Determination of micrometeoroid/ orbital debris (MMOD) impact on orbiting spacecraft currently requires visual inspection. For human-rated spacecraft such as the International Space Station (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 ascertain potential damage.
NASA’s Langley Research Center has developed a strain-sensing system that can be affixed to a spacecraft’s MMOD shielding layer or structure. This technology detects the occurrence, time, location, and severity of a MMOD strike on the shield, allowing for detection and location of potentially harmful MMOD strikes on both crewed and unmanned spacecraft. This knowledge is important because prolonged exposure to the on-orbit MMOD environment increases risk to vehicles including commercial crew vehicles expected to visit and remain for considerable periods of time at ISS.
Multiple strain sensors encoded into one or more optical fibers are affixed to a MMOD shield or structure. The optical fiber(s) is/are connected to a data collection device that records strain data at a frequency sufficient to resolve MMOD impact events. Strain data are processed and presented on a computer display. MMOD impact imparts a transient shock loading to a structure that is manifested as transient strain as the shockwave moves through the structure. MMOD impacts are determined from the time signature of both measured strain from multiple sensors on the optical fiber(s) as well as strain resulting from plastic strain induced in the MMOD shield and structure as a consequence of the MMOD impact (for materials exhibiting plastic strain). The array of strain sensors, encoded into one or more optical fibers using Fiber Bragg Grating (FBG) technology, records time-varying strain to identify that a strike has occurred and at what time it occurred. Strike location information can be inferred from the residual plastic strain recorded by the multitude of strain sensors in the fiber(s). One or more optical fibers may be used to provide optimal coverage of the area of interest, and/or to ensure a sufficient number of strain measurements are provided to accurately characterize the nature of the impact.