Environmental Testing Campaign: Vibration Days 4-5

Whilst UoBSat’s vibration campaign ended 2 weeks ago now, we have been busy going over some of the footage that was taken of our tests and we are so excited to be able to share this with you! This one was worth the wait!

Days 4 and 5 of the vibration campaign saw the exciting part of the week, some shaking! 3 types of tests were conducted, these were a sine burst, a sine sweep and a resonance search. These were repeated for each of the X, Y and Z axes and the aim was for them to cover all of the possible vibrational profiles that Pathfinder could expect to undergo in launch. The levels that we used were a “worst case” scenario that covered the characteristics of launch vehicles across the globe so that we would be covered for any rocket that we choose to fly on.

The axes layout for Pathfinder can be seen below in Figure 1.

Figure 1: Pathfinder’s coordinate frame

The first axis that we tested was the X axis and the first test that we ran was a sine burst test. This is a destructive test that sweeps a wide range of frequencies in a short period of time. You can see the shaker visibly ramping up different levels until it reaches its maximum level of 23.44g. For context, most people can only withstand “five to 10 seconds at 4 to 5 g vertically” without the assistance of g-suits before the “loss of consciousness” [source]. Sine burst tests are designed to evaluate the satellite’s ability to handle sudden changes in frequency or amplitude without malfunctioning or becoming damaged.

Video 1: X-Axis Sine Burst Test

After the test has run, the team then carry out two tasks to determine if there has been any damage to the payload, the first is an inspection. Visible torches are used to carefully inspect Pathfinder for any external signs that something has been damaged or loosened. Particular attention is paid to looking out for cracks in panels, bolts that have loosened and Surface Mount Device (SMD) components on our electronics boards that have dislodged. We can tell if bolts have loosened by looking at the witness marks that we place on them to check if they are still aligned, examples of these can be seen in Figure 2.

Figure 2: An example of the witness marks on Pathfinder’s bolts whilst the team carries out their inspections behind

The second thing that we do to check for damage is to run a resonance search. Resonance searches are an important tool used in satellite testing to check for any shifts that may occur in the satellite’s components during operation. This is because when an object is subjected to a force or vibration that matches its natural frequency of vibration, it will begin to resonate, which can cause it to vibrate more. This is similar to how a tuning fork will vibrate when it is struck at its natural frequency. We can then detect these increased vibrations with our test accelerometers. A resonance search is a low-level, 0.5g, sine sweep from 5-200 Hz. This means that we can pick up all of our mode shapes between 5 and 2000 Hz. If the frequency of our mode shapes change before and after a test, then this is an indication that something has shifted or broken.

The next test that we run is a high-level sine sweep. The loads for this were determined from a range of possible launchers and deployers. The considered launchers and deployers were; Arianespace Vega, Small Spacecraft Mission Service VEGA-C, Arianespace V, SpaceX Flacon 9, ABL RS1, Skyrora XL, ISIPOD CubeSat Deployer, NanoRacks CubeSat Deployer and Rocket Labs Satellite Dispenser. A high-level sine sweep is different from a sine burst test because it is a continuous wave that is swept across a range of frequencies over a longer period of time. In contrast, a sine burst test is a short burst of sine waves at various frequencies, typically swept across a wide range of frequencies in a short period of time.

Video 2: X-Axis High Level Sine Test

The final test that we ran was a random vibration test. These simulate various sources, such as the rocket engines, other equipment onboard the rocket and environmental aspects from the atmosphere. Compared to a high-level sine sweep or sine burst test, the random vibration test is more realistic because it simulates the actual vibration environment that the satellite will experience. The vibrations used in this test are not sinusoidal or periodic, meaning they do not repeat in a regular pattern over time. Instead, they are made up of a wide range of frequencies that are randomly distributed and this is why the test sounds like white noise. An example of this can be seen in video 3.

Video 3: X-Axis Random Vibration Test

After the inspections and resonance searches were carried out and the team were happy, they then repeated the tests along the Y and Z axes. Below one of the Y-axis tests can be seen in video 4, the sine burst.

Video 4: Y-Axis Sine Burst Test

One of our Z-axis tests can be seen in video 5:

Video 5: Z-Axis Sine Burst Test

After all of the tests were completed, the team then carried out a full functional test to confirm that the electronics still worked and a post-test review. After this was all carried out, they then placed Pathfinder into the bakeout oven – ready for the thermal campaign!