Stability of in-space cryogenic systems

CRYOGENIC PROPELLANTS LIQUID OXYGEN AND LIQUID HYDROGEN OR LIQUID METHANE ARE THE MOST EFFICIENT PROPELLANT COMBINATIONS FOR IN SPACE TRAVEL. THE CAPABILITY FOR CRYOGENIC REFUELING ON ORBIT AND IN SPACE REPRESENTS A PARADIGM SHIFT IN THE ARCHITECTURE FOR LARGE BEYOND LOW EARTH ORBIT (LEO) MISSIONS WITHOUT SUPER HEAVY LIFT VEHICLES. MISSION ARCHITECTURE CONSIDERS TWO OPTIONS FOR PROPELLANT RESUPPLY EITHER VIA TANKERS OR IN-SPACE PROPELLANT STORAGE DEPOTS. HOWEVER AN EFFICIENT AND RELIABLE REFUEL TECHNOLOGY FOR SAFE AUTONOMOUS TRANSFER OF A CRYOGENIC PROPELLANT FROM A TANKER OR A DEPOT TO A RECEIVER IN LONG-DURATION HUMAN AND ROBOTIC MISSIONS HAS YET TO BE ACCOMPLISHED. SPACE CRYOGENIC SYSTEMS ARE SUBJECT TO HEAT LOADS FROM A VARIETY OF SOURCES SUCH AS INCIDENT SOLAR RADIATION ALBEDO OF CELESTIAL BODIES AND HEAT GENERATED BY EQUIPMENT. WHILE SPACE CRYOGENIC FLUID TECHNOLOGIES REQUIRE VAPOR-FREE LIQUID DELIVERY THE TIME- AND LOCATION- DEPENDENT LIQUID-VAPOR FLOWS OF CRYOGENIC FLUIDS ARE ENCOUNTERED IN MOST OPERATIONS DUE TO THEIR VERY LOW BOILING POINT LOW SPECIFIC HEAT AND ENTHALPY OF VAPORIZATION AND UNUSUALLY LOW SURFACE TENSION. NUMEROUS TERRESTRIAL STUDIES DEMONSTRATE THAT THE MAJOR COMPLEXITY IN CONTROLLING LIQUID-VAPOR FLOW RESULTS FROM INSTABILITIES BROUGHT BY INTRICATE INTERACTIONS OF THE FLOW WITH LIQUID-VAPOR PHASE TRANSITIONS SUCH AS SLOWER PROPAGATION SPEED OF PRESSURE PERTURBATIONS IN TWO-PHASE REGIONS ACCUMULATION OF VAPOR DOWNSTREAM FROM THE LOCALLY HEATED SECTIONS AND ACOUSTIC WAVES GENERATED BY VAPOR BUBBLES. COUPLING OF THEIR LOW-FREQUENCY MODES WITH MECHANICAL VIBRATIONS AMPLIFIES EACH OTHER. ALL THESE FEATURES MAKE CRYOGENIC PIPELINES HIGHLY SUSCEPTIBLE TO THERMAL HYDRODYNAMIC INSTABILITIES THAT CAN GENERATE LARGE-AMPLITUDE FLOW OSCILLATIONS AND HYDRAULIC SHOCKS (FLUID HAMMER) CAUSING FLOW CONTROL FAILURE AND EQUIPMENT DAMAGE. THE ABILITY TO MAINTAIN STABILITY OF CRYOGENIC FLUID TRANSFER IN SPACE IS A TECHNOLOGY CHALLENGE THAT MUST BE ADDRESSED FOR DESIGNING EFFICIENT CRYOGENIC REFUEL SYSTEMS FOR LONG DURATION SPACE MISSIONS. COMPARED TO NORMAL GRAVITY ENVIRONMENT FLOW OF A CRYOGENIC FLUID IN MICROGRAVITY IS MUCH MORE COMPLICATED DUE TO THE UNCERTAIN DISTRIBUTION OF LIQUID AND VAPOR FORMED WITHIN A SYSTEM. UNDERSTANDING THE ROLE OF GRAVITY IN TRIGGERING THERMAL-HYDRODYNAMIC INSTABILITIES IS URGENTLY NEEDED TO ENSURE CONTROLLABILITY AND SAFETY OF IN-SPACE PROPELLANT STORAGE AND TRANSPORT OF CRYOGENIC PROPELLANTS. THE PROPOSED EFFORT IS THE FIRST STUDY TO FIND THE CRITERIA FOR STABILITY OF TRANSPORT OF CRYOGENIC FLUID WHICH IS THE BASIC REFUEL-OPERATION OVERHEAT AND MECHANICAL DISTURBANCES INEVITABLE IN MICROGRAVITY SPACE ENVIRONMENT. THE ROLE OF GRAVITY IN CRYOGENIC TRANSPORT OPERATION WILL BE ASSESSED BY CARRYING OUT TESTS ON EARTH AND ONBOARD AIRCRAFT FLYING PROFILES TO SIMULATE MICROGRAVITY AND THE REDUCED GRAVITY OF THE MOON OR MARS. THE CONTRAST IN EXPERIMENTAL DATA GATHERED IN FLIGHTS AND ON EARTH SHOULD ELUCIDATE THE SALIENT FEATURES OF THE GRAVITY INFLUENCE. THE PROJECT RESULTS WILL PROVIDE DIRECT GUIDELINES FOR DESIGNING AND SIZING OF COST-EFFICIENT AND SAFE SYSTEMS FOR TRANSFER CRYOGENIC PROPELLANTS ON ORBIT AND IN SPACE SUCH AS OPTIMUM PRESSURE AND FLOW RATE FOR REFUEL CORRECT THERMAL INSULATION FOR PIPING LEVEL OF ACCEPTABLE EQUIPMENT VIBRATIONS AND PRESSURE FLUCTUATIONS IN TANKS. THE KNOWLEDGE GAINED FROM THE PROPOSED FLIGHT EXPERIMENTS WILL ADVANCE DEVELOPMENT OF TECHNOLOGIES OF IN-SPACE STORAGE AND TRANSPORT OF CRYOGENIC PROPELLANTS IN SUPPORT OF NASA SPACEFLIGHT OPERATIONS AT THE MOON TO SUPPORT SUSTAINED LUNAR ACTIVITIES AND FACILITATE EXPANSION OF ECONOMIC ACTIVITY INTO CISLUNAR SPACE. THE PROJECT WILL SUPPORT INVOLVEMENT OF STUDENTS IN THE DESIGN AND DEVELOPMENT OF THE PROPOSED TECHNOLOGY. INVOLVEMENT OF K-12 EDUCATORS WILL PROVIDE EDUCATION TO HIGH-SCHOOL STUDENTS FROM UNDERREPRESENTED GROUPS THROUGH SCIENTIFIC RESEARCH AND EXPERIENCES.