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Author
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Topic: Tape-delay broadcasting live from the Moon?
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moorouge
Member Posts: 2458
From: U.K.
Registered: Jul 2009
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posted 09-01-2009 09:14 AM
   
Whilst rummaging through the dark recesses of my memory - not something for the faint hearted - about the possible postponement due to the loss of an Atlantic communications satellite, I was reminded that the TV pictures from the Moon were hardly live television. Was there not a 3 second delay (?) built in so that NASA could pull the plug if anything untoward happened? Does anyone know anything more about this? If true - when did the practice stop or is this delay still current? |
ilbasso
Member Posts: 1522
From: Greensboro, NC USA
Registered: Feb 2006
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posted 09-01-2009 12:41 PM
There was not a tape delay for such purposes. There is a 1.5 second delay of the images from the Moon simply due to the speed of light travel from the Moon. (The delay between a message being sent from Mission Control and receiving its echo back to the ground would be a 3-second round trip.)On Apollo 16 and 17, there was an additional slight delay introduced which was entirely due to the use of a new signal processing system to clean up the TV images. It's discussed in Spacecraft Films' "Live from the Moon." |
moorouge
Member Posts: 2458
From: U.K.
Registered: Jul 2009
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posted 09-01-2009 01:04 PM
I know there was a delay because of the distance factor. What I'm talking about was an additional delay built in to the release of pictures by NASA to give them time to cut the feed in the event of things going wrong. |
Blackarrow
Member Posts: 3160
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 09-01-2009 08:10 PM
I have never heard or read any indication that there was a deliberate delay in the transmissions to allow the picture to be cut if something untoward happened, but there is no doubt that the picture-enhancement process on Apollos 16 and 17 caused a delay of many (8 or 9?) seconds. If you listen carefully to the voices coming from the Moon, you can hear the sounds faintly in the background many seconds before you see the associated pictures. For example, if Charlie Duke is handling a rock, in the background you might hear a faint "Oops!" Then, about 8 seconds later, you see the picture of him dropping the rock and again hear him (at normal volume) saying "Oops!"I suppose if Ed Fendell had been looking at the "raw" picture (which only suffered a speed-of-light delay) and if an astronaut had suffered an abrupt and obviously fatal accident, he would have had time to "pull the plug" but I rather doubt whether he or anyone else would have been able to make such a decision in the very limited time available. |
Colin Anderton
Member Posts: 154
From: Great Britain
Registered: Jan 2005
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posted 09-02-2009 03:16 AM
I recall reading about a built-in delay in case of a catastrophe. I believe this occurred right from the first TV broadcast from Apollo 7.This may have been applied in all audio broadcasts as well. During the Gemini 11 launch phase - the first launch in which 'live' communications were broadcast - there was much comment on the networks about the five-second built-in delay in the audio feed. When - indeed, if - this practise ceased I've no idea.
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moorouge
Member Posts: 2458
From: U.K.
Registered: Jul 2009
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posted 09-02-2009 05:24 AM
Mystery solved - well almost. What follows is taken from "On Eagle's Wings - Parkes Apollo 11 support." In Houston, NASA introduced a six second delay before releasing the TV worldwide. This was to give NASA enough time to cut the broadcast in case an accident occurred to the astronauts - NASA didn't want the world to witness a disaster. The ABC on the other hand didn't have this delay; it broadcast the TV live. Also, because the signal for the Australian broadcast did not have to travel to Houston (via satellite) and then back again as it did for the rest of the world, a further delay of 300 milliseconds was avoided. As a result of these, Australian audiences saw the pictures some 6.3 seconds before the rest of the world. [Updated 25 February 2009: The six second delay was not in place during the Apollo 11 mission. This statement is now known to be incorrect. The six second delay was in fact introduced during the Apollo 16 and 17 missions and was due to the time required for improving the TV. The 300 millisecond transmission delay was of course in place, so the correct statement should read "Australian audiences saw the pictures some 0.3 seconds before the rest of the world."] I missed the update - hence my belief of the delay. However, it does leave the question about TV from Apollo 14 and 15. Why wasn't their TV enhanced?
Also, note the curious wording in the correction. "The six second delay was not in place during the Apollo 11 mission." Does this imply that there was a delay for other missions? If so - which? But perhaps the most important question is why did such a reputable organisation such as Parkes think that there was an inbuilt NASA delay in the first place and then leave it so long to correct? |
Blackarrow
Member Posts: 3160
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 09-02-2009 07:00 PM
Why wasn't the TV on Apollos 14 and 15 enhanced? Because it was a new and secret process which only became available to NASA in 1972 (as reported in the press just before Apollo 16). |
Dwight
Member Posts: 577
From: Germany
Registered: Dec 2003
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posted 09-03-2009 02:31 AM
G'day and sorry for joining the discussion so late - so apologies if I repeat what what has already been written.There was no tape delay per se during the Apollo missions. That is, no delay solely for the grounds of security/public interest. The conversion to color introduced a delay of about 12 seconds as two 2" video machines were used to compensate for the doppler effect. The first VTR recorded the incoming signal. The machine was syncronized to the spacecraft video signal. The tape was then fed to a second VTR machine which replayed the newly recorded tape. This machine was synched to the ground timebase and thus the signal was made fully compatible to the NTSC TV system. The sequential B&W TV signal was put vthrough a video disk recorder which buffered the 3 colors so as to create the full color image. So the delay in the TV signal is roughly as follows: 1.28 seconds from the moon to the ground station.
240 ms from the groundstation to Houston.
~10 seconds for the doppler effect and color conversion. On Apollo 10 you can hear Charlie Duke explain that he was only watching the B&W feed. Around 10 seconds later he sees the color signal. |
Scott
Member Posts: 3307
From: Houston, TX
Registered: May 2001
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posted 09-03-2009 10:55 AM
My guess is that this delay is what caused Armstrong to pause in the middle of his famous quote after landing ("Houston, uh ... Tranquility Base here, the Eagle has landed."). When you account for the delay in the speed of light to the Moon, his pause occurs when (and for about the length of time) he would have heard Duke say, "We copy you down, Eagle." I believe Armstrong was likely politely pausing to hear what Duke was saying before he (Armstrong) continued, as opposed to just gathering his thoughts. |
moorouge
Member Posts: 2458
From: U.K.
Registered: Jul 2009
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posted 09-03-2009 11:04 AM
In Houston, NASA introduced a six second delay before releasing the TV worldwide. This was to give NASA enough time to cut the broadcast in case an accident occurred to the astronauts - NASA didn't want the world to witness a disaster. Might I go back to my original query. Why did Parkes make this statement? There must be a reason for it. And why wasn't it corrected until February of this year? |
Dwight
Member Posts: 577
From: Germany
Registered: Dec 2003
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posted 09-03-2009 01:18 PM
There was discussion at some point of introducing a tape delay for the purpose of emergency break. It was however abandoned. I gather the Parkes statement was simply faulty memories of 40+ years. It was only until someone sat down and figured the signal path that the error was corrected. Often it is a case of someone reading a particular document and finding out that their commonly held belief was just plain wrong. In the case of Australia, the TV signal was seen earlier than the rest of the world. I imagine the earlier discussion of a tape delay, combined with the fact that Australian TV was seen slightly earlier, resulted in a false memory of events. |
moorouge
Member Posts: 2458
From: U.K.
Registered: Jul 2009
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posted 11-13-2010 05:32 PM
I have just come across this - NASA did, for a time, maintain a seven-second delay in the audio downlink. Because of the public relations problem that might accompany the slip of an astronaut's tongue, NASA elected to delay live transmission of the audio so that a ground controller could, if necessary, "bleep" inappropriate vocabulary. This is the only legitimate example of censorship by NASA of a "live" transmission. In the wake of the Apollo 1 fire NASA realized it was more important to be fully candid with the public, and so the audio delay was discontinued. Despite this 'open' policy, am I not correct in thinking that there was a secure channel which was not available to the media? |
Blackarrow
Member Posts: 3160
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 11-14-2010 12:28 PM
quote:
Originally posted by moorouge:
... am I not correct in thinking that there was a secure channel which was not available to the media?
You are correct. On Apollo 15 the code-words to begin a communication on the "secure channel" were "West Point." The secure channel (very surprisingly, I would say) was not used on Apollo 15. See "Footprints in the Dust", page 264. |
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