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What is a gimbal -- and what does it have to do with NASA?


Gimbals in Space
NASA's multi-axis gimbal rig is used to test astronauts by simulating a dangerous spacecraft spin condition.
NASA's multi-axis gimbal rig is used to test astronauts by simulating a dangerous spacecraft spin condition.
Courtesy NASA

­What do gimbals have to do with NASA? The answer boils down to this: almost everything. Not only does NASA use gimbals when designing navigational systems and instrument panels, but also for building training simulators and other terrestrial components. Without gimbals, it would have been very difficult for NASA to find a way to send the first astronauts up into space safely.

In training missions, NASA uses gimbals to simulate situations astronauts will encounter while in space. Some early training simulations required astronauts to put on a harness and dangle from a suspended, gimbaled system to simulate a spacewalk. Because the astronauts were in a set of gimbals, they could reorient themselves to different directions, just as they could in space. Gimbals also played an important role in motion simulators, giving simulator cabins a higher degree of freedom of movement.

The One-Man Extravehicular Gimbal Arrangement (OMEGA) lets NASA test subjects maneuver as if they were in a zero-g environment.
The One-Man Extravehicular Gimbal Arrangement (OMEGA) lets NASA test subjects maneuver as if they were in a zero-g environment.
Courtesy NASA

NASA used gimbals in early spacecraft for everything from instruments to propulsion systems. In navigational systems, gimbals are useful for determining and changing the orientation of a spacecraft in relation to something else, such as the Earth or a space station. Gimbals are also useful for components like solar panels. Mounted on a gimbal system, the panels can tilt and rotate to face the sun even as the spacecraft's orientation changes.

One of NASA's most important spacecraft instruments is the inertial measurement unit (IMU). An IMU measures changes in pitch, roll and yaw as well as acceleration. The IMU contains accelerometers and gyroscopes to monitor changes in spacecraft velocity and attitude. For the Gemini missions, NASA used a four-gimbal system. But for the Apollo missions, NASA decided to go with a three-gimbal system. That's because engineers worried that they would miss their goal of landing a man on the moon before 1970 if they waited to perfect a four-gimbal system. Because the Apollo spacecraft IMU only used three gimbals, astronauts had to stay alert and realign the spacecraft to avoid gimbal lock.

NASA also used gimbals when building the propulsion systems for spacecraft. A fixed rocket engine or thruster would only be able to provide thrust in a single direction. Mounted on gimbals, the same propulsion unit could tilt to provide thrust in different directions. This is critical whenever a spacecraft must align itself with another body, whether it's another spacecraft, a planet or the moon.

It's pretty amazing to think that a simple series of interconnected rings made it possible for NASA to send a manned spacecraft to the moon. Without gimbals, we couldn't navigate or travel in space with any precision.

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