This document has been created for instructing new or potential team members for SFU SAT Club’s structural team. It goes over the necessary skills that one will need to be a productive member for the team as well as the skills one will be able to refine with the team. Any skills you don’t have you can learn with us! It gives some in depth look at the previous CSDC design ideas and the results in which we obtained. This document is also meant to be an open document that members can add to as new things come up or new resources are found. There is also a lessons learned document in the google drive which goes over a few of the structural teams short comings and where we went wrong. The information in there is invaluable to any new members as to do the same mistakes we did.
Hello new members!
Structural team is a practical applications based team that applies knowledge of, 3D modeling, 3D design analysis, materials analysis, finite element analysis, thermal analysis, and mechanisms. The most common students in the structural team tend to be MSE students however other engineering students or students going into IAT are also common.
How do I get started?
The structural design needs to fit under many criteria outlined in a document called the Design, Interface, and Environmental Testing Requirements (DIETR). This lists off all the design constraints in which need to be adhered to for our satellite to past review. The first step of design starts here and outlining how each requirement is going to be met. This is also a great place to look for motivation or a new challenge as there are some cool requirements, such as vibration analysis, in which not many people have knowledge about and provides an opportunity to learn new things well before the opportunity to take classes for it.
The fun one. Creating the designs and the models using SOLIDWORKS. Solidworks gives us a great amount of freedom to explore new designs while allowing those designs to be tested for fitting and material properties quickly. Solidworks is typically taught during the first two years of MSE however Solidworks tutorials are something that can always be done for anyone in the club who is interested in adding some knowledge to their resume.
Our previous CSDC structure started with inspiration from Pumpkin Space Systems own structural interface (a). With those structures costing $7,000 – $22,500 each they were definitely not an option for us to purchase however their design was straight forward and something that we could easily mimic for a very low cost. Budget and volume requirements were tight which lend to this rail-less design which could accommodate the large area PC104 PCBs that were the intended chipset.
After all the parts for each team had been settled the design was shifted into a much more accurate model that incorporated all of the mounting holes and components that would need to be integrated together so that volume and space restrictions could be figured out. The time in-between the initial design and the manufacturing model was extensive as a vast number of the parts such as # of PCBs had not been figured out. Now that all of the teams know what kind of space that they will need better estimations can be made and production can start a lot quicker.
3D Design Analysis
3D design analysis is the study of the design of the system in terms of its mass, volume, balance, inertia, and dimensions. We again use Solidworks to test these design criteria. Most of these criteria are not design limiting in that the majority of designs can accommodate extreme features and still pass the criteria with a simple bit of balancing. Overall if the cubesat is as symmetrical as it can be without any extreme asymmetry then it will most likely pass the required criteria.
Keeping these criteria in mind when allocating mass and volume resources to the other teams such as computing PCBs volume allowance and radio antenna volume allowance is an organisational task that if done properly will not cause any headaches or redesigns in the future.
Material analysis is a big part of this topic, as knowing exactly what is going into every part and what the properties of those materials are will allow the designer to add those materials into the solidworks model. One of the strange requirements within the DIETR is the off gassing requirements. This is basically how much a substance decomposes over time. It is a requirement that we do not send material into space that off gasses above a certain amount.
A database which outlines material details for space use is listed below.
Finite Element Analysis (FEA)
FEA allows us to test the properties of the system as a whole assembly and to locate areas of weakness or potential fault. We use the program ANSYS which is available on SFU workstation computers. This program is a bit daunting at first but is in fact a very methodical and simple to use program. Ansys allows us to do three main tests on our system model; thermal, modal, and static loading. Each test uses the same model which can be meshed once and shared between the tests. The meshing is 80% of the work when it comes to Ansys as it requires a simple 3D model that accurately describes the structure (a bit of a balance between simplicity and accuracy. Proper joins between the parts need to be established in the mesh to allow for the parts to interface properly. Since FEA is an upper level course that is taught at SFU and is not available to many students, tutorials on how to conduct the tests in which we use for Sat Club can be done for any members who have an interest in FEA.
The really fun part! Antennas and any deployables or moving parts fall into this category. Last CSDC antenna deployment was section off into a entire different section of the structural team forming a sub-team that focused on the, housing, deployment system, and integration of the CubeSats 4 antenna. Many CubeSats have deployable solar panels in addition to antenna in which need reliable and simple designs.
Our previous solution to antenna deployment was to have 4 coiled antennas that were attached to a spring loaded door. This door would be held back by a burnable cord and a wire that could be heated up by passing current through it. This created a simple electrically controlled mechanical system
The antenna project was a great test of prototyping and integration skills which allowed for the team to use 3D printed components to test and bring their designs to a reality.
Construction and Manufacturing
The structural team is the baseline for integration with all the teams. Every team has a PCB or component in which they need to fit within the chaotic mess of cables and components that make up the inside and outside of a CubeSat. Once the designs have been completed and the parts have been analyzed fitting everything together and remaining adaptable is a key element that the structure needs to have. Every fastener needs to be listed and every material needs to be sourced. Once this has all been done, the ordering of parts can begin. This is a big difference between many school projects that get left in the design or prototyping phase. An actual CubeSat needs to be built.
Aluminum everything! Very light weight and high enough strength for our uses 5051 or 7075 T6 aluminum is the go to for the majority of the structure with the exception of the fasteners. Luckily fasteners and aluminum is relatively cheap.
Machining is extremely expensive however considering the tolerances in which we need to maintain. The only option is to CNC machine components. Most of this will need to be done by a 3rd party machine shop.
Turning your 3D solidworks models into manufacturable designs can be challenging when the designs get complex however there are plenty of reliable people within the club who have gone through this process and can offer advice. In general, keep things simple and understand where a bit would have to go to make the cuts required goes a long way in prepping for manufacturing.