Gimbal Lock and Apollo 13

We've all heard the phrase gimbal lock in the movie Apollo 13, and it was a real problem on the real mission as well. But what exactly did it mean?
Title image via NASA/Bruce Yarboro and Smithsonian Institution. Music "The Coup" by AudioQuattro from Music Loops.
For more in depth Vintage Space, be sure to check out the blog on Popular Science: www.popsci.com/blog-network/vi...
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[@jchigheagle]

I was the lead Retrofire Officer for Apollo 13 mission. I appreciate your videos.

[@KSSilenceAU]

Flipping the spacecraft around 180 degrees so the rocket is pointing in direction of travel, then firing it to slow down instead of speeding up.

[@Awol991]

@John Rackley Or as they say on The Expanse, "flip and burn"

[@epiendless1128]

Great job there! Apollo 13 is where I first learned of Gimble Lock! :-)

[@suekennedy8917]

LOL! Why no video showing Jim Lovells great piloting skills. Do you have any numbers for the MTBF for the steering motors used on the CSM?

[@aussiehomecafeandcoffeeroa4475]

@jchigeagl When the explosion happened with Apollo 13 did you guys hear it in mission control, as I've watched videos on both KZbin and Netflix where I beleive I heard something that sounded like and explosion?

[@markfonner723]

Just a note. It is refreshing to see someone so young this involved in the early space program! Well done!

[@bosshog8844]

not so young anymore mark

[@JTMarlin8]

Please refrain from patronizing people who are likely smarter than you.

[@sasquatchycowboy5585]

I was an avionics mechanic for a regional airline back in the 2000's. Our "INU" was about thr size of a shoe box and didnt use gimbel exactly. I was at the Space and Rocket Center a few months ago and saw these. It's so cool seeing how the technology started out, and how its matured.

[@geckoproductions4128]

Well done! I worked on SkyLab in crew training & flight simulation in the early seventies. We used the Apollo command module to get back and forth to SkyLab. We (and the back up crew) flew the simulator in parallel with the live mission, and would try out problem fixes before the primary crew to ensure no ugly unforeseen consequences. BTW: flying your girlfriend around the moon on the weekend worked every time! Keep up the good work, great video!!!

[@LostOliven]

Nice explanation! Gimbal lock is not just something physical, it can also happen in software simulations, like games, where the rotation is represented with rotations in three dimensions. However, most games these days use what is called quaternions to represent rotation, which is essentially the "fourth wheel" that is shown in this video. :-)

[@bostonseeker]

Yup. Quaternions can be represented as four components, with one constraint, and so three independent degrees of freedom. Same information, represented a different way.

[@fizipcfx]

i have been reading about 3d rotation, gimbal lock, quaternions for an half hour and your comment is just allowed me to understand most intuitively.

[@AmyShiraTeitel]

And yes, guys, that's a very agile Pete weaving around my desk in the background!

[@Thessalin]

Amy Shira Teitel I enjoy playing "Where Pete" on the videos. Thanks for the videos as always.

[@tmnathe]

I was a tad concerned for the health of Saturn V.

[@israrulhaq9683]

Nice

[@Graytoke]

Amy Shira Teitel cat in video = awsome :)

[@chloejade4690]

hello what's your name

[@pesterenan]

I'm just greatful that KSP doesn't have gimbal lock ^^

[@IanTester]

I remember some PC flight simulators could get gimbal locked by pitching up to vertical, then rolling 90 degrees. Bingo, you could no longer pitch up or down to return to the horizontal. You could only yaw sideways. Anyway, I gather everyone uses quaternions now for rotations.

[@RamsesTheFourth]

It has something like that when you go directly to a pole of a planet.

[@devinviltan2564]

Sure it does! Just lose the command module, all rcs thrusters, and run out of power. Then your good to go!

[@ArcherAC3]

Pesterenan Você aqui também :D

[@ArcherAC3]

Brian M And I'm one of the other lunatics that would love to download and install it

[@crackedcandy7958]

The benefit of getting a new phone is it is recommending videos I've already watched. Ah vintage space, my first love. You are amazing.

