Ice moon research – A phenomenon called plume

4th Symposium on Space Educational Activities Barcelona, April 2022 Page 1 of 6 Ice Moon Research – A phenomenon called plume Mario Andre Zuegner 1 __________________________________________________________________________ Abstract Based on the observations of the Cassini-Huygens space exploration mission, Saturn's moon Enceladus was found to be a very promising subject in the solar system for further exploration and follow-up research, especially focusing on the potential of extraterrestrial life and its origin. Near its South Pole, fountains, specified plumes, consisting mostly of water vapor and small salt-rich ice grains with intermittent activity were observed at the surface. With supersonic speed the water vapor is exiting the trenches known as Tiger Stripes. The driving force of these plumes are not completely understood yet. In current models, Enceladus is expected to consist of a rocky core, surrounded by an ocean of liquid water and covered by a layer of ice. The observed phenomenon is assumed to be caused by the tidal forces that act upon Enceladus. However, several models try to describe the underlying physical processes. Various investigations have recognized the astrobiological potential of Enceladus, even proposed a concept for a sample return for further research in relation to the subsurface ocean. Cassini´s existing analysis already identified CH4, CO, CO2, simple and complex organics at an altitude of approximately 190 km which allow the assumption of supersonic speeds. That said, the goal of our experiment is to gain further indices/evidence to support the current models of the plumes. Our experiment takes place on a sounding rocket which gives access to a stable vacuum and microgravity in addition. The achieved altitude with its physical environment provides almost the conditions at Enceladus related to the gravitation. The rocket module contains a pressurized and heated water reservoir which is connected via an injection system with the evaporation chamber. On the top a convergent-divergent nozzle is welded. Furthermore a nozzle cover system and a locking mechanism are integrated. At apogee, the nozzle shall be opened and the fluid stream (assumingly made up of ice, water droplets and vapor) shall exit the module at about Mach 2. The necessary fluid-dynamic data is gathered by multiple temperature and pressure measurements at different points on the module. So, the vapor stream shall be compared to the expectations based on the models. Finally it is to mention that our project is still running and waiting for its launch. Caused through the Corona crisis and the Ukraine war the launch cycle was canceled two years in succession. With much luck the rocket will launch in March 2023. Keywords Enceladus, Icemoon, Plume __________________________________________________________________________ 1 Mario Andre Zuegner: University of Applied Science Aachen, Germany, [email protected] 4th Symposium on Space Educational Activities Barcelona, April 2022 Page 2 of 6 1. Introduction The µMoon student team consists of about 19 students from two universities in Aachen, the University of Applied Sciences (UAS) and the Rhine Westphalia Technical University (RWTH). The project is allocated at the facilities of the Faculty of Aerospace Engineering at UAS. A Master Thesis 2 at Technical University (TU) Delft set the foundation for our experiment approach. The thesis provides the basic fluiddynamical model and a summary of the explorative knowledge on the topic. Mr. Becx simulated the plumes by creating artificial ice trenches in a vacuum chamber. Although his experiment setup was close to the original, the tests failed due to the limitation of the vacuum chamber. In the past various research and study projects from FH Aachen UAS like "IceMole", "Enceladus Explorer (EnEx)" and currently "Enceladus Explorer – Environmental Experimental Testing (EnEx-nExT)" already broached the issue of the ice moon research. µMoon will tie in at this state of work by approaching the scientific observations with space engineering methods. 1.1. Mission Statement Our mission is to simulate Enceladus' plumes and to characterize the uncharted fluidmechanical behavior within the Rocket Experiments for Students (REXUS) program. The experiment data shall assist validating current hypothesis on the mechanisms of the plumes and further to break down the characteristics of the subsurface oceans. µMoon is committed to identify new possible insights about the solar system and to create a small steppingstone for further follow-up research. 1.2. Experiment Objectives The mission statement described above translates into several experiment objectives that have to be achieved by µMoon. The primary objectives are: o Obj.A1: Fluid-mechanical recreation of an Enceladus-like plume o Obj.A2: Characterization of the created plume The secondary objectives are: o Obj.B1: Storage of acquired data related to evaporation of water in space The tertiary objectives are: o Obj.C1: Analysis of residuals in the reservoir after landing 1.3. Experiment Concept To recreate natural evaporation and expansion of water due to pressure difference, the experiment will be positioned in an environment close to Enceladus wit. It is designed starting with an injection system, containing a water mixture with a similar composition to Enceladus´ ocean. This liquid is injected from a hydraulic accumulator with lowly pressurized nitrogen into the evaporation chamber during flight, just before reaching the maximum altitude. A convergent-divergent nozzle is connected to the evaporation chamber. The nozzle is further covered by a movable cover system (Nozzle Cover System (NCS)). When the nozzle's outlet is opened up in the residual atmosphere, the natural evaporation of the liquid water into the vacuum leads to a pressure difference between nozzle intake and exhaust sections that will expand the vapor into space. Pressure and temperature sensors will measure the flow parameters to characterize the flow at any time during the experiment run. A camera will observe the visual development of the plume. This data will be sent to the ground station for post-flight analysis. 