FAILED gyroscopes need not doom satellites to a fiery end, say engineers at
the Aerospace Corporation in California. They have developed a “pseudogyro”, a
software-only gyroscope that satellites can upload to take over from failed
gyros.
A spacecraft cannot orient itself without a gyro. Astronomical
instruments have to point at the right place in the sky, while communications
satellites need to aim their antennas at ground stations.
Mechanical gyros measure angles against the axis of a fast-spinning wheel.
Laser and fibre-optic gyroscopes sense changes in the phase of light around a
circular laser or loop of optical fibre. But the pseudogyro calculates the
satellite’s orientation and direction using data from a multitude of sensors
that are carried by the spacecraft and from knowing its mass distribution.
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Girard Manke, an engineer at Aerospace Corp, says the software also collects
data from sensors that monitor positions of movable components such as solar
panels and exterior antennas, and calculates the effects of the Earth’s magnetic
field on the satellite. In this way, the pseudogyro mimics a conventional gyro.
It also collects data from star-tracking cameras.
Once the pseudogyro has determined orientation, it controls thrusters and
reaction wheels which turn the spacecraft to keep it pointed in the right
direction. The inventors know it works because the prototype software was used
when failed gyros crippled a satellite launched by the US National
Reconnaissance Office. It kept the craft operating for two weeks, says Manke.