Survive 60

Universal Event | Exploring Venus Together

THE E-BANK 238

High-Level Project Summary

We developed a solid-state energy storage system that converts heat generated from the decay of radioisotope Plutonium-238 enclosed within a Radioisotope Heater Unit (RHU) to electrical energy via a tungsten foil and a multijunction thermal photovoltaic cell developed by MIT and NREL labs. The presence of an exterior aeroshell coating made of polymer-based aerogel protects the interior components from high temperatures, pressure and toxic gases. The E-BANK 238 is a potential solution to the world’s current energy needs due to Plutonium-238's good power density to account for low energy conversion efficiencies and long half-life to provide useful power output over a long lifespan.

Link to Final Project

https://mehaksingal13.wixsite.com/mysite-1

Link to Project "Demo"

https://m.youtube.com/watch?v=q6Loc1Gk5n8

Detailed Project Description

BACKGROUND

PLUTONIUM-238

Plutonium-238 (Pu 238) is a unique material, known as a radioisotope, that decays due to its instability by the emission of high energy particles. The particles emitted include alpha particles, beta particles and gamma rays. As the Pu 238 decays, the emitted alpha particles interact with surrounding material, leading to heat generation.

Pu 238 possesses a high power density of 0.56W/h, half life of 88 years, shielding requirements low enough to be stopped by paper.

238Pu94 → 234U92 + 4He2

238Pu94 → 234U92 + α

WHAT ARE MULTI JUNCTION TPV CELLS?

TPV cells are basically solar cells but instead of absorbing light energy from the sun, they use a hot emitter surface. They convert thermal radiation from various heat sources such as the combustion of fuels, industrial waste heat, and concentrated solar or nuclear energy into electricity. Multijunction TPV cells are cells with multiple p–n junctions made of different semiconductor materials in which each junction produces an electrical current in response to different wavelengths of light. The many junctions allow for the absorption of a broader spectrum of wavelengths that enhances the cell’s absorption of photons to convert to electrical energy.

COMPOSITION AND WORKING OF THE E-BANK 238

The E-BANK 238 is made up of a radioisotope of Pu 238, in the form of plutonium dioxide as its primary source of energy. This substance is reinforced with its own corrosion- and heat-resistant shielding, in the form of iridium and high-strength graphite, followed by a carbon-to-carbon aero shell for impact protection and containment, during entry and exit of the landing planet. This entirely forms a Radioisotope Heater Unit (RTU). Heat from the unit is then transferred via heat distributor block to a tungsten foil, which then converts 15% of the conducted heat to light of a broad spectrum of wavelengths emitted. This light is incident on the multijunction TPV cells developed by an MIT research team. The cells are made of an outer gallium arsenide coating of low conductivity, to prevent the cell from overheating, and to absorb more photon energy. Each junction layer is composed of different semiconductor pairs and band gaps. Each band gap is tuned to absorb a specific array of light, enabling a wider range of it to be converted to electricity.

A gold mirror is placed at the bottom, reflecting any stray photons back to the cell to be absorbed, or to the tungsten to be recycled. This gives the cell an improved efficiency from approximately 33% to 40%. The waste heat produced is removed via a heat sink, made of a thin layer of aluminium and heat pipes that pass a cooling agent. The inner components are further enclosed within protective layers of more iridium, Multi layer Insulation(MLI) and a polymer-based aero shell made of aerogel which together combat the extremely high external temperatures, pressure, corrosion and toxic gases.

POWER CALCULATIONS

Every time plutonium-283 decays, it releases 5.5MeV of heat.

1kg of Plutonium then yields 3.5x10^15(MeV) and this equals 550J/s.

The Tungsten foil converts only 15% of this energy to light.

This results in a 82.5W/h output.

40% of this energy is then converted to electricity which yields 33W, and powers up the lander.The E-BANK 238 has a plutonium composition of 1.5kg, which yields an estimated energy requirement of 49.5W/h

The final energy output is 594W/h, considering the 12 PV cells on this energy bank.

Our power estimations calculations were guided by the Current Best Estimation (CBE) of the power needs of the future Automation Rover for Extreme environments (AREE).

Its total power needs are approximated to 400W/h.

OPERATIONAL TEMPERATURE

The E-BANK 238 operates across a wide range of high temperatures. Given that its outer casing of the E-Bank 238 is made of both iridium, and aerogel which have melting points above 1200 degrees Celsius, this is enough protection for the battery from Venus’ high temperatures.

MAKING OF E-BANK 238

https://youtu.be/x_Ee4VlGMgg

3D MODEL LINKS

E-Bank 238 with outer covering:

https://sketchfab.com/3d-models/sketch-fab-9b6bb9015ca247d19ebe2b6e3f4e3f53

E-Bank 238 without top covering:

https://sketchfab.com/3d-models/ess-3d-model-54a5fb42107f46ddb512fe2949b249c9

Space Agency Data

For this particular project, we utilized information about the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) as a reference for our prototype model. Information about the solar intensities at the different altitudes of Venus enabled us to rule out the use of solar energy as a power source for our ESS as we discovered that the solar intensity at the surface of the planet was low. The facts on Plutonium 238 was key in coming up with a heat unit which is the primary source of energy in our E-Bank 238. Data on the energy needs of the future Venus landers specifically the Automation Rover for Extreme Environments (AREE) provided estimations for the power output of our solution.

All this information was retrieved from NASA.

Hackathon Journey

This is our first time participating in this competition. It was a great experience as we learned how to work together virtually, how to be flexible, and how to summarize essays worth of information within just a few sentences. We chose this challenge as it was relevant to our engineering field and it required critical thinking and analysis. The team’s approach to developing this project, and to resolving setbacks, was constant communication across several virtual platforms at once. Having several platforms was a handy backup whenever Internet connectivity faltered, which made online meetings difficult to maintain. Our favorite thing about this journey was the many skills and scientific principles we mastered in such a short time.

We wish to thank: all space stations across the globe, for being so resourceful and supportive, the SpaceApps Discord chat for giving plenty of guidance, and our families for giving us the time and space. We are grateful for this opportunity and platform that allowed us to work on our creativity and ideation.