Travis and Michelle Fitzgerald's blog

Today was a joyous day for those of us who work on the Motion Control System (MCS) on the International Space Station (ISS). A brand-spanking-new Control Moment Gyroscope (CMG) was installed in the place of a previously failed one. Once Todd and Matt finish checking it out, they’ll spin the wheel up to its normal speed of 6600 rpm and we’ll be back to having 4 functional CMGs!

What is a CMG? Well, it’s a large (200 lb) spinning wheel mounted on 2 gimbals. We use electric motors to move those gimbals, and when that happens with the wheel spinning, it creates torque that we use to control the attitude (or orientation) of the entire ISS. That’s right, 4 x 200 lb wheels are all we need (most of the time) to control a 350,000 lb vehicle.

The whole CMG assembly weighs about 600 lb. Yet it only took 2 crewmembers during a spacewalk to remove one and install another. Ain’t space cool?

Here’s a picture of a CMG. It may not look like much, but it’s got it where it counts.