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.
What 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 gimbal lock possible.
The three gimbals account for the spacecraft’s three axis of motion,
也就是俯仰轴 倾斜轴 侧滑轴
motion it’s axis of 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 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 prevents them 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 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,
如果没有的话 请在下面留下你的问题 我会尽力回答
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 wanted 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 exactly what the title says,
it is the details of how Apollo flew 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.
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