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When Gimbal Lock Is A Bad Thing.

NeoMorph

By NeoMorph
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NeoMorph

NeoMorph

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Just a bit of space flight knowledge that I came across that is cool to know.

If you mention "Gimbal Lock" to an Apollo astronaut did you know they would cringe?

This is the Apollo Flight Director Attitude Indicator... or what we lovingly call the "Nav Ball".

1vXOXmi.jpg

If the ship rotates so the indicator shows they are facing somewhere in the red section of the ball that means they are in "Gimbal Lock"... nothing to do with engines this time. It just means the spacecraft has gotten its gyros out of whack because it doesn't like being in that attitude. To fix it so that the FDAI points in the right direction again the astronauts had to make several star sightings with the space equivelant of a sextant. Talk about going old school.

That's why there is a "Gimbal Lock" indicator on the Apollo dashboard (in the picture of the DSKY below you can see the Gimbal Lock indicator in the second row, second down)... I thought it was a bit weird on a single stack rocket which is why I went looking for this info in the first place.

dsky_lm.jpg

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NeoMorph

NeoMorph

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Gimbal lock is not your friend :)

Have you read any mission transcripts, yet? Good stuff!

Yeah... I've been reading up on a lot of stuff for my hardware system research and OMG... at times it sounds like the astronuts (sp on purpose) didn't know what they were doing. How they got to the moon and back is mind boggling... And then the Apollo 11 lunar return almost never happened because during EVA someone busted one of the breaker switched that let them activate the engine.... and Buzz fixed ti by shoving a biro into the hole where the switch used to be and wiggled it and it activated the engine. Definitely a WTF moment.

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regex

regex

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at times it sounds like the astronuts (sp on purpose) didn't know what they were doing. How they got to the moon and back is mind boggling...

So what you're saying is that Kerbals are actually pretty realistic?

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RogueMason

RogueMason

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That nav-ball was commonly known as the '8-Ball' by those in the know. It has 3 axes and would lock if 2 became aligned. A 4 axis ball was developed and placed on the Saturn V to avoid gimbal lock, but on the CSM, the 3 axis 8-Ball was required to save weight and size, and increase reliability through simplicity, and 2 of these were located on both the CM and LM control panels, for safety. The astronauts never really liked having it on board, as it was an extra burden avoiding gimbal lock. Apollo 13 nearly hit gimbal lock several times after the explosion.

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NeoMorph

NeoMorph

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That nav-ball was commonly known as the '8-Ball' by those in the know. It has 3 axes and would lock if 2 became aligned. A 4 axis ball was developed and placed on the Saturn V to avoid gimbal lock, but on the CSM, the 3 axis 8-Ball was required to save weight and size, and increase reliability through simplicity, and 2 of these were located on both the CM and LM control panels, for safety. The astronauts never really liked having it on board, as it was an extra burden avoiding gimbal lock. Apollo 13 nearly hit gimbal lock several times after the explosion.

Did you know the Gemini spaceship had a FOUR axis version that apparently didn't get into Gimbal Lock like the Apollo did?

On Apollo, the Flight Director had a three-axis gyroscope system and was therefore subject to "gimbal lock," a condition which meant loss of attitude reference and a subsequent need to reorient the system through star sightings, which was a pain in the ass. This would occur if you managed to screw up and get your attitude into the red circle. Borman and every other astronaut wished that Apollo had the Gemini program's four-axis system, which was not subject to this quirk of physics.

My guess is the extra gyro would have added too much weight as they were stripping things down in the CSM as it was...

Edited by NeoMorph
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NeoMorph

NeoMorph

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:D I was actually just joking around :P

I posted on the topic I believe the Op was trying to Lead us on with.

Ummm... I honestly have no clue what you are on about Amster. I wasn't trying to lead you on anything. I was just looking to find why there was a gimbal lock indicator on the DSKY and found out that it wasn't anything to do with the Gimballed Engines like in KSP. I always wondered what the red on the 8-Ball was for...

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AmpsterMan

AmpsterMan

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Ummm... I honestly have no clue what you are on about Amster. I wasn't trying to lead you on anything. I was just looking to find why there was a gimbal lock indicator on the DSKY and found out that it wasn't anything to do with the Gimballed Engines like in KSP. I always wondered what the red on the 8-Ball was for...

:-O Just goes to show you that people could really think into things XD.

I thought you were going to post a pic of your ship exploding because you forgot to put Gimbal lock on or something. Or maybe talk about instances where you don't want to lock the gimbals of your engines, etc. etc.

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regex

regex

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I thought you were going to post a pic of your ship exploding because you forgot to put Gimbal lock on or something. Or maybe talk about instances where you don't want to lock the gimbals of your engines, etc. etc.

This. Instead we were treated to a cool history/engineering lesson.

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DMagic

DMagic

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The KSP NavBall may not suffer from gimbal lock, but the camera does. That's why you can't just continually rotate in one direction. Once you hit that maximum rotation you have to spin it around 180o and rotate it back the other way.

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andrewas

andrewas

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Verb tells the computer the next number is a verb. Noun is for entering nouns. For instance, Verb 37 is 'change program', which then takes a noun which indicates which program to change to. This was done to save on memory, the computer didn't need a lookup table to convert a string of text into a command, it was getting the raw numbers. Remember, this was the 60s, core memory was all the rage, and ROM was a variant of core memory called rope memory, which had the data hand woven into it. They didn't want to waste bits on luxuries like a text interface.

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Kimberly

Kimberly

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I'm pretty sure it had something to do with programming the computer.

Here: http://history.nasa.gov/computers/Ch2-7.html

Thank you for the link. :) I like how the standard for the software was that the astronauts wanted the bugs to be "non-life-threatening". :P Gives you some perspective on the way people complain about bugs on this forum!

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numerobis

numerobis

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Thank you for the link. :) I like how the standard for the software was that the astronauts wanted the bugs to be "non-life-threatening". :P Gives you some perspective on the way people complain about bugs on this forum!

I've had the chance to write code where "crash" meant "safety override puts spacecraft into lawn dart mode". Luckily I was fresh out of college and did not worry about it much. Now that I know what I'm doing, I work in a field where, "crash" means "the artist lost five minutes of work, so the next film will not be quite as pretty as it could have been."

In that capacity, I spent a couple days wrangling gimbal lock issues last month. We couldn't use quarternions in our setting -- in math as in physical systems, the real solution is to add a degree of freedom.

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regex

regex

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Thank you for the link. :) I like how the standard for the software was that the astronauts wanted the bugs to be "non-life-threatening". :P Gives you some perspective on the way people complain about bugs on this forum!

No problem. I Googled "csm noun verb keys" if you're interested in more, there's a ton of documents out there.

BTW, "csm" stands for "Command Service Module" on the Apollo craft.

E: And like numerobis even the most "mission critical" bug in my code means restoring a database from backup, not death. :cool:

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Deadweasel

Deadweasel

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"noun" and "verb" were indeed for programming the computers, and they were necessary to allow astronauts to enter programs into the flight computers at the appropriate times without spending days doing it. When people say they flew to the moon using computers less powerful than most digital watches today, they aren't exaggerating.

Even the shuttle was necessarily limited to systems that were less powerful than a Pentium, due to the way solar rays could interfere with processors built with smaller traces. Though the fleet eventually did get more powerful systems (not by much, really), they really didn't need a crazy amount of computing power when even a 486 clocked fast enough to handle the shuttles' needs.

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