We've known for a while that HEPI trips kick the suspensions prett badly. One of the things SamC found looking at earthquakes, is that during very large earthquakes, HEPI is often the first platform to trip. Hugh and I have used the post-vent time to minimize the differences between the free hanging HEPI positions and the target positions, by tweaking the springs. I used ETMY to test if this reduced the kick to the quad and it seems to be pretty good. The first plot shows the ETMY ISI T240s and the IPS cart locations during a trip before (blue traces on all plots) and after we reduced the offsets (red on all plots). Before offloading, the HEPI trip immediately tripped the ISI and kicked everything around quite a bit. After, the ISI actually stayed isolated until the T240s saturated, some 30+ seconds later, and even then the kick to the table wasn't that violent. The quad sees pretty much the same thing. Before, the suspension gets a pretty kick from the HEPI trip, but after the quad barely sees any motion at all.

This may not reflect what we see during an earthquake, but I don't see how this could make things worse. We'll need to monitor this for a little while because HEPI seems to be prone to drifting more that the ISIs, and we don't really know how much it drifts long term.