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CubeSat world: has anybody run a vibration test where you put accelerometers both on the dispenser (or shaker plate) and your spacecraft inside the dispenser?

For the SunCET CubeSat, we're trying to figure out if dispensers dampen or amplify the NASA GEVS vibrational profile as a function of frequency.

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Turns out that Steve Furger wrote a whole Masters thesis on exactly this topic! It was an excellent read and contained answers to my question and lots more.

In the Z-direction, where CubeSats get loaded in against a spring, they close the door and then turn some plungers/bolts to fully constrain the CubeSat in the Z-direction. This makes the CubeSat behave like it's basically a part of the dispenser. The dispenser tends to amplify the input load (the vibe table or the rocket), pretty much at all frequencies but most severely at its natural frequency (i.e., where there's max resonance). So CubeSats tend to see much more vibrational load in the Z-axis than is being input from the outside (vibe table or rocket). Z-axis

In the X/Y directions, the story is different because the CubeSat can rattle around inside. This tends to have a dampening effect at all but the very lowest frequencies. But it is also a function of how tight those Z-axis bolts/plungers are cranked down -- if torqued above the standard practice, this creates so much friction with the bolt that the X/Y is effectively fixed as well and you again get amplification all over the place. If the bolts are not constraining the Z, then the X/Y (and Z for that matter) enter the "isolated" regime where the resultant acceleration load is significantly lower than the input at all but the lowest frequencies. Comparison of tight bolts versus loose

When torqued to the standard practice, you get a bit of an inbetween behavior that evolves over time. The first few seconds when the table (or rocket, presumably) is just ramping up, the CubeSat load looks like it's fixed. But after a few seconds, the friction from the bolts lessens somewhat (probably what's happening is there's enough energy to overcome the coefficient of static friction and you're then left with the lesser coefficient of kinetic friction) and by 20 seconds in, the X/Y direction is looking pretty isolated, i.e., significantly lower vibrational energy at all but the lowest frequencies. X-axis response with standard bolt torque

Really grateful for this excellent work!

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    $\begingroup$ This is a great answer! $\endgroup$ Jul 27, 2023 at 16:19

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