ApolloHoax.net
Apollo Discussions => The Hoax Theory => Topic started by: DAKDAK on May 10, 2012, 03:48:38 AM
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Since the people on this site reply and explain in great detail the questions I think that alot of people have about the Apollo program I might as well ask if there is a plausible explanation for a few other of the many inconsistencies that I noticed about the Apollo program. When Apollo 11 blasted off from Kennedy space center Neil Armstrong was clearly heard saying Houston we have a roll program. And that has been standard ever since. Of course if you watch the extremely edited versions of any Apollo liftoffs now the massive Saturn V rockets are silent. How is this possible?I was there and we had to be kept several miles away due to the noise and yet supposedly Neil was actually inside the rocket only a couple hundred feet from the massive Saturn V engines The shuttle pilots say that the noise and vibration of pulling several "G"s is all consuming and the shuttle should be less noisy than a Saturn V. I also read that the heat shield on the command module was designed to melt away during reentry this seems odd since today heat shields are not designed to melt but just the opposite. Finally,Were the large inflatable balls and the orange float on the bottom of the command modules already on the command module? Or did the divers have to put them on before they got the astronauts out if so where were they kept during flight (I am referring to the big floatable balls and the orange tube float underneath the command module in all the recovery pictures) I hope I am not posting too much or wasting your time with seemingly dumb questions but I really would like to know
[Post restored by LunarOrbit]
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Actually, except for the former NASA Space Shuttle, the now sadly destroyed Soviet Buran, and the unmanned X-37, all which used a system of reusable tiles for their heat shield, all spacecraft, for Mercury and Vostok to Soyuz and Shenzou use a system in a disposable heat shield melts and burns away, taking the heat of re-entry with it.
As for the noise, astronauts and cosmonauts on the former shuttle, and Soyuz also communicate with their respective launch centres. The microphones in all cases are right by their mouths, and are designed to pick up noises only right near by.
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Of course if you watch the extremely edited versions of any Apollo liftoffs now the massive Saturn V rockets are silent.
No they're not.
How is this possible?I was there and we had to be kept several miles away due to the noise and yet supposedly Neil was actually inside the rocket only a couple hundred feet from the massive Saturn V engines
He was also sealed inside a multi-layered spacecraft, wearing a spacesuit with a thick lexan helmet sealed over his head, and a microphone set designed especially for use in noisy environments that was right next to his mouth. It had an excellent ability to pick up sound from something very close by, and an excellent ability not to be bothered by extraneous noise that would be somewhat muted by the multiple layers of spacecraft walls and suit helmets.
I also read that the heat shield on the command module was designed to melt away during reentry this seems odd since today heat shields are not designed to melt but just the opposite.
Actually this is normal. It's called ablation, and it works by cherring and burning away, which takes away the heat. In the whole of the space program of both the US and the Soviet Union right up until the shuttle program, only the first two sub-orbital Mercury spacecraft used a heat shield system that was not ablative. Soyuz has been using it reliably for over 40 years now. The Chinese Shenzhous spacecrfat also uses an ablative heat shield. It's a well-known, tried and tested, and highly reliable way of protecting something from the heat of a re-entry.
Finally,Were the large inflatable balls and the orange float on the bottom of the command modules already on the command module?
The large inflatable balls on the apex of the command module are indeed stowed inside the upper section around the tunnel, alongside the parachutes. The command module, when in the water, had two possible stable floating configurations. One was what was known as 'stable 2', which is the upright position used to allow the astronauts to exit the spacecraft. Unfortunately the other, known as 'stable 1', was upside down in the water with the hatch submerged. Since that is obviously not a good position for the astronuats to be able to exit the spacecraft, those three inflatable spheres would be inflated, and the buoyancy they provided was enough to flip the command module over to stable 2 and allow egress.
The large flotation collar was attached by the recovery personnel prior to opening the hatch, to ensure that the command module remained stable and upright during egress.
