CubeSat Structures: Stressful Work
Designing a CubeSat’s structure is, in many ways, relatively easy because of ESA’s stringent requirements. Designing a CubeSat’s structure is also, in many ways, very difficult because of ESA’s stringent requirements.
ESA define exact lengths, heights and widths, as well as mass ranges for each variation of CubeSat to fly on its Fly Your Satellite scheme. STRATHcube is currently deciding between a 2U and a 3U CubeSat:
A 2U CubeSat must be 100mm wide, 100mm tall, 227mm long and no heavier than 2660g.
A 3U CubeSat must be 100mm wide, 100mm tall, 340mm long and no heavier than 4000g.
So our satellite will be around the size of a loaf of bread, and easy to pick up with one hand! If you’re interested in the hundreds of other specifications laid out by ESA, you can request them here.
Our 2U and 3U structures are basically identical, apart from their length. The structure features four deployment rails, which are attached to a mounting plate on each z-axis facing end, and another mounting plate in the middle for good measure. Throw on some very lightweight panels to hold components in and things start to look CubeSat-ish.
Here’s our stripped-back 3U structure:
Yes, it looks very empty and doesn’t even have any solar panels. The configuration of components and their deployment mechanisms is a topic for another day.
The CubeSat structure looks great, but it needs to be strong and light too. For that reason, we had a good think and have chosen to make the structure primarily from Aluminium 7075-T6. Aluminium alloys are used all the time in the world of aerospace because of their good strength:mass ratio.
Our 3U structure alone is about 270g and our 2U structure is about 175g! The components which will go inside, and the solar panels which will go outside of the CubeSat will raise the mass value close to the maximum mass allowed.
It’s all fine and well saying our CubeSat structure is strong, but we need to prove it. To do so, we’ve used ANSYS to perform Finite Element Analysis on a simplified structural model. Basically, we have applied some pretty big forces to our CubeSat and see how it acts. Of course, ESA has specified which tests to carry out:
Test 1- Loading: Make sure it can withstand the loads generated during deployment from the ISS
Test 2 – Loading: Make sure it can withstand the acceleration loads generated on a big rocket during launch from Earth
Test 3- Random Vibration: Make sure it can be shook A LOT without breaking.
All of our test results so far have been positive. During launch, deployment or any other possible load-bearing situation, our lovely CubeSat won’t yield, fail or break. Hopefully.
So to summarise, designing a CubeSat’s structure is easy; its’ just a case of making it very light and very strong while complying with what ESA say is acceptable.
