More than a million objects, large enough to threaten operational spacecraft, are believed to reside in low Earth orbit (LEO) and this value is expected to increase significantly in the next decades. The resulting hazard to operational spacecraft could render certain LEO altitudes unusable, particularly above 500 km where atmospheric drag is ineffective for removing orbital debris. Certain objects, such as spent rocket stages and large defunct satellites, have the potential to create thousands of smaller bodies through impacts with other objects, some too small to track. Dr. J.C. Liou from the National Aeronautics and Space Administration (NASA) Orbital Debris Program Office prioritized the hazard posed by thousands of objects in orbit as a function of object mass and collision probability. The study concluded that the breakup of a just three of the 500 highest priority objects would lead to collisions with other objects and debris populations that would render certain altitudes too hazardous for satellite operations. NASA researchers determined that the removal of just five high-priority objects each year would likely prevent anticipated growth in the debris population.