A recent report funded and published by the United Launch Alliance outlines the the potential viability of mining the Moon for rocket fuel. At over 170 pages, it is quite a read but Philip Metzger, one of the authors wrote a good summary on his website. I thought I would try and make a similar summary here with slight more explanation, and where it fits into the future NASA plans of getting back to the Moon and going onward to Mars and beyond. It all revolves around water, or more specifically ice. For many years we thought the Moon was a baron rocky cold desert. The samples that the Apollo astronauts brought back from the Moon, and the Soviet Luna samples imply that there is no water in the rocks or regolith. The trace amounts of water found in the samples were assumed to be contamination. Although, in 2008, a study of the Apollo rock samples did show some water molecules trapped in volcanic glass beads. Also in 1978, Soviet scientists published a paper claiming the 1976 Luna 24 probe contained 0.1% water by mass. Plus the Apollo 14 ALSEP Suprathermal Ion Detector Experiment (SIDE) detected the first direct evidence of water vapor ions on March 7th 1971. None of these discoveries were taken as conclusive proof of water on the Moon at the time.
On September 24th 2009 it was reported that the Moon Mineralogy Mapper (M3) spectrometer on India’s Chandrayaan-1 spacecraft had detected water ice on the Moon. The map of the features show that there is more at cooler, higher latitudes, and in some deep craters. Basically, the parts of the Moon that see the least light like the poles and far into craters near the poles have managed to keep the water on and below the surface. This water is in a number of different states, some locked up in minerals, some in ice form, and others in OH form, not technically water but near. This has lead to a number of new possibilities of inhabiting the Moon and using its resources. This is why the United Launch Alliance funded a paper on the possible use of mining this water and using it as a future fuel source. By some estimates there could be as much as 10 billion tonnes of water on the Moon. The water could in theory be mined, and through electrolysis turned into hydrogen and oxygen, the fuel that got men to the Moon on the famous Saturn V.
But you have to ask, why does it matter? the Moon is far away, and surely water is just useful for astronauts living on the Moon to survive. Well the report talks about the business case to use the water as fuel, in the form of hydrogen and oxygen. First we need to understand the commercial satellite world, and geostationary satellites. When first sending up such satellites, the way to do it was to use a multi stage rocket, with the first stage getting to a Geostationary Transfer Orbit (GTO) and then the second (upper) stage being used to get into the Geostationary Orbit (GEO). Recent years have allowed the first stage to be hugely improved and often reusable by companies like SpaceX and Blue Origin. The second stage hasn’t had the same improvements though. Traditionally the second stage was a normal, and very heavy liquid rocket. This meant that it was very expensive to get things to GTO, much more difficult than LEO. The rocket was also thrown away afterwards, and as it is so far out it will take hundreds or even thousands of years to burn up in the atmosphere.
Now we do have a better way to do it, sort of. I talked recently about the rise of electric thrusters. A lightweight, cheap and powerful solution when used over a long period of time. Over the time span of years they can pick up speeds of thousands of miles per hour. That is the biggest downside of them though, in this situation, slowly pushing the satellite to orbit, they take up to a year to get a satellite into position. That is a year that it could be making the owner money. By some estimates that year could lose $100 million in revenue just waiting for the slow thrusters. By all accounts though, this is still cheaper than launching a large traditional rocket upper stage. The electric thrusters are amazingly light comparatively, which means you need a smaller first stage to get it up to space in the first place. The key thing you have to remember about these geosynchronous satellites is that they already have a huge price tag, some can cost upwards of half a billion dollars to build and launch.Part of the reason is that they tend to be huge, in size and weight. Some have been as big as London double Decker buses, and weigh 6 tonnes. The rockets then need to get them to one of the furthest and time consuming orbits, a costly exercise.
So why can this Moon mining idea help? well the Moon is in lots of countries space plans at the moment. China are currently sending lots of probes, and by some accounts looking to get humans there. The USA are building the SLS which should be able to get humans to the Moon, and are also developing the LOP-G idea. The concept to have an orbital station around the Moon, almost like a fuel stop for rockets going on to further parts of the solar system. This idea to mine the Moon for hydrogen and oxygen could be transferred up to this orbital space station to be transferred to the rockets that need it. This is where the geosynchronous satellites come in. Imagine if this fuel, that is dug up and processed by robots, and then sent up to an orbital station could be brought back closer to Earth via a space tug. This space tug could meet up with the rocket with the satellite on board. The upper stage rocket could have been sent up with no fuel (the heaviest bit) and is fueled by this space tug. It would allow for the speed of the old style engines, but the weight of newer electric engines. As long as the price for this whole system is cheaper than the $100 million it currently costs, then it could be a viable option. All the while, setting ground work for space agency’s to have viable water sources that can be used for future exploration. It may be the future of space travel.
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