Week 8: Three Dimensional Madness in FreeCAD
Kira A -
Welcome back, everyone! I hope you are all as excited to learn something new as I was this week. While this project has required that I learn many concepts related to orbital mechanics and spacecraft design and become proficient in programs such as Overleaf and MATLAB, one of the most enjoyable learning moments of this project was my time learning FreeCAD.
As per my last post, this week I was able to dive deeper into the design of my spacecraft and implement that into a computer-aided design program called FreeCAD. FreeCAD is an open-source parametric 3D modeling software that allows users to create and edit 3D objects. Because FreeCAD is open source, or maintained by its users, it is FREE to use, which means that if any of you guys find the process of designing my spacecraft’s components as intriguing as I did, you can download it today at a low cost of FREE ninety-nine (not-sponsored)!
To begin the part design process, we must first open a sketch. This is where we can use different tools to create shapes and lines to parameterize the 2D version of our object. Below is an image of a sketch that I have created on one of the faces of a rectangular prism I created from a previous sketch.
Here we can see the words “Fully constrained” in our taskbar to the right. This indicates that each parameter (height, width, distance from the x-axis, distance from the y-axis, etc.) has been restrained to a set value. From this, we can close the sketch and perform the pad operation, which takes our sketch from 2D to 3D! Here is an image of the 3D version of our sketch that I have performed a few more operations on to create a hinge component.
Once we have created a 3D object, we can assemble a more complex object by combining it with any other 3D object we have created. Here are some images of a design I am considering for the solar panel assembly of the Moon Bound Mission. I opted for two panels on each side with hinges in between to reduce the space taken up by the panels when in a collapsed position.
Using the following simplified equation for the surface area of a solar panel based on the solar cell efficiency, solar irradiance, and desired power output, I calculated the size of the panels that I would need for my mission.
To find our solar cell efficiency we can look toward the Europa Clipper, one of the model spacecraft for my mission, which uses the AZUR 3G27 / 3G28 triple solar cell in its solar panels. Not only are these very light solar cells, but these solar cells are highly efficient, featuring a maximum efficiency of about 28%. This translates to 28% percent of the energy from the sun that reaches the solar cell being converted to usable energy. Next, we can determine how much energy we need our solar panels to produce by looking at the Dragon 2 capsule, or the Cargo Dragon, another spacecraft I am modeling my own after. The solar panels on the Cargo Dragon produce around 5000W to supply instrumentation and any cargo that might need a power source.
Finally, we will be using the solar irradiance, or the intensity of the sun’s rays, at the Moon to calculate the surface area needed. This is because the Moon is the farthest point the spacecraft will be traveling from the Sun and therefore the least efficient distance for the solar panels. A value of 1361.0 W/m2 can be found by looking at the Moon fact sheet released by NASA.
Using these values and the equation above, we find that around 13.12 m2 is needed to produce 5000W. Taking into account that the solar panels may not always be perpendicular to the incident rays of the Sun (this is the most efficient orientation and where we find the maximum value of 28% efficiency), we can calculate an extra 20% surface area to account for it. This is 15.84 m2, but for the sake of easier dimensions, I rounded to 16 m2.
Using FreeCAD, I was able to directly scale down these dimensions to create the solar panels in the pictures below.
After designing the solar panels, I started to model one of the options I am leaning toward for my spacecraft’s motor: the ArianeGroup 400N Apogee Motor. This motor is very similar to the Draco thruster I discussed in a previous blog: however, I was able to find a lot more information on the specifications and therefore model it more closely.
Next week, I plan to begin 3D printing the objects I have designed for my spacecraft using the equipment available in the Rocket Design Laboratory (RDL) of the Aerospace and Rocketry Club (ARC). Additionally, I was able to do some more work on the plane-change maneuver this week, but I do not feel confident enough yet to implement it into my code in MATLAB so I will continue to work on that in the coming days. Finally, as presentations are approaching, I have begun to work on mine so I can provide those of you who attend with an enthralling and educational experience!
Thank you to Dr. Farooq and Dr. Goodwin for guiding me through this project and to Mr. Joseph for the constant support and openness to help me learn these new concepts. Thank you to all of you for tuning in and to those of you who continue to interact with each post! Lastly, thank you to ARC for allowing me to use their state-of-the-art equipment to complete my project.
Ad Lunam!
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