Engineering

Martian Batteries

by Neus Sabaté

Since the launch of Explorer in 1958, batteries have been used in Earth orbital and planetary spacecrafts to supply primary electrical power or store electrical energy generated by on-board solar or radioisotope power systems. These energy storage systems are used on spacecraft for various functions, being the most relevant ones: to provide power to the spacecraft subsystems before deployment of the solar panels, fire rocket motors for mid-course correction, meet temporary power needs during eclipse periods, provide power for payload instruments and meet peak power demands derived from data transmission or surface mobility. Primary batteries (single discharge only) are typically used in missions, such as planetary probes, that require electrical power for a period of a few minutes to several hours. Rechargeable batteries (also referred to as secondary batteries) are used mostly in solar-powered spacecraft to provide electrical power during eclipse periods and for load levelling. When considering Mars Surface Missions, the need of advanced rechargeable batteries with high specific energy, energy density, cycle life capability and low-temperature operational capability has been largely identified. Perseverance rover, for example, carries a radioisotope power system that uses the heat of plutonium’s radioactive decay to generate a temperature gradient on a thermoelectric generator. The generated power is stored in two rechargeable lithium batteries. The power generator weights 50 kg (5 kg corresponding to plutonium) and produced approx. 100 watts. The generated energy is partially stored in the batteries in order to provide power to the rover overnight. Although this solution is dimensioned to provided constant power for at least 10 years of operation, it is clear that it cannot be the sole source of power for portable/movable appliances. Yet, to meet peak power demands, large solar panels and large (and therefore heavy) batteries for energy store will have to be transported to Mars in future missions. Ultimately, this turns into a heavy expense of fuel and need of space in every
mission.

To ease this concern, I propose to proceed in the same way as my research group is already doing on Earth: to built-up batteries from the rough and abundant materials present near the location where the energy is needed. On Earth, we seek for identification of organic and inorganic electroactive compounds present in organic waste and test their capability to be oxidized or reduced in primary cells. When transferring the idea to Mars planet, my goal is to build up a primary battery with the compounds readily available on Mars. In particular, Mars surface seems to be rich on iron and more specifically in iron oxide and their derivates, which give a characteristic reddish colour to the planet surface. Therefore, during my stay at the Mars Desert Research Station, I will develop an iron-based battery. First, with commercial iron compounds and later, with iron extracted from the rocks present at Station surroundings, which are rich in hematite (iron oxide), one of the materials identified in Mars. Moreover, as water is scarce on Mars surface, I will use urine from the crew as battery electrolyte. Finally, in order to show a practical use of energy generation with the Martian batteries, I will power an LED lighting system to germinate and grow edible greens.