Gimbal Lock and Apollo 13

those who followed my Apollo 13 lives who probably saw the phrase gimbal lock pop-up a number of times and a lot of you asked me what it is so today I'm venture space we're looking at what exactly is gimbal lock so we need to break this one down just a little bit before getting into the question of gimbal lock at the heart of the Apollo guidance computer was an inertial measurement unit or IMU the IMU is a spherical housing about the size of a soccer ball that contains three nested gimbals they're set at right angles from one another supporting a central platform mounted on the innermost gimbal the outer gimbal is mounted on the navigation base and this is mounted rigidly to the spacecraft every time the spacecraft moves or rather every time the IMU detects any kind of change of attitude the gyro is signaled two motors return the platform to its original orientation so as the spacecraft moves around on its path the moon the guides platform inside remain stable the guidance platform was aligned on the ground before the flight and of course it would drift occasionally during the mission to compensate for this drift astronauts would rely on the platform using star sighting but its use still remained and it still gave the astronauts information on their attitude in space the information from these Darrow's was displayed on the flight director attitude indicator more commonly known as the eight ball so it's the fact that there are three gyros involved in the IMU that make in bilac possible the three gimbals account for the spacecraft's three axis of motion it's AK sees a pitch yaw and roll because the IMU works in all three directions any change in the attitudes orientation at all is registered on the eight ball the constant attitude information about these three axes gives the astronaut a very keen sense of exactly where they're pointing in space but it's also something that you can lose the phenomenon of gimbal lock is one where in the outer gimbal moves with the spacecraft to a point where it lies parallel to the inner gimbal at this point all three gimbal axes would be lined up on a single plane and none would be able to move around the basic plane to resume a normal orientation in short once the gimbals are lined up they can't realign themselves to give you an orientation and they become locked it's the confluence of three angles of the gimbals that creates gimbal lock and from moving around to get out of that situation the Apollo guidance computer was actually designed to prevent gimbal lock by giving the astronauts a warning when they approached that devastating alignment however it was possible still to fall into gimbal lock this was what was happening on Apollo 13 when the spacecraft was wildly pitching and yawing around in the wake of the oxygen tank explosion and that is why you hear in the movie and read in the transcript astronauts yelling about watching the gimbals losing their attitude in space would have made the entire situation on Apollo 13 just that much worse the simplest way to avoid gimbal lock would have been to add a fourth gimble into the IMU just giving it another reference point so that the four wouldn't be able to align the same way this is what Mike Collins actually asked for for Christmas jokingly when he was orbiting the moon on Apollo 11 from his orbital vantage point in the command module it calls us trying to find the lunar module eagle on the surface but every time he got close to gimbal lock he had to stop and that's why he wished he'd had a fourth gimble on board so I hope that clears up gimbal lock for you guys if not leave question below and I'll try my best to answer it but I also want to give you two quick book recommendations of things that would maybe explain it in a lot more detail the first is Frank O'Brien's the Apollo guidance computer which is everything you ever slashed never one to know about the Apollo guidance computer and it is a brilliant resource and the second is how Apollo flew to the moon by Dave woods it is is exactly what the title says it is the details of how Apollo to the moon including the guidance computer both are fantastic resources by excellent authors and I would highly recommend it if you guys want all the nitty-gritty details on things like attitude control and space on Apollo so as always leave any questions comments and ideas for things you'd like to see covered in future episodes in the comment section below be sure to follow me on Twitter for venture space content every single day of the week and with new episodes going up every Tuesday and Friday be sure to subscribe right here so you never miss an episode

Channel: The Vintage Space

Views: 1,130,370

Keywords: Apollo Program (Space Program), Apollo 13 (Space Mission), Gimbal Lock, Spaceflight, NASA, History

Id: OmCzZ-D8Wdk

Length: 4min 15sec (255 seconds)

Published: Tue Apr 21 2015