Tag Archives: CAD

Winter Mechanical Engineering Internship

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During my time at Princeton Satellite Systems, I worked on a momentum unloading project for NASA’s Gateway, a component of the Artemis program. I designed a deployable parasol that is controlled by Canadarm using Solidworks.

Solidworks is a platform I am familiar with, but I was still able to learn new functions. My favorite part of working with Solidworks is the puzzle-like nature of assemblies. When trying to make dynamic parts you have to think about how to best add relations without over-constricting or under-constricting the part. Once I finalized my initial design I was able to attend a Zoom meeting and present it to another company.

When not working on my Gateway project, I fiddled with the 3D printer to print models of the PFRC fusion reactor.

Although I have used 3D printers several times before, this time was more of a learning process. I was an acting 3D printer technician and wrote a guide with troubleshooting tips for future employees. Due to problematic unspooling and tangled filament the printer became jammed a few times, and I was unable to do the typical loading/unloading to set the filament free. This gave me the opportunity to take apart the 3D printer and see the internal mechanisms, which in turn allowed me to unjam the printer and solve the problem. I was thrilled to see inside the 3D printer and how the parts blend together!

Through my internship I learned about the complexity of the design process and how many things you need to consider when creating a product. Conceptualizing is one step, but bringing that concept into the real world requires much more research and planning. Overall, this internship was a great opportunity that allowed me to learn how to solve several engineering problems.

Reaction Wheel CAD Project

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Hello!

I’m a sophomore at MIT who joined PSS as an extern over Independent Activities Period (IAP). Free to choose how to spend the month of January, students can take an extended vacation,  attend short, intensive classes, do research in MIT’s various labs, etc. Many like myself choose to participate in short internships with MIT alumni – the correct lingo for this type of job experience is “externship”.

I was assigned the task of 3D modeling a reaction wheel for a 25 kg satellite. Essentially, the wheel controls the orientation of the satellite in space. Comprised of a small axial flux motor and a flywheel for added inertia, the wheel sits at 40 mm tall and 80 mm wide. It must spin in both directions, and meet tight dimensional constraints. I believed I really had my work cut out for me.

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Moon Lander Design

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Our last post showed the mission planning script for our lunar lander. The next step was to layout the lander. We did this using the BuildCADModel function in the Spacecraft Control Toolbox. The propulsion system is designed to meet the requirements of the mission plan. We use six 1 N HPGP thrusters for attitude control and one 220 N thruster for orbit maneuvers and landing. We have two HPGP tanks for the fuel. There are two cameras. One is used as a star camera for attitude determination and navigation and the second, which is articulated, is used for optical navigation, descent navigation and science. The IMU and C&DH box can bee seen in the drawing.

LunarCAD

The solar array has two degrees-of-freedom articulation. The high gain antenna is also articulated. We adapted the landing legs from the Apollo Lunar Module. The thruster layout is shown in the following figure and is done using the ThrusterLayout function in the toolbox.

LunarThruster

We get full 6 degree-of-freedom attitude control and z-axis velocity change control. We use the 220 N engine as the primary engine for landing but can also use four of the 1 N thrusters for fine terminal control.

We are working on the science payload for the mission. One experiment will be to mine helium-3 from the surface. Helium-3 would be a fuel for advanced nuclear fusion power plants and nuclear fusion propulsion systems.

Spacecraft CAD Design in the Spacecraft Control Toolbox

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AutoDesk Inventor and SolidWorks are powerful software packages for the computer-aided design of spacecraft. Ultimately you need to use one of those packages for the mechanical design of your satellite, but what about the preliminary design phase when you are still determining what components you even need? The CAD software in the Spacecraft Control Toolbox can provide you with a valuable tool to do your conceptual layouts and early trade studies, and the same model can be used as the basis for disturbance analysis in later design phases.

A CAD model in SCT is built in a script which allows you to build your models algorithmically. You can call design functions, use for loops and revision-control your source code. For example, within the script you can do an eclipse analysis and compute the battery capacity. This number can generate the volume of your batteries which you can then use to size your spacecraft.

The function BuildCADModel provides the model-building interface. The CreateComponent function is used to generate the individual components using parameter pairs as arguments. Components are grouped into bodies to allow for rotation and articulation. A GUI displays your finished model and allows you to visualize it in 3D. You then store your finished models as mat-files. Our disturbance model uses every triangle in your model for disturbance analysis.

The example figure shows a solar sail design, with the spacecraft bus in the middle. BuildCADModel allows you to group components into subsystems as on the left-hand side, which can then be highlighted using transparency.

The figure below shows the BuildCADModel GUI which allows you to verify the body and component properties.

There are many examples of spacecraft models in the SCT to help you get started, and a lengthy chapter in the User’s Guide discussing the finer points of component location, orientation, and physical properties such as drag and optical coefficients. Your CAD model essentially functions as a database for your entire spacecraft model!