nearly 15% spare time, and the 6400 bit/s pulse trains from the radar induced PINCs that wasted exactly 15% of the AGC's time. On the instructions of Steve Bales and Jack Garman, the errors were over-ruled, and the mission was a success.
Amongst the computer's other error codes was the very first '404_error', albeit that error 00404 was shorthand for "IMU orientation unknown".
But how do you know that 4k RAM with 74K ROM aren't enough to land on the moon? Just because you don't think you can do it, does that mean that NASA can't do it?
Or are you just the smartest person alive?
Edit:
I had previously posted that it only had 2k of RAM and 36k of ROM, however, I did not take into account that these were of word values, which doubles the size, making BigBrain's numbers correct. |
Why continue? Because we must. Because we have the call. Because it is nobler to fight for rationality without winning than to give up in the face of continued defeats. Because whatever true progress humanity makes is through the rationality of the occasional individual and because any one individual we may win for the cause may do more for humanity than a hundred thousand who hug their superstitions to their breast.
- Isaac Asimov |
| Edited by - Ricky on 08/15/2005 08:20:40 |
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Valiant Dancer
Forum Goalie
USA
4826 Posts |
Posted - 08/15/2005 : 08:48:14 [Permalink]
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quote:
Originally posted by Ricky
quote:
Originally posted by Valiant Dancer
quote:
Originally posted by bigbrain
Hi all, I must go out tonight 
Don't get run over.
You just seem like you could use some practical advice.
Hey! Sometimes it isn't your fault if you do get run over.
There is a difference between being run over while asleep and being run over because you believe that we have not the technology to steer our cars and step into traffic.
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Cthulhu/Asmodeus when you're tired of voting for the lesser of two evils
Brother Cutlass of Reasoned Discussion |
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sts60
Skeptic Friend
141 Posts |
Posted - 08/15/2005 : 09:46:42 [Permalink]
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I was thinking about tracking a little bit. It's not my area of expertise, but it occurred to me that there are more ways to do it than I originally thought.
1. Suppose you only have one station. You know the direction in the sky based on where your radio dish is pointing. You know the range to the spacecraft, based on turnaround of a signal transmitted from the ground. (You can reference the range to a particular time t0 because you know where your ground station is on the Earth, and how the Earth moves in space.) Range and direction = location in space.
Of course, it's not quite that easy. Your knowledge of distance and in particular direction are a little fuzzy; what you have is a 3D chunk of space where the spacecraft was at t0. So you repeat the ranging sometime later, when the Earth has carried your station to another point in space, and get another 3D chunk where the spacecraft is at t1. And so on to tN. Your trajectory line gets better the more observations you make.
You know the spacecraft's velocity relative to the ground station from its Doppler shift (and, of course, correcting for the Doppler contributions from the Earth's rotation and heliocentric motion). The ground station's motion through space is extremely well known. Your observation times are well known because we have extremely accurate clocks. The range and direction unknowns are reduced by repeated observations from different locations courtesy of the Earth's motions. The well-known principles of orbital dynamics allow you to model the trajectory line to fit the data.
2. In real life, two ground stations make such observations simultaneously. Straight triangulation won't work at great distances (like Saturn) because the pointing accuracy isn't enough to resolve the small angle observation from two ground stations. But very long baseline interferometry (VLBI) allows the distance to be known with great accuracy, and the directional uncertainty is much reduced because the spacecraft must be inside the intersection of the two 3D chunks of space determined by the seperate ground stations. You can repeat the observations from more stations or the same stations as the Earth moves you along (again, on a path known with great accuracy from centuries of observation).
3. Optical navigation is a newer technology, where the spacecraft can determine its position to a target as it gets close enough to image it directly. But you can do the same thing based on downlink imagery and computers on the ground.
4. Differenced Doppler takes advantage of the slightly different views of the spacecraft's path through 3D space seen by two ground stations, and that Doppler measurements are extremely accurate. It's somewhat like two observers standing apart and using radar guns to get the speed and direction to a distant speeding car. Rather than triangulating, they can combine the range and geometrical interpretation of the different Doppler shifts to get a "fix" on the car at a certain time.
5. Of course, if you start out with a known orbit based on, say, optical tracking of an outbound spacecraft (which has been done well past the Moon), you can in principle predict its position in interplanetary space based on the well-known laws of orbital motion and inertial measurements during any maneuver. But your knowledge gets progressively fuzzier the longer you go, so you need to use the accurate methods in (2), (3), and (4).
