The Apollo Digital Ranging System: More Than Meets The Eye

If you have not witnessed [Ken Shirriff]’s teardowns and reverse engineering expeditions, then you’re in for a treat. His rationalization and demonstration of the Apollo electronic ranging procedure is a intriguing browse, even if classic computing and engineering are not portion of your normal fare.

The normal Hackaday reader need to be familiar with the principle of figuring out the distance of a faraway object by measuring how very long it will take a audio or radio wave to be reflected, these as in sonar and radar. Heading yet another move and measuring Doppler Change – the change in the returned signal’s frequency – will notify us the velocity of the object relative to our place. It’s so simple that an Arduino can do it. But in the times of Apollo, there was no Arduino. In actuality, there were being no Integrated Circuits. And Apollo missions went all the way to the moon- far way too distant for relatively very simple Radar measurements.

How could selection (length), position, and pace then be measured? The reply is a single that [Ken] aptly describes as fractal: Each individual layer of complexity hides beneath it a different layer of complexity. Applying equations relationship from 3rd century China as properly as slicing edge weak sign telemetry, Apollo engineers devised a sophisticated but workable system that made use of an S-Band transponder to choose information transmitted from a effective ground station and send out it back on another frequency. 1 great hack was to use Phase Modulation to encode the downlink as a substitute of Frequency Modulation so that Doppler facts attained on the uplink would not be missing on the downlink.

By knowing the exact place of the floor station and the really substantial parabolic antennae, not only could the distance and speed be calculated, but a very good estimation of the spacecraft’s placement in 3d space could also be experienced.

From the use of hold off line memory to aggregate weak alerts to a condition equipment computer system made up of discrete transistor logic, all the way to the chopping edge transponder on the Command Module, the Apollo electronic ranging technique is an fantastic instance of great hacks coming out of a plan with restricted technical constraints.

We very advise offering [Ken]’s website a browse and be confident to check out the interactive demonstration world-wide-web webpages he’s put up to assist us grasp the genius of the Apollo engineering groups. [Ken]’s been showcased on Hackaday a variety of periods reverse engineering this kind of varied factors as a Yamaha DX7 Synth chip.