NASA's main source of data for debris in the size range of 1 to 30 cm is the Haystack radar. The Haystack radar, operated by MIT Lincoln Laboratory, has been collecting orbital debris data for NASA since 1990 under an agreement with the U.S. Department of Defense. Haystack statistically samples the debris population by "staring" at selected pointing angles and detecting debris that fly through its field-of-view. The data are used to characterize the debris population by size, altitude, and inclination. From these measurements, scientists have concluded that there are over 500,000 debris fragments in orbit with sizes down to one centimeter. NASA also collects data from the Haystack Auxiliary Radar (HAX) located next to the main Haystack antenna. Although HAX is less sensitive than Haystack, it operates at a different wavelength (1.8 cm for HAX versus 3 cm for Haystack) and has a wider field-of-view.