Gyros and Gimbals, oh my! — The James Webb Space Telescope Reliability Lessons

First image from the James Webb Space Telescope — showing it pointed at a star with all mirrors aligned. (NASA)
Illustration of a simple three-axis gimbal set. The central disk does not move no matter how the entire complex rotates. (Wikipedia)
On the left, image of Apollo 16 Casper orbiting the Moon with Earth in the background. On the right, astronaut John Young on the Moon. (NASA)
Astronauts reaching into Hubble Space Telescope to replace gyroscopes in 2009 (NASA)
  • Instead of using mechanical spinning gimbals, the gyroscope is a “hemispherical resonator gyroscope”. In plain English, this means that there are no mechanical spinning wheels and instead there is a special quartz crystal which has an electrical current sent through it. Less moving parts, less chance of failure.
  • While Hubble moved the entire spacecraft to point the telescope, Webb has a special mirror designed to keep the telescope pointed accurately even when the spacecraft drifts slightly off point or jitters. This means less stress on the systems to keep perfectly aligned.
  1. Yes, Apollo 16 also had gyroscopes, but they’re not part of this story.
  2. Hubble’s maintenance was not just to repair malfunctioning components but also to upgrade older equipment with more modern and capable ones. This is the reason why Hubble has continued working for decades in space.



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Robert Barron

Robert Barron


Lessons from the Lunar Landing, Shuttle to SRE | AIOps, ChatOps, DevOps and other Ops | IBMer, opinions are my own