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© 2006 by Donald F. Robertson.

E-MAIL: DonaldFR@DonaldFRobertson.com.

This article originally appeared in substantially shorter form in SPACE NEWS

Trade has had a storied role in humanity’s expansion across our globe. From the ancient Silk Road, to the trade in tea and spices that grew the British Empire, to today’s undersea drilling platforms and supertankers, trade has motivated and financed many difficult exploratory expeditions and outlandishly expensive projects.

How can we use the power of trade to help propel us into the inner Solar System?

The Silk Road was a network of land and sea routes that delivered raw materials, high-value items, as well news -- lapis lazuli from Afghanistan; British tin; Chinese jade, gold, and indeed silk -- over truly amazing distances. At different times, it extended over land from North Africa, to the northern reaches of China, and even to Europe. By sea, it reached as far south as India and Ceylon.

The Silk Road had its origins thousands of years before the common era, though it was formalized much later by China and Persia. By 475 BCE, the Persian Royal Road ran almost three thousand 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. According to the Roman historian Annaeus Florus, “Indian [envoys] who dwelt beneath the vertical sun [thought the city of] Rome of less moment than the vastness of the journey . . . which they said occupied four years.”

The requirements of trade on the Silk Road pushed existing technologies and skills to new heights and in new directions. This may have included the domestication of some pack animals. Caravan-related technologies involved improved rigging and the ability to store and transport water over long stretches of open desert and grassland. It also motivated on-going improvements in littoral shipping on the seas. The existence of trade led directly to better tools for trade, which in turn made trade easier.

Creating the Silk Road took no central planning. It required no directed research and development. It resulted from the accumulated, unplanned actions and inventions of generations of small companies of traders. These groups came from many mutually-alien and distrustful civilizations. Collectively, they created a whole far greater than any of its parts and 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 create similar kinds of long-distance trading routes and technologies?

Many ideas have been proposed. A key part of what was traded over the Silk Road was news and information. We currently trade information via communications satellites. We disseminate and barter knowledge obtained by scientific, military, and civil applications spacecraft. In turn, these information activities support spacecraft manufacturing and launch vehicle assembly. It is worth noting that by requiring regular transportation to a relatively high energy location -- geostationary Clarke Orbit -- the communications industry has kept viable our ability to reach deep space. 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 someday be used to fuel clean nuclear fusion reactors, but it is diffused in the moon’s regolith and therefore may be difficult to mine, and a suitable market for this product has yet to materialize.

Any or all of these old ideas may yet prove important, but they will be realized far in the future. To quickly us get beyond the Space Shuttle and Station, we need something sufficiently valuable to finance private or partially private expeditions into 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. It should be marketable in small volumes or large. It must be in great demand, yet simultaneously, it must be extremely valuable.

Oxygen perfectly fulfills that stringent set of requirements.

The demand can hardly be in question. Either by itself, or in a compound, oxygen is by far the heaviest component of 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. We grow our food and bathe in it.

Oxygen is dense, 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 may be possible to simply scoop them up, then melt the oxygen out with solar heat concentrated with mirrors -- while leaving behind another useful resource, the glass needed to make the 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 may 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 return trajectories into Earth’s atmosphere, limiting the opportunities to deliver oxygen anywhere else.

That may 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, do they see 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 reenter 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 stored for the next flight back to the moon. With even a few flights per year, it may 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 would already be in place. Later, next-generation applications satellites could also 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 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 based in San Francisco. He has a degree in archaeology.

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