Processing and Analysis of ISS Accelerometer Data

In an effort to better understand the properties and dynamics of planetary regolith, the Strata experiment was flown on the ISS from 2016-2017. Three-axis accelerometer data was collected by an ISS SAMS (Space Acceleration Measurements System) measurement unit attached to the front face of the Strata experiment, providing high frequency and time-resolution acceleration profile data at the exact location of the experiment, which is important because of the variations in acceleration and gravitational profiles that can occur across the body of the ISS (Jules et al., 2004). We use this data to pull out acceleration profiles as a function of time, frequency, and magnitude to look for forcing functions relevant to the observed granular behavior in the experiment. The raw data is analyzed in one-hour chunks (each with roughly 1.8 million data points), and is initially filtered to eliminate both low frequency and suspected electronic noise. The filtered data is then analyzed to identify higher magnitude acceleration events and characterize features including the timing and duration of the event, highest magnitude acceleration, and peak frequencies. We will describe trends, i.e., broad spectrum high magnitude events vs. longer-term forcing at specific frequencies, that might produce convective motion as observed in other granular materials experiments. For a preliminary analysis, the identified events are compared against another set of data that tracks the bulk motion of grains in the experiment tubes. We expect that different types of events will produce distinct signatures in the observed particle motion in the experiment tubes. These parameters can also be compared to existing numerical models.