Gimbal Lock, Apollo, and How NASA Navigates Space

In this episode, we explain Gimbal Lock and how this is a deceptive term. Hint, you can "unlock" the gimbals, but for Apollo 13 you would not have been able to do it. We will show you exactly what gimbal lock is in simple terms that anyone can understand. Then we will explain why this would make the navigation computer useless for the 250,000 mile journey to the Moon. We will show how NASA created a visual warning that was so affective, anyone could understand it in time critical situations. Finally we will explain why Gimbal Lock was so bad for Apollo 13.
NASA Navigates Space using Star Charts because Stars don't move that much in Space. Feeding a star's position and angle from one another into the computer give the position of the spacecraft in space. But the computer gets confused and is useless if it experiences Gimbal Lock. But it is not mean the Astronaut can't correct it. Watch this video to see how.
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NASA
NASA Glenn Research Center - • Gimbal Rig
Guerrilla CG - • Euler (gimbal lock) Ex...

[@ApolloFlightJournal]

A couple of comments on the topic of gimbal lock as it relates to Apollo. I think it is overdramatised in many accounts. As long as it occurs away from major manoeuvres, there is plenty of time for a crew to realign the orientation of the stable platform. As a good example of this, Neil Armstrong put Eagle into gimbal lock in the moments before Collins docked with the LM after rendezvous. What did he do? He immediately switched to the AGS, his backup system and used that to hold the LM's attitude while Collins brought Columbia towards it. It was no big deal. You mention about Apollo 13 having an issue with three gimbal axes lining up. I've never heard of such a thing before and wonder where the idea came from. Gimbal lock, at its simplest, is when the middle gimbal angle approaches 90 degrees, causing the axes of the outer and inner gimbals to approach being in line with each other. As this condition is approached, it becomes harder and harder for the motors that drive the gimbals to maintain the platform's orientation. Essentially, one of the three degrees of freedom of the system is being lost. I hope this helps.

[@edrafacz724]

You are correct. I used a bad source that said all three aligned. I want to do a correction on my next episode. Can I reference you in the video?

[@humanonearth1]

What is the geometry or physics reason for the system failing and a degree of freedom being lost?

[@SpacecraftGuide]

What if they dump all the data on their position because the computer loads the position on the launch pad?

[@PepperHand]

In Michael Collin’s book Carrying the Fire, he notes they were aware of this issue with their attitude reader in the early stages; and working around anything but gimbals at the time would be a challenge. Math and technology always seem to jump ahead after you put in so much dang work huh!?

[@kimbalcalkins6903]

so how much is angular drift and what is the error margin for the gyros?

[@SpacecraftGuide]

That is a good question. I know they corrected at least once to and from the moon

[@humanonearth1]

Sounds like a divide by zero error.