[@AmyShiraTeitel]

Quick note, guys. Frank O'Brien who wrote "The Apollo Guidance Computer" pointed out a little error on my part. Gimbal lock on Apollo was possible with the inner and outer gimbal lying on the same plane, the gimbal mounted on the central platform and the one mounted to the spacecraft. Those are the two you really don't want to line up!

[@jafarpato7714]

Mindbolowing

[@jimgorycki4013]

Yes Gimbal lock is a bad thing. I remembered that in Avionics tech school. Thanks for the video. Thanks for the Inertial Measurement Unit and other buzzwords. BTW does your cat knock over your effects that you have to retake a video or scene?

[@premkumar8935]

Very very nice

[@marckjavierblanco3607]

Interesante video.

[@davemanley7637]

Amy Shira Teitel If my memory serves me right, Gemini did have a fourth gimbal to prevent lock.

[@AxcelleratorT]

I love how your copy of "How Apollo Flew to the Moon" is stuffed full of paper notes. That's proof right there that you are serious about this stuff. Well done!

[@Nostalgianerd]

Your cat jumped off your desk just before mine jumped onto my desk. Really confused the hell out of me. Also... great videos, really enjoying your channel!

[@jimmyj100]

noob

[@ItsKruski]

HAHA weird

[@kiwidiesel]

It's a cat thing, they are evil.

[@goddyneil]

I am so glad that I came across your channel!! I am currently a Masters student, Aerospace Engg. And like you'd know, none of this, is taught- I learn more through your videos, than at school, about Aerospace! Thank you so much!! you're doing a wonderful job, and I couldn't be more grateful!!! Wish you the best!!

[@evertdeboer]

Thank you for your wonderful recommendation on 'How Apollo flew to the Moon!' I love it! Exactly the book I have been looking for, with just the right amount of (technical) detail.. I was 11 years old, watching TV, when Neil Armstrong set his first historical step on the Moon. Keep up the good work!

[@bushelfoot]

I wasn't the lead retrofire officer, because I was 8 but I remember watching the landings on the moon, and I appreciate your videos too ! And your as cute as a bug's ear !

[@agonizin]

Odd

[@charliebowman785]

Hey Amy, very well explained. I'm a commercial pilot and during my first steps of my formal training in the aviation, I got noticed about what a gimbal is and importance of understanding what presession force is, etc., but certainly when they in the movie talk about gimbal lock, it comes to mind a number of conclutions. Your explanation is so good. Thank you.

[@gregmurray1918]

Interestingly enough, it was reading the transcripts from the Apollo 11 mission where Collins asked for the fourth gimbal for Christmas which then lead me to look up “gimbal lock” which lead me to this video. Thank you for your concise explanation.

[@ApolloWasReal]

Owen Garriott was Capcom when Michael Collins made his request for a fourth gimbal. I asked Owen a few years ago if he remembered the exchange, and he didn't. He was unaware that the exchange had been so widely quoted in explanations of gimbal lock!

[@ncc74656m]

Just stumbled on your channel, you're awesome!

[@gregrtodd]

What a great channel! Can't believe I haven't stumbled across you before. You really have a gift for being able to explain complex concepts in a way that's easy for the non-engineer to understand. Keep up the brilliant work.

[@harrymallory7963]

Ive popped in on your videos from time to time and found them interesting and informative. Ive been enthralled with the early space program as a kid. Im now a subscriber! Looking forward to more!

[@3lbtrigger]

Almost had another problem to report to Houston. Your cat almost knocked down the Saturn V on the desk.

[@almostfm]

That's what the LES is for-giant cat knocks over the rocket, the crew can escape :-)

[@acgsmith5937]

I think it would have been funny if the cat knocked over the Saturn 5. But thats just me.

[@davidprince1138]

lol

[@vladbcom]

I wanted it to happen so bad truth be told

[@acgsmith5937]

The question is....if the cat knocked over the Saturn 5, would she have edited it out?

[@420spuzzard]

acg smith lol

[@Zoomer30]

acg smith It would just be more proof that "cats don't like things".

[@StereoSpace]

Really great series you're doing here. Thanks for these.

[@420spuzzard]

Wow! thanks so much for that... really great delivery without losing me technically speaking in such a technologically intensive topic! Look forward to more interesting stuff from you!