I hope I am not posting too much or wasting your time with seemingly dumb questions but I really would like to know
There is nothing wrong with the questions. I would point out that you raised several points in your first post that were responded to and you have yet to address them. It would be appreicated if you would do so.
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Since the people on this site reply and explain in great detail the questions I think that alot of people have about the Apollo program I might as well ask if there is a plausible explanation for a few other of the many inconsistencies that I noticed about the Apollo program. When Apollo 11 blasted off from Kennedy space center Neil Armstrong was clearly heard saying Houston we have a roll program. And that has been standard ever since. Of course if you watch the extremely edited versions of any Apollo liftoffs now the massive Saturn V rockets are silent. How is this possible?
Have you ever flown on a commercial airliner? Have you ever stood next to a commercial airliner when its jet are running? It is deafening. You will notice the ground crew is wearing hearing protection. Yet the passengers inside do not need hearing protection.
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When Apollo 11 blasted off from Kennedy space center Neil Armstrong was clearly heard saying Houston we have a roll program.
If you take a ride in a small general aviation aircraft like a Cessna 152 or 172, you will most likely be wearing a headset with hearing protectors and a microphone. The microphone has to be very close (sometimes touching) to your lips to pick up your voice. While you will hear some engine and air noise coming over the mic to the headset, the other person's voice is far louder. This is how it works.
Try separating your thoughts and questions into separate paragraphs, this makes it easier for other people to follow when reading your posts.
Reading your posts makes it look like you have very little experience with the world other than what you see on TV or your computer. It will do you very good to get out into the world and experience something once in a while.
Ranb
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DAKDAK wrote:
Since the people on this site reply and explain in great detail the questions I think that alot of people have about the Apollo program I might as well ask if there is a plausible explanation for a few other of the many inconsistencies that I noticed about the Apollo program.
DAKDAK, what about all the "inconsistencies" you already brought up which were debunked in the "I don't know..." thread? Would you please address these issues before wandering off to new topics?
When Apollo 11 blasted off from Kennedy space center Neil Armstrong was clearly heard saying Houston we have a roll program. And that has been standard ever since. Of course if you watch the extremely edited versions of any Apollo liftoffs now the massive Saturn V rockets are silent. How is this possible?
First, your claim is wrong. There are plenty of available versions of Apollo liftoffs - online, no effort or expense required - with the roar of the launch vehicle. This claim is so easily debunked and so obviously incorrect I am surprised you would make it.
Second, why does it matter? Why would you compare "heavily-edited" versions to other, presumably more complete, versions?
I was there and we had to be kept several miles away due to the noise
Due to the explosion hazard, primarily.
and yet supposedly Neil was actually inside the rocket only a couple hundred feet from the massive Saturn V engines
Can you think of any differences between being inside the spacecraft atop the launch vehicle, and being outside it?
Here's a hint for you. I cannot stand near a 747 at takeoff power without hearing damage. But I can sit inside the aircraft a few dozen feet from the engines quite comfortably.
The shuttle pilots say that the noise and vibration of pulling several "G"s is all consuming and the shuttle should be less noisy than a Saturn V.
I've worked with a number of Shuttle astronauts. Please provide a reference for your claim.
I also read that the heat shield on the command module was designed to melt away
Wrong. It was designed to char in a very specific way - ablative shielding.
during reentry this seems odd since today heat shields are not designed to melt but just the opposite.
No. Some do (e.g., X-37B); some don't (Russian Soyuz, Chinese Shenzhou, U.S. Orion...).
... I hope I am not posting too much or wasting your time with seemingly dumb questions but I really would like to know
You are certainly not posting too much, nor wasting time, but you really should go back and address the claims you made (and the rebuttals to them) in the "I don't know..." thread; I for one would like you to address my rebuttals in this post (http://www.apollohoax.net/forum/index.php?topic=77.msg1353#msg1353).
