From the ancient Silk Road, to the trade in tea and spices that helped expand the British Empire, to today’s deep-sea drilling platforms and supertankers, trade has motivated and financed many outlandishly expensive projects into new frontiers. How can we use the motivational power of trade to help propel us into the inner solar system?
The Silk Road — a network of land and sea routes extending over land from North Africa to China and even to Europe, and by sea, from India and Ceylon — delivered news, raw materials and high-value items over truly amazing distances.
By 475 B.C. it ran almost 3,000 kilometers, complete with regular postal stations. Travel times — like those today in space — were often measured in months and years, and undoubtedly involved great danger and physical hardship.
The trade requirements on the Silk Road pushed existing technologies and skills to new heights and in new directions. From the domestication of some pack animals, to c aravan-related technologies such as improved rigging and the storage and transportation of water, to improvements in littoral shipping on the seas, trade led to better tools for trade, which in turn made trade easier.
Creating the Silk Road took no central planning but resulted from the accumulated, unplanned actions and inventions of traders and their sponsoring governments. These groups came from many mutually alien and distrustful civilizations, yet collectively they created a whole far greater than any of its parts. Many historians argue that the Silk Road was key to the flowering and integration of the great civilizations of the ancient world.
Is there anything we can trade in space that would quickly motivate new technologies and finance commerce over similar kinds of long-distance trading routes?
Many ideas have been proposed. A key part of what was traded over the Silk Road was news and information. Today, w e trade information via communications satellites, and we disseminate and barter knowledge obtained by scientific, military and civil applications spacecraft. In turn, these activities support spacecraft manufacturing and launch vehicle assembly. B y requiring regular transportation to a relatively high-energy location — geostationary o rbit — the communications industry has kept viable our ability to reach deep space, which is exactly the kind of synergy we’re looking for.
Unfortunately, these markets, while real and positive, are mature and provide little opportunity for rapid growth or breakthrough advances.
Most suggestions for the future have significant economic shortcomings. Mining asteroids for heavy metals, while potentially a market of literally astronomical value, requires equally astronomical up front investments. Large amounts of private capital would need to be held at great risk for long periods of time before even the smallest return could be expected.
Importing solar power from space has the same problem. Lunar helium-3 may some day be used to fuel clean nuclear fusion reactors — once such reactors have been built — but helium-3 is diffused in the Moon’s regolith and therefore may be difficult to mine. A suitable market for this product has yet to materialize.
Any or all of these old ideas might yet prove important, but they will not be realized until we are well into the future. To quickly get us beyond the space shuttle era, we want something that is needed right away in small volumes, and later in very large quantities. Simultaneously, it must be sufficiently valuable to finance private or partially private expeditions in space. To limit up front costs, it should be readily obtained, easily packaged and close to home so that we can trade it with the tools, techniques and launch vehicles we have today.
This is a stringent set of requirements, but everyday oxygen fulfills every one of them.
The demand can hardly be in question. Either by itself, or in a compound, oxygen is a heavy part of any rocket fuel. We can’t take a useful breath without it. Combined with hydrogen, it is the heaviest part of the water we drink. Water is one of the best radiation shields, and we grow our food and even bathe in it.
Oxygen is dense and readily packaged either as a compound or refrigerated. Oxygen will be needed, in small quantities and large, from the moment astronauts return to the Moon.
Why lift this very heavy element from Earth? In theory, oxygen is easily separated from lunar regolith. It exists as oxides of titanium and iron combined into illmenite. Layers of orange and black glass beads, probably from ancient lunar volcanoes, were found buried under a lava flow at the Apollo-17 landing site. They were exposed in the sides of a later impact crater, and they are rich in oxygen.
Similar pyroclastic deposits are believed to be near the surface at other locations. It might be possible to simply scoop them up and use solar heat concentrated with mirrors to melt the oxygen out — while leaving behind another useful resource, the glass needed to make more mirrors. NASA’s Lunar Reconnaissance Orbiter will use an ultraviolet camera to provide detailed maps of oxygen-rich minerals on the lunar surface.
If water really does exist in the permanently dark interiors of deep polar craters — as is strongly suspected — it could be widely scattered and therefore difficult to mine. If found in useful concentrations, oxygen could be electrolytically separated from hydrogen. The latter would no longer need to be imported from Earth to manufacture water.
At first, lunar oxygen would be used only by astronauts on the Moon, and possibly to fuel Earth-return rocket stages, reducing the logistics train from Earth. Early flights of NASA’s proposed lunar transportation infrastructure will fly direct return trajectories into Earth’s atmosphere, limiting the opportunities to deliver oxygen anywhere else.
That might quickly change. The most likely location for an early lunar base is the lunar south pole, to search for water and to take advantage of the “peaks of eternal sunlight.” These are high polar mountains that stick out of the Moon’s shadow during the two-week lunar night, rarely if ever seeing darkness. They provide abundant solar heat next to a near-infinite heat sink in the permanently shadowed interiors of the craters, ideal conditions for generating power and running industrial processes.
Spacecraft returning from the lunar poles would skip off the top of Earth’s atmosphere over a terrestrial pole to re-enter again, before landing at a temperate latitude on Earth.
It is only a short technological step from a skipping re-entry to aerobraking into orbit around Earth. Once regular flights are contemplated to Earth’s Moon, it makes sense to enter Earth orbit before landing, leaving the propulsion module in space for re use .
Two-way transport, with empty space tugs returning to Earth orbit for refueling, makes it easy to bring surplus lunar oxygen back in the tug’s empty tanks. Some can be drained off to fulfill the space station’s growing requirements for oxidizer and water — itself in a high-latitude orbit — and the rest can be stored for the next flight back to the Moon. With even a few flights per year, it could prove less expensive to supply oxygen this way than to lift it from Earth.
When it is time to prepare the first expeditions to the martian moons, Mars’ surface or an asteroid, the infrastructure to supply oxygen from the Moon already would be in place. Later, next-generation applications satellites also could be designed to use lunar oxidizer for propulsion. If orbital tourism takes off, the oxygen requirement in Earth orbit could rapidly escalate.
Once the basic transportation infrastructure is in place, private individuals or companies could manage the oxygen trade at low marginal costs. Over time, they may find new sources of oxygen and new ways to deliver it, creating diversity of supply and competition.
Here we have the earliest beginnings of trade in oxygen — the start of a new silk road. Like the ancient Silk Road, it can be implemented without much planning or new technology, just by returning to the Moon. Since every conceivable activity in space requires large quantities of oxygen, such a trade would grow in step with further space exploration. Once the trade routes are in place, other high-value products could cheaply be added.
To use oxygen beyond the lunar surface, NASA will need to revisit the decision to use hypergolic propellants to return to the Moon. NASA has decided to use this well-understood technology — instead of the methane/oxygen engines planned earlier — for breaking into and out of lunar orbit and for landing. We will not be manufacturing complex and dangerous hypergolic chemicals on the Moon any time soon, but raw oxygen to be burned with methane is there for the taking.
If we want to establish truly spacefaring civilizations, the oxygen trade is exactly what we need. The United States should do everything in its power to encourage an early “oxygen road” to the planets.
Donald F. Robertson is a freelance space industry journalist with a degree in anthropology specializing in archaeology. He is based in San Francisco.