[@danconser6709]

LOL, your kitty is exploring in the background while you're shooting. Nice kitty :-)

[@humbertothebeliever2443]

Is that a Catsronaut in the background?

[@CurtisLittlechild92]

Humberto The Believer The Saturn v was nearly toast.

[@rustworker]

It was nearly a Catastrophe, it could have turned into a catalog of disasters or... ok I’ll stop

[@humbertothebeliever2443]

What the heck did I spell? LOOOOOL.

[@humbertothebeliever2443]

Ooooooh. The cat,,,,LOOOOOL.

[@bjbrochu]

I recently discovered your channel. You have no idea how much I have fallen in love with this KZbin Channel! Thank you so very very much!

[@makkanan]

Thank you! My new favourite KZbin prog. Great stuff. Loved the Gemini episode. Keep it up!

[@MegaFPVFlyer]

This video right here, if I remember correctly, was kind of pivotal in my interest in the Apollo program. Here's how: First, it inspired me to watch Apollo 13, this time actually having a better idea of what's going on. Next, it made me research the Apollo guidance and navigation system (because I thought gimbal lock was pretty interesting). Eventually I discovered things like the Apollo Operation handbooks and Apollo flight journal. At the moment I'm reading the journal, Apollo 12 is nearing lunar orbit insertion. Keep doing what you're doing!

[@MrBioniclefan1]

LOL the cat in the background was so funny.

[@KC2MFCs]

Could you do a weekly episode on any book recommendations/finds you might have? It could be an easy episode to write up, not to mention its a great introduction to stuff other space buffs might not be acquainted to. These are great by the way, keep up the tremendous work!

[@mudthe1st512]

I love watching your videos. You explain everything in fine details.

[@StrategicRescue]

"Good landing Pete! Outstanding man! Beautiful!"

[@landslug]

I'm going to name my band Four Gimbals. We're a 3-piece :)

[@petermooney2228]

Nice

[@evanfinch4987]

+Mike Flavin Yussss

[@MattOGormanSmith]

This backfires when you get to the gig and they complain that you're one man short...again. ask Blackadder.

[@landslug]

I used to have a band called The Five Bobs. There were two of us, not named Bob :)

[@Dragonblaster1]

Not all the Murderdolls actually have the surname Murderdoll.

[@dell-tone6472]

This is a marvellous channel! Thanks so much for your splendid work.

[@itascaparkk]

Thanks, Amy. Learned a lot, as usual. Great book recs, too!

[@PikaPetey]

kitty in the background

[@fabrb26]

Books on the library

[@allgood6760]

I thought it was going to knock the model rocket over..

[@daendk]

Just for a few seconds, I thought the kitty was trapped in the monitor! (0:57-1:00) :D

[@railfink]

That's Pete

[@cleverusername9369]

Pete! Named after one Pete Conrad, 3rd man to walk on the moon with Apollo 12!

[@leftcoaster67]

Your cat likes the Saturn V. :)

[@eliterry3785]

Thumbs up for lean content served quickly with zero fluff. Strong eye contact, facts recited clearly, video length cut to fit my attention span. Well done!

[@pileggitech]

I just came across your channel and subbed to it because of this video. Loved the movie which made me read up on space stuff in general. Great job!

[@Sutterjack]

You are beautiful and a brainiac! I've had the honor of having lunch with Jim Lovell right after the film was released. He said the film was quite accurate - with the exception of the hollywood-portrayed tension with Jack Swigert - Lovell said there was complete faith in all the crew.

[@ChristopherUSSmith]

Sutterjack Not to mention other tensions and extended burns not present on the flight. Swigert wrote the emergency procedures for the CM, so he was the best possible CMP to have on that flight. Good thing T.K. "Ken" Mattingly got exposed to (but never got) measles. ;)

[@nlgatewood]

I've actually wondered about this ever since I was a kid and first saw Apollo 13, but never thought to go look it up. Thanks!

[@Dr_Larken]

I know this video is old as hell, but I totally forgot about the channel existing! Still, I love this channel !

[@joechaos13]

Thanks for the info! Lately I've been obsessed with the Apollo navigation system and will definitely be looking into these books.

[@navtium]

Cat in the background!

