The NASA Orbital Debris Program Office (ODPO) is a Delegated Program in the NASA HQ Office of Safety and Mission Assurance (OSMA). NASA Procedural Requirements for Orbital Debris Mitigation, NPR 8715.6E, establishes the roles and responsibilities of the ODPO, which include (1) collection of orbital debris measurement data in situ and via radars, telescopes, and laboratory experiments, (2) development of orbital debris models and mission support tools, (3) evaluation and documentation of NASA mission compliance with orbital debris mitigation requirements, and (4) contributions to orbital debris mitigation policy and best practices within the U.S. and with the international community. A high priority of the ODPO is to characterize risk from small, millimeter-sized orbital debris in low Earth orbit (LEO). Millimeter-sized orbital debris represents the highest mission-ending risk to spacecraft operating at altitudes from 600 to 1000 km, where hundreds of spacecraft operate, but there is a lack of direct measurement data on such small debris in the environment. Direct measurement data of the millimeter-sized orbital debris is needed to support the development and implementation of cost-effective protective measures for the safe operations of future space missions. The need to address this critical data gap in LEO has also been recognized by the 2018 U.S. National Space Traffic Management Policy, the 2021 U.S. National Orbital Debris Research and Development Plan, and the 2022 U.S. National Orbital Debris Implementation Plan. The ODPO has explored various particle detection technologies for in situ measurements of small orbital debris since the early 2020s. The outcome of the efforts is the Multi-layer Acoustic & Conductive-grid Sensor (MACS), a collaboration with JAXA. MACS combines several simple detection principles to maximize information that can be extracted from each debris detection for data to support meaningful improvements to the definition of the small orbital debris populations in LEO. MACS is a four-layer sensing system. The first layer is JAXA’s conductive-grid thin film Space Debris Monitor (SDM), the second and the third layers are identical Kapton thin films, and the last layer is a low-density syntactic foam panel. Multiple acoustic sensors are attached to each layer to measure impact time and location. The acoustic sensors on the foam panel are also used to measure impact kinetic energy. The combination of data from all four layers provides information on the size, mass, density, impact time, speed, and direction of each impacting orbital debris particle. The ODPO has established several agency agreements with JAXA to develop, test, and optimize the design of MACS since 2017. An opportunity for a technology demonstration of MACS on a future HTV-X flight was identified in 2022 and confirmed in 2023. The MACS HTV-X3 technology demonstration missionis sponsored by OSMA, NASA Science Mission Directorate, and the International Space Station (ISS) Program. The mission profile of HTV-X3’s technology demonstration phase, after it leaves the ISS, has not been finalized but HTV-X3 can potentially reach a maximum altitude of 500 km with a duration up to 18 months. The HTV-X3 demonstration provides a great opportunity to fully mature the MACS technology readiness level and demonstrate its small debris detection capability, which will pave the way for the ODPO to pursue a mission to address the critical millimeter-sized orbital debris data gap above 600 km altitude in the near future.
J.‐C. Liou (Fri,) studied this question.