PDA

View Full Version : Question on Saturn V launches.



Vega115
2003-Jul-27, 01:14 AM
Ok, i was recently watching Final Destination, and when the plane explodes (i know...perfect movie for me eh? a plane en route to paris blows up and im going to paris! #-o ) you see the explosion and hear it a few seconds later. The director explained it as "I thought it would be cool to involve something i heard on the Saturn V launches - you would see the rocket lift off and then you would hear the engines a few seconds later...sort of light is faster than sound, so we basically applied that to the movie, you would see the explosion, followed by the sound of it" heres my question:

When the Saturn V's took off, would you first see it, then a few seconds later, hear it? Like when you look up at a plane, you see the plane, but the sound sounds like its trailing behind.

:-?

Archer17
2003-Jul-27, 01:50 AM
...When the Saturn V's took off, would you first see it, then a few seconds later, hear it? Like when you look up at a plane, you see the plane, but the sound sounds like its trailing behind.

:-?It depends on distance. Since the speed of light (your seeing the liftoff) is much, much faster than the speed of sound you'd notice a delay unless you were really close to the launch pad. Think of the delay between seeing lightning and hearing the thunder. I thinks it's like 5 sec for every mile. So unless you were dangerously close to the Saturn, you'd probably notice some delay in hearing it. I've never had the pleasure of seeing a launch in person so I don't know how close they let you get.

ToSeek
2003-Jul-27, 02:09 AM
When the Saturn V's took off, would you first see it, then a few seconds later, hear it? Like when you look up at a plane, you see the plane, but the sound sounds like its trailing behind.

:-?

Definitely. No observers were allowed to get closer than three miles to a Saturn V launch, so sound would be delayed at least fifteen seconds (sound travels a mile every five seconds). However, the engines start revving up at T-9 seconds, so the sound could arrive as soon T+6. But still the rocket would be most of the way up the tower by then.

Hale_Bopp
2003-Jul-28, 02:30 AM
I saw a Space Shuttle launch from Sanford, Florida. I started my stop watch when I saw liftoff in the hotel lobby. It was almost two minutes and forty seconds later when I finally heard the launch!

Rob

kucharek
2003-Jul-28, 06:13 AM
I don't know what's so extraordinary about this. Every child learns that from the time delay between the flash and the thunder you can compute how far away the lightning struck. For the metric kids, it's "divide seconds by three and you get the kilometers". As no-one was alowed closer than five kilometers to the Saturn V launch pad, the first sound arrived 15 seconds after ignition, some 8 seconds after lift-off. This time, the Saturn had nearly cleared the tower.

Kaptain K
2003-Jul-28, 06:53 AM
Not everybody understands the delay between sight and sound. I saw Paul McCartney (not yet "Sir Paul") in '93. Next day, there was a letter to the editor of the paper, complaining that McCartney was 'lip-synching', because "I was watching him with binoculars and what I saw did not match what I was hearing". :roll: Well, DUH!! If you are so far away that you have to use binocs to see his lips move, there is going to be a noticeable delay! I have mixed live sound and even at 40 meters, I can't monitor the mix with headphones unless I delay them to the sound from the main stacks.

kucharek
2003-Jul-28, 07:02 AM
If you had to make the sound for a big open air, you put also loudspeaker towers some hundred feet in front of the stage for the audience in the back. IIRC, they are called delay towers, because you've to delay the signal to the right amount. Otherwise, the sound from the boxes in front of the stage and those in the delay tower would give an awful mix for those who could hear both.

AGN Fuel
2003-Jul-28, 07:23 AM
I don't know what's so extraordinary about this. Every child learns that from the time delay between the flash and the thunder you can compute how far away the lightning struck. For the metric kids, it's "divide seconds by three and you get the kilometers". As no-one was alowed closer than five kilometers to the Saturn V launch pad, the first sound arrived 15 seconds after ignition, some 8 seconds after lift-off. This time, the Saturn had nearly cleared the tower.

IIRC, because the shock wave travels through the ground faster than the sound wave, the (unbelievably) fortunate spectators to the Saturn V launches would first see the exhaust, then a few seconds later feel the ground tremor and then a few seconds later again, the deafening roar/crackle combined with a pressure wave that literally 'pushed' them backward. It must have been one h*** of an experience. In September as part of an assignment, I am going to interview a gentleman who was present at the A-11 & A15 launches - I can't wait. He will have some wonderful stories to tell! :)

Again, IIRC, didn't Walter Cronkite's temporary TV studio suffer some damage during the broadcast of the first S-V launch, with ceiling tiles etc falling down live on camera?

kucharek
2003-Jul-28, 07:30 AM
Hey AGN, did you ever replied to my answer to your PM?