[@Dzambor]

time travler

[@82ndaa31]

Thanks for the additional references. You have explained this phenomenon better than anyone else I've seen so far. Thank you again.

[@AmyShiraTeitel]

+82nd AA Cheers! It was a bit of an awkward one but I'm glad I helped!

[@gollum6665]

+Amy Shira Teitel (Vintage Space) I know this is off topic a bit but I've noticed on some videos of the base of a rocket before it takes off that a bunch of sparks are shot underneath the rocket before it lights up....why is that?

[@82ndaa31]

Petey Wheatstraw While waiting for her reply, I'll give my response, if you don't mind. If I'm not mistaken, I was under the impression the sparks were used to initiated the combustion of the fuel. Again, I am only offering conjecture.

[@danielwilson6398]

+The Dude the sparks are there to remove any excess hydrogen before the liquid rocket ignites, in order to prevent any accidents. not, as I used to think, to ignite the rocket ( there's a programme called secret space escapes that explains it in more detail)

[@82ndaa31]

***** Awesome! Thanks, Daniel.

[@halskarl]

Just stumbled across your videos - I must say, you have very interesting content! Also you explain it at just the right level for me to understand. New subscriber!

[@whistletutor]

I can't believe I'm just now finding your channel - great stuff!

[@USWaterRockets]

You did a good job explaining the concept, but trying to imagine what it would be like to someone who doesn't understand this already it's not clear that some people are not going to remain confused. You might need a whiteboard and some drawings to get everyone up to speed. By the way, how does your cat NOT knock everything over?

[@AmyShiraTeitel]

USWaterRockets That's true, and if I had a setup for something like Minute Physics does it would be great for this kind of topic. Alas, all I have are my models. And sadly couldn't find any good vintage NASA animation to go along with it!

[@Darthbelal]

Amy Shira Teitel WaterRockets does make a good point, the presentation was fast paced and information packed. However, I'd rather watch your kind of video and be slammed with data than other science documentaries where info is s-l-o-w in coming and dumbed down to boot.

[@leighjacobs4800]

USWaterRockets Cats don't get gimbal lock.

[@USWaterRockets]

Leigh Jacobs What about that breed that doesn't have a tail?

[@casportflyers]

Leigh Jacobs Made me chuckle irl (pilot/programmer)

[@coffeeisgood102]

Please don't let your cat climb on the furniture. My cat watches your videos and it is setting a bad example for her.

[@joaohenriques9838]

Put your cat in another room! I like to see the cat climbing the furniture.

[@drewm6925]

You don't let you cat on the furniture?

[@twlson49]

The cat went into gimbal lock

[@steward1321]

Ever try and stop a cat from doing what it wants; it tends to get bloody quickly. And in case you don't know... you don't own a cat, it owns you.

[@dustyblack5048]

Toby Wilson first you have to rotate the cat in three axis till it locks.

[@starsiegeplayer]

This is great. I really like learning things like this on your channel.

[@rivco5008]

Great post, informative as always. I followed the space program closely growing up and I'll never forget that week, when Apollo 13 was in trouble. It was like a miracle when they splashed down.

[@kitsune9726]

Truly. As the resident space-geek, I was having to explain over and over again why they just didn't turn around and come back.

[@littleloner1159]

I wonder how people can be obsessed with the thought we didn't land on the moon... how would we know about all these specific problems and solutions?

[@ChucksSEADnDEAD]

Apparently not only did NASA get Kubrick to film the landing, they also got George R. R. Martin to write the lore.

[@greghvazda7048]

They're complete idiots, completely oblivious to reality!

[@jamesrosencrans644]

Ironically, Gemini (Apollo's predecessor) had a 4th gimbal to avoid lock (as was referred to in the post). In Mike Collins wonderful book "Carrying the Fire", Collins laments that the McDonnell's learning from Gemini was not adopted by North American Aviation Apollo design. He laments this fact that there was a bit of 'not invented here' attitude (NIH) or "we don't do it that way in Apollo".

[@mikejanowski3752]

It had more to do with weight. Gimbals weighed 50 pounds. 50 pounds was a lot bigger of a deal in Apollo than Gemini.

[@coriscotupi]

Weight and added slop, however small, of yet another gimbal. Gemini was just orbiting the earth, but Apollo couldn't afford the precision loss of one added gimbal. And the weight.

