I’ve completed another portion of my work-in-progress Viking '75 Mars lander high-fidelity model - the deployment mechanism of the lander’s S-Band High Gain Antenna (HGA). The HGA has a 30-inch parabolic dish that needed to be located above the lander (to avoid line-of-sight obstructions from other components). In order to fit within the lander’s aeroshell capsule during launch and cruise the HGA dish was folded down close to the lander body. The deployment mechanism, seen here, was used to raise the antenna to its final vertical position shortly after landing on Mars. Two sets of curled constant-force springs provide the energy to rotate and raise the HGA. In order to avoid a damaging shock at the end of a potentially fast deployment travel, a governor with escapement mechanism is located in the tear-drop end of the deployment’s horizontal hub.
Here is a comparison between actual Viking lander hardware (photographed at the Virginia Air and Space Center, and the Smithsonian National Air and Space Museum) and the model:
This is the deployment mechanism shown in place on the work-in-progress lander (the actual HGA would be attached to the top-most flange of the short vertical elbow tube):
Close-up of the deployment mechanism hub; the clothespin-like device on the left is the uplock, and the governor is within the right end of the hub:
Close-up of the deployment mechanism, showing the two sets of nine-layer constant-force springs that power the deployment mechanism:
Exploded view of the overall deployment mechanism (green-tinted components are simplified or approximated due to lack of reference material):
Exploded view with governor and escapement in the foreground: