March 14, 2011 Leave a comment
After the successful launch and recovery of the SQUID experiment there is still a huge amount of things to do. The experiment recorded a lot of data from the different sensors (gyros, accelerometers, magnetometers etc.) and now we have to analyze the data in order to understand how the system behaved. One of the interesting sensors onboard the FFU were the gyros, that give the angular rate on the three axis. During the deployment of the wire booms, due to the increase of the moment of inertia of the FFU, the spin rate (or angular rate along the z axis) would decrease, so by looking at the recorded data from the gyros we could have a good idea of how the wire booms have behaved, which is specially important as the FFU was lost from the field of view of the camera very soon.
From the gyro data (see figure) one can clearly see the slow down of the spin rate just after ejection along the z axis, while the angular rate along the x and y axis is very close to zero, meaning that the ejection was almost perfect. What one can see on the slow down period is that there is a sudden change of the slope of the spin rate curve. By comparing this curve to a dynamical model of the system we could see that the reason for this seems to be that one of the wire booms failed after deploying around 30 cm. This was of course not good, but it didnt have a big impact on the overall performance of the FFU as it keept on spinning stably.
At the end of the slow down sequence one can see that the curve becomes flat, which means that the other three of the spheres stopped deploying (as it was expected) and the FFU kept on spinning with the wire booms deployed. After this, the retraction sequence starts, and again one can see a slight slope change of the curve, which means that a second SCALE system failed during retraction. The objective of retracting the wire booms was only for preventing them to entangle with the parachute, but luckily this did not happen and therefore it was not a major failure on the system.
One can also see another interesting event on the plot. At the end of the retraction phase, the spin rate of the FFU should be very similar to the initial one, but as one can see this did not happen, as it seems that the spin rate is decreasing (as expected due to the decrease of the moment of inertia of the FFU), but then suddenly it starts spinning up again, and becomes unstable (one can see that the data from the gyros on the x and y axis starts becoming messy). It seems that this was because the FFU started “feeling” the atmosphere before expected. One of the curves is the dynamic pressure, which was derived from the data recorded by the Rexus service module, and as one can see, at the moment on which the FFU becomes unstable, the dynamic pressure starts increasing, meaning that aerodynamic effects start being noticeable.
There is still a huge amount of data to analyze carefully, so this task will keep us busy the next months. We will keep you informed about our progress!