SUPPORT OF CISIRPA OPERATIONS CALIBRATIONS AND SCIENCE INVESTIGATIONSTHE CLUSTER MISSION IS A COLLABORATIVE PROGRAM BETWEEN THE EUROPEAN SPACE AGENCY AND NATIONAL AERONAUTICS AND SPACE ADMINISTRATION. CLUSTER WAS LAUNCHED IN 2000 AND BECAME OPERATIONAL IN 2001. THIS PROPOSAL REQUESTS SUPPORT IN THE OPERATION AND CALIBRATION OF THE RETARDING POTENTIAL ANALYZER (RPA) PART OF THE COMPOSITION ION SPECTROMETRY (CIS) EXPERIMENT ORIGINALLY DEVELOPED BY UC BERKELEY AND TOULOUSE FRANCE. THE PRINCIPAL INVESTIGATORS (PI) OF CIS ARE PROFESSOR HENRI REME AND DR. IAONNIS DANDOURAS FROM CENTRE D'ETUDE SPATIALE RAYONNEMENT TOULOUSE FRANCE. DR. GEORGE K. PARKS AT THE SPACE SCIENCES LABORATORY UNIVERSITY OF CALIFORNIA BERKELEY IS THE LEAD US CO-INVESTIGATOR (CO-I) OF THE CRS/RPA EXPERIMENT.CIS EXPERIMENT PERFORMS THREE TYPES OF MEASUREMENTS: HIGH ENERGY ION ANALYZER (HIA) MEASURES ALL IONS FROM THE POTENTIAL OF THE SPACECRAFT TO ABOUT 40 KEV/Q; COMPOSITIONOF DISTRIBUTION FUNCTION (CODIF) COMBINED WITH TIME OF FLIGHT (TOF) MEASURES MAJOR SOLAR WIND AND IONOSPHERIC ION SPECIES H+ HE+ HE++ AND 0+; CODIF CAN ALSO BE OPERATED IN THE RPA MODE THAT DETECTS THE SAME ION SPECIES IN THE LOW ENERGY RANGE FROM THE SPACECRAFT POTENTIAL TO ABOUT 25 E V .