  Meteoroids pose one of the largest risks to spacecraft outside of low Earth
orbit. In order to correctly predict the rate at which meteoroids impact and
damage spacecraft, environment models must describe the mass, directionality,
velocity, and density distributions of meteoroids. NASA's Meteoroid Engineering
Model (MEM) is one such model; MEM 3 is an updated version of the code that
better captures the correlation between directionality and velocity and
incorporates a bulk density distribution. This paper describes MEM 3 and
compares its predictions with the rate of large particle impacts seen on the
Long Duration Exposure Facility (LDEF) and the Pegasus II and III satellites.