[@andrewgwilliam4831]

corisco tupi I'm genuinely ignorant about this stuff. Why would a 4th gimbal mean the instrument was less precise?

[@coriscotupi]

+Andrew Gwilliam *" Why would a 4th gimbal mean the instrument was less precise?"* The gimbal assembly is a series of gimbals, one inside the other. Granted, they obviously use very high quality bearings but are not _perfect_. Since all the gimbals are one inside the other, whatever slop or backlash each bearing has is added to the next gimbal, so the total play is the sum of all the bearings' individual backlash or play. Adding a fourth gimbal will add to the total play or backslash, making the gimbal that much less precise.

[@andrewgwilliam4831]

corisco tupi Thanks!

[@wasatchrangerailway6921]

we had gimbals on the BIAS system. We could detect a hiccup, flat spots, and even weigh the train while it was crossing the bridge. Those were the funnest days of my life, other than as a little kid watching all of the Apollo missions back in the 60s. I would give almost anything to be there again. All of the family was alive and healthy. train sets, microscopes, telescopes, brothers, sisters, mom , dad. life was a hoot!!!!! Then I turned 13 and everything went to absolute hell!!!!! I had no idea that life as a disabled vet would be like this. The family games of keep-away, the water fights, the giant innertube fights, out milkin' the cows in the snow at Christmas. My mother could decorate Christmas like no other, goin' for rides in my dads new cop car at 130 MPH chasing drunk drivers. I ache to be with them all again sitting there watching them land on the moon during the dog days of summer. That was a hell of a good life!!!!!!!!!!!!!

[@bgildersleeve]

Just discovered your channel after searching for some more details on gimbal lock. Great video! Subscribed!

[@stridermt2k]

Super cool channel! Wow nice model too! Always a sucker for those little control thrusters

[@gordondean2110]

I think you are talking about the RCS (Reaction control system) nozzles. Several engineers at the Cape had rejected ones on their desk as pencil holders. I was to able to get one.

[@theice-nineproject9275]

You fortunate canine! So Jealous...

[@abrahamchapman]

Is that a space cat in the background?

[@poozizzle]

I love your take on the history of space flight. More fun than the History channel!

[@RADIXCHRISTUSMOLE]

Jay Atwood it’s also more history than the History Channel.

[@johnarmstrong4329]

This popped up in my news feed. You are a super person, scientist and author. For some reason I haven't gotten any notifications lately.

[@highspeedfistfight]

Detective John Gimble!

[@elvis3571]

you can illustrate the phenomena with a simple compass. - hold the compass base (plate) horizontal to ground. the needle shows (magnetic) North and you can read your bearing in degrees due to North. OK OK we all know this :) - then hold the compass base vertical (i.e. pitch the compass 90 up in Apollo terms). the needle will struggle to show North and you cannot get a reading. - at this point the needle is LOCKED. you can roll the compass as much as you want.... everywhere is North.

[@matillia]

great explanation.

[@Nehmo]

But that's why you have gimbels in every dimension.

[@elvis3571]

I m not sure if I understood you correcly... three gimbals on three axes (x, y, z or roll, pitch, yaw) will lock at some position as well as one gimbal on one axis at some position. thats not multiple gimbals in three dimensions. solution is a fourth gimbal (properly positioned of course). perhaps you were saying this...

[@schizophrenicenthusiast]

+elvis3571 If you read one of Amy's comments above, she corrected herself, saying that onky 2 of the gimbals lock together.

[@elvis3571]

I didnt say all 3 gimbals are locked into each other, srry if it sounded that way, an INS with 3 gimbals at 3 axis will lock at some position, solution is a fourth gimbal, thats what I was saying,

[@j.j.c.s2802]

Thank you! Thank you! Concise and to the point PLUS reference material - FANTASTIC! - now that IS a proper KZbin channel! Keep up the FAB work! And cheers from the U.K.! X! Subscribed!

[@evilAshTheDog]

Amy, KZbin is serving me up videos of yours that I watched six years ago. And sure enough I'm watching them all again!

[@donaldsmalleypublishing401]

You are the smartest person on KZbin. Thank you for your reports.

