THIS PROPOSAL IS REQUESTING SUPPORT FOR THE OPERATIONS AND MAINTENANCE OF THE ARECIBO PLANETARY RADAR PROGRAM FOR A FIVE-YEAR PERIOD FROM JANUARY 2019 TO DECEMBER 2023. THE ARECIBO PLANETARY RADAR SYSTEM IS ONE OF THE WORLDS MOST POWERFUL INSTRUMENTS FOR POST-DISCOVERY ORBITAL REFINEMENT AND PHYSICAL CHARACTERIZATION OF NEAR-EARTH OBJECTS (NEOS). WE WILL USE THE ARECIBO PLANETARY RADAR SYSTEM TO CHARACTERIZE THE NEO POPULATION WITH OBSERVATIONAL PRIORITY GIVEN TO POTENTIALLY HAZARDOUS OBJECTS AND POTENTIAL SPACEFLIGHT DESTINATIONS. THE REQUESTED FUNDING WILL BE USED FOR PROGRAM COSTS OPERATIONAL MAINTENANCE AND UPGRADE COSTS FOR THE RADAR SYSTEM INCLUDING THE 2.38-GHZ TRANSMITTER AND SOME SUPPORT AND OPERATIONAL COSTS FOR THE ARECIBO OBSERVATORY THAT ARE DIRECTLY RELATED TO THE PLANETARY RADAR PROGRAM. WE EXPECT TO DEVOTE 700-800 HOURS PER YEAR OF TELESCOPE TIME TO THE PLANETARY RADAR PROGRAM WITH APPROXIMATELY 600-700 HOURS ALLOCATED TO STUDY 100 NEOS PER YEAR AND THE REMAINDER TO OBSERVATIONS OF OTHER SOLAR SYSTEM BODIES. WE WILL OBSERVE A RELATIVELY UNBIASED SAMPLE OF NEOS OBTAINING PRECISE ASTROMETRY AND BASIC CHARACTERIZATIONS FOR ALL DETECTIONS. ARECIBO RADAR ASTROMETRY AND CHARACTERIZATIONS ARE CRITICAL FOR IDENTIFYING OBJECTS THAT ARE TRULY HAZARDOUS TO EARTH AND FOR THE PLANNING OF MITIGATION EFFORTS. THEY WILL ALSO INFORM FUTURE MISSION PLANNING BY CONSTRAINING THE SIZE SHAPE MASS SPIN STATE COMPOSITION BINARITY TRAJECTORY AND GRAVITATIONAL AND SURFACE ENVIRONMENTS OF NEOS. THESE CHARACTERISTICS CAN BE DETERMINED BY RADAR IN THE CASE OF ANY OBSERVABLE ASTEROID OR COMET SUBJECT TO SUFFICIENT SIGNAL STRENGTH. RADAR CAMPAIGNS FOR NEOS THAT MAKE CLOSE APPROACHES TO EARTH (WITHIN ~0.05 AU) ARE ROUGHLY EQUIVALENT IN THEIR SCIENCE CONTENT TO SPACECRAFT FLYBY MISSIONS BUT COST ORDERS OF MAGNITUDE LESS AND MORE EFFICIENTLY PROBE THE OVERALL POPULATION. CHARACTERIZATIONS OF THE LARGE NUMBER OF OBJECTS PROPOSED HERE CANNOT BE OBTAINED BY OTHER CURRENT GROUND-BASED TECHNIQUES. BEYOND NEOS THE PROPOSED PROGRAM WILL SUPPORT OBSERVATIONS OF ALL SOLID BODIES FROM MERCURY TO THE GALILEAN SATELLITES OF JUPITER.