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I might as well ask if there is a plausible explanation for a few other of the many inconsistencies that I noticed about the Apollo program.
Of course there are. And it should be telling you, after all this, that your idea of what constitutes an "inconsistency" is really just something you didn't know about Apollo before.
Yes, you may have been taught only the rudiments of space engineering in school. That's because only a very few people at your school go on to study space engineering and become experts. I flounder through business accounting because I only ever learned the rudiments. I rely on the expertise of the few others at my school who went on to study corporate accounting and know its details intimately.
The conspiracy theorists who are feeding you bad information don't know anything but the rudiments either -- if even that. But they make an art out of trying to delve into the details, only from a completely ignorant (or worse, solely common-sensical) point of view. They talk, for example, about "radiation" when they themselves know practically nothing about it.
When Apollo 11 blasted off from Kennedy space center Neil Armstrong was clearly heard saying Houston we have a roll program.
Yes. He's speaking into the best noise-cancellation microphone that Plantronics made at the time, pressed against his lips, inside a bubble helmet inside a heavily insulated and shielded command module 300 feet away from the engines -- and, most importantly, in front of the engines.
Of course if you watch the extremely edited versions of any Apollo liftoffs now the massive Saturn V rockets are silent. How is this possible?
Because they're heavily edited. Or more likely, because you're looking at something that ultimately traces its lineage back to film, and film doesn't naturally record sound. The pad cameras, for example, don't record sound. They're just 16mm data-acquisition cameras in hardened enclosures.
I was there and we had to be kept several miles away due to the noise...
Not so much noise as explosion and crash hazard.
You've already been shown how ordinary jet engines are deafening if you happen to be around them outside, but are noticeably quieter as heard from the airplane cabin just a few feet away. I also mentioned it matters what direction you are in relation to the engine.
Experienced airline passengers learn that the rear of the cabin is considerably noisier than the front of the cabin, in airframes with wing-mounted engines. Why? Because if you're seated aft of the wing, you get the directional noise produced by the engine's tailcone -- or more accurately, by the effect of the exhaust stream hitting the ambient. This tends to radiate outward (i.e., at right angles to the direction of thrust) and rearward (i.e., behind the plane) but not so much forward (i.e., the forward part of the cabin and the flight deck).
Observing a Saturn V launch, you were at right angles to the thrust axis, and then likely somewhat behind it. Where was Neil and company? They were on the "flight deck" forward of the engine exhaust.
The shuttle pilots say that the noise and vibration of pulling several "G"s is all consuming and the shuttle should be less noisy than a Saturn V.
Where did you hear that?
I also read that the heat shield on the command module was designed to melt away...
No. Melting means changing from a solid to a liquid without altering the chemical composition. The ablative heat shield on the CM chars, which means to change chemical composition in a material by means of applying heat. The heat consumed by the chemical reaction keeps it from penetrating further. Also the product of the reaction is a species of gas that has excellent thermal insulation properties. The plasma heat generated forward by the compression of gases has a hard time penetrating this layer of gas, char, and sheer bulk.
this seems odd since today heat shields are not designed to melt but just the opposite.
No, only the space shuttle had a non-consumable thermal protection system, and that's because it was designed to be reused.
Were the large inflatable balls and the orange float on the bottom of the command modules already on the command module?
They were up on the ELS ring, near the parachutes. No, they were not contained within the pressurized volume of the spacecraft.
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this seems odd since today heat shields are not designed to melt but just the opposite.
No, only the space shuttle had a non-consumable thermal protection system, and that's because it was designed to be reused.
Notable recent examples using ablatives: the Soyuz capsules (which still fly regularly), Stardust, Genesis, Hayabusa, Fobos-Grunt (failed on launch, but was intended to return samples), all of the Mars landers, China's Shenzhou spacecraft, the Indian SRE, the Indian ISRO (which hasn't flown yet), the SpaceX Dragon (which has a reusable ablative heat shield), and the Orion MPCV. This isn't an exhaustive list.