[@WizzRacing]

They had plenty of things that could go wrong to deal with. One being the guidance computer could mistake a crater if deep enough and shut off the engines dissent engines on the LEM before it had landed. But they said only 4 craters on the moon could do that and they never went them.

[@pucool0927]

Your videos are always very informative :)

[@k.andrewdeffley570]

Thank you for this. I knew how gimbals were an important part of their navigation but was having a hard time visualizing how they registered outside until you showed with the model CM/LM. Also kinda thought gimbal lock for 13 would immediately make the ship look like when you’d shoot down the helicopter in GTA III in 2002. So yes, that’s a big help. Thanks!

[@peterrafeiner9461]

Nice videos. Just wish you'd switch to decaf and slow down a bit :-)

[@duerrs]

+Peter Rafeiner I would not change a thing!!!!!!!!!!!!!!!

[@erlybird3122]

She can slow down when she gives her TED Talk. Otherwise, Peter needs to stop mansplaining her awesomeness.

[@Criosdaidh]

I got the gist of it. Mostly the video was like "if a 4th gimbal.....OMG she's gorgeous........yaw and pitch....OMG she's gorgeous". Human beings can't be this well spoken, this gorgeous and this smart. She should be tested for alien DNA. She might be one of the moon people. No but seriously, good stuff. First saw you on one of those aliens on the moon things on Netflix and ended up here. Your videos are fantastic. Russian photos of the surface of Venus? Mind blown.

[@bostonseeker]

Amy is actually an hallucination. Her cat is real. ^=^ |

[@buttersstotch6752]

she can lock my gimbals up any time @@@bostonseeker

[@jimstorie4937]

Loved the video, I did wonder about gimble lock, now I know! Glad I found this channel also!!

[@LD-qj2te]

Thx I love free learning and conversations !!! It stimulates thought and creates a community and conversation

[@planegaper]

Amy can you do one on nouns and verbs..? not grammar, but in the apollo context.. pete is awsome :) any relation Wally ?

[@AmyShiraTeitel]

+plane gaper Yes on the nouns and verbs - I'm actually surprised no one has brought that up before!

[@planegaper]

here's an interesting one you may want to sink your teeth into," mercury 13"...the subject is becoming very relevant on long duration missions..nice little tidbit of vintage space

[@82ndaa31]

+plane gaper I just saw a YT upload from the History Channel on the Mercury 13. I hadn't heard of them before today. Good call.

[@FosterZygote]

+plane gaper Here's a link to the verb/noun checklist. www.ibiblio.org/apollo/FabrizioPresentationPhotos/A17_VN_Checklist.png

[@82ndaa31]

FosterZygote That's awesome. Thanks for sharing that.

[@davidtoddhoward]

Excellent explanation. Thank you.. Oh and thanks for the book recommendations too. PS: I think I spotted Pete talking a stroll around your Saturn V :-)

[@Chris-ji4iu]

Great summary and thank you for the book recommendations!

[@MrJamesjustin]

These videos are great. Cheers for that.

[@THEATMOPROJEKT]

its silly i know, and i'm sure everyone says it, but YOU are an awesome woman. thank you for a very cool and informative addition to this occasionally very crappy internet. it soo does NOT suck. hahaha!!!! love the cat. make him a star too!

[@drfiberglass]

Smart lady... Love your hair...

[@gasser5001]

reading a script =/= smart. :)

[@theice-nineproject9275]

Check out her credentials, should you doubt. She lists it in one video, as i recall.

[@Cybjon]

A script she wrote.

[@d1agram4]

Clarice.. do you hear the lambs?

[@tomam258]

D1agram But they are silent?

[@tarekfadaak]

Thank you so much for your explanation and for all your great videos.

[@ggsmith48906]

Thanks for that explanation Amy. If I recall correctly, ultimately their efforts to avoid gimball lock (essentially messing up the calibrated settings) were moot when they shut down the command module to save the battery. The lack of power would have allowed the gyros to spool down and the settings were lost anyway. At least that's what I remember, it's been a while since I read the book. Also if I recall recalibrating the IMU during the CM powerup was difficult because the window with calibrated markings that the crew would use to align the spacecraft with certain stars was frosted over from the O2 tank explosion making vision difficult.

