And while there is currently a recognized network of business gas stations in place to make refueling your car a cinch, there are no cryogenic refueling stations or depots at the Moon or on the way to Mars.Furthermore, storing volatile propellant for a long time and moving it from an in-space depot tank to a spacecrafts fuel tank under microgravity conditions will not be simple because the underlying microgravity fluid physics affecting such operations is not well understood. Thus, valuable fuel is continuously lost throughout both storage and move operations, rendering long-duration expeditions– particularly a human Mars mission– infeasible utilizing current passive propellant tank pressure control methods.Introducing ZBO: A New Horizon in Fuel EfficiencyZero-Boil-Off (ZBO) or Reduced Boil-Off (RBO) technologies provide a effective and innovative methods to replace the existing passive tank pressure control design. The proposed ZBO system would offer a 42% saving of propellant mass per year.These numbers also indicate that with a passive system, all the fuel carried for a three-year Mars mission would be lost to boil-off, rendering such a mission infeasible without resorting to the transformative ZBO technology.The ZBO method provides a promising technique, however before such an intricate technological and operational improvement can be totally established, implemented, and showed in space, essential and decisive scientific questions that affect its engineering execution and microgravity performance need to be clarified and resolved.The Zero-Boil-Off Tank (ZBOT) Microgravity Science ExperimentsThe Zero Boil-off Tank (ZBOT) Experiments are being carried out to form a clinical structure for the advancement of the transformative ZBO propellant conservation approach. The main focus of this experiment was to investigate the self-pressurization and boiling that takes place in a sealed tank due to regional and global heating, and the feasibility of tank pressure control via subcooled axial jet mixing. (ZBOT-1 Experiment, 2018) Credit: Dr. Mohammad Kassemi, Case Western Reserve UniversitySome of the intriguing findings of the ZBOT-1experiment are as follows: Provided the very first tank self-pressurization rate information in microgravity under regulated conditions that can be utilized for approximating the tank insulation requirements.
Figure 1. The Gateway spaceport station– mankinds very first spaceport station around the Moon– will be capable of being refueled in space. Credit: NASA, Alberto Bertolin, Bradley ReynoldsNASAs Zero-Boil-Off Tank experiments resolve the obstacle of managing cryogenic propellants in space, crucial for future Moon and Mars objectives, with possible Earth-bound advantages in hydrogen energy applications.Do we have sufficient fuel to get to our location? This is most likely among the first concerns that comes to mind whenever your family gets ready to embark on a trip. If the journey is long, you will require to go to gas stations along your path to refuel throughout your travel.NASA is facing similar concerns as it gets ready to start a sustainable mission back to the Moon and prepares future missions to Mars. But while your vehicles fuel is gasoline, which can be safely and forever saved as a liquid in the automobiles gas tank, spacecraft fuels are volatile cryogenic liquid propellants that should be kept at extremely low temperatures and protected from environmental heat leakages into the spacecrafts propellant tank. And while there is already an established network of industrial filling station in location to make refueling your vehicle a cinch, there are no cryogenic refueling stations or depots at the Moon or on the way to Mars.Furthermore, saving volatile propellant for a long time and transferring it from an in-space depot tank to a spacecrafts fuel tank under microgravity conditions will not be easy considering that the underlying microgravity fluid physics affecting such operations is not well understood. Even with todays technology, protecting cryogenic fuels in space beyond several days is tank-to-tank and not possible fuel transfer has actually never been previously carried out or evaluated in space.Propellant Management in Space: Overcoming Boil-OffHeat conducted through assistance structures or from the radiative space environment can penetrate even the formidable Multi-Layer Insulation (MLI) systems of in-space propellant tanks, causing boil-off or vaporization of the propellant and causing tank self-pressurization. The current practice is to secure against over-pressurizing the tank and endangering its structural integrity by venting the boil-off vapor into space.Onboard propellants are also utilized to cool off the hot transfer lines and the walls of an empty spacecraft tank before a fuel transfer and filling operation can occur. Hence, valuable fuel is constantly wasted during both storage and transfer operations, rendering long-duration expeditions– especially a human Mars objective– infeasible utilizing present passive propellant tank pressure control methods.Introducing ZBO: A New Horizon in Fuel EfficiencyZero-Boil-Off (ZBO) or Reduced Boil-Off (RBO) technologies provide a effective and ingenious means to replace the current passive tank pressure control style. This method counts on an intricate mix of active, gravity-dependent blending and energy removal processes that permit maintenance of safe tank pressure with absolutely no or significantly reduced fuel loss.Zero Boil-off Storage and Transfer: A Transformative Space TechnologyAt the heart of the ZBO pressure control system are two suggested active blending and cooling systems to counter tank self-pressurization. The very first is based on periodic, required, subcooled jet mixing of the propellant and involves complex, vibrant, gravity-dependent interaction between the ullage and the jet (vapor volume) to manage the condensation and evaporation stage modification at the liquid-vapor interface.The second mechanism uses subcooled bead injection through a spraybar in the ullage to control tank pressure and temperature. While the latter option is promising and acquiring prominence, it is more complicated and has actually never ever been checked in microgravity where the phase change and transport behavior of droplet populations can be very various and nonintuitive compared to those on Earth.Although the dynamic ZBO method is technologically intricate, it assures an excellent advantage over the currently used passive approaches. An assessment of one nuclear propulsion idea for Mars transport estimated that the passive boil-off losses for a big liquid hydrogen tank carrying 38 lots of fuel for a three-year mission to Mars would be roughly 16 tons/year. The proposed ZBO system would offer a 42% saving of propellant mass per year.These numbers likewise indicate that with a passive system, all the fuel carried for a three-year Mars objective would be lost to boil-off, rendering such a mission infeasible without resorting to the transformative ZBO technology.The ZBO method provides an appealing technique, however before such a complex technological and operational change can be fully established, executed, and demonstrated in space, essential and decisive scientific questions that affect its engineering application and microgravity performance must be clarified and resolved.The Zero-Boil-Off Tank (ZBOT) Microgravity Science ExperimentsThe Zero Boil-off Tank (ZBOT) Experiments are being undertaken to form a scientific structure for the development of the transformative ZBO propellant conservation technique. Following the suggestion of a ZBOT science review panel comprised of members from aerospace industries, academic community, and NASA, it was chosen to perform the proposed examination as a series of three small science experiments to be carried out onboard the International Space Station. The 3 experiments outlined listed below develop upon each other to deal with crucial science concerns related to ZBO cryogenic fluid management of propellants in space.Figure 2. Astronaut Joseph M. Acaba setting up ZBOT Hardware in the Microgravity Science Glovebox aboard the International Space Station. Credit: NASAThe ZBOT-1 Experiment: Self-Pressurization & & Jet MixingThe initially experiment in the series was brought out on the station in the 2017-2018 timeframe. Figure 2 shows the ZBOT-1 hardware in the Microgravity Science Glovebox (MSG) system of the station. The primary focus of this experiment was to examine the self-pressurization and boiling that takes place in a sealed tank due to global and local heating, and the feasibility of tank pressure control by means of subcooled axial jet blending. In this experiment, the complicated interaction of the jet flow with the ullage (vapor volume) in microgravity was carefully studied.Microgravity jet mixing information was likewise gathered throughout a large range of scaled flow and heat transfer specifications to characterize the time constants for tank pressure decrease, and the thresholds for geyser (liquid water fountain) formation, including its stability, and penetration depth through the ullage volume. In addition to really precise pressure and regional temperature sensor measurements, Particle Image Velocimetry (PIV) was carried out to obtain whole-field flow speed measurements to verify a Computational Fluid Dynamics (CFD) model.Figure 3. Validation of ZBOT CFD Model Predictions for fluid flow and contortion of a round ullage in microgravity by a subcooled liquid jet mixing versus ZBOT experimental outcomes: (a) Model prediction of ullage position and contortion and flow vortex structures during subcooled jet blending; (b) PIV image capture of flow vortex structures during jet blending; (c) Ullage contortion captured by white light imaging; and (d) CFD design representation of temperature contours during subcooled jet blending. (ZBOT-1 Experiment, 2018) Credit: Dr. Mohammad Kassemi, Case Western Reserve UniversitySome of the fascinating findings of the ZBOT-1experiment are as follows: Provided the very first tank self-pressurization rate data in microgravity under regulated conditions that can be utilized for estimating the tank insulation requirements. Outcomes likewise showed that classical self-pressurization is rather vulnerable in microgravity and nucleate boiling can happen at hotspots on the tank wall even at moderate heat fluxes that do not induce boiling on Earth.Proved that ZBO pressure control is feasible and efficient in microgravity utilizing subcooled jet mixing, but likewise demonstrated that microgravity ullage-jet interaction does not follow the anticipated classical program patterns (see Figure 3). Made it possible for observation of unexpected cavitation during subcooled jet blending, resulting in enormous stage modification at both sides of the screened Liquid Acquisition Device (LAD) (see Figure 4). If this type of phase change takes place in a propellant tank, it can cause vapor intake through the LAD and disruption of