Venus Power Bank

https://drive.google.com/drive/folders/1gdEBPKIXlsbdDfmxdjAlHIMEHxw3bUCk

https://drive.google.com/file/d/1xzBNJIfWAG8SDJgBTA3U7eKQjk-Jj2Rv/view?usp=sharing

1 Research of existing solutions

We conducted a study of existing solutions and came to the conclusion that the current solutions run into these problems:

• adaptation of cell and battery designs for space applications
• thermal stability of components under Venusian surface conditions
• stability of seals and terminals under conditions of high temperatures and pressures on Venus
• corrosion of current collectors at high temperatures
• impact of weightlessness on performance.

Based on NASA-provided resources (which are attached to this challenge), we concluded that molten salt batteries with lithium alloys and a metal sulfide cathode with an optimized cell design showed an extended lifespan of ~30 days at Venusian surface temperatures.

These systems have shown good recharging capability and can be combined with a power source (eg wind power, solar power, RTG) to support extended exploration of the surface of Venus.

We also highlighted the main strategies for finding a solution and fixing the problems of current batteries:

• Identify new cathodes with reduced solubility and higher specific capacitance.
• Modify FeS with surface coatings (carbon, metal oxides)
• Evaluate self-discharge and rechargeability (of Li-FeS cells)
• New electrolyte with reduced cathodic dissolution
• Solid electrolytes
• Change cell design with improved seals

(Taken from https://solarsystem.nasa.gov/resources/549/energy-storage-technologies-for-future-planetary-science-missions/)

2 Choose LiAl-FeS2 (lithium aluminum-iron disulfide)

2.1 Li-Ion Batteries Characteristics

Advantages:

• It has high energy density which is two times compare to Ni-Cd.
• The battery can hold the charge and it can lose only 5% of its charge every month.
• The Lithium-Ion battery is rechargeable.
• The battery can handle many charge/discharge cycles.

Disadvantages:

• Li-ion batteries: Not stable above 70C.
• Even with thermal management, the survivability life is limited to a few hours.
• It is relatively expensive.
• If the "separator" gets damaged, it can burst into flames.

2.2 LiAl-FeS2 (lithium aluminum-iron disulfide) details

The operating temperature range is about 375°C - 450°C.

The most advanced version uses a cylindrical bipolar configuration with disc-shaped elements. The unit cell consists of anode and cathode disks, separator, electrolyte and interelement connectors. The anode is made from pressed alloy powders and some electrolyte. The cathode is made of pressed FeS2 and electrolyte. The separator is made of pressed MgO powder.

With optimized cell components, cell design and operating parameters, lab test cells were fabricated and demonstrated continuous operation for ~26 days at 475°C (https://www.sciencedirect.com/science/article/abs/pii/S0378775319314855)

2.3 Idea of using LiAl-FeS2

Our main idea is to keep the battery from degrading. We ship batteries dry charged (no electrolyte added). Using the voltage demand trigger-detector (with the complete degradation of the used battery), we connect the next one in series and so on in turn.

The concept of the solution is to use special heat-resistant materials to create a battery that can withstand extremely high temperatures without reducing efficiency (up to 26 days at 500 C), and a dry-charged battery, the separator of which does not contain a conductive electrolyte until the start of use.

The cathode is made of LiAl, the anode is Fe2S, and the separator is pressed MgO. Thus, we have a practically ready-to-use energy keeper, but at the same time we eliminate the main drawback of this solution - the destruction of the cathode and the loss of stored energy due to self-discharge. This is due to the fact that without an electrolyte in the separator, the electrons between the electrodes do not flow from one to the other. The electrolyte itself is located in a tank adjacent to the battery, locked with a shutter, which is controlled by a servo, with two redundant activation systems on the first battery, and three on the other two.

The first activation system is a timer that opens the reservoir shutter on the first battery upon landing on the surface, activating it.

