Artillery wheel Artillery wheel The artillery wheel was developed for use on gun carriages when it was found that the lateral forces involved in horse artillery manoeuvres caused normally constructed cart wheels to collapse. Rather than having its spokes mortised into a wooden nave (hub), it has them fitted together (mitred) then bolted into a metal nave. Its tyre is shrunk onto the rim in the usual way but it is also bolted on for security. A normal wagon wheel is dished so that in its lowest part, the spokes are perpendicular to the ground thus supporting the weight (with the axle
Reaction wheel temporary changes in its speed result in small changes in angle. The wheels therefore permit very precise changes in a spacecraft's attitude. For this reason, reaction wheels are often used to aim spacecraft carrying cameras or telescopes. Over time, reaction wheels may build up enough stored momentum to exceed the maximum speed of the wheel, called saturation, which will need to be cancelled. Designers therefore supplement reaction wheel systems with other attitude control mechanisms. In the presence of a magnetic field (as in low Earth orbit), a spacecraft can employ magnetorquers (better known as torque rods) to transfer angular momentum