THE KNOWLEDGE OF THE ORIGIN OF THE STARTING MATERIAL OF OUR SOLAR SYSTEM IS AN ISSUE OF FUNDAMENTAL INTEREST IN PLANETARY SCIENCE. AFTER THE DISCOVERY OF PRESOLAR GRAINS (PSG) IN 1987 IT WAS POSSIBLE FOR THE FIRST TIME TO STUDY SOLID SAMPLES OF STARS IN THE LABORATORY. THIS PROVIDED A UNIQUE PERSPECTIVE ON THE ORIGIN AND COMPOSITION OF THE MATERIAL FROM WHICH THE SOLAR SYSTEM FORMED. WE PROPOSE TO USE ATOM-PROBE TOMOGRAPHY (APT) TO STUDY THE COMPOSITIONS OF PRESOLAR NANOGRAINS THAT ARE TOO SMALL TO STUDY WITH NANOSIMS. THE GOAL IS TO BETTER UNDERSTAND THE ORIGINS OF THESE UNDERSTUDIED SAMPLES, INFORMATION NOT OBTAINABLE OTHERWISE (TASK 1). WE ALSO PROPOSE TO EXTEND THE SMALL NUMBER OF KNOWN PRESOLAR EXPOSURE AGES OF LARGE PRESOLAR SIC GRAINS. OUR APPROACH IS TO USE HE AND NE, AND LI ISOTOPIC ANALYSIS IN CONJUNCTION WITH IMPROVED NUCLEAR RECOIL CORRECTIONS AND PRODUCTION RATES FOR COSMOGENIC NUCLIDES TO STUDY THE PRESOLAR CHRONOLOGY OF THE SOLAR SYSTEM S STARTING MATERIAL (TASK 2). TASK 1: MUCH FRUITFUL EFFORT WAS DEVOTED TO THE ANALYSES OF PSG IN THE UM-SIZE RANGE TO DETERMINE STELLAR SOURCES AND TO GAIN UNPRECEDENTED INSIGHT INTO PROCESSES OPERATING WITHIN THOSE STARS. WHILE PSG IN THIS SIZE RANGE ARE READILY ACCESSIBLE TO ION PROBES, THEY ARE NOT NECESSARILY REPRESENTATIVE OF SMALLER PSG. THE SMALLEST SIZE FRACTION OF PRESOLAR CR-RICH SPINELS WAS DISCOVERED TO CARRY THE LARGEST ISOTOPIC ANOMALIES. THE SMALL FRACTION OF PRESOLAR NANODIAMONDS HAS NOT YET BEEN QUANTIFIED. EVEN WITH THE LATEST GENERATION OF THE HIGHEST RESOLUTION ION PROBE, THE NANOSIMS, SAMPLES SMALLER THAN 50-100 NM ARE DIFFICULT TO ANALYZE DUE TO LIMITATIONS IN SPATIAL RESOLUTION AND SENSITIVITY. TO ADDRESS THIS ISSUE WE DEVELOPED METHODS TO APPLY APT TO EXTRATERRESTRIAL SAMPLES. THE NEAR ATOMIC-RESOLUTION AND HIGH SENSITIVITY MAKES APT THE IDEAL TECHNIQUE TO ANALYZE THE ELEMENTAL AND ISOTOPIC COMPOSITIONS OF SAMPLES THAT ARE TOO SMALL FOR THE NANOSIMS (<50 NM). WE SUCCESSFULLY PERFORMED APT OF METEORITIC NANODIAMONDS, A LUNAR DUST GRAIN, AN IRON METEORITE, AND QUANTIFIED INSTRUMENTAL BIAS. WE CAN NOW RELIABLY ANALYZE WITH APT SMALL SAMPLES, INCL. PRESOLAR NANOGRAINS THE GOAL OF OUR PROPOSED INVESTIGATION (TASK 1). COMPARED TO NANOSIMS THE TOMOGRAPHIC APPROACH OF APT PROVIDES AN UNDILUTED SAMPLE ANALYSIS WITHOUT CONTRIBUTIONS FROM THE UNDERLYING SUBSTRATE OR SURROUNDING MATRIX. THE OBJECTIVE OF THIS TASK IS TO PERFORM APT ON PRESOLAR NANO-OXIDES AND NANODIAMONDS TO OBTAIN ELEMENTAL AND ISOTOPE DATA TO PROVIDE NEW INSIGHTS INTO STELLAR ORIGINS, FORMATION PROCESSES, AND POSSIBLY ALTERATION IN THE EARLY SOLAR SYSTEM. TASK 2: THE KNOWLEDGE OF THE TIME SPAN BETWEEN THE FORMATION OF PSG AND THEIR INCORPORATION INTO FORMING PLANETESIMALS IS STILL LIMITED. WE HAVE SUCCESSFULLY MEASURED COSMOGENIC HE AND NE IN LARGE PRESOLAR SIC GRAINS, APPLIED NUCLEAR RECOIL LOSS CORRECTIONS, AND CALCULATED PRESOLAR COSMIC-RAY EXPOSURE AGES USING PRESOLAR PRODUCTION RATES OF COSMOGENIC NUCLIDES. SO FAR, A TOTAL OF ONLY 40 PSG HAVE BEEN DATED. MOST GRAINS HAD PRESOLAR AGES<300 MA AND ONLY A FEW HAD HIGHER AGES UP TO ~2 GA. THE KNOWLEDGE OF THE PRODUCTION RATES IN THE INTERSTELLAR MEDIUM IS ONE OF THE MOST CRITICAL ELEMENTS IN THE CALCULATION OF PRESOLAR EXPOSURE AGES. SINCE OUR LAST PUBLICATION MORE REALISTIC PRODUCTION RATES HAVE BEEN DEVELOPED. FOR THE FIRST TIME, THESE RATES USE THE GALACTIC COSMIC-RAY SPECTRUM AS OBSERVED OUTSIDE THE HELIOSPHERE BY VOYAGER. WE PROPOSE TO MEASURE PRESOLAR COSMOGENIC NUCLIDES OF HE, NE AND LI IN LARGE PRESOLAR SIC. WE WILL USE OUR NEW DATA TO TEST THE HYPOTHESIS THAT THE DOMINANCE OF YOUNG PRESOLAR AGES IS A CONSEQUENCE OF A STARBURST EVENT AND TO EXPLORE THE PRESOLAR CHRONOLOGY OF THE STARTING MATERIAL OF OUR SOLAR SYSTEM. WHILE OUR METHOD HAS LARGE UNCERTAINTIES COMPARED TO RADIOMETRIC CHRONOMETERS, IT IS CURRENTLY THE ONLY METHOD THAT PROVIDES AGES OF PSG, THE OLDEST MATERIAL AVAILABLE FOR STUDY IN THE SOLAR SYSTEM.