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Gyroscopes take on zero-gravity conditions

Posted: 04 Jan 2016     Print Version  Bookmark and Share

Keywords:gyro  MEMS  zero-g  space  sensor 

Editor's Note: Bill Schweber gives some details on the use of gyroscopes for space applications.

It's always interesting to see how engineers adapt older devices for radically new uses. A good example is the work being done at Draper Laboratory to counter the difficulties of working and having tangible motion feedback when working in the weightlessness of space. The IEEE Spectrum article "A New Spin on Space Suits" explains how an array of classic gyroscopes is being used in spacesuits as an analogue sensor and actuator to counter the lack of "weight" feedback that astronauts must deal with, especially when doing projects, repairs or spacewalks.

Just remember: weightlessness sounds like so much fun, until you have to do work in that environment, and there are the other weightlessness-related issues such as body-mass and muscle deterioration, among other consequences.

The Draper design, which has been prototyped and is in preliminary tests including zero-g flights, uses the gyro's spinning mass to sense motion and create a force which resist such movement. Unlike MEMS-based gyro sensors and accelerometers which have become ubiquitous for motion and acceleration sensing in many products, this application needs mass to generate force, so the classic spinning wheel gyro must be used; this configuration is known as a control moment gyro (CMG). There's something that the MEMS-based devices cannot do despite their well-known advantages.

CMG

A new Control Moment Gyroscope (CMG) sits in its cradle in the payload bay of the Space Shuttle Discovery prior to its installation on the International Space Station in 2005, to replace one which failed in 2002. The International Space Station has three of the 272kg gyroscopes controlling its attitude. (Source: NASA)

Gyros are not new in aerospace applications, of course. They have been used in guidance systems for aircraft and spacecraft for decades (including the International Space Station), and a highly refined PIGA (pendulous integrating gyroscope accelerometer) is still the highest-performance accelerometer available, see "Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance."

Along with their sibling, the reaction wheel, they are also used for stabilising spacecraft. The choice between the two uses of a spinning mass involves a set of interesting basic-engineering trade-offs, as discussed in the paper "Comparison of Control Moment Gyros and Reaction Wheels for Small Earth-Observing Satellites."

We tend to look towards the latest, most-innovative sensors and actuators for solutions to difficult design problems, which generally makes sense. Still, it's important not to be blinded by the glamour of the new, as there are times when a reversion to a modified or updated version of a classic transducer makes the most sense.

Thermocouples, invented in the mid-19th century, are still preferred in many situations for temperature measurement for many reasons, and are also the basis for thermoelectric generators (TEGs) used to power spacecraft for decades (using heat provided by radioactive decay).

Have you ever reverted to a classic device or solution in place of a more recent one? Did you get push-back from others who felt it was too old and outmoded to be used?

- Bill Schweber
  Planet Analog





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