The second system is a voltage sensor installed on the second and third batteries, which measures the voltage level on the current active battery. At low voltage, signaling the end of the life of the previous battery, the valve of the tank opens on the next one. However, consumption is transferred to a new battery.

The third signaling system is a manual radio control that allows us to manually send a signal over a period of 2 to 10 minutes, based on the location of the planets next to each other.

After the separator is soaked with electrolyte, it leaves the mothballed state and enters operation, powering the rover. Thus, the general solution to the problem under consideration lies in two ideas:

1) The use of batteries, consisting of materials specified by us, withstanding uncompromisingly aggressive conditions on Venus, which is confirmed by relevant laboratory experiments

2) Creation of a "mothballed" sequential chain of energy carriers waiting in the wings for activation until the moment of need. The separation of the electrolyte from the magnesium oxide (separator) allows us to solve the problem of self-destruction of the most vulnerable element of the storage system - the ferum disulfide cathode.

Summing up - the solution developed by our team with a chain of 3 batteries allows the rover to operate up to 78 sols. With an increase in the number of links, the service life can be increased almost directly proportionally.

3 LiAl-FeS2 Battery power calculations

We calculated energy consumption for Rover from Nasa article in assuamption that it's consume only electrisity energy.

(https://www.nasa.gov/sites/default/files/atoms/files/niac_2016_phasei_saunder_aree_tagged.pdf)

In article we can see in Table 4: Power Estimation List (PEL) we can see some assuption how mach energy consume each Rover action and quite short description about mission:

So, we need make some asumption about 1 Rover life cycle per some period of some time to estimte needed amount of energy. We will assume that Rover do in 12 hours set of de low actions:

We assume that power consumption given with losses due resistance of metal.

So, in 12h do this actions and consume some energy. We have some margins and we wil take in account them Min without margins and Max with margin.

4 Recharging capabilities

We see that weight of batteries set to high. So, lets assume that we can rechage batteries several times per day. LiAl-FeS2 Battery has the ability to recharge. Depending on the number of recharges per day, the amount of battery mass required to maintain the required power of the rover varies. We calculated the power of the battery and the rover, and also built a graph of the dependence of the amount of battery (in kilograms) on the number of recharges. And in table below we can see that can significant reduce batteries set weight:

4.1 Best case (minimum losses from power source)

So, if we can recharge our batteries 2 times per day (each 12 hours) we can fit Rover restriction on Power storage weight from Table 1: Mass Equipment List (MEL)

4.2 Worst case (50% losses from power source)

We need to consider worst case when we have 50% loses, due high temperature. Lets do the same calculations, but assume that we need 2 time more energy due 50% of electrisity energy loses.

4.3 Conclusion

For 24h Rover activities we need too much batteries, so if we can recharge batteries several times per day we can significantly reduce their weight. 2 times per day recharging (each 12 hours) will fit Rover restriction on Power storage weight (in best case).

1. https://solarsystem.nasa.gov/resources/549/energy-storage-technologies-for-future-planetary-science-missions/ - used for research the existing solvings
2. https://www.nasa.gov/sites/default/files/atoms/files/niac_2016_phasei_saunder_aree_tagged.pdf - used for rover and battery power calculations

Our team has been participating in the NASA hackathon for the second year in a row. We are very glad that this opportunity is given to show our knowledge. We are mostly mathematicians and programmers, but we are always happy to get closer to chemistry and physics.

During the invention of the idea, we communicated with many experts, we were glad to make new acquaintances. The advice of a person who was developing batteries for Venus in the USSR was especially helpful.

Unfortunately, we spent most of the time online, but in the final stage we still managed to meet in person and discuss the structure of the project and presentations.

Each member of our team is inspired by the idea of ​​changing this world, so we have chosen a task that will be a real challenge for everyone and will help science get a little closer to the solution.

https://www.sciencedirect.com/science/article/abs/pii/S0378775319314855

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