NUTS - NTNU Test Satellite, a Norwegian CubeSat Project

Mechanical Design

Written by: Anders HÃ¥land
Published: 05.11.13
The NUTS group has an overall goal to have working mechanical model finished by Easter 2014. To be able to achieve the goal several different and unique task have to be completed, and now there are special attention to finishing primary structure, antenna module and to produce and “lock” parts.

To be able to finish the primary structure many task have to be done. Firstly the material selection is of special importance for the project, due to space environmental effects, and general mechanical reason. It has been decided to make the side panels of the primary Structure in Carbon Fiber Reinforced Plastic (CFRP) (see pictures below) and rails of 7075 aluminum. Then design and production method have to be decided, courses has to be completed to be able to produce parts, material have to be found, bought or shipped and then the production of the parts can take place. Special attention is now on making panels with high enough quality to pass an out-gassing test, and the primary joining of the panels to the rails.  An out-gassing test is performed to ensure that a material does not consist of too much fluids that will evaporate in vacuum, and to see to the joining of the parts a special jig has been designed to properly align the rails and panels.

Figure 1. Adhesive Jig

The project has been ongoing since 2011 and thus many parts have been designed, re-designed, and in some cases dismissed. Some parts or solutions have been designed according to the equipment and machinery available at that time and therefor been improved as more advanced equipment has come in, and in other situations a new student have taken over the responsibility and with new eyes found new solutions. For example the quality of the old primary structure was not found accepted, and to simplify and meet demands of the CubeSat Design Specifications it was changed

Figure 2. Old primary structure

Figure 3. New primary structure

The antenna module has gone through several iterations and are hopefully going through one last now. There have been some unsolved issues, and questions have been raised regarding the robustness of the latest solution. This has led to the making of the antenna elements and they are made of a special material named Beryllium-Copper (BeCu). This is a material with a very high specific toughness, meaning that we can make “long” antenna elements of very thin strips. The longest element is over 500 mm long, 6 mm wide and only 0.05 mm thick with a specific curvature to ensure proper stiffness. Different tools have been made to plastically deform the elements to designated curvature.

Figure 4. Curvature Tool 1

Figure 5. Curvature Tool 2

Figure 6. Curvature measured to R12.5 mm

Figure 7. Punching tool for making holes for fasteners in antenna elements

Figure 8. Rapid prototyping of antenna module, without antenna elements.
There are some particular parts that are decided and unlikely would be changed, thus it should be produced, finished and locked down in a safe to be taken up when assembly take place.