Micrometeoroid/Orbital Debris (MMOD) Impact Detection and Location Using Fiber Optic Bragg Grating Sensing Technology

Abstract

Spacecraft in low earth orbit (LEO) experience a variety of hazards including exposure to micrometeoroids and orbital debris (MMOD). Average impact speeds for orbital debris on spacecraft in LEO are 9 to 10km/s, and 20km/s for micrometeoroids. Due to their high speeds, MMOD can cause considerable impact damage to sensitive spacecraft surfaces such as windows, structural elements, electronic boxes, solar arrays, radiators, thermal protection system (TPS) materials covering crew/cargo return vehicles, as well as crew modules. Prolonged exposure to the on-orbit MMOD environment can potentially compromise the TPS covering return vehicles such as the future crewed vehicles expected to visit and remain for a half-year or longer at the International Space Station (ISS). However, determination of MMOD impact damage to the TPS on crew/cargo return vehicles, or damage to other orbiting spacecraft currently requires visual inspection. For human-rated spacecraft such as the ISS and, previously, the Space Shuttle Orbiter, this has required crew time as well as vehicle assets to identify damage due to MMOD strikes. For unmanned spacecraft, there are no human assets present to conduct detailed surveys to identify potential damage. While the practice of visual inspection may successfully indicate the location of a debris strike, it does not currently allow precise determination of exactly when the debris strike occurred. It is only possible to determine that a debris strike has occurred between two successive inspection events unless damage to other components can allow inference that a debris strike occurred at a specified time. Initial development testing of a novel MMOD sensing concept amenable for potential implementation in a structural health monitoring system is discussed. Using fiber Bragg grating (FBG) sensing technology, a test article representative of a spacecraft MMOD shield layer or spacecraft structure was subjected to hypervelocity impact testing. The FBG array successfully detected that an impact had occurred, when it occurred and where it occurred on the structure. Detection of both the impact wave and the residual strain in the structure can be used to infer the location of the impact. The potential application of this technology to spacecraft is discussed.