The SCALE wire boom deployment system

The most important scientific instrument to be tested on SQUID is the SCALE system, the wire boom system in charge of deploying the cable with the spherical probes in order to perform the electric field measurements.

It consists of two coaxial cylinders with a small gap between them. On its initial configuration (before deployment), the cable is coiled along this gap between a pushing ring and a feeding system. The feeding system is composed by a channel machined on the main cogwheel driving the mechanism, which guides the cable from the gap between the two cylinders towards a groove machined on the plate covering the gear system. The cable is held on the groove for an arc of around 300 degrees and conducted again by another channel machined on the main cogwheel towards an aluminum tube guiding the cable towards the shaft, which releases the cable parallel to the deployment direction inside the cylinders, where the spherical probes are initially stored. When the deployment starts, the motor drives this gear system, collecting the wire from the gap and redirecting it towards the radial direction of the FFU.

 

At the same time, a gear system will move the PEEK pulling ring, displacing the cable that remains coiled along the inner cylinder against the feeding system. The ring is displaced by two threaded rods that are placed in diametrically opposite positions. Before the deployment the inner cylinder is covered by a circular door for protection and stabilization of the spherical probes during launch. This door is held in place by two bolts placed at the end of each of the threaded rods, in such a way that when the wire boom system is activated and the rods start rotating, the door is released and ejected both due to the effect of the centrifugal force induced by the spinning spacecraft and the preload of three springs placed on the inner side of the door.