With regards to the subject:
When I'm moody and see a Saturn V launch on tv, I can feel really p..... that I'll never have the chance to see this in reality. Though a shuttle launch must be pretty similar, there is some big difference to me I can't really explain.

Colt
2003-Jul-28, 07:35 AM
There is a difference for me also. Seeing a Saturn-V launch.. You have a feeling that it is doing something special, something important. Seeing a shuttle launch is like "Oh, there goes another load of cargo." -Colt

man on the moon
2003-Jul-28, 09:37 AM
i'd like to see a launch some day, that'd be cool.

i had a comment about the delay of sound though. even at one hundred meters there is a marked difference. (about 300 feet, plus or minus). when i was running varsity track in high school, i would help out after practice when the middle school team had meets. i can remember when i first ran the backup (secondary) clock for the two hundred meter dash. they told me to start the watch when i saw the smoke, not when i heard the crack.

(the two hundred is the one that starts on the far corner from the starting line and only runs half a lap).

later i learned that it was because if i waited for the pistol crack there would be an extra .5-.75 seconds on the clock, a big difference when the times between runners can be .1 seconds or less! on windy days the difference could be even more.

before that, i'd always thought it was distances of miles that made sound delay, but now i know it can even be a few hundred feet. not to say i'd want to be a few hundred feet from the launch pad... :o

kucharek
2003-Jul-28, 09:50 AM
On serious racetracks, every starting block has its own loudspeaker, so everyone hears the shot at the same time. Maybe one athlete is just two meters from the starter, the outermost maybe 10 meters. 8 meters, that is roughly between 2 and 3 hundreth of seconds delay. In a 100m sprint, that's half an eternity.

man on the moon
2003-Jul-28, 09:56 AM
it certainly is! i've seen those systems at the olympics (ok ok...only on tv). pretty neat, but a bit of overkill for a middle school meet hwere half the kids don't even know the right way to run on the track. some of the states and rgionals had something like that, with a speaker at the finish line for the clocker, but not for every runner.

and yes, i remember now that we had to do the same thing for the 100 (starts at the far end of the straight away) and the 300 hurdles. (starts after the first corner, straight across from the finish line).

pretty impressive the things you can learn when you aren't trying to! (i'd still like to go to the olympics someday...)

(ok ok, and a launch or two too...)

ToSeek
2003-Jul-28, 02:35 PM
Again, IIRC, didn't Walter Cronkite's temporary TV studio suffer some damage during the broadcast of the first S-V launch, with ceiling tiles etc falling down live on camera?

Yes, I've read that in a few places, though I can't find any documentation for it online.

Russ
2003-Jul-28, 02:53 PM
Hey guys:

I think your math is off a little. My little book of official values says the speed of sound at sea level is 750 feet/second. 5280 / 750 = 7.03. That makes it 7 seconds per mile if you're calculating the distance to a noisy event, e.g. Apollo launch, race starting gun, lightening strike, etc. You have to be at sea level of course, otherwise add time as you increase altitude. :D

kucharek
2003-Jul-28, 03:00 PM
I think your math is off a little. My little book of official values says the speed of sound at sea level is 750 feet/second. 5280 / 750 = 7.03. That makes it 7 seconds per mile if you're calculating the distance to a noisy event, e.g. Apollo launch, race starting gun, lightening strike, etc. You have to be at sea level of course, otherwise add time as you increase altitude. :D
I used the pretty well approximation of one kilometer in three seconds at sea-level. 750ft/s looks much too slow to me, as 750ft=228m (1ft=30.48cm, isn't it?)

Do you work for NASA? Would explain something... :lol:

I think, speed of sound is some 750miles/hour...

You work for NASA... :lol:

Kaptain K
2003-Jul-28, 04:09 PM
At 20 degrees C. (68 F.), the speed of sound is 344 m/s (1128 ft/sec - 770 mph)

AGN Fuel
2003-Jul-28, 11:41 PM
Hey AGN, did you ever replied to my answer to your PM?

Sorry Kucharek.....it's high on my 'to-do' list. :oops: #-o

I'll send you a reply when I get home from work tonight.

Regards,

kucharek
2003-Jul-29, 05:53 AM
Hey AGN, did you ever replied to my answer to your PM?

Sorry Kucharek.....it's high on my 'to-do' list. :oops: #-o
Don't mind, I'm also often slow with these things.

Darkwing
2003-Jul-29, 06:01 PM
When I was in grad school (and during the summer when the undergrads were around) there was a long hallway in which I could stand and snap my fingers and hear the echo off the doors at the end of the hall. As I changed my distance from the doors, the delay would change accordingly. I would play a little "sonar" game in which I could close my eyes, walk around, and listen to my "pings" off the end of the hallway and try to estimate my distance from it.