2. Experiment Description Figure 1.1.: Entire Setup 4th Symposium on Space Educational Activities Barcelona, April 2022 Page 3 of 6 In order to fulfill the requirements and to achieve all objectives of the µMoon project, the experiment must ensure mechanical and structural safety and requires an unusual effort in fluid-mechanical design considerations and measurement technology. The experiment setup is divided into 4 subsystems, the Flow System Assembly (FSA), the Structure Mount Assembly (SMA), the Injection System (IS) and the NCS. Additionally, the hang-on parts (HoP) are attached on all subsystems. 2.1.1. Mechanics Flow System Assembly This subsystem is designed to generate the plume and serves as a storage for residual water for further analysis. It is made up of an evaporation chamber, a nozzle, fittings for sensors, a pressure relief valve and three check valves which are responsible for the water injection. The heart of the experiment, the nozzle, is linked to the evaporation chamber. The nozzle offers fittings which serve as mountings for temperature and pressure sensors. During rocket ascent a pressure relief valve that is connected to the fitting of the evaporation chamber reduces the internal pressure to 30:000 Pa. Three check valves of the IS are also connected to the fittings. Through these check valves water is injected. Because of this injection the internal pressure increases temporary to 50:000 Pa. The nozzle cover of the NCS is placed on the top of the nozzle sealing up the FSA against an unintended pressure loss. By opening the nozzle cover the experiment starts. During the sudden pressure drop the water begins to boil and the emerging vapor exhausts through the nozzle. To end the experiment the nozzle cover gets closed again. Structure Mount Assembly The Structure Mount Assembly has a Primary Structure (PS) and a Secondary Structure (SecS) with Hop´s attached. The PS carries the main flight loads and defines the overall stiffness whereas the SecS is only attached to the PS and has negligible participation in the main load transfer and overall stiffness. Two Abeams of the primary structure are mounted on the Nose Cone Adapter Plate (NCAP) and are connected via struts. The beams and struts are also linked by the Evaporation Chamber Mounting Plate ECMP) to enhance the stiffness and stabilize the FSA. Furthermore the IS is attached onto the NCAP via two clamp brackets. Each side Carbon Fibre Reinforced Plastic plates were added to support lateral stability. The secondary structure consists of a camera mounting, brackets for lighting, bearings for the NCS and sensor brackets for pressure and temperature sensors detecting ambient condition data. A plumb pad, which absorbs water from possible leakages, is placed above the NCAP to protect the located project beneath against damage. As the last part the housing for electronic parts is positioned underneath the NCAP. Injection System Assembly This system consists of 4 main parts: o Hydraulic Accumulator o Pivoted Armature Valve o Cross Manifold o Check Valves (3x) Figure 2.1. Flow System Assembly Figure 2.2: Structure Mount Assembly Figure 2.3: Injection System 4th Symposium on Space Educational Activities Barcelona, April 2022 Page 4 of 6 A hydraulic accumulator is separated into two filling volumes by a diaphragm. The first sector filled with gas and has an overpressure compared to the second sector that will be filled with water. The second sector is connected to the pipeline system which shall be permanently flooded. The first connected part to the hydraulic accumulator is a T-fitting, connected by a reducing adapter. It is connected to the pivoted armature valve and a second T-fitting which provides an appliance for the temperature sensor 0 and serves as a device for water refill and venting. By release of the pivoted armature valve the water is enabled to flow through the pipe elbow to the cross manifold. Latter distributes the fluid to the three check valves, via hoses. Due to the pressure difference which is based on the low pressure in the evaporation chamber, the force applied on the diaphragm pushes the water into the evaporation chamber. Nozzle Cover System Assembly There are two fundamental mechanisms that activate and deactivate the experiment. NCS and locking mechanism (LM) depend on each other and work in sequence. The nozzle cover is closed when the locking pin is blocked by the rotating sleeve. To initiate the opening mechanism a small servo drive spins the rotating sleeve by 90°, so that the locking pin is able to exit the apparatus. A shaft driven by a stronger, second servo drive, is linked to the lever arm of the Nozzle Cover. This shaft is pivot mounted via sleeve bearings and is connected to the servo drive by a force transmission wheel. The transmission wheel is screwed on the servo drive shaft. When the nozzle cover is fully opened, and the experiment time has ended, the closing process is initiated. Driven by servo drive 2, the shaft moves in opposite direction to shut the nozzle cover. Finally, the rotating sleeve turns once again into starting position to lock the Nozzle Cover as before. 