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| Fig. 1: Standard electrolysis process. (Source: Wikimedia Commons) |
H2O can be found almost everywhere in our universe. Although we normally refer to it as water, the appearance of ice and water vapor has a near common appearance among our nearby celestial bodies. [1] The Moon has it, Mars has it, as well as many other orbital bodies close to the proximity of Earth. This ice, water, and water vapor has the potential to be turned into rocket fuel through the process of electrolysis. [2] With an ever increasing ability to harness the power of the Sun through efficient solar panels, as well as the ability to take decaying radiation generators further into space, the ability to travel further, quicker and more efficiently is becoming a reality.
The process of electrolysis involves running a current through a sample of water which contains a soluble electrolyte. This breaks the bonds of the H2O molecule, creating oxygen and hydrogen gas which are released separately at the different electrodes. Modern catalysts incorporate many different elements and configurations, for example cobalt-phosphate catalysts. [3] On Earth, with the presence of gravity, the gases can then be separated through difference in density so that they can be gathered and processed. In space, centrifugal forces of rotation would have to be employed in the absence of gravity. If the process occurred on a large mass, like another planet or moon, the local gravity would be sufficient to continue the process.
The process of electrolysis involves running a current through a sample of water which contains a soluble electrolyte. This breaks the bonds of the H2O molecule, creating oxygen and hydrogen gas which are released separately at the different electrodes. Modern catalysts incorporate many different elements and configurations, for example cobalt-phosphate catalysts. On Earth, with the presence of gravity, the gases can then be separated through difference in density so that they can be gathered and processed. In space, centrifugal forces of rotation would have to be employed in the absence of gravity. If the process occurred on a large mass, like another planet or moon, the local gravity would be sufficient to continue the process.
This process has been proven before in space in order to provide oxygen supplies for manned space missions, avoiding the need to carry large, high pressure oxygen storage tanks for the crew. The International Space Station once conducted this process to test the feasibility and benefits of local oxygen creation. Should the process of space based electrolysis continue to develop and be successful, the ability to process the abundance of water spread throughout our solar system would drastically decrease our cost to move about between destinations.
Splitting molecules doesn't happen just from wishful thinking, however. Energy is needed to break the bonds in a H2O, requiring a readily accessible power source able to convert the water compounds into rocket fuel. In space, there are two commonly used sources of energy: solar and nuclear.
Solar energy is one such abundant power source in space. With naturally occurring energy beaming to a spacecraft from far, far away, the use of solar panels provide a near infinite access to solar energy. However, the further you are from the Sun upon collection of solar rays, the weaker those rays will be. Solar efficiencies are increasing every year with some economical units being optimized for mass production. [4]
Nuclear energy, on the other hand, needs to be carried with the spacecraft. Spacecraft based nuclear power plants are designed for a nuclear material to naturally decay, producing heat in the process, which is thermally converted to energy for the satellite to use. Some advantages of this local source of energy include the constant access to power, even when the Sun isn't in a direct line of sight, as well as the ability to provide heat for a satellite's electronics to function. Some disadvantages include adding to the overall weight of the system compared to solar panels, as well as having to add radiation shielding to protect the onboard electronics.
H2O exists in many forms on the orbiting bodies in our universe, but none in closer proximity and greater abundance than the moon. The moon is estimated to have water-ice built up in the permanent shadow of lunar craters on the order of hundreds of thousands of pounds. [5] Mars has ice on its cooler north and south poles as well as spread about in glaciers on its surface. [6] Europa, one of Jupiter's moons, has long been thought to have a vast ocean of water beneath its frigid surface, occasionally launching signs of geysers of water hundreds of feet into the air. [7] These kinds of diverse fuel stockpiles provide an incredible opportunity for spacecraft to collect, process and use space-based rocket fuel on the way to their destination.
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| Fig. 2: These images show a very young lunar crater on the side of the Moon that faces away from Earth, as viewed by Chandrayaan-1's Moon Mineralogy Mapper equipment. (Source: Wikimedia Commons) |
Instead of having to carry fuel with a spacecraft all the way from Earth, the ability to refuel in space makes travel around the universe hyper-efficient in terms of both time and money. Launching satellites into orbit is not an inexpensive endeavor. In recent times, launch costs have recently hovered around $10k USD per kilogram lifted to earth transfer orbits, but newer advances in technology by companies like SpaceX have reduced costs nearer to $2k USD per kilogram. [8] For comparison, the weight of a baseball is about equivalent to 0.45 kilogram (1 pound).
Maneuvering spacecraft using that same fuel into further reaches of the universe requires an ever increasing amount of fuel to achieve the task. Having fuel already processed and ready for use on extraterrestrial locations can greatly reduce the cost of exploring our universe. Transporting devices which would harvest water resources and convert them into rocket fuel would need to be constructed on Earth and then sent to their destination using conventional methods. However, once that up-front cost has been invested in, the payout would begin immediately upon the transfer of rocket fuel to a spacecraft.
Should the exploration of our universe still remain a priority for the human race, further research must be made into the feasibility of remote, autonomous water harvesting and rocket fuel production units in order to re-supply our next generation of spacecraft. Although the up-front cost of this research might prove to be expensive, the investment in future cost-saving space travel technologies will pay in abundance.
© Jack Goodwin. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. Wenz, "23 Places We've Found Water in Our Solar System," Popular Mechanics, 16 Mar. 2015.
[2] S. Siracusano et al., "An Electrochemical Study of a PEM Stack For Water Electrolysis," Int. J. Hydrogen Energy 37, 1939 (2012).
[3] M. W. Kanan, Y. Surendranath, and D. G. Nocera, "Cobalta Phosphate Oxygen-Evolving Compound," Chem. Soc. Rev. 38, 109 (2009).
[4] M. A. Green et al., "Solar Cell Efficiency Tables," Prog. Photovoltaics 23, 1 (2015).
[5] N. J. S. Stacy, D. B. Campbell, and P. G. Ford, "Arecibo Radar Mapping of the Lunar Poles: A Search For Ice Deposits," Science 276, 1527 (1997).
[6] "N. B. Karlsson, L. S. Schmidt, and C. S. Hvidberg. "Volume of Martian Midlatitude Glaciers From Radar Observations and Ice Flow Modeling," Geophys. Res. Lett. 42, 2627 (2015).
[7] E. J. Gaidos and F. Nimmo, "Planetary science: Tectonics and water on Europa," Nature 405, 637 (2000).
[8] D. Kestenbaum, "Spaceflight Is Getting Cheaper. But It's Still Not Cheap Enough," NPR, 21 Jul 11.