Why did I spend my grad school days in a hallway snapping my fingers, you may ask? Usually I was just passing the time waiting for someone...

kucharek
2003-Jul-30, 05:51 AM
Back in the days when remote controls worked with ultrasonic, I exploited the Doppler effect. The key for the second channel was dead. Then I figured out from the schematics, that every channel simply sends a slightly higher frequency beep when pressed. So I pressed the key for the first channel and with a fast move of my arm I moved the remote control towards the telly. Voilá! It switched to the second channel. Also worked the other way around. Keep channel three pressed and move the remote control away from the telly. Never say the things you learn are of no real-life value...

man on the moon
2003-Jul-30, 07:39 AM
At 20 degrees C. (68 F.), the speed of sound is 344 m/s (1128 ft/sec - 770 mph)

sound about right. a 200 meter race is 200 meters total, but distance to the starting line is far less. half the race is on a corner, and half on a straightaway. the runners run along the two legs of the "triangle" and the sound only along the hypotenuse. total distance from the gun to the clock at the finish line is about 120 meters. at sea level time delay would have been about .3 seconds. at 600 feet elevation it would have been more. not sure how much more, but indeed it would be more. temp and humidity also affect the speed, and windy days seemed to make it even more noticable. i was estimating .5-.7 seconds, but it could have been slightly less. not much though. either way, it's along itme when hundredths count!

i'd have liked to have seen those cieling tiles. that sounds interesting. not impossible either! does anyone know, when a shuttle launches are the shockwaves P and/or S like an earthquake or something else?

BlueAnodizeAl
2003-Jul-30, 01:20 PM
Living in Orlando, I've had the opportunity to see the shuttle launch quite frequently. I've seen and heard the lauch from on the base (before 9/11, when you could still be on site when it launched) and from the area around Universal Studios Orlando (you can only hear it from this location if conditions are just right and even then it's extremely faint). There is quite a delay because the speed of sound in Florida is around a third of a kilometer per second, while the speed of light is 300,000 km/s.

It used to be that the closest you could be to the shuttle upon launch is approximately three miles (~4.8km), now it's more like 7 miles since you can only observe from the intracoastal shore. This was also the closest you could get to the Saturn V during launch. (I was once told that since the first stage of the Saturn contained 52 railcars of RP-1 fuel, that if there was any catestrophic failure, three miles was the closest you could be and survive.) Now the speed of light is so fast it can be considered instantaneous, light can travel the circumfrence of the globe (~40,000 km) in a fraction of a second (~0.13s); the few picoseconds it takes light (and, therefore, the visual image of the rocket lifting off) to travel three miles is negligible. Sound on the other hand takes almost 15 seconds (4.8km /.33km/s) to travel the three miles. From a distance like the pad to West Orlando (~65-70 km) it would take more than 3.5 MINUTES (65 km / .33km/s)!

ToSeek
2003-Jul-30, 04:16 PM
It used to be that the closest you could be to the shuttle upon launch is approximately three miles (~4.8km), now it's more like 7 miles since you can only observe from the intracoastal shore. This was also the closest you could get to the Saturn V during launch. (I was once told that since the first stage of the Saturn contained 52 railcars of RP-1 fuel, that if there was any catestrophic failure, three miles was the closest you could be and survive.)

One of my favorite anecdotes about the Saturn V is that before that monstrous beast, launch control centers used to get in a well-fortified blockhouse right next to the launch pad. However, for the Saturn V, this was virtually impossible. So launch control is next to the VAB, over three miles away. I daresay that's the closest anyone gets to a shuttle launch these days.

SeanF
2003-Jul-30, 04:29 PM
. . . launch control is next to the VAB, over three miles away. I daresay that's the closest anyone gets to a shuttle launch these days.

Well, there're seven people who are closer . . . ;)

BlueAnodizeAl
2003-Jul-30, 05:28 PM
Have you seen the escape buckets and armored personel carriers too? If anything serious happened, these two escape systems would be insufficient. I guess they only really exist to put the crew's mind at ease. I suppose a person's security and safety really are a things of the mind.

ToSeek
2003-Jul-30, 05:33 PM
Have you seen the escape buckets and armored personel carriers too? If anything serious happened, these two escape systems would be insufficient. I guess they only really exist to put the crew's mind at ease. I suppose a person's security and safety really are a things of the mind.

I can conceive of a situation where the booster conveniently refrains from exploding just long enough for the astronauts to get themselves to safety, but the possibility seems very remote.