How Apollo Astronauts Didn’t Get Lost Going to the Moon

http://blogs.discovermagazine.com/vintagespace/2019/06/15/how-apollo-astronauts-didnt-get-lost-going-to-the-moon/

by eaguyhn • 7 years ago

3 2 7 years ago

blogs.discovermagazine.com

In addition to celestial navigation, there was very precise radio based ranging between tracking stations and the spacecraft. You could call it a precursor to GPS, where a pseudo-random noise was transmitted in the microwave signal to the spacecraft. The spacecraft sent back that PRN stream on its microwave downlink to Earth.

I have forgotten how precise and accurate the tracking data was, but it was more than enough for the missions.

NASA would take measurements and then uplink nav data to the guidance computers as necessary. With that and periodic celestial position fixes, there was no getting lost on the journey.

"Just don't screw up a procedure or have a burn go bad and everything will be okay."

ncmncm• 7 years ago

The article doesn't actually answer the question it poses. Yes, you can find angles to stars and horizons, but how does that help?

What it doesn't say is that measuring the angles between stars and horizons gives you a measure that doesn't depend on which way the spacecraft is pointing. Those angles change in predictable ways as the spacecraft moves. It also doesn't say that what matters is not what what the angles are, and where the spacecraft is, but how they change over the course of a series of readings, telling which direction the spacecraft is going, and how fast.

It really would not have taken more column inches to say what I said, especially if they struck reminding us over and over that the stars' apparent motion is negligible.

How Apollo Astronauts Didn’t Get Lost Going to the Moon

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