Making Rocket Fuel From Water
How it will change the future of space exploration
Nothing excites us quite like the discovery of water on another world. We marvel at the channels and alcoves on Mars, or sit daydreaming about the alien life that may crowd beneath Europa’s sinister and mysterious covering of ice. Even our own planet’s water is a precious resource tied closely to the emergence of all organisms. Yet the discovery of water on the moon excites us for a different reason. It’s not necessarily because the moon may share an Earth-like history as is the case with Mars. Nor is it because we believe alien organisms slink across those shadowy poles. Ice on the moon excites us because it could allow us to create rocket fuel in space, and to open up immense new economic opportunities for a few pioneering countries.
Turning water into rocket fuel is a gorgeously simple process. Water, as we all know, is composed of hydrogen and oxygen atoms bound together into a molecule. Hydrogen is both the most abundant and the lightest of all known elements, yet it burns at an intense 5,500°F (3,038°C). It is the most efficient rocket propellant to date as it gives us the highest specific impulse. Oxygen, on the other hand, is taken in by airplanes where it is then combined with the plane’s fuel to create combustion. Rocket ships do not have this luxury since they operate in the oxygen-starved belly of space. They must bring their own oxygen reserves along. But these two elements must first be separated from one another if we’re going to use them to power our rockets.
To do this we introduce an electric current to the water. Through the process of electrolysis the hydrogen and oxygen atoms are split apart. The hydrogen will act as the fuel while the oxygen acts as an oxidizer. These must be stored as liquids in two different containers until they are pumped into the combustion chamber and then ignited. Liquifying oxygen and hydrogen is not an easy task. Liquefaction requires temperatures hundreds of degrees below 0. In the case of liquid hydrogen it must be stored at -423°F (-253°C). Any source of heat during spaceflight can cause the hydrogen to evaporate or expand and explode. It must therefore be insulated from air friction, sunlight, and rocket exhaust, as well as being fitted with vents in case it does absorb heat and expands. Within the combustion chamber the liquid hydrogen and oxygen ignite and then burn, creating exhaust which in turn passes through a nozzle and provides the rocket with thrust.
Thrust is what allows the rocket ship to then escape the Earth’s pleading gravity well, like prying yourself away from the hand of someone you love. And with that — with not much more than a couple simple elements found in a small pond of water — you can explore the dusky dark bounds of the Solar System.
There are an estimated 600 million metric tons of lunar ice which can be harvested and used in a future extraplanetary refueling station. Rockets would no longer have to take so much propellant with them, lowering the rocket’s weight and amount of fuel needed for liftoff from Earth. A fueling station on the moon would significantly reduce the cost of missions to any nearby worlds, including the ever dreamy destination of Mars. Being able to make oxygen and hydrogen would also make missions safer since astronauts could replenish their supplies during an emergency. Lunar ice is promising to say the least. But the problem comes with the harvesting.
Blanketed over the moon’s bedrock is a layer of loose dust and rock known as regolith. The ice on the moon doesn’t come in huge sheets the way we sometimes see here on Earth. It instead manifests as fine grains mixed into the lunar soil. Most of these ice deposits are located at the poles where permanent shadows and unforgiving temperatures make the terrain punishing for our robotic machines. Temperatures can get as low as -415°F (-248°Ç). Ideally there will be a number of these machines working to mine lunar resources all at one time but it isn’t reasonable to have teams of people watching over each machine. One of the main goals in lunar mining technology is to make them as autonomous as possible so that only one person is required for a group of machines — not the other way around.
One of the proposed methods for extracting this ice involves something known as sublimation. Sublimation is when a substance in a solid state jumps straight to the gas state without first becoming a liquid. In this case ice would become a vapor without ever passing through the phase of liquid water. Lenses towering over the edge of craters would concentrate sunlight onto the soil, heating the soil up to -63°F (-53°C). This would be enough to cause sublimation of the ice. The water vapor is collected by a cold surface and then ushered away into a processing plant where it can undergo the process of becoming rocket fuel. The energy needed for this could come from solar panels or from a nuclear reactor.
Collected water must also be purified before use. Failing to properly purify the water could not only make the fuel unusable, but also unstable and dangerous to handle. The purification process presents a unique challenge. Engineers do not have samples of lunar soil with which to repeatedly test their purification systems, meaning that at least some of their work will have to hinge on hope — the hope that all these robotics will be able to do their job once they’re finally on the surface of the moon.
Other precious resources available on the moon include helium-3 for use in fusion energy and rare earth metals vital to our modern electronics. NASA’s Artemis program already has a goal of returning astronauts to the moon by 2024, including the first woman to ever set foot on its surface. China and Russia also plan to send their own people with China setting a goal of doing this by 2030 and Russia of doing it by 2040. It is an endeavor that will cost at least $20 billion according to NASA’s estimates. This plan to return to the moon includes a proposal for mining its many resources and proposals to keep countries’ bases from intervening with one another.
In the past our companion satellite has been everything from a deity to a destination. She has given us a radiant light to admire even after the sun has long set. Now the moon is transforming into a stepping stone: a place where we will test our technology — and ourselves — before we set off deeper into the Solar System. Here is a treasure-trove of a world, and one ripe for conflict between countries. For myself it is both exciting and yet heart-wrenching to hear about the plans for lunar mining. I do not want the moon to be seen as just another resource in our universe. Some of us have forgotten how to cherish the Earth as we industrialize its once wild, untouched body. It is disheartening to think this sentiment might stretch into the rest of the universe, beginning first with a waning moon.
Don’t forget to watch the beautiful alignment of Saturn and Jupiter this Monday night. While this alignment does happen every 20 years, 2020 will be the first time in 400 years that the planets pass so closely to one another. You can see them in the sky with your naked eye just after sunset. I find 30 mins after sunset is the best time to see them. They will reside just southwest of the moon.
Here is NASA’s guide to finding the Great Conjunction:
“Find a spot with an unobstructed view of the sky, such as a field or park. Jupiter and Saturn are bright, so they can be seen even from most cities.
An hour after sunset, look to the southwestern sky. Jupiter will look like a bright star and be easily visible. Saturn will be slightly fainter and will appear slightly above and to the left of Jupiter until December 21, when Jupiter will overtake it and they will reverse positions in the sky.
The planets can be seen with the unaided eye, but if you have binoculars or a small telescope, you may be able to see Jupiter’s four large moons orbiting the giant planet.”
