LArID: Concept of a large area low resource integrated impact detector

In-situ impact detectors were among the first sensors flown onboard early satellites. Acoustic sensors and penetration detectors helped showing that the micrometeoroid impact threat was not as strong as initially feared at the beginning of the space age. Since the 1970ies, scientific detectors, based on impact charge detection and PVDF depolarization, are used to sample micron-sized interplanetary dust. Derived detector concepts were developed with the growing space debris problem. However, until now the results of these developments are limited. Thus, a gap of observational space debris data exists for millimetre-sized particles below the sensitivity limit of ground-based tracking with radar and telescopes in the centimetre range. A systematic approach for data collection of > 0.1 mm space debris, i.e. particles that may have significant effects on spacecraft when impacting, requires an in-situ detector that is resource-effective and adaptable for various space missions. A large detection area is needed to obtain statistically meaningful samples for supporting the modelling of the orbital environment. In this paper, we present the concept of LArID, a large area low resource integrated impact detector that is currently being developed by Fraunhofer EMI for ESA. The focus here is on the trade-off between detection techniques for measuring impact effects and the derived instrument concept for the ongoing breadboard development phase. The combination of different sensing principles is considered a key for both noise immunity and discrimination of impact parameters like particle size, velocity and angle. Three sensor techniques are combined for LArID: piezoelectric sensors, resistive grids and impact flash photodetectors. Piezoelectric vibration sensors are attached to a thin trigger membrane, the outermost layer of the detector. Triangulation of signal arrival times allows to trace back the impact location of perforating impactors. The second layer uses resistive grids for determining impactor size and location. Impact velocity and trajectory are derived from time-of-flight measurement, backed by photodiodes that are integrated between the two detection layers. The layer and sensors are integrated with the read-out electronics to a LArID detection base unit. Larger detection areas are realized through combining several base units. While the modular LArID detector is a stand-alone system, its data output can be combined with attitude knowledge data from the spacecraft to study impactor mass for larger particles.