[@ApolloWasReal]

Most of the time gimbal lock would not have been a disaster on Apollo, just a major hassle as the crew would have to realign the platform from scratch using the stars as a reference. It *would* have been a disaster (or at least a very serious problem) during a time-critical mission phase like powered flight, and it would also have been a big problem during Apollo 13 since there was too much debris around the spacecraft to sight any stars.

[@badguy1481]

The Gimbal Lock Warning light told the astronauts they needed to rethink the way they should reorient the space craft when preparing to fire the main engine of the CM or LM (called a Delta V burn). They would have to rearrange the sequence of vehicle rotation using pitch, roll and yaw commands. As the comment above indicated. if they entered gimbal lock they would lose knowledge of the stable platform orientation in the IMU and they would be required to take sightings off known stars (and/or the earth, moon or sun) in order to reestablish that orientation. (The stable platform was the ONLY way they could tell what was "up", "down" or "sideways". That was required in order to point the vehicle in the right direction to make course corrections...So knowing the orientation of the stable platform was EXTREMELY IMPORTANT.)

[@ppsh43]

I like your sneaky cat

[@tsman2709]

Excellent explanation, and I've already add those books to my buying lists. Thanks!

[@nickdiamond1938]

Awesome. I kind of thought I knew. Thank you for the facts and for the book recommendations!

[@alext9067]

We like Pete.

[@DavidWoroner]

What is the difference between a gyroscope and a gimbal?

[@lucaschamorrotuduri2563]

+David W The gyro is the rotating mass, the gimbal is the setup that allows it to rotate relative to the spacecraft.

[@Lowraith]

+David W Each ring in the apparatus is itself a separate gimbal. The navigational device is an apparatus comprised of 3 (in Apollo 13) or 4 (as described to avoid gimbal lock) connected gimbals, and navigational equipment mounted to the inner-most gimbal. A gyroscope is a spinning core (important for gyroscopic actuation) mounted to the inner-most gimbal of a multi-gimbal apparatus. The relationship between a gyroscope and a gimbal is akin to the relationship between a doorway and one of its hinges.

[@bzakie2]

A gimbal is just a universal joint. The stove on a yacht is mounted on a gimbal so that when the yacht tips or rolls, the stove is always upright.

[@ChristopherUSSmith]

Milt Farrow (cue classic Electric Company skit): You mean *Gambles* ! LOL

[@antigua930]

What an awesome service! -Always been a fan of all things space travel. Great idea!

[@211topgun]

A most excellent explanation ...And beautifully delivered

[@rocketrider1405]

Great cat at 1:10 ...

[@adamkendall997]

What is this!? A space capsule for ants?

[@mytube082007]

Nice explanation and narration. Thank you!

[@williamblair9597]

It's great to see someone whose passion for science is obvious from your books and videos. Keep up the good work.

[@insideoutsideupsidedown2218]

Seems like she has stopped making videos

[@insideoutsideupsidedown2218]

Seems like she has stopped making videos

[@Nghilifa]

Ya'll are making a gimbal lock event out to be much more dramatic than what it really is. If the spacecraft is coasting (i.e not under powered flight) NOTHING is going to happen, except that they obviously will not know where they are pointing in space. That is easily rectifiable by performing a P52 IMU alignment, (although it was a little bit time consuming) which they routinely did, during the mission. A gimbal lock occuring during TLI/TEI, MCC, DOI is obviously something that you wouldn't want to happen, but if it were to happen during a coasting phase, it wouldn't be critical.

[@ReddwarfIV]

It was dramatic because if they went into gimbal lock while they were trying to correct after the oxygen tank exploded, they would end up flailing around wildly and without the information they'd need to fix the problem.

[@benshepherd2076]

Apollo 13 was venting into space, so it was as if they had an engine running with no way to turn it off. If they went into Gimbal lock then it would have been terrible.