Ablatives aren't some idea cooked up for Apollo and then abandoned, they're the standard approach to bringing things back to Earth's surface from orbit. In fact, the material to be used on the MPCV (if it ever flies) is an updated version of the Avcoat material used on the Apollo command modules. The only new spacecraft that's actually flying with a non-ablative heat shield appears to be the X-37.
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I hope I am not posting too much or wasting your time with seemingly dumb questions but I really would like to know
We don't mind answering questions provided that you actually pay attention to our answers.
I, for one, seriously question whether you do. It might help if you were to answer the questions we pose to you.
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[quote authorDAKDAK]
I hope I am not posting too much or wasting your time with seemingly dumb questions but I really would like to know
We don't mind answering questions provided that you actually pay attention to our answers.
I, for one, seriously question whether you do. It might help if you were to answer the questions we pose to you.[/quote]
I definitely want to reply to each response but the first time I tried I guess I sent the reply to someones personal mailbox and that person seemed upset is this the proper place and way to reply?
I also have to think about my replies more because I dont want to sound like an idiot,and I dont know the answers that is why I asked the questions. I will say that the replies I have received so far are very convincing and I am definitely rethinking the whole Apollo subject. I also travel for work alot(not an excuse just saying)
[Post restored by LunarOrbit]
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Yes, this is the proper place.
Don't worry about sounding like an idiot just for asking questions. Any question intended to help improve your understanding of something is a perfectly good question, no matter how basic. That's how all of us learn. So ask away.
But what does make you sound like an idiot is to say "I'm convinced Apollo was faked" and in the same breath admit that you have absolutely no basis for this conclusion other than your emotions because you don't know how any of it worked. Or perhaps you think it was faked simply because you don't understand it.
There's a lot of talent, experience and knowledge on this board. Just about everyone is willing to patiently answer your questions as long as you're sincere about learning. But if you make it obvious that you're not really listening but are just mining for quotes to support your predetermined position, then don't expect much sympathy.
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It would probably be easier to handle all the replies if you didn't throw out so many things at once.
Ask one question. It will be answered. Then ask the next.
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But what does make you sound like an idiot is to say "I'm convinced Apollo was faked" and in the same breath admit that you have absolutely no basis for this conclusion other than your emotions because you don't know how any of it worked. Or perhaps you think it was faked simply because you don't understand it.
I cannot agree with this enough. Seriously, if you know you don't know all that much about Apollo, what makes you think you know enough about it to know that it was faked? If people who obviously know a ton about Apollo don't think it was faked, what makes you think you know better than they do?
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DAKDAK, it's not a problem to take time between replies if you need to, as long as you're reading and digesting the answers you're getting.
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DAK, the folks here know an awful lot about spaceflight, Apollo, engineering and everything else that made Apollo "work". Frankly, some of it seems like magic to me, but to them it's just another engineering problem.
I mean, they built 1st stage engines with fuel pumps which delivered tons of fuel per second to the engines. And the engines could slightly, and accurately,"gimbal" while putting out over a million pounds of thrust each. They could determine the position and velocity of the spacecraft while in lunar orbit with amazing accuracy. Then a heat shield to protect them from reentry heating just inches thick...and they maneuvered their craft using it's lifting body characteristics to make near pinpoint landings every time.
It's all amazing stuff, no doubt about it. And it's a real testament to the smart and imaginative folks that put it all together, solving the innumerable problems one by one.
Please do stick around and ask questions. The people here know the answers, several are in the space flight business.
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I might add in that sticking around, you read some of the previous topics. I have ingested so much information reading the replies here my brain implodes (what there is of it). Someone challenges and the replies are so informative it is most enlightening to human kinds abilities.
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I just watched the "Moon Machines" series on YouTube, another great piece highlighting not only the amazing technical leaps but also the folks directly involved in the challenges of developing the hardware and processes. Five stars for sure!