Like I said, astrogation isn't my area, so I'm not claiming to be an authority; I'm just pointing out that There's More Than One Way To Do It. A much better explanation, with nice diagrams, can be found at http://www2.jpl.nasa.gov/basics/bsf13-1.html.
Some other references:
Doppler velocity measurement, signal-delay ranging, attitude determination via star tracker:
http://astro.hit.edu.cn/news/36/200472143747.htm
Very Long Baseline Interferometry
http://www.drao-ofr.hia-iha.nrc-cnrc.gc.ca/science/vlbi/principles/principles.shtml
Deep Space Mission Systems telecommunications link design handbook, to look at the nitty-gritty:
http://eis.jpl.nasa.gov/deepspace/dsndocs/810-005/
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astropin
SFN Regular
USA
970 Posts |
Posted - 08/15/2005 : 10:22:04 [Permalink]
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Fascinating how one man's idiocy can increase the general knowledge of many; indirectly of course. Thanks folks, I have learned allot about modern space travel. sts60 you should hang around. If you have even a 10th of the knowledge in other topics as you do in space travel I would encourage your participation here.
Hey LittleBrain,
Why don't you tell us how the Holocaust never happened, and don't forget about how the Earth is really flat, and only 6-10,000 years old, and Aliens crashed is Roswell, and the Illuminati control everything (or was that the Mason's?), and....and....and.... |
I would rather face a cold reality than delude myself with comforting fantasies.
You are free to believe what you want to believe and I am free to ridicule you for it.
Atheism:
The result of an unbiased and rational search for the truth.
Infinitus est numerus stultorum |
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sts60
Skeptic Friend
141 Posts |
Posted - 08/15/2005 : 11:13:03 [Permalink]
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Thanks, astropin. One thing I like in particular is when I find out I didn't know something as well as I thought, and have to go read about it and think on it.
The widely-acknowledged master when it comes to space-hoax claims is "JayUtah", an engineer with rather formidable knowledge of a lot of topics, especially the Apollo program. You can see some of his work at http://www.clavius.org. |
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GeeMack
SFN Regular
USA
1093 Posts |
Posted - 08/15/2005 : 11:20:35 [Permalink]
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Oh man, that could wreck my day. Hey, astropin, are you trying to say that aliens didn't really crash at Roswell?
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 08/15/2005 : 11:42:36 [Permalink]
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| No it was an Alien publicity stunt, the craft was destroyed on the ground. Also, "They" are out to get me, and dont want me to know about natural cures. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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bigbrain
BANNED
409 Posts |
Posted - 08/15/2005 : 12:56:27 [Permalink]
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Originally posted by sts60
" ... I am of course mainly thinking of Apollo HBs. On the one hand, they claim that the vast gummint conspiracy corps could use sophisticated computer hardware and software to fake an enormous array of still and motion imagery - the "Photoshopped Moon". Then they turn around and claim that the technology did not exist to { control the launch vehicle | navigate the CSM/LM stack | land the LM }, because their space game needs a Pentium 4 with a fancy graphics card to run ... "
No, you are on the wrong way.
The landing on the Moon wasn't made with 3D softwares and Photoshop: it was made with technology used to make films.
I say nobody could land Lunar Module (LM) in 1969 because this heavy, ugly piece of metal
http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-001131.jpg
couldn't go backwards using its rocket engine as a brake.
Helicopters can perform hovering because the thrust is on the top and gravity forces act below and can balance it.
Instead Lunar Module (LM) was thrusted from the bottom and gravity forces acted above spinning it in any direction at 360 degrees.
Only a powerful computer would have been able to keep it in hovering as a helicopter.
But I think not even today a powerful computer could keep it in hovering with its gimballed rocket engine because this displacement of the engine (on the bottom) makes it uncontrollable
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"Obsequium amicos, veritas odium parit" (Flattery gets friends, truth hatred)
Publius Terentius Afer, "Terence", Roman dramatist
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| Edited by - bigbrain on 08/15/2005 12:57:43 |
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pleco
SFN Addict
USA
2998 Posts |
Posted - 08/15/2005 : 13:04:40 [Permalink]
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quote:
Originally posted by bigbrain
Helicopters can perform hovering because the thrust is on the top and gravity forces act below and can balance it.
Not quite...don't forget what the tail rotor does. Also remember there is a human (or auto pilot) manipulating the collective. And autopilot for helicopter has been around for a while and is not a "powerful computer".