liquid circulation in the transfer line, potentially leading to engine failure.Developed a modern two-phase CFD design confirmed by over 30 microgravity case research studies (an example of which is shown in Figure 3). ZBOT CFD models are presently utilized as an efficient tool for propellant tank scaleup style by numerous aerospace companies taking part in the NASA tipping point chance and the NASA Human Landing System (HLS) program.Figure 4. White light image captures of the undamaged single hemispherical ullage in ZBOT tank before depressurization by the subcooled jet (left) and after subcooled jet mixing pressure collapse that resulted in massive stage change bubble generation due to cavitation at the LAD (right). (ZBOT-1 Experiment, 2018). Credit: Dr. Mohammad Kassemi, Case Western Reserve UniversityThe ZBOT-NC Experiment: Non-Condensable Gas EffectsNon-condensable gases (NCGs) are used as pressurants to extract liquid for engine operations and tank-to-tank transfer. The second experiment, ZBOT-NC will examine the effect of NCGs on the sealed tank self-pressurization and on pressure control by axial jet mixing. Two inert gases with quite various molecular sizes, Xenon, and Neon, will be utilized as the non-condensable pressurants. To accomplish pressure control or decrease, vapor particles must reach the liquid-vapor interface that is being cooled by the blending jet and after that cross the user interface to the liquid side to condense.This research study will focus on how in microgravity the non-condensable gases can slow down or resist the transport of vapor molecules to the liquid-vapor user interface (transport resistance) and will clarify to what extent they may form a barrier at the interface and restrain the passage of the vapor molecules across the user interface to the liquid side (kinetic resistance). By affecting the interface conditions, the NCGs can also alter the flow and thermal structures in the liquid.ZBOT-NC will utilize both local temperature sensing unit data and uniquely developed Quantum Dot Thermometry (QDT) diagnostics to collect nonintrusive whole-field temperature level measurements to examine the impact of the non-condensable gases throughout both self-pressurization heating and jet mixing/cooling of the tank under weightlessness conditions. This experiment is arranged to fly to the International Space Station in early 2025, and more than 300 various microgravity tests are prepared. Results from these tests will likewise make it possible for the ZBOT CFD design to be additional established and validated to include the non-condensable gas impacts with numerical and physical fidelity.The ZBOT-DP Experiment: Droplet Phase Change EffectsZBO active pressure control can likewise be accomplished through injection of subcooled liquid droplets through an axial spray-bar straight into the ullage or vapor volume. This mechanism is very appealing, but its efficiency has actually not yet been evaluated in microgravity. Evaporation of droplets consumes heat that is provided by the hot vapor surrounding the beads and produces vapor that is at a much lower saturation temperature level. As an outcome, both the temperature level and the pressure of the ullage vapor volume are decreased. Bead injection can also be used to cool down the hot walls of an empty propellant tank before a tank-to-tank transfer or filling operation. Beads can be created throughout the propellant sloshing triggered by acceleration of the spacecraft, and these droplets then go through phase change and heat transfer. This heat transfer can cause a pressure collapse that might cause cavitation or an enormous liquid-to-vapor stage change. The behavior of bead populations in microgravity will be dramatically different compared to that on Earth.The ZBOT-DP experiment will examine the disintegration, coalescence (droplets merging together), phase change, and transportation and trajectory qualities of bead populations and their effects on the tank pressure in microgravity. Specific attention will likewise be dedicated to the interaction of the droplets with a heated tank wall, which can lead to flash evaporation topic to problems caused by the Liedenfrost effect (when liquid beads move far from a heated surface area and thus can not cool the tank wall). These complicated phenomena have actually not been scientifically analyzed in microgravity and needs to be dealt with to assess the feasibility and efficiency of droplet injection as a pressure and temperature control system in microgravity.Back to Planet EarthThis NASA-sponsored essential research study is now helping industrial suppliers of future landing systems for human explorers. Blue Origin and Lockheed Martin, participants in NASAs Human Landing Systems program, are using data from the ZBOT experiments to inform future spacecraft designs.Cryogenic fluid management and use of hydrogen as a fuel are not limited to area applications. Tidy green energy supplied by hydrogen may one day fuel aircrafts, ships, and trucks in the world, yielding enormous climate and economic advantages. By forming the clinical structure of ZBO cryogenic fluid management for area exploration, the ZBOT science experiments and CFD model development will likewise assist to profit of hydrogen as a fuel here on Earth.Project LeadDr. Mohammad Kassemi (Dept Mechanical & & Aerospace Engineering, Case Western Reserve University) Sponsoring OrganizationBiological and Physical Sciences (BPS) Division, NASA Science Mission Directorate (SMD).
