4.1 Definition

The structures and mechanisms subsystem is responsible for all the mechanical interfaces of the spacecraft throughout its lifetime:

• Adhere to mass constraints set out by form factor and launch provider (during design)
• Mechanically support all other spacecraft subsystems (during integration)
• Attaches the spacecraft to the launch vehicle (during launch)
• Provides for ordnance-activated separation (during orbit insertion)
• Provides deployment and other moving mechanisms (during a mission)
• Shielding from space environment, like radiation, atmosphere, pyrotechnic shocks (during a mission)

The mechanical design must satisfy all strength and stiffness requirements of the spacecraft and launch vehicle, such as deflection during thermal expansion in space and vibration tolerance during launch. The structures and mechanisms subsystem may be separated into a primary structure and a secondary structure: the primary structure carries the spacecraft’s major loads and the secondary structure supports components and provides non-load bearing covers, etc.

Structural components include skin panel assemblies, trusses, ring frames, pressure vessels, fittings, brackets, equipment boxes, and much more. Structural interfaces include attachments, joining options, and fittings. Attachment or joining options in adhesive bonds, welds, and mechanical fasteners. Adhesive bond strength depends on the process and workmanship and requires strict process control and testing. Welds are possible for most aluminum alloys but the heat from welds can lower material strength near welds by more than 50%. Welds require strict process control and testing. Mechanical fasteners, such as bolts and rivets, can experience fatigue.

Artemis Kit Specific

Most composite material structures have metal end fittings or edge members attached by bonding. Bolts can be used but local stress concentrations around fasteners can cause premature failure at lower load levels.

^{Aerospace Fasteners Application: An Aerospace Manufacturing Perspective. Slide show courtesy of Randy Swinger.}

                                                                 ^{3D Exploded Image of CubeSat Created by Kevin Williams with HFSL}

In the Artemis CubeSat kit, the structures and mechanisms subsystem consists of the 1U CubeSat frame, an antenna deployment mechanism, a threaded rod, spacers, and various fasteners. The structural frame is made of aluminum 6061 T6 and hard anodized. When stowed, the antenna deployment mechanism relies on a spring-loaded antenna, fastened by a fishing line. Upon deployment, the fishing line is burned through by a nichrome wire, releasing the antenna. The threaded rod is made of super-corrosion-resistant 316 stainless steel. The various-length spacers are made of aluminum. The inserts are made of stainless steel. The stainless steel fasteners include slotted screws, hex nuts, and washers.

The custom structure’s CAD can be found in the Artemis repository but the list of parts for the remaining structural components is as follows: