In 1969, NASA not only went to the moon, but broadcast the whole thing live on TV.
How did they achieve the TV broadcast? What technology did they need to use to send a video and audio signal from the moon to earth? Was there much of a lag?
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4$\begingroup$ I have a related question on "who filmed the First Big step?", space.stackexchange.com/questions/3012 $\endgroup$– ValDec 3, 2013 at 11:13
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3$\begingroup$ The round trip time when sending a light beam from earth to the moon and back (reflected on a mirror) is 2.556 seconds, so half that time is how long it took for the radio transmission to reach the earth. $\endgroup$– Anders LindénDec 3, 2013 at 14:09
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1$\begingroup$ There's a book about exactly this subject: livetvfromthemoon.com $\endgroup$– LocalFluffJul 2, 2014 at 19:45
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$\begingroup$ @LocalFluff Might give that a read :) $\endgroup$– JMKJul 2, 2014 at 21:12
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$\begingroup$ The amazing thing was, at the time, that there was any live broadcast from the Moon at all, and that by Apollo 17, it was color, and there was a live view of "Challenger" (the lunar module) lifting off, as seen from the rover parked nearby. $\endgroup$– Anthony XJul 3, 2014 at 1:58
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3 Answers
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Apollo 11 mission had two modules
Lunar module - which descent to moon carrying two astronauts
command / service module- CSM was designed to return astronauts from the lunar surface on a direct-descent mission to earth and splash down.
Direct telecast from the Command service module is not possible but CSM stored the recording of conversation which is transmitted by LM (which occur once in a rotation because the LM is stationary while CSM is orbiting the moon) then CSM sents to earth.
In this image you can see the high gain antennas which are used in transmission of live data
This is the actual camera used in Apollo
Originally, these slow-scan television (SSTV) cameras, running at 10 frames-per-second (fps), produced only black and white pictures and first flew on the Apollo 7 mission in October 1968.
NASA states as
The equipment onboard the Apollo Command Module that was used to make the recordings was called the Data Storage Equipment (DSE). Its contents were transmitted to the ground periodically during the mission. Also, the Command Module DSE had the capability to record data live during certain periods from the Lunar Module as it flew separately in lunar orbit. The equipment used aboard the Lunar Module to make the recordings was called the Data Storage Electronics Assembly (DSEA). It made recordings onboard the Lunar Module, but the DSEA flown on the Eagle during Apollo 11 malfunctioned. As a result, many of its recordings are barely, if at all, audible, with a constant high-pitched background tone. In the attached database, the recordings that are virtually inaudible are highlighted, but they are available on the web to ensure a complete release of the recordings made during the mission.
The portion of the broadcast spectrum traditionally used for video was sending vital ship data to Earth, and there was no room left for the standard black-and- white video format of the era: 525 scan lines of data at 30 frames per second, transmitted at 4.5 MHz. So Lebar helped devise a smaller "oddball format" – 320 scan lines at 10 fps, transmitted at a meager 500 kHz. Tracking stations back on Earth would take this so-called slow-scan footage, convert it for TV broadcast, and beam it to Mission Control, which would send it out for the world to see.
Transmission stations
To ensure a direct transmission signal from the moon, NASA had to maintain stations in three continents – two in Australia (the Honeysuckle Creek Tracking Station near Canberra and the Parkes Radio Observatory surrounded by sheep paddocks west of Sydney); one at the Goldstone Deep Space Communications Complex in the Mojave Desert of California; and one at the Madrid Manned Flight Tracking Site in Spain........ the tracking stations with a direct line on the Apollo 's signal were the ones in Australia. The 200-foot-diameter radio dish at the Parkes facility managed to withstand freak 70 mph gusts of wind and successfully captured the footage, which was converted and relayed to Houston.
location of receiver in earth
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2$\begingroup$ @Hash Could you speculate how large the delay from the astronauts to TV was. Minutes, Hours...? $\endgroup$– thisDec 2, 2013 at 20:14
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1$\begingroup$ As I understand it, wasn't the slow scan footage decoded & displayed on a screen at Houston and the conversion for TV was just a camera pointed at that screen? $\endgroup$ Dec 2, 2013 at 21:25
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3$\begingroup$ @self. Less than a minute. The distance between the earth and moon is a bit more than 1 light second. The video format conversion was done live (literally a camera pointed at a monitor). There are delays involved in relaying the signal to the television networks, but they will all be on the order of seconds. I have been inside a TV truck while it was live on the air. One of the monitors displayed what the station was broadcasting, so when they were live the monitor displayed the signal after it had travelled all the way across the country and back. The delay was only a couple of seconds. $\endgroup$ Dec 3, 2013 at 6:30
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2$\begingroup$ If you want to know about the Earth side of the equation, you can look up the movie: The Dish. It is about how they turned a radio telescope in Australia into the receiver for that broadcast because that's the part of the Earth that was pointed at the Moon at the time. $\endgroup$– ShadoCatMar 29, 2017 at 0:36
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From this article, and this article:
Live television was transmitted from the moon to 3 grounds stations, two in Australia and one in California. The signal was converted to a standard broadcast signal and then sent to Houston, via, satellite, landline or microwave antenna. These graphics show the path of the television feed.
Bottom line is, the video was transmitted to one of the large dishes that the DSN uses, and then re-broadcast to the world using standard worldwide broadcasting methods. Specifically, a format was used called slow scan, which according to Wikipedia:
The SSTV system used in NASA's early Apollo missions transferred ten frames per second with a resolution of 320 frame lines using less bandwidth than a normal TV transmission.
answered Dec 2, 2013 at 14:59
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20$\begingroup$ Just a note that this image is not in any way geographically accurate. The location of Parkes (based on the star) seems to be off by around 2000km. It also puts Canberra somewhere near the location of Adelaide (1200km off), and Sydney is similarly way off. Parkes, Canberra and Sydney are all within 350km of each other, with Sydney on the coast (obviously). $\endgroup$ Dec 3, 2013 at 5:06
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12$\begingroup$ @jozzas: It also puts Tranquillity Base in Indonesia and the United States in the south Indian Ocean! $\endgroup$ Dec 13, 2014 at 17:40
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1$\begingroup$ @jozzas I've just asked Where exactly were the two Australian dish antennas used in the Apollo missions? $\endgroup$– uhohJul 18, 2019 at 23:14
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The slow-scan signal mentioned in the other replies had to be converted to broadcast video. This was done by playing back (pdf) the slow-scan video on a kinescope, and reading the image with a broadcast TV camera. The setup also involved a magnetic video disc recorder which briefly stored each frame of video (so that one recorded frame could be used to fill 3 frames of broadcast video).
This was a bit of a Rube Goldberg setup, and accounts for the mediocre quality of many of the early images we have, esp. of Apollo 11, where the output of the scan converter survived but the input (with potentially higher quality, if converted on a better system) was lost.