EDIT: doing some research - it appears autopilot with hover appeared in 1950: http://www.piasecki.com/xhjp-1(h.htm for example (got to love google) |
by Filthy
The neo-con methane machine will soon be running at full fart. |
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| Edited by - pleco on 08/15/2005 13:12:44 |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 08/15/2005 : 13:17:28 [Permalink]
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quote:
Originally posted by bigbrain
The landing on the Moon wasn't made with 3D softwares and Photoshop: it was made with technology used to make films.
With cameras on the Moon, even.quote:
Only a powerful computer would have been able to keep it in hovering as a helicopter.
Hey, maybe that's why it did not hover, but instead landed on the Moon. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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pleco
SFN Addict
USA
2998 Posts |
Posted - 08/15/2005 : 13:25:56 [Permalink]
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quote:
Originally posted by Dave W.
quote:
Originally posted by bigbrain
The landing on the Moon wasn't made with 3D softwares and Photoshop: it was made with technology used to make films.
With cameras on the Moon, even.quote:
Only a powerful computer would have been able to keep it in hovering as a helicopter.
Hey, maybe that's why it did not hover, but instead landed on the Moon.
It could have "hovered" if it wanted to. It didn't have to worry about little things like the couter rotation of any rotors or wind, which a helicpoter autopilot does have to account for.
Point being if you don't understand how a helicopter is able to hover, then how dare you call NASA engineers buffoons (this including the inability to understand triangulation, gravity assisted trajectories, etc etc etc) (PS: this paragraph not aimed at Dave W. obviously) |
by Filthy
The neo-con methane machine will soon be running at full fart. |
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| Edited by - pleco on 08/15/2005 13:38:28 |
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Dave W.
Info Junkie
USA
26022 Posts |
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pleco
SFN Addict
USA
2998 Posts |
Posted - 08/15/2005 : 13:29:48 [Permalink]
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quote:
Originally posted by Dave W.
Geez, pleco, just ruin my fun, why dontcha?
Sorry, thought I was helping. I'll step out. |
by Filthy
The neo-con methane machine will soon be running at full fart. |
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Valiant Dancer
Forum Goalie
USA
4826 Posts |
Posted - 08/15/2005 : 13:36:06 [Permalink]
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quote:
Originally posted by bigbrain
Originally posted by sts60
" ... I am of course mainly thinking of Apollo HBs. On the one hand, they claim that the vast gummint conspiracy corps could use sophisticated computer hardware and software to fake an enormous array of still and motion imagery - the "Photoshopped Moon". Then they turn around and claim that the technology did not exist to { control the launch vehicle | navigate the CSM/LM stack | land the LM }, because their space game needs a Pentium 4 with a fancy graphics card to run ... "
No, you are on the wrong way.
The landing on the Moon wasn't made with 3D softwares and Photoshop: it was made with technology used to make films.
I say nobody could land Lunar Module (LM) in 1969 because this heavy, ugly piece of metal
http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-001131.jpg
couldn't go backwards using its rocket engine as a brake.
Helicopters can perform hovering because the thrust is on the top and gravity forces act below and can balance it.
Helicopters also are "thrusted" laterally through their tail rotor. Harrier jets are vector thrusted from beneath and do not suffer the same type of instability.
quote:
Instead Lunar Module (LM) was thrusted from the bottom and gravity forces acted above spinning it in any direction at 360 degrees.
It is also "thrusted" from the sides as well and the main thrust downwards is throttlable. This means it isn't a on/off setting for the main thrust. It's more like a common dimmer switch for a light.
quote:
Only a powerful computer would have been able to keep it in hovering as a helicopter.
But I think not even today a powerful computer could keep it in hovering with its gimballed rocket engine because this displacement of the engine (on the bottom) makes it uncontrollable
A claim of complexity? Nope. The computing systems don't have air resistance to deal with. Secondly, the systems were able to be bypassed to allow a human pilot.
Again, simple physics textbooks could unlock the mystery of movement that you consistantly fail to grasp. |
Cthulhu/Asmodeus when you're tired of voting for the lesser of two evils
Brother Cutlass of Reasoned Discussion |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 08/15/2005 : 13:49:50 [Permalink]
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quote:
Originally posted by pleco
Sorry, thought I was helping. I'll step out.
Nonononono! You are helping. I'm the one who was batting the half-dead mouse around.
I just wanted to see bigbrain move the goalposts from "hover as a helicopter" to something even simpler (the craft of the Lunar missions didn't so much hover as they accomplished a controlled fall - even if they could hover). And then even simpler, and simpler. Had he stayed on-course, we might have gotten to the point at which bigbrain would state that NASA engineers don't have the ability to navigate between bed and bathroom in the middle of the night. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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