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...I also read that the heat shield on the command module was designed to melt away during reentry this seems odd since today heat shields are not designed to melt but just the opposite...
Dakdak, have you considered the faster Earth entry speeds of the manned lunar missions, compared with earth orbital missions of Apollo and the Space Shuttles, and thought about whether the faster speeds might require a different heat shield? You might find that the Shuttle and it's protective tiles would have burnt up if it re-entered at the slowest Apollo lunar mission's speed, that of Apollo 17.
I don't have entry speeds of the Shuttles and leave it to you to find them, but the following link in the Apollo By the Numbers series gives figures for the Apollo missions:
http://history.nasa.gov/SP-4029/Apollo_18-40_Entry_Splashdown_and_Recovery.htm
and I show the mph conversion for the slowest and fastest figures.
Earth Orbit Mission -- Earth entry velocity
Apollo 7 -- 25,846.4 ft/sec -- 17,622 mph
Apollo 9 -- 25,894 ft/sec
Lunar Mission -- Earth entry velocity
Apollo 8 -- 36,221.1 ft/sec
Apollo 10 -- 36,314 ft/sec -- 24,759 mph -- over 7,000 mph faster than Apollo 7
Apollo 11 -- 36,194.4 ft/sec
Apollo 12 -- 36,116.618 ft/sec
Apollo 13 -- 36,210.6 ft/sec
Apollo 14 -- 36,170.2 ft/sec
Apollo 15 -- 36,096.4 ft/sec
Apollo 16 -- 36,196.1 ft/sec
Apollo 17 -- 36,090.3 ft/sec
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I don't have entry speeds of the Shuttles and leave it to you to find them
I would guess that it is pretty similar to the Apollo 7 and 9 missions - the braking power applied to de-orbit is pretty minimal, isn't it?
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17,500 mph is given as a "typical" figure for Shuttle here: http://www.grc.nasa.gov/WWW/BGH/hihyper.html
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17,500 mph is given as a "typical" figure for Shuttle here: http://www.grc.nasa.gov/WWW/BGH/hihyper.html
OK, and the Wikipedia page claims that the braking applied to de-orbit slowed the shuttle down by about 200 mph. Then given the loss of altitude, it may be possible that the re-entry speed was actually higher than the orbital speed, I haven't run the numbers.
ETA - specifically, this Wikipedia page. http://en.wikipedia.org/wiki/Space_Shuttle
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The shuttle would accellerate at a very slowly increasing rate as it descends after the deorbit burn, but entry interface at it's high (and banked) AOA puts a stop to that. Orbital mechanics say that the maximum orbital speed would be at periapsis, where vertical speed and horizontal Deltav has dropped back to zero. (edit...this is only in a vaccuum, descending into the atmosphere changes everything)
I recollect seeing a report in the shuttle reentry profile, it talked about the tradeoffs between shorter reentry profiles, where high dynamic surface heating is the problem, vs longer profiles, where heat soak into the structure becomes an issue. The operational reentry profile was a very carefully designed compromise.
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I recollect seeing a report in the shuttle reentry profile, it talked about the tradeoffs between shorter reentry profiles, where high dynamic surface heating is the problem, vs longer profiles, where heat soak into the structure becomes an issue. The operational reentry profile was a very carefully designed compromise.
OK, this is interesting stuff.
Purely speculative here, I haven't studied these things, but I would guess you would want to use all the fuel you've got for the re-entry burn, to get your velocity down as low as possible? (After all, what are you going to do with it, if you don't burn it.) So you need to come in at the right angle, and you also need to time it so that your landing spot has rotated to be approximately underneath you when you reach the ground (and you also need to be at the right latitude). So I am wondering, if you are in a moderately eccentric orbit, there may be reasons to do your re-entry burn at a time other than immediately before you take the plunge. Might you even want to do it while your altitude is increasing?
Just thinking out loud here, some of these thoughts may be rubbish.
