WE REQUEST A 60 KS TARGET-OF-OPPORTUNITY OBSERVATION OF THE NEXT OPTICALLY BRIGHT OR FERMI-DETECTED NOVA OUTBURST. THE DETECTION OF GAMMA-RAYS FROM NOVAE DEMONSTRATES THAT THEY ARE CAPABLE OF ACCELERATING PARTICLES TO HIGH ENERGIES. HOWEVER THE SITE OF PARTICLE ACCELERATION AND THE MECHANISM RESPONSIBLE FOR THE GAMMA-RAY EMISSION REMAINS POORLY UNDERSTOOD. X-RAY OBSERVATIONS AT E>20 KEV CAN PROBE THE LOW-ENERGY TAIL OF THE NON-THERMAL EMISSION THAT IS DETECTED BY THEFERMI-LAT AND PROVIDE IMPORTANT CONSTRAINTS ON THE PHYSICAL CONDITIONS IN THE PARTICLE-ACCELERATING SHOCK. NUSTAR WITH ITS UNPRECEDENTED SENSITIVITY ABOVE 10 KEV CAN THEREFORE PROVIDE A UNIQUE PROBE OF THE SHOCKS TAKING PLACE IN NOVA OUTBURSTS AT EARLY TIMES. WE WILL TRIGGER ON A GAMMA-RAY BRIGHT NOVA (AS DETERMINED BY THE FERMI SATELLITE) AND CARRY OUT X-RAY OBSERVATIONS WITHIN 48 HOURS OF THE REQUEST. BY CONSTRAINING THE RATIO OF X-RAY TO GAMMA-RAY LUMINOSITY WE CAN DETERMINE THE PARTICLE ACCELERATION MECHANISM AT PLAY IN NOVAE. UNDERSTANDING THE ORIGIN OF THE HIGHEST ENERGY PARTICLES IN THE UNIVERSE IS A KEY ROLE OF SEVERAL NASA PROGRAMS. NOVAE OFFER A NOVEL ENVIRONMENT (SLOW SHOCKS HIGH PARTICLE AND RADIATION DENSITY) IN WHICH TO STUDY THE PHYSICS OF PARTICLE ACCELERATION.