Acute Radiation SyndromeRadiation-Protective AgentsWeightlessness CountermeasuresBed RestWeightlessness SimulationSpace FlightBiological Warfare AgentsRadiation DosageHead-Down TiltRadiation InjuriesRadiation, IonizingGravity, AlteredWeightlessnessRadiation ProtectionDose-Response Relationship, RadiationNational Institute of Allergy and Infectious Diseases (U.S.)Civil DefenseRadiation ToleranceRadiation Injuries, ExperimentalRadiationBiological WarfareChemical Warfare AgentsCardiovascular DeconditioningRadiation MonitoringRadioactive Hazard ReleaseMuscular AtrophyDisaster Planning