DRG ARRIVAL, THE AIRCREW OF A GATES LEAR JET 35A, N873LP, CANCELED THEIR IFR CLEARANCE & CONTACTED THE AUBURN UNICOM, THEN ENTERED THE TRAFFIC PATTERN TO LAND ON RWY 18. THE UNICOM OPERATOR RPRTD THAT THE LEAR JET CREW HAD RPRTD THEIR POSITION ON EACH PORTION OF THE TRAFFIC PATTERN. AT APRX THE SAME TIME, THE PLT OF AN UNREGISTERED, EXPERIMENTAL, CHALLENGER II WAS IN THE TRAFFIC PATTERN FOR RWY 10. THE 2 RWYS INTERSECTED AT THEIR APCH ENDS. JUST BEFORE LANDING, THE 2 ACFT COLLIDED AS THEY WERE CROSSING OVR THE INTERSECTION & CRASHED ON THE ARPT. THE CHALLENGER (A 2 PLACE VERSION OF AN ULTRALIGHT VEHICLE) WAS NOT EQUIPPED WITH A RADIO & THE UNICOM OPERATOR WAS UNAWARE OF ITS PRESENCE IN THE TRAFFICPATTERN. THE LEAR JET PLT STATED THAT NEITHER HE NOR HIS COPLT HAD SEEN ANY OTHER TRAFFIC AT THE ARPT. NO INDICATION WAS FOUND THAT EITHER CREW HAD TAKEN EVASIVE ACTION. AN EXAM OF THE CRASH SITE REVEALED EVIDENCE THAT THE COLLISION HAD OCCURRED APRX 50 FT ABV THE INTERSECTION.