[@epiendless1128]

They can and did realign the guidance computer during 13, but they found it intensely difficult because, if I recall correctly: - they were venting stuff that obscured the stars they were trying to align to - the LM had a fixed sextant, so they needed to align the spacecraft to the stars, and LM wasn't designed to maneuver the command and service module -- they kept coming close to gimbal lock while trying to do this - the astronauts were frozen and exhausted

[@Zoidberg227]

Not just that they were venting into space, they were venting on an unknown axis, at an unknown and non-constant rate (and thus thrust). Maybe it wasn't "critical" because the SM engine didn't rocket them thousands of miles off course, but if they weren't able to stabilize the spacecraft, they would have tumbled off into oblivion, or into the surface of the moon. The net effect is the same here regardless.

[@grimlock1471]

Is gimble lock a function of absolute angle or rate of change?

[@tbrian838]

I still have no idea what a gimble is. 😂 So once locked, it can no longer tell the astronauts their pitch and yawn etc.?

[@EVAUnit4A]

"Gimbal" is another word for a powered, motorized gyroscope- a specialized metal disc or ring spinning very fast. In short, any object (alive and not, big and small) moving in our Universe _must_ do so along three invisible lines running perpendicular to each other, the so-called X, Y and Z-Axis (aka "pitch", "roll" and "yaw"). The _Apollo_ guidance system uses the IMU to detect the slightest movements to the spacecraft. (I promise I won't use any big scientific words in the following, since I am neither scientist nor engineer.) Here on Earth, we humans (and many other animals) have our inner ear, which has three very tiny hollow tubes with fluid that freely moves through them. When you turn your head specifically, the liquid in those tiny rings moves, and even-tinier hairs inside of each tube detects the motion and then tell your brain "Yo! You're movin', dude!" Well, things get significantly more complicated when you move into outer space, away from the influence of gravity. While inertia alone still can move the fluid in your inner ear, the loss of gravity disorients you and the signals coming from your inner ear _don't_ match up with what your eyes, skin, nose and other senses are telling you; your body has not evolved to understand movement _without_ gravity. (NOTE: there are a number of movement-sensory disorders out there- among them seasickness, airsickness and vertigo- so this does not work perfectly in everyone nor all the time.) The same thing applies to a spacecraft. How does it know which way is the correct direction to point, since there is no "up" or "down" in space, and the distances between anything are stupidly, unimaginably huge!? The _Apollo_ IMU used three high-speed gyroscopes ("gimbals") which were deliberately pointed in different directions, just like those inner-ear loops inside your head. You know how when you have a single spinning gyroscope in your hand, and you feel resistance anytime you try to move it? The IMU does _exactly the same thing-_ it detects those tiniest of changes to the directions of _all three_ gimbals at the same time. So, for example, if the spacecraft turns slightly to the right, one of the three dedicated IMU gimbals will notice the change and inform the navigational computer of such. The IMU is setup to begin measuring motion just before launch, and will continue to do such until either the end of the mission or the spacecraft is discarded. So, with all of this said, what Amy is trying to tell us in the video above is that there was a very real risk that if _Apollo 13_ turned in more than one direction too quickly, the gimbals would _unintentionally_ line-up with each other ("gimbal lock"), thus losing their unique settings and the ability to tell the navigation computer which direction the spacecraft was pointing. On _Apollo 13_ in 1970, this was especially hazardous because _Odyssey_ (the Command/Service Module) and _Aquarius_ (the Lunar Excursion Module) were tumbling out of control for a significant amount of time, and if the astronauts were not _very_ careful, the three gimbals would IMproperly line up with each other and "lock", and the onboard computer would not be able to keep them pointed in the right direction. Once gimbal lock happened, there was absolutely no way for the astronauts to reset it while they were in space.

[@suekennedy8917]

Gimble is a fancy word for not turning on the cameras inside the Command Module or LEM to show Jim Lovells great piloting skills in outerspace with no restraints to keep him from moving relative to the studio LEM because it was a a gigantic hoax.

[@asagady2552]

Outstanding science/engineering/technical commentary!

[@mikeharrison4768]

Great information. Great presentation. Fantastic enthusiasm. Keep up the great work!

[@DavidKeaInOldOrcuttCA]

The Saturn are beautiful but they pale in comparison to the presenter of this video!

[@Martinit01]

Hot red haired girl talking about space stuff... Subscribing!

[@mattmaynard3553]

Love your programs!!! You're a space angel.

[@KCFlyer2]

I wish my science teachers looked as good as you. Stunning.