13
$\begingroup$

This answer to Has anyone in space beyond LEO seen or has anything photographed a non-pointer laser from Earth? shows a frame from video shot by Surveyor 7 on the Moon, looking at Earth, and specifically two lasers beams coming from Earth seen as two dots on Earth's nighttime side.

Unlike the retroreflectors left on the Moon that could be optimally oriented by the astronauts before they went home and modern landers like Insight that had inertial navigation systems and could orient themselves during landing, I don't think that the Surveyors couldn't possibly land such that the TV camera was already pointed at Earth.

So my premise is that the Surveyors probably received tilt/pan commands from Earth to move the camera around to look at various things, including the Earth.

Certainly the camera that broadcast the launch of the astronauts back off the Moon into lunar orbit was controlled by the ground.

Question: What kind of signals and encodings were used to send tilt/pan commands to early TV cameras on the Moon (up through Apollo)?

Were there digital commands like "pan left, 20 degrees" (or "for 5 seconds") or was it done with tones somehow, like a modulation at say 10 kHz would cause the camera to continue to pan left as long as it was turned on, or something else entirely?

note: I'll ask separately about the Soviet Lunokhod rovers as they were developed by a different space agency and researching the question will require different sources.

$\endgroup$

1 Answer 1

19
$\begingroup$

For the Ground-Commanded Television Assembly (GCTA) mounted on the rover that was used to image Apollo liftoffs from the moon:

The real-time command messages consist of three vehicle address bits (using vehicle address sub-bit codes) followed by three system address bits and six command data bits (using system/data sub-bit codes) . The vehicle address ( bit numbers 1, 2, and 3) are always fixed as binary 0, 1, 1, respectively ( octal 3) . The system address (bit numbers 4, 5, 6) are always fixed as binary 0, 1, 0 (octal 2). Command data codes (bit numbers 7 through 12) for all GCTA command function are given in Table 4-1.

enter image description here

Source: GCTA Operation and Checkout Manual

See also What is the model name of video camera that filmed the lunar lift-off?

As @Uwe commented

So it was possible to start a pan right, then a tilt up, run both for a second and then stop tilt and pan using only four command messages.

and that is basically how the liftoff was imaged, sending a set of pre-planned commands based on time.

I actually sent the first command at liftoff minus three seconds. And each command was scripted, and all I was doing was looking at a clock, sending commands. I was not looking at the television. I really didn’t see it until it was over with and played back. Those were just pre-set commands that were just punched out via time. That’s the way it was followed.

Source: Ed Fendell Oral History

$\endgroup$
1
  • 3
    $\begingroup$ So it was possible to start a pan right, then a tilt up, run both for a second and then stop tilt and pan using only four command messages. $\endgroup$
    – Uwe
    Feb 24 at 0:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.