Recent articles have identified the growing promise of space solar power engendered by advancing technology and new approaches to the century-old concept first proposed by Russia’s Konstantin Tsiolkovsky. True, the recent and ongoing studies undertaken by Japan, China, the European Space Agency, the U.S. Naval Research Laboratory and especially space solar power guru John Mankins, in his NASA Innovative Advanced Concepts project and his book “The Case for Space Solar Power,” do indeed reflect a growing optimism that the delivery of boundless energy from space-based solar power plants may someday come to pass.

There are, however, two missing elements that continue to postpone the realization of such hopes.

One has been evident right from the beginning, and does indeed pervade every study conducted to date: the lack of affordable transportation to put large quantities of hardware into Earth orbit. Although it is not yet clear how this barrier might be surmounted, hope has been expressed that a solution might evolve via the recent surge of space launch development by private-sector companies such as Space Exploration Technologies Corp.

But despite this discouraging aspect, which has been cited by former NASA Administrator Michael Griffin as the showstopper, the other missing element in space solar power development is probably the more important one: the lack of investment by deep-pocketed commercial entities seeking to market space solar power products or services.

Why not? The terrestrial demand for electric power is certainly not declining — trillions of dollars are invested annually in meeting that demand — and the environmental benefits are certainly arguable. No, it is the high risk facing such investment that keeps the real money away.

But there is a potential solution. A 1998 NASA workshop titled “New Space Industries for the Next Millennium” identified two such industries: space tourism and space solar power. Of these, space tourism is currently being pursued actively by a number of commercial entities, notably not by NASA, other government agencies or not-for-profit organizations, who are the primary studiers of space solar power concepts. What, then, would stimulate commercial interest in space solar power? How can the risk be retired, or even ameliorated?

The answer has been evident for a long time: an evolutionary development that doesn’t seek to begin with thousand-ton spacecraft (or even scaled-down versions thereof) that are designed and built to deliver power to terrestrial customers.

As first identified in a 1999 assessment by the American Institute of Aeronautics and Astronautics and extensively expounded on by Mankins in his book, systems using space solar power technologies and concepts (including power beaming) can provide useful levels of power to spacecraft performing other functions — communications, remote sensing (especially radar), military applications, science, exploration or whatever. Space solar power systems can deliver both operations and transportation power to these spacecraft in much greater quantities than conventional power systems. One promising potential market is reflected in the recent strong interest by both commercial companies and government agencies in all-electric communications satellites. Note, too, that NASA currently sponsors a sizable program in multi-kilowatt solar-electric propulsion for space exploration missions, whose main stumbling block is the lack of affordable, robust systems to generate sufficient onboard electric power.

Griffin agrees that such services are eminently salable commercially, especially since they can offer new and desirable options (such as laser space-to-space communications) that become viable only with large amounts of power. Another desirable option is to beam power via lasers to commercial and other satellites from solar “energy depots” in space, a concept espoused by Electricite de France in 1988.

Moreover — and this is perhaps the most important consideration — these space solar power-enhanced satellites can be orbited by current launch vehicles, thereby resolving the long-time affordability conundrum. And clearly, once a viable commercial business in enhancing satellite power has demonstrated its economic worth, the big step of developing and building space solar power systems to deliver terrestrial power would be far less risky — and hence more palatable — to “big money” investors.

Jerry Grey, an honorary fellow of the American Institute of Aeronautics and Astronautics (AIAA) and a fellow of Britain’s Royal Aeronautical Society, was a professor of aerospace engineering at Princeton University, director of science and technology policy for the AIAA, and the founder and first publisher of “Aerospace America.” He now consults on space policy and space propulsion and lives in London and Key Biscayne, Florida.