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February 19

Chinese first satellite (Dong Fang Hong I)

Dongfanghong I broadcasting "East is Red" and telemetry data

I have a question about the first Chinese satellite launched in 1970. What exactly is the 'telemetry data' we hear in this recording?

And also, what was the music player installed? Was it a record player? Tape player? Someone trapped inside playing the keyboard?

Please give me an easy ,dumbed down answer as I know nothing about this. Thank you. --Rankaper Pace (talk) 06:07, 19 February 2021 (UTC)[reply]

From an article on the website of Xinhua News Agency:

Among the various technical problems, the most impressive one researchers had handled was to make it play in orbit "Dongfanghong," the folk song lauding Chairman Mao, and allow all the Chinese people to hear it through the radio.
According to CAST [China Academy of Space Technology --L.
], researchers made a special musical device to simulate the song with electronic music, designing it to play the first eight sections of the music in 40 seconds and transmit the telemetry signals in the following 20 seconds.
— China recollects first satellite stories after entering space for 50 years

The telemetry data was essentially digital data, which had to be transmitted through an analog channel, for which the standard approach is modulation-demodulation. The digital data is converted into a wave signal of a sequence of segments at different frequencies, to be transmitted by radio. The same wave signal as an analog audio signal will sound as a sequence of whistled tones if the frequencies are within the human hearing range. Telemetry data in the recording can be heard from 44 seconds to 54 seconds, again from 1:43 to 1:53, and finally from 2:42 to 2:52. By artificially supplying a suitably chosen data stream to the modulator, you can create a musical melody. It is kind of like pumping out a very primitive MIDI file. The article does not explain this, but almost certainly the "special device" was a piece of electronic equipment to produce a data stream that, after modulation and interpreted as an audio signal, sang the praise of Chairman Mao. I do not know if it has been made public what the telemetry data represented, but since this was ten seconds per minute at a low baud rate, it cannot have been much. --Lambiam 09:23, 19 February 2021 (UTC)[reply]