ATOMIC HYDROGEN IS USUALLY THE MOST ABUNDANT SPECIES IN THE ATMOSPHERE (OR COMA) OF A COMET AND IS PRODUCED IN A PHOTODISSOCIATION CHAIN ORIGINATING WITH WATER WHICH IS THE MOST ABUNDANT VOLATILE SPECIES IN A COMET S NUCLEUS. MEASUREMENTS OF THE ABUNDANCE AND DISTRIBUTION OF H WHEN APPROPRIATELY MODELED PROVIDE A RELIABLE TIME HISTORY OF THE WATER PRODUCTION RATE IN COMETS. VIRTUALLY ALL COMPOSITIONAL INFORMATION IS COMPARED TO WATER MAKING WATER THE MOST IMPORTANT FOR OBTAINING ACCURATE PRODUCTION RATES. VARIATIONS OF PRODUCTION RATE WITH TIME AND WITH HELIOCENTRIC DISTANCE IN PARTICULAR PROVIDE INFORMATION ABOUT THE COMPOSITION AND STRUCTURE OF THE NUCLEUS AND THE OVERALL ACTIVITY LEVEL OF THE COMET OVER ITS ORBIT. THE OBJECTIVES OF THIS PROGRAM ARE TO OBSERVE A NUMBER OF COMETS WITH THE SWAN INSTRUMENT ON THE SOHO SPACECRAFT AND CALCULATE WATER PRODUCTION RATES FROM THESE OBSERVATIONS. WE HAVE DEVELOPED MODEL ANALYSIS TOOLS FOR EXTRACTING DETAILED DAILY-AVERAGES OF WATER PRODUCTION RATES FROM SEQUENCES OF IMAGES OF THE H LYMAN-ALPHA COMA. THE SWAN INSTRUMENT CONTINUES TO OPERATE AND WE OBSERVE NEW COMETS. WE WILL DETERMINE BOTH SINGLE-IMAGE WATER PRODUCTION RATES OF ALL COMETS AND EXTRACT DAILY-AVERAGE WATER PRODUCTION RATES FROM SEQUENCES OF IMAGES FOR MODERATELY ACTIVE COMETS USING OUR TIME-RESOLVED MODEL WHEN POSSIBLE. THE OBSERVING PROGRAM HAS PROVIDED REMOTE TEMPORAL CONTEXT FOR PAST CURRENT AND LIKELY FUTURE NASA SPACECRAFT MISSIONS E.G. OUR PAPERS ON FOUR PREVIOUS SPACECRAFT TARGET COMETS (COMBI ET AL. 2011 AJ 141:128) THREE PREVIOUS APPARITIONS OF THE ROSETTA TARGET COMET 67P/ CHURYUMOV-GERASIMENKO (BERTAUX ET AL. 2014 ICARUS 91 14) AND THE EPOXI MISSION TARGET 103P/HARTLEY 2 (COMBI ET AL 2011B APJ LETT. 734:L6). RECENTLY WE HAVE ARCHIVED THE FULL SET OF WATER PRODUCTION RATES DETERMINED FROM 65 APPARITIONS OF 50 COMETS OBSERVED BY SWAN FROM 1996 TO 2012 IN THE SMALL BODIES NODE OF THE PDS (COMBI M. SOHO SWAN DERIVED COMETARY WATER PRODUCTION RATES COLLECTION URN:NASA:PDS:SOHO:SWAN_DERIVED::1.0 L. FEAGA (ED) NASA PLANETARY DATA SYSTEM 2017). THIS PROGRAM HAS SUPPORTED OTHER GROUND-BASED AND SPACECRAFT-BASED OBSERVING PROGRAMS BY PROVIDING IMPORTANT TIMELY OBSERVATIONS OF TARGETS OF OPPORTUNITY. OUR SPECIFIC SCIENCE GOALS ARE: (1) TO OBSERVE AND ANALYZE OBSERVATIONS OF PERIODIC AND BRIGHT TARGET OF OPPORTUNITY COMETS DURING THE NEXT PROJECT PERIOD. (2) TO USE OUR TIME-RESOLVED MODEL (TRM) BASED ON THE PHYSICS FROM OUR MONTE CARLO PARTICLE-TRAJECTORY HYDROGEN MODEL TO EXTRACT HIGH TIME RESOLUTION WATER PRODUCTION RATES SYSTEMATICALLY FROM THE BROAD SAMPLE OF COMETS IN THE CONTINUALLY EXPANDING SET OF SWAN COMET OBSERVATIONS. (3) SOME SHORT PERIOD COMETS THAT REACH PERIHELION AND HAVE POSSIBLE FAVORABLE APPARITIONS DURING THE PROPOSED GRANT PERIOD INCLUDE 21P/GIACOBINI-ZINNER 64P/SWIFT-GEHRELS 46P/WIRTANEN 38P/STEPHAN-OTERMA 88P/HOWELL 7P/PONS-WINNECKE AND 15P/FINLAY. 4) TO ANALYZE OBSERVATIONS ANY NEW LONG-PERIOD AND OORT CLOUD COMETS; ALREADY EXPECTED COMETS ARE C/2016 M1 (PANSTARRS) AND C/2016 R2 (PANSTARRS) BUT BASED ON PAST EXPERIENCE THERE ARE NORMALLY 2 OR 3 NEW COMETS DURING EACH CALENDAR YEAR. (5) TO PERFORM ONGOING ANALYSIS OF SWAN COMET OBSERVATIONS BEGUN DURING THE PREVIOUS GRANT PERIOD TO ADD TO OUR STATISTICALLY SIGNIFICANT SAMPLE OF COMETS OF VARIOUS TAXONOMIC TYPES AND OVER AS WIDE A RANGE OF HELIOCENTRIC DISTANCE AS POSSIBLE. (6) TO STUDY THEIR PRODUCTION RATE VARIATIONS WITH TIME COVERING BOTH LONG TIME SCALES OVER HELIOCENTRIC DISTANCE AS WELL AS SHORT TIMES SCALES TO INVESTIGATE OUTBURSTS FRAGMENTATION AND SPLITTING WHICH CAN PROVIDE VALUABLE INFORMATION ABOUT COMETARY NUCLEI. THIS PROGRAM IS RELEVANT TO THE SSO PROGRAM AS IT INVOLVES A DOMINANT ELEMENT OF NEW COMET OBSERVATIONS. IT HAS BEEN SUPPORTED BY SSO/PAST ON THE BASIS OF PERFORMING ULTRAVIOLET OBSERVATIONS OF COMETS AND PROVIDING TIMELY RESULTS FOR THE COMMUNITY.