The CONTOUR (COmet Nucleus TOUR) Spacecraft was one of NASA's Discovery missions, and was launched on July 3rd 2002. It's mission was to perform 2 close flybys of Comets Encke and Schwassmann-Wachmann-3, and a possible 3rd flyby of another Comet that it was hoped would be discovered during the mission.
On 15th August 2002, at 8:49UT, it was scheduled to fire it's main engine to take it out of Earth orbit, and into a heliocentric orbit. However, after this firing, all attempts at contact with the spacecraft failed. Telescope surveys were carried out in the hope of finding what had happened to the craft, and 3 objects were found near the expected location of CONTOUR.
This led investigators to the conclustion that the firing did take place, after which there was an explosion or some other sort of major malfuncion.
In the .xyz file, CONTOUR-A is the brightest object of the 3, CONTOUR-B is the second brightest, and CONTOUR-C is the dimmest.