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The Shuttle did it's deorbit butn over the Indian Ocean, roughly half an orbit before landing. The capsules of the earlier programs did them significantly later, and much closer to their desired ocean landing points. They had solid motors of fixed total impulse which have them a more significant, but still precise, decelleration (when burned in a precise vector). The shuttle, with it's significant lift, could make a longer, and less rigouous, decelleration through the atmosphere. It also had less g tolerances, so couldn't withstand the higher decelleration (g) forces experienced by the earlier capsules. Apollo was something of a "lifting body", so it could do a "double dip" reentry coming back from the Moon, with some ability to control it's descent rate through the upper atmosphere. It was actually a gentler (and longer) reentry than experienced in Mercury and Gemini.
The shuttle did it's deorbit burn to get it's periapsis to a certain level at a certain point, and burned just enough to get it to that orbital configuration . After that, there was an "OMS fuel dump" to discard some excess OMS fuel and adjust it's weight and balance for reentry.
It's still magic to me how it's done so precisely, but that's what makes spaceflight so interesting.
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The Shuttle deorbited from a variety of orbits depending on the mission it performed, thus there is no single answer regarding the magnitude of the deorbit burn, the velocity at entry interface, etc. However, I can provide an example to give an idea of the velocities we're dealing with. According to the STS-1 pre-flight mission plan, the Shuttle was to deorbit from a 150 nautical mile circular orbit. The planned delta-V of the deorbit burn was 299 m/s. After the burn the Shuttle's orbit would be 149 n.mi. X 2 n.mi. This orbit has an apogee velocity of 25,121 ft/s (17,128 mph) and a perigee velocity of 26,200 ft/s (17,864 mph). The velocity at entry interface (400,000 feet altitude) is 25,729 ft/s (17,542 mph), and the entry angle is -1.19 degrees. The velocity would continue to increase for a time after interface until drag started to slow the Shuttle down. I don't have the data to tell me what the maximum velocity was, though I would guess it wasn't more than about 100 m/s higher than the interface velocity. The actual flight data varied somewhat from the pre-flight plan, though not by much.
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OK, interesting stuff.
My first thought was, "use all the fuel to slow down as much as possible", but if the change in velocity is 300 m/s relative to an orbital velocity of roughly 26,000 fps, we're talking about a whopping 0.15% decrease in kinetic energy. So more effective than pissing out the window to slow down, but not by too much - sounds like it is the atmosphere doing almost all of the work.
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The Shuttle did it's deorbit butn over the Indian Ocean, roughly half an orbit before landing.
My previous calculations appear to agree with this. Based on the example, entry interface is crossed at a true anomaly of 276.7 degrees, i.e. 96.7 degrees past apogee and 83.3 degrees before perigee. If the deorbit burn is performed over the Indian Ocean, entry interface would then be crossed somewhere over the middle of the Pacific Ocean. Of course, entry interface is just the beginning of the atmosphere. The Shuttle would travel considerably further before maximum deceleration occurs.
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My first thought was, "use all the fuel to slow down as much as possible"
The deorbit burn is used to lower the perigee to a point deep inside the atmosphere so that drag can then be used to slow the spacecraft. As you correctly figured out for yourself, the deorbit burn contributes almost nothing to decreasing the spacecraft's kinetic energy. The burn is designed more to get the entry angle right for an optimal reentry.
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When Apollo 11 blasted off from Kennedy space center Neil Armstrong was clearly heard saying Houston we have a roll program. And that has been standard ever since. Of course if you watch the extremely edited versions of any Apollo liftoffs now the massive Saturn V rockets are silent. How is this possible?
The microphones used by the Apollo astronauts were designed to only pick up immediately close sound. You'd be lucky to hear much engine noise and Neil was pulling only a few G's. The average human can easily withstand 3G's for quite a bit of time. The Saturn didn't give them much more than that. Besides, Neil was one of the best astronauts in the whole program. Hell, look at his work on Gemini 8. That guy was a BOSS. A few G's is nothing for the astronauts and most of the vibration on the Saturn was attributed to its "gimballing" engines. That means that you'd feel a lot of movement, but not necessarily notice it being carried over to your voice.
