DURING THE EARLY 2000S SCIENTISTS WORKING ON SATELLITE ACCELEROMETER DATA DISCOVERED TWO SUBSTANTIAL AND PERMANENT ENHANCEMENTS OF THERMOSPHERIC MASS DENSITY LOCATED NEAR THE FOOTPRINTS OF THE NORTH AND SOUTH GEOMAGNETIC CUSPS AND OCCURRING AT AROUND 400 KM ALTITUDE. THESE DENSITY ENHANCEMENTS INCREASE THE WEIGHT OF THE ATMOSPHERE IN THESE REGIONS. BECAUSE THE ENHANCEMENTS ARE STABLE THIS EXTRA WEIGHT MUST UNAVOIDABLY BE SUPPORTED BY LOCAL PERTURBATIONS OCCURRING IN ONE OR MORE OF THE OTHER TERMS THAT APPEAR IN THE ATMOSPHERE S MOMENTUM EQUATION I.E. EITHER IN WIND TEMPERATURE OR ION VELOCITY. THIS PREDICTION IS CONFIRMED BY 3D FLUID MODELS. HOWEVER AS OF TODAY MORE THAN A DECADE AFTER THE DENSITY ENHANCEMENTS WERE DISCOVERED THERE ARE STILL NO OBSERVATIONS OF ANY OTHER CORRESPONDING ATMOSPHERIC PERTURBATIONS TO INDICATE WHAT IS SUPPORTING THE EXTRA WEIGHT. IT IS CRITICAL THAT WE RESOLVE THIS DISCONNECT BECAUSE THE DENSITY ENHANCEMENTS DIRECTLY AFFECT SATELLITE ORBITS. OUR CURRENTLY POOR UNDERSTANDING OF WHY THEY OCCUR AND WHAT SUSTAINS THEM MEANS WE CANNOT MODEL THEIR BEHAVIOR. THIS IN TURN MEANS WE CANNOT ACCURATELY ACCOUNT FOR THEM IN ORBITAL PREDICTIONS USED TO DETERMINE AN OPERATIONAL SATELLITE S COLLISION PROBABILITIES DURING ITS (FREQUENT) NEAR MISSES WITH SPACE DEBRIS. TO REVEAL HOW THE EXTRA MASS IS SUPPORTED WE PROPOSE TO LAUNCH A BLACK-BRANT 12 (OR SIMILAR) SOUNDING ROCKET FROM ANDOYA SPACE CENTER DIRECTLY INTO THE ENHANCEMENT REGION IN AN INVESTIGATION THAT WILL MEASURE ALL RELEVANT TERMS IN THE ATMOSPHERIC MOMENTUM EQUATION. REGARDLESS OF THE ROOT CAUSE OF THE DENSITY ENHANCEMENTS THEIR MOST LIKELY SUPPORT MECHANISMS INVOLVE NEUTRAL UPWELLING AND HORIZONTAL DIVERGENCE. THE FOUNDATION OF THE INVESTIGATION WILL THEREFORE BE TO OBTAIN ABSOLUTE NEUTRAL WIND MEASUREMENTS BY FOLLOWING THE DRIFT OF 20 NEUTRAL STRONTIUM CLOUDS RELEASED FROM THE ROCKET AT ALTITUDES BETWEEN 200 AND 400 KM. DRIFT TRACKING WILL BE DONE BY PHOTOGRAPHIC TRIANGULATION USING CAMERAS LOCATED ON SVALBARD AND ABOARD A NASA AIRCRAFT FLYING ALONG THE EAST COAST OF GREENLAND. STRONTIUM TRACERS PROVIDE THE ONLY DIRECT AND ABSOLUTE WAY TO MEASURE WINDS SIMULTANEOUSLY WITHIN A NUMBER OF VERY SMALL SAMPLE VOLUMES DISTRIBUTED FROM 200 TO 400 KM ALTITUDE. MULTIPLY REDUNDANT MEASUREMENTS OF THE DENSITY ENHANCEMENT ITSELF WILL BE OBTAINED FROM ACCELEROMETERS ABOARD THE GRACE-FO AND SWARM SATELLITES. EXISTING DATA STRONGLY SUGGEST THAT INTENSE NARROW SHEETS OF UPWARD ION DRAG MAY ALSO BE IMPORTANT CONTRIBUTORS TO SUPPORTING THE ENHANCED DENSITY. TO EXAMINE THIS POSSIBILITY WE NEED TO MEASURE MANY ADDITIONAL NEUTRAL AND ELECTRODYNAMIC QUANTITIES. ION DRIFTS WILL BE MEASURED TWO WAYS: BY TRACKING 20 BARIUM ION CLOUDS THAT WILL BE CREATED ALONG WITH NEUTRAL STRONTIUM TRACERS AND FROM ABOARD THE ROCKET WITH AN IN-SITU MINIATURE PLASMA IMAGER INSTRUMENT. ION DENSITY AND TEMPERATURES WILL BE MEASURED INSITU WITH A SUITE OF PETITE ION PROBES WHEREAS ELECTRON TEMPERATURES WILL BE MEASURED IN-SITU USING AN ELECTRON RETARDING POTENTIAL ANALYZER. THE ENERGY AND PITCH ANGLE DISTRIBUTION OF AURORAL ELECTRON PRECIPITATION WILL BE MEASURED IN-SITU USING A STRETCHED TOP-HAT ELECTROSTATIC ANALYZER. NEUTRAL TEMPERATURES WILL BE MEASURED BY REMOTE SENSING WITH AN ALL-SKY IMAGING FABRY-PEROT SPECTROMETER AT LONGYEARBYEN WHICH WILL ALSO GIVE NEUTRAL WINDS OVER A WIDER SPATIAL REGION AND TEMPORAL INTERVAL THAN THAT COVERED BY THE ROCKET. NUMEROUS ADDITIONAL GROUND-BASED INSTRUMENTS ON SVALBARD WILL FURTHER CHARACTERIZE THE THERMOSPHERIC IONOSPHERIC AND MAGNETOSPHERIC CONDITIONS DURING THE EXPERIMENT. SCIENTIFIC CLOSURE WILL BE OBTAINED BY USING A LOCAL-SCALE HIGH SPATIAL-RESOLUTION VERSION OF THE NON-HYDROSTATIC GITM MODEL TO INTERPRET THE OBSERVATIONAL DATA. THE INVESTIGATION WILL BE A COLLABORATION BETWEEN FIVE US AND FOUR INTERNATIONAL INSTITUTIONS.