2.1.2. Sensors and Instrumentation The measurement sections are shown in the picture above. Point 0 is inside the hydraulic accumulator. Point 1 is inside the evaporation chamber. Point 2 is in the throat area. Points 3 and 4 are in the divergent section of the nozzle. Point 5 is attached at the top on the PS. The behavior of the plume is described by three different flow characteristics: pressure, temperature and velocity. There is a temperature measurement at Point 0. So, monitoring the temperature development in the hydraulic accumulator is mandatory, as the water shall be externally heated to ensure that it remains at 70 °C. At point 1 there are temperature and pressure sensors. Later it shall be referred to these measured values as temperature and pressure at rest. They are important for subsequent calculations. The temperature and pressure sensors at points 2, 3 and 4 there will provide information about the local flow characteristics. At point 5 there are temperature and pressure sensor installed which will measure the ambient conductions. Figure 2.4: Schematic: Injection System Figure 2.7: Measurments Location Figure 2.5 :Nozzle Cover Figure 2.6: Locking Mechanism 4th Symposium on Space Educational Activities Barcelona, April 2022 Page 5 of 6 There are also a camera and LEDs attached to the SecS in order to perform an optical analysis of the advancing experiment. There will be no direct velocity measurement, but the local Mach Number at points 2,3 and 4 shall be calculated with the isentropic relation between temperature and pressure at rest and the local values of pressure and temperature: 𝑝/𝑝0 = 𝑓(𝑀)(1) T/T0 = 𝑓(𝑀) (2) Both calculations should provide appropriate values for the local Mach Number. So with respect to redundancy there shall be four equal values for each measuring point. Velocity itself cannot be calculated because calculations for sonic speed only work with ideal gases which cannot be assumed for water vapor. 2.1.3. Electronic The complete electronic system is realized by one big PCB mounted in the electronic housing below the experiment construction. It supplies all components with the appropriate voltage and receives signals from the RXSM. Placed on it are all sensor systems, naming the Temperature Measurement System (TMS) 1 and 2, the MPR Sensors and the Analog-todigital converter (ADC) to readout the TPR Sensors. The TMS 1 and 2 provide the digital conversion of the temperature sensors placed in different parts of the experiment. The two servo motors that are used to open and close the NCS are powered and controlled by the Mainboard as well. The valve is activated (and thereby opened) by a voltage supply that is also placed on the Mainboard. The camera gets it power from a DCDC converter on the Mainboard while the set of three LEDs is powered by a constant current LED driver which can be turned on and off by the mainboard as well. All digital control and recording of the data are realized by a Raspberry Pi Compute Module Version 4 (CM4). It acts as the “brain” of the experiment, receives the status links from the service module and controls every actor and sensor. There will be an external heating foil to condition the water before lift-off. This setup is separated from the main electronics design and will be supplied with an external power line which will be shared. 3. Fluid Dynamic Design To ensure an Enceladus-like plume with supersonic flow, the nozzle shall provide an exhaust Mach number of 2. In the experiment the used nozzle is a convergent-divergent nozzle. The geometry of the nozzle, particularly throat diameter and nozzle length, will be designed according to the parameters in table. According to the phase diagram of water (compare figure 4.58), liquid water will evaporate at a temperature of 373:15K at sea level on Earth in a standard atmosphere. With decreasing ambient pressure, the boiling temperature of water will also decrease. During RGP in flight, the outside pressure will be around 100 Pa (ICAO n.d.), where no liquid water exists (below triple point pressure of 611 Pa). As the phase change from liquid to gaseous shall be used to provide a sufficient pressure difference between reservoir and ambient, the formation of solid water (ice) must be avoided. To be sure that the water will evaporate, it is heated up to reach a safer position in the vapor area of the state diagram of water. The given diagram is only for a first short overview about the behavior of water in different pressure environments. It does not show the µMoon water composition. Anyway, the formation of ice due temperature variations caused by compressible flow effects cannot be ruled out. In the first scientific test three different temperatures were tested and a final water temperature is chosen to 328K. At that temperature the stored energy is high enough to evaporate the water. 3.1. Experiment Water Composition To leave out salts and other pH value altering agents, it was decided to put a mixture of water and silicates into use. The water composition for the µMoon experiment shall contain 2:5 g of silicates (0.8 µm) to 100 ml of distilled water. Figure 3.1: State of Diagram of Water 4th Symposium on Space Educational Activities Barcelona, April 2022 Page 6 of 6 4. Conclusion Finally it is to mention that our project is still running and waiting for its launch. Caused through the Corona crisis and the Ukraine war the launch cycle was canceled two years in succession. With much luck the rocket will launch in March 2023. I really want to give thanks to all my team members and professors who supported us during the project. Especially huge thanks to the REXUS program, the Swedish Space Company (SSC) Kiruna Sweden, the German Aerospace Center (DLR), the European Space Agency (ESA) and all other participants. Nomenclature T0 Ambient Temperature T Temperature p0 Ambient Pressure p Pressure M Mach Acronyms/Abbreviations DLR German Aerospace Centre EnEx Enceladus Explorer EnEx-nExT Environmental Experimental Testing (EnEx-nExT) ESA European Space Agency FSA Flow System Assembly HoP Hang-on part IS Injection System LM Locking Mechanism NCS Nozzle Cover System NCAP Nose Cone Adapter Plate REXUS Rocket Experiments for Students RXSM Rexus Service Modulator RWTH Rhine Westphalia Technical University SMA Structure Mount Assembly TU Technical University UAS University of Applied Science PS Primary Structure SecS Secondary Structure SSC Swedish Space Company References [1] Composition and Origin of Enceladus Plume, ESA [2] Icy Moon Plume Simulator Chamber, Master Thesis, T.J. Becx