CLUSTER IS A JOINT ESA/NASA MISSION WITH PRIMARY MISSION AND OPERATIONS CONTROL UNDER ESA AND MOST OF THE SCIENTIFIC INSTRUMENTS PROVIDED BY VARIOUS EUROPEAN COUNTRIES. THE AIM OF CLUSTER IS TO STUDY THE SMALL-SCALE STRUCTURES OF THE MAGNETOSPHERE AND ITS ENVIRONMENT IN THREE DIMENSIONS. CLUSTER TOGETHER WITH THE SOLAR HELIOSPHERIC OBSERVATORY (SOHO) COMPRISE THE ESA SOLAR TERRESTRIAL SCIENCE PROGRAMME (STSP). THE FOUR CLUSTER SPACECRAFT WERE LAUNCHED IN JULY AND AUGUST 2000 FROM BAIKONUS KAZAKHSTAN. CLUSTER HAS BEEN ORBITING THE EARTH SINCE THAT TIME IN AN APPROXIMATE 3 X 19 RE 57-HOUR ORBIT WITH AN INCLINATION OF GREATER THAN 50 DEGREES. THIS ORBIT ALLOWS FOR MULTO-SPACECRAFT OBSERVATIONS OF EARTH'S MANY BOUNDARY LAYERS (BOW SHOCK FORESHOCK MAGNETOSHEATH MAGNETOPAUSE PLASMA SHEET) AND DYNAMICALLY ACTIVE REGIONS (THE INNER MAGNETOSPHERE PLASMASPHERE CUSP AND MAGNETOTAIL).AFTER 16 YEARS IN ORBIT THE SPACECRAFT STILL HAVE A SMALL RESERVE OF FUEL WITH WHICH TO CARRY OUT A LIMITED NUMBER OF MANEUVERS IN ORDER TO ADJUST THE SPACECRAFT CONFIGURATION AND SEPARATIONS TO ONES WHICH ARE IDEAL FOR STUDYING A CONTINUALLY CHANGING (BASED ON ORBIT EVOLUTION) WELL-DEFINED SET OF SCIENTIFIC OBJECTIVES. THE CURRENT CLUSTER MISSION HAS BEEN EXTENDED TO DECEMBER 31 2016 BY ESA BASED ON THOSE SCIENTIFIC OBJECTIVES AND THE RELATIVELY GOOD HEALTH OF THE SPACECRAFT AND SCIENTIFIC INSTRUMENTS. CLUSTER OPERATIONS HAVE BEEN APPROVED THROUGH DECEMBER 31 2018 BASED ON THE HEALTH OF THE HARDWARE WITH LIKELY CONFIRMATION OF THE MISSION EXTENSION TO BE GRANTED BY THE ESA SCIENCE PROGRAMME COMMITTEE (SPC) IN THE FALL OF 2016. FOR PURPOSES OF THE CLUSTER WBD EFFORTS PROPOSED BELOW WE ASSUME THAT THIS EXTENSION THROUGH 2018 WILL BE APPROVED BY ESA BASED ON THE PROPOSED SCIENTIFIC OBJECTIVES PRESENTED TWO YEARS AGO AT WHICH TIME THE SPC GAVE AN INDICATIVE APPROVAL FOR THIS EXTENSION SUBJECT TO A MID-TERM REVIEW (APPROVED IN MAY 2016) AND SUBSEQUENT SPC CONFIRMATION (EXPECTED FALL 2016).THE WBD INSTRUMENT IS THE ONLY SCIENTIFIC INSTRUMENT MOUNTED ON EACH OF THE CLUSTER SPACECRAFT WHICH WAS FULLY FUNDED BY NASA IN ALL PHASES OF THE MISSION FROM DESIGN PHASE IN THE LATE 1980S TO THE CURRENT TIME. IT IS ONE OF TWO CLUSTER INSTRUMENTS WITH A U.S. PRINCIPAL INVESTIGATOR APPOINTED BY NASA. THE CLUSTER WBD INSTRUMENTS OBTAIN ELECTRIC OR MAGNETIC FIELD WAVEFORMS (NOT BOTH SIMULTANEOUSLY) WITH A HIGH TIME RESOLUTION BETWEEN 4.55-36.4 MICROSECONDS DEPENDING ON THE BANDPASS FILTER MODE CHOSEN IN THE FREQUENCY RANGE OF 0.075-577 KHZ. A FULL DESCRIPTION OF THE CLUSTER WBD INSTRUMENTS CAN BE FOUND IN GURNETT ET AL. (SPACE SCIENCE REVIEWS 79 195-208 1997). ALL FOUR OF THE WBD INSTRUMENTS ARE CURRENTLY OPERATING THREE WITH FULL FUNCTIONALITY AND ONE WHICH CAN OPERATE ONLY 10 MINUTES EVERY HOUR DUE TO AN OVERHEATING PROBLEM THAT DEVELOPED IN LATE 2003. DURING 2017 AND 2018 ROUGHLY THE PERIOD OF THIS PROPOSAL THE WBD INSTRUMENT WILL OBTAIN DATA THAT ARE PERTINENT TO WBD-SPECIFIC SCIENTIFIC OBJECTIVES AS WELL AS MOST OF THE MISSION SCIENTIFIC OBJECTIVES.