The NASA Orbital Debris Program Office has been supporting the development of particle impact sensors since 2002. The main objective is to eventually conduct in situ measurements to better characterize the small (millimeter or smaller) micrometeoroid and orbital debris populations in the near-Earth environment. In addition, the Program Office also supports similar instrument development to define the micrometeoroid and secondary ejecta environment for future lunar exploration activities.The instruments include impact acoustic sensors, resistive grid sensors, fiber optic displacement sensors, impact ionization sensors, and laser curtain sensors. They rely on different mechanisms and principles to measure particle flux. A system consisting of these different sensors will provide data that are complementary to each other, and will provide a better description of the physical and dynamical properties of the particles in the environment. Several systems being considered by the Program Office and their intended mission objectives are summarized in this paper.