MISSION: IMPOSSIBLE

Cairo | Exploring Venus Together

Mission Impossible

High-Level Project Summary

The idea is a hybrid storage system of mechanical and electrical storage techniques. The system consists of flywheels, that store mechanical energy resulting from the Stirling radioisotope engine when using nuclear decay as a power source, or from the wind turbines as discussed in future mechanical designs. First, kinetic energy is stored in the flywheel that powers the main parts of the rover. In addition, Sodium Sulfur batteries store the electrical energy needed to power the electronic components. The Sodium Sulfur batteries and the electronic components are isolated in a spherical shell and cooled by a Stirling cooling system to maintain a suitable temperature range.

Link to Final Project

https://drive.google.com/drive/u/1/folders/1YdYiOMZ70VWUeqphl8JEpXIcLHCyfTI8

Link to Project "Demo"

https://docs.google.com/presentation/d/1MprA-EFapzR1Us_nJRPuySMJ7-jnu_Z5/edit?usp=sharing&ouid=100949547295359505491&rtpof=true&sd=true

Detailed Project Description

Considering prior missions sent to Venus, the energy storage system was designed to withstand both high temperatures and pressure of the planet. The design is a hybrid system of flywheel and Sodium Sulphur batteries to power the rover for 60 days, with the addition of a cooling system as shown in the 3d model. The flywheel stores the mechanical energy and powers the main parts of the rover, and Sodium Sulfur batteries with a provided cooling system, for the electrical energy storage and powering the electronic components.

The system’s design is flexible; thus the power source will be either a Stirling radioisotope generator (nuclear decaying) or a wind turbine ,both provide power in a form of mechanical energy, as shown in the figures 1, 2.

The Stirling engine was chosen to be a beta type with a rhombic drive as shown in the following figure. The engine converts temperature differences to a mechanical energy either in reciprocating or rotational motion. The motion is then sent to other parts of the system.

The source of heat for the Stirling engine will be the natural decay of plutonium 238 dioxide (emitting constant heat without the need for any type of control). The heat is supplied to the Stirling engine’s head, raising its temperature to around 1200 kelvin. Meanwhile, the other rejecting heat end (the cold part) will have a temperature of around 750 kelvins (comparable to Venus’ temperature). The engine’s conversion mechanism is mainly focused on the expansion and contraction of gas by heating and cooling respectively.

  The energy generated is transferred directly to a flywheel via the gears in figure 3. The flywheel is located outside in the extreme condition with the engine. It stores energy in form of kinetic energy. The flywheel stores a portion of the generated energy, and another portion converted to electricity for storage in the Sodium Sulphur batteries, which is located in the cooling system.

The vessel has an associated cooling system. The cooling system is composed of two parts: a cooling engine and an enclosure or vessel. From all technologies, the free piston Stirling-cooler was used. It was chosen due to its high efficiency (the efficiency is that of Carnot), simplicity, and availability. Its design is like our power system vendor: The Stirling engine. The cooling engine will operate continuously (if it were to stop, it will reverse its motion direction. As a result, acting as a cold-end engine, giving heat back to the vessel and increasing its temperature). The engine provides the cooler with a specific frequency to achieve the highest efficiency. However, the frequency couldn’t be determined nor calculated, since we couldn’t neither build the engine nor simulate it, especially in Venus’ conditions. The Stirling cooler has a similar cycle of compression and expansion. However, it has a reversed mechanism compared to the Stirling engine. The mechanism follows and cools the system via 2 stops: pumping heat out of vessel and then rejecting to the environment.

The enclosure will take the shape of sphere. A sphere is a highly sturdy structure. The uniform distribution of stresses on the sphere's surfaces, both inside and externally, indicates that there are no weak places. Hence, providing maximum structural strength against high pressure.

The enclosure consists of two spherical and rectangular vessels with a vacuum in-between. The inner rectangular vessel , where the electronic components, has a temperature of 250° C (523K). The key aspect to prevent heat penetration in each vessel is providing sufficient heat insulation from the environment. The insulation was chosen to be a Multi-Layer Insulation (MLI) with a vacuumed space between its layers.

MLI mainly depends on the vacuum for heat insulation. MLI’s layers cannot touch each other since heat will be transferred via conduction. As a result, netting is used between the layers. It is vacuumed to prevent heat transfer via convection. The only option left for heat transfer will be thermal radiation (according to Stefan–Boltzmann law, any body that has temperature emits radiation, and its energy is directly proportional to its temperature). However, the sheet reflects the radiation back to its source. Add more sheets, the portion of waves reflected will be much higher.

Inside the cooling system, both the Sodium Sulphur batteries and electronic components are located. Sodium Sulfur batteries are used as they do not experience the fatigue and degradation problems associated with the continuous cycling of solid electrodes and could continue to cycle forever in an ideal cell; its efficiency is 85-90% with an energy density of 220 (W -h/kg).

While working on this design, there were some discussed features; so that the idea meets our goals. The features include the efficiency of the flywheel’s energy storage density and the sustainability of it providing the energy at any conditions, and the batteries ‘constant energy supplement as shown in the following tables 1 ,2.

Given all these outstanding features, this solution shall fulfill the requirements of the challenges and can survive on Venus for over 60 Earth days. 

*note * all figures are located in the final project link

Space Agency Data

When developing the proposed solution, various resources were used in the process. From all of those resources, the most vital ones were the sources found on NASA’s websites. The information gathered from those sites ranged from the daunting problems on Venus to underdevelopment solutions (recommendations). From the sites, Venus’ extreme conditions were understood. Moreover, the reasons behind the failure of previous missions. Based on the gathered info, the approach to solve the problem was determined. The approach made the design mainly focuses on overcoming Venus’ high temperature and pressure, using some of Nasa’s proposed solutions. For instance, the used high-temperature sodium Sulphur batteries and the recommended Automaton Rover for Extreme Environments (AREE). 

Hackathon Journey

The Nasa Space Apps hackathon is one of the world's largest annual hackathons for space and science. It is the first destination of many dreams to come true, and the end of small journeys; to give chances for bigger ones to be started. Managing time by making plans and putting in powerful work strategies was the key to running a successful hackathon.

The journey to the final phases of the solution was fruitful and pleasant. We've learned a lot about Venus, the previous missions conducted there, and the studies that followed them. We used them as a starting point to continue working on the flaws while taking into consideration the approach of the forthcoming planned missions.

Our strategy was to divide the tasks into portions according to our skills and interests. The tasks include researching, media designing, documentation, and preparation for the evaluation. We were able to overcome the challenges of finding the solution more easily by dividing the roles. Each member has been in charge to finish their portions, thus putting our idea in the spotlight.

References


Exploring Venus Together

Your challenge is to design an energy storage system that will power a surface lander or rover on the surface of Venus for at least 60 days, so that there is a viable energy storage capability for long-duration exploration missions.