EXPOSURE TO WEIGHTLESSNESS RESULTS IN THE REMOVAL OF HYDROSTATIC PRESSURE GRADIENTS AND A PERMANENT HEADWARD FLUID SHIFT CAUSING A REDISTRIBUTION OF BLOOD. ADDITIONALLY IN SPACE POSTURAL CHANGES DON T OCCUR AND THUS ASTRONAUTS ARE NOT EXPOSED TO DAILY FLUID SHIFTS (BETWEEN SUPINE AND UPRIGHT POSTURES) AS WE ARE ON EARTH. THIS HAS CURRENTLY UNKNOWN CONSEQUENCES BUT IT MIGHT BE RELATED TO A SERIES OF NEURO-OCULAR AND FUNCTIONAL CHANGES DEVELOPED IN SOME ASTRONAUTS DURING BOTH SHORT AND LONG-DURATION SPACEFLIGHT COLLECTIVELY KNOWN AS SPACEFLIGHT ASSOCIATED NEURO-OCULAR SYNDROME (SANS). WHILE THE EXACT ETIOLOGY OF SANS IS CURRENTLY UNKNOWN CHRONIC FLUID REDISTRIBUTION AFFECTING INTRAVASCULAR INTERSTITIAL AND CEREBROSPINAL FLUIDS AND PRESSURES IS WIDELY HYPOTHESIZED TO BE A CONTRIBUTING FACTOR. ADDITIONALLY RECENTLY DEMONSTRATED STAGNANT AND RETROGRADE BLOOD FLOW AND VENOUS THROMBOSIS IN THE LEFT INTERNAL JUGULAR VEIN DURING SPACEFLIGHT COULD ALSO BE ASSOCIATED WITH SUSTAINED HEADWARD BLOOD AND TISSUE FLUID SHIFT. THE OBJECTIVE OF THIS GROUND-BASED RESEARCH EFFORT IS TO GENERATE ACUTE GRAVITATIONAL DOSE-RESPONSE CURVES OF CARDIOVASCULAR (CV) AND OCULAR VARIABLES DUE TO CHANGES IN THE GRAVITATIONAL VECTOR WITH AND WITHOUT COUNTERMEASURES.