I also read that the heat shield on the command module was designed to melt away during reentry this seems odd since today heat shields are not designed to melt but just the opposite.
Yes, the heatshields were actually designed to melt away. This allowed the heat to be absorbed, save weight for the chutes and work as a more efficient method of keeping the 3000 degree flames safely confined. I'm sure the exact technicalities could be researched. Hey, that's a good word. You should try it!
Finally,Were the large inflatable balls and the orange float on the bottom of the command modules already on the command module?
Yes, they were on the CM already. When the CM hit the water, they pulled a breaker to detach the parachutes and then another to deploy those inflatable bags. Actually, those bags were the reason Apollo 11 got righted from "stable II" to "stable I". Would you have guessed it? NASA actually thought ahead to give them inflatable bags. LOL. What's your point here?
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I've seen Apollo deniers seriously arguing that the Apollo missions were fake because they didn't hear enough stress and noise in the commander's voices to suit their expectations. For "proof" they show a cockpit video of a shuttle launch -- a totally different beast than a Saturn V with totally different acceleration-vs-time, noise-vs-time and vibration-vs-time curves.
Both vehicles were pretty rough from liftoff to tower clear because of ground reflections and tower strike avoidance maneuvers (e.g., the Saturn's yaw maneuver), but the parallel-staged Shuttle had a very different acceleration profile than the serially staged Saturn V. The Saturn V lifted off the pad very slowly - barely more than 1 g, but peaked (twice) at 4g during S-IC flight: first at inboard shutdown and again at outboard shutdown. The S-II and S-IVB stages were considerably smoother and gentler, their H2/O2 engines optimized for high Isp rather than the high thrust (but low Isp) of the S-IC's F1's.
In fact, with full propellant loads the S-II and S-IVB upper stages gave initial accelerations of less than 1 g -- the astronauts weighed less than they had while waiting for launch!
So if you listen to an Apollo launch, you will note that the air-to-ground channel is pretty quiet throughout first stage flight, with just the commander's brief acknowledgements of abort mode changes. If they do say anything near the end of S-IC flight, you will hear it in their voices. They all become far more talkative after staging when things settle down to a far easier ride. Their abort options also become far less critical once they're out of the atmosphere.
The Shuttle, on the other hand, is especially loud and violent during early SRB burn and MaxQ (solids are very turbulent), tapering to near silence as the stack reaches vacuum even before the SRBs burn out. But unlike the Saturn where the peak loads were at the end of first stage flight, the highest Shuttle g-loads come toward MECO as the external tank steadily empties; the engines are actually throttled back to limit those loads to 3g's. But even though the acceleration late in a Shuttle launch is considerably than that of the Saturn V late in its boost, both rides are pretty smooth and quiet.
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There was a nice reference to noise-canceling microphones I ran across while brushing up in my Yamaha Sound Reinforcement Handbook. The technique is, essentially, a dual-ported capsule. Sounds from far away reach both sides of the capsule at more-or-less the same time and being in phase, are canceled. Sounds that are much closer to one port than the other create a pressure differential. Obviously this is frequency dependent, and in practice you have to roll off the low end considerably, but otherwise is an elegant solution.
Basically, it's a humbucker for a human voice. Can also do the trick with a pair of capsules wired out of phase.
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Yes. Listening to the Apollo 17 onboard voice recorders, you can hear a little bit of stress in the voices of the astronauts during Max-Q.
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Err, let me edit, I was describing phase and meaning pressure differential....anyhow, the principle of the dual ported/twin capsule is that sound propagates through air in the usual inverse-square. So if the astronaut's mouth is two cm away, and the mic is two cm between the ports, the pressure of that wave has dropped to a quarter by the time it hits the rear port. So you have a big difference in pressure and that difference is what you amplify. The sound of the engine several meters away is pretty much identical in pressure on both ends of the mic, thus it gets canceled.
Of course phase WILL rear its ugly head here, as any wavelengths around the size of that distance between the ports are going to be amplified or attenuated based on their phase difference as much as by the pressure difference. And in the real world, sounds aren't perfect point sources in still air -- the human voice emanates both from air moving out of the mouth, and the resonating surfaces of the sinuses (which is why we tape microphones to people's foreheads in live stage musicals). But the general idea is still there!
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This method of passively adding wavefronts with different phases from different directions is also exactly how directional radio antennas work, albeit with electromagnetic waves rather than sound pressure waves. A noise-canceling microphone is nothing more than a highly directional microphone, with the main lobe pointed directly at the speaker's mouth.
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Here's the acceleration profile of a Shuttle launch (and landing):
http://www.russellwestbrook.com/Acceleration.htm
You can see how acceleration is (relatively) high at liftoff, 1.5-2g, much higher than the Saturn V (1.15g). For the pass through MaxQ at about 1 minute, it dips back to 1.5 g due to main engine throttleback (to about 65%) and the shape of the SRB propellant grain. Due to the rapidly decreasing atmospheric pressure as the shuttle gains altitude, aerodynamic pressure falls just off as rapidly as it peaks. So after MaxQ the engines are then throttled back up ("Go at throttleup"). MaxQ is a very obvious peak in wind noise in the cockpit video recordings.
Acceleration drops markedly at SRB burnout, as you'd expect.
I do not quite understand the constant 1-g region just after SRB separation. I'd expect acceleration to immediately increase exponentially from that point, not 80 seconds later. Perhaps the ET is still too full at that point for the main engines to gain much altitude without the help of the SRBs. Maybe a "lofted" trajectory is flown during the SRB phase to gain altitude relatively rapidly, allowing the shuttle to pitch down after staging to decrease gravity losses until the ET can lose enough weight to allow the shuttle to pitch back up and gain orbital altitude without excessive gravity losses.
After about 200 seconds the acceleration increases exponentially as the ET loses weight, followed by the throttleback to limit acceleration to 3g just before MECO.
And here it is for an Apollo/Saturn V launch, specifically Apollo 11:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900066485_1990066485.pdf (pdf page 54, memo page 4-5).
Liftoff acceleration is barely more than 1g, and it takes a long time to clear the tower. Acceleration builds exponentially as propellants are burned off, so the inboard F-1 engine is cut off early to prevent exceeding 4g. Acceleration quickly builds up again on the remaining four until they also cut off at S-IC propellant depletion.
The S-II starts at less than 1g, again building exponentially as it depletes its propellants but never exceeding 2g. There are drops at center engine cutoff and again at EMR (mixture ratio shift). EMR decreases the flow of LOX to the engines relative to LH2, decreasing thrust but increasing Isp slightly. It is timed dynamically to result in simultaneous depletion of both propellants.
The first burn of the S-IVB is especially gentle, reaching only 3/4 g before MECO because most of the propellants are kept for the TLI burn.
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This method of passively adding wavefronts with different phases from different directions is also exactly how directional radio antennas work, albeit with electromagnetic waves rather than sound pressure waves. A noise-canceling microphone is nothing more than a highly directional microphone, with the main lobe pointed directly at the speaker's mouth.
Actually, that is what I thought at first. And that confused me. I work with cardiods and hypercardiods, and the off-axis rejection of those just didn't feel sufficient to be the whole story.
The cuteness of turning the microphone into a pressure-differential microphone is that it cares about proximity. Sources with proximity have a greater difference in pressure. Sounds that are not proximate are largely rejected. Maybe the humbucker is a bad example -- because you can look at the humbucker just as you look at a balanced audio cable; it's all common-mode rejection.