Spacecraft distance measurement

[molesworth]

Being a computer nerd I thought I'd seen everything to do with the guidance, telemetry, data handling etc. for the Apollo missions, but I've just discovered this fascinating and ingenious system which was used to measure the spacecraft distance and velocity.  I'm sure a few folks here will be familiar with it already, but I love finding stuff like this, and it really brings home the amazing efforts which went into the design and implementation of these systems.  Hats off to whoever came up with this idea!

Long-ish Twitter thread - https://threadreaderapp.com/thread/1517923273769570304.html

Related YouTube video -

[bknight]

I didn't know this information and procedure existed when I was arguing with Apollo "lack of computing power" with some ignorant individuals.  But I did know that the bulk of computation was done by ground computers leaving guidance to the onboard computers.
Cool stuff.

[smartcooky]

This concept appear to be almost like a secondary* radar altimeter.

* For those not familiar with this term, "primary" radar is where the primary broadcast signal is reflected by the target and the returnes picked up by the receiver (for example, search radar & weather radar), while "secondary" radar is where the target is equipped with a a transponder that rebroadcasts the